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Operando III - Rostock-Warnemünde 2009 - Book of Abstracts Posters

Program Section: 1 Preferred form of presentation: Oral

Space- and Time-resolved In-Situ Spectroscopy on the Coke formation on H-SAPO-34 and H-ZSM-5 during the Methanol-to-Olefin Conversion

Davide Mores, Eli Stavitski and Bert M. Weckhuysen

Inorganic Chemistry and Catalysis Group, Department of Chemistry, Utrecht University, [email protected]

Introduction and Objectives

The ability of in-situ spectroscopy to unravel structure-function relationships makes it an essen-tial tool for the fundamental understanding of catalytic reactions. [1-2] Most of the applied tech-niques however average the information over the whole sample. In many cases however, probing a distinct area of a catalyst particle or grain can reveal valuable information concerning the func-tion of structural features in the catalytic action. For this, the application of micro-spectroscopic methods can be of assistance.

The selective conversion of methanol into light olefins (MTO) is interesting because the metha-nol can be produced from an oil alternative feedstock. At this moment, the most promising cata-lysts for the MTO reaction are H-SAPO-34 and H-ZSM-5 catalytic crystals. [3] However, be-sides a high olefin yield, these crystals suffer a fast deac-tivation caused by the formation of carbonaceous deposits. Here we aim to elucidate the differences in coke forma-tion between large H-SAPO-34 and H-ZSM-5 single crys-tals during the MTO reaction in a space and time resolved manner. This has been made possible by applying a high-temperature in-situ cell in combination with UV-Vis and confocal fluorescence micro-spectroscopy techniques. [4]

Results and Discussion

Upon exposure of methanol vapour, the large translucent H-SAPO-34 and H-ZSM-5 catalytic crystal undergo dark-ening due to the formation of carbonaceous species. In H-ZSM-5, coke is initially formed at the triangular crystal edges, where straight channel openings directly reach the external crystal surface. During the reaction, two absorp-tion bands at 415 nm and 550 nm are observed, assigned to the formation of coke compounds and its precursors inside the crystal. With TOS, a background absorption is obtained that extends over the whole visible region, indicat-ing the formation of graphite coke on the external surface of the crystal (Figure 1). Confocal fluorescence microscopy

Figure 1: a) Optical Microphotographs of H-ZSM-5 crystals taken during the MTO reac-tion at 745K. b) corresponding absorption spectra taken from a spot in the middle of the crystal

Operando III - Rostock-Warnemünde 2009 - Book of Abstracts Poster P1-01


confirms these observations and shows that the formation of fluorescent carbonaceous species inside the catalytic crystal is initially formed at the near surface area and gradually diffuses in-wards the crystal where internal intergrowth boundaries hinder the facile penetration for the more bulky aromatic compounds (Figure 2).

H-SAPO-34 also shows two distinct temperature regions. The formation of an absorption band at 400 nm increase with time and then decreases when the reaction is carried out between 530 and 575K, whereas at higher temperatures its inten-sity remains steady and the formation of an addi-tional band around 480 nm is observed combined with a increasing background absorption. In these crystals, the formation of fluorescent spe-cies formed during the course of the reaction is limited to the near surface region, where the for-mation of polyaromatic coke compounds leads to channel blockage that creates diffusion limita-tions for the coke front moving towards the mid-dle of the crystal thereby making the internal

region of the crystal less accessible to the reactant molecules.

Conclusions

The combination of in-situ UV-Vis and confocal fluorescence micro-spectroscopy is a valuable tool to probe coke deposits and their precursors during a catalytic reaction. We demonstrate that clear differences can be observed in the rate and patterning of the coke formation in a space and time resolved manner in these molecular sieve crystals. The formation of two distinct coke sys-tems i.e. aromatic hydrocarbons in the internal pores and graphitic coke at the external surface of the crystals is illustrated. The hydrocarbons contribute to the internal aromatic coke formation as well olefin production while graphitic coke compounds block the pore openings at the external surface of the crystal. The differences in coke formation will be explained in terms of pore archi-tecture and intergrowth structure.

References [1] J.F. Haw, In-situ spectroscopy in heterogeneous catalysis, Wiley-VCH, Weinheim, 2002[2] B.M. Weckhuysen, In-situ spectroscopy of catalysis, American Scientific Publishers, Stevenson Ranch, 2004 [3] M. Stöcker, Micropor. Mesopor. Mater. 1999, 29, 3 [4] D. Mores, E. Stavitski, M.H.F. Kox, J. Kornatowski, U. Olsbye, B.M. Weckhuysen, Chem. Eur. J. In press

Figure 2: fluorescence intensity profiles of H-ZSM-5 crystals during the MTO reaction at 660K depicted with time on stream at laser exitation (a) 488 nm (detection at 510-550 nm) and (b) 561 nm (detection at 565-635 nm). (c) Schematic representation of the slice where the confocal fluorescence measurement has been per-formed. Corresponding time is indicated in minutes.


Program Section: 1 Preferred form of presentation: Poster

The role of additives in the ethylene oxychlorination chemistry N. B. Muddadaa, U. Olsbyea, T. Fuglerudb, E. Groppoc, S. Bordigac, C. Lambertic

aUniversitetet i Oslo, Sem Sælands vei 26, 0315 Oslo, (NO), bINEOS Norge A/S, 3907 Porsgrunn, (NO), cDepart. of Inorganic, Physical and Materials Chemistry and NIS Centre of Excellence,

Università di Torino, Via P. Giuria 7, 10125 Torino, (I) and INSTM Centro di Riferimento.


Nowadays, almost all the world production of PVC is obtained by the polymerization of vinyl chloride (VCM), which is produced using ethylene, oxygen and chlorine as reagents. Production of VCM is based on cracking of 1,2-dichloroethane (EDC) which in its turn is produced by two parallel processes, viz. direct chlorination and oxychlorination, the latter being summarized as:

C2H4 + 2HCl + ½ O2 → C2H4Cl2 + H2O (1)

This reaction, recycling HCl produced by the cracking of 1,2-dichloroethane, is particularly important in industrial applications because it was specifically developed to reduce the raw material (Cl2) consumption and the exit of useless product (HCl) outside the cycle, in agreement with the modern requests of chemical industry. Oxychlorination reaction (1) is performed at 490-530 K and 5-6 atm. using both air and oxygen in fluid or fixed bed reactors. Commercial catalysts are produced by impregnation of γ-alumina with CuCl2 (4-8 wt% Cu). Other chlorides, (mainly alkaline or alkaline earth chlorides) in a variable concentration, are also added in order to improve the catalytic performances making the catalyst more suitable for use in industrial reactors. In particular, KCl is always present in the catalysts used in fixed bed technologies, sometimes together with other alkali-metal chlorides such as CsCl, NaCl or LiCl. Rare-earth-metal chlorides such as LaCl3, added to CuCl2 and KCl, are also claimed in the patent literature. MgCl2 is the base additive in the catalysts used in fluid bed processes, where alkali-metal (such as LiCl) or rare-earth-metal chlorides (such as LaCl3) can also be added.


In the past some of us have deeply investigated the bare catalyst (without additives) [1-4], showing that the overall ethylene oxychlorination reaction (1) is catalyzed by the CuCl2 phase following a three steps redox mechanism: (i) chlorination of ethylene by reduction of CuCl2 to CuCl, (ii) oxidation of CuCl to an oxychloride and (iii) re-chlorination with HCl (closure of the catalytic cycle) according to equations (2-4):

2CuCl2 + C2H4 → C2H4Cl2 + 2CuCl, (2)

2CuCl + ½ O2 → Cu2OCl2 , (3)



Cu2OCl2 + 2HCl → 2CuCl2 + H2O. (4)

Successively [5], an in situ, time resolved, XANES study has allowed us to determine the Cu(II) → Cu(I) transformation occurring on the CuCl2/γ-Al2O3 base catalyst in ethylene oxychlorination environment along the 373-623 K range. These data, together with the simultaneous determination of the catalyst activity, have demonstrated that the rate determining step of the ethylene oxychlorination reaction is the oxidation of CuCl according to equation (3).

In this contribution we extend the study done on the bare catalyst [1-5] to the study of MgCl2/CuCl2/γ-Al2O3, CsCl/CuCl2/γ-Al2O3, LiCl/CuCl2/γ-Al2O3, LaCl3/CuCl2/γ-Al2O3, samples, representing the most used dopants present in the catalysts employed in both fixed and fluid bed technologies. The main used experimental techniques are time resolved Cu K-edge XANES spectroscopy in operando conditions (collected at ESRF, ID24), in situ FTIR spectroscopy of adsorbed CO, ex situ UV-Vis spectroscopy and ethylene conversion reaction in pulse reactors.

Conclusions

It has been shown that the KCl/CuCl2/γ-Al2O3 and CsCl/CuCl2/γ-Al2O3 catalyst behaves differently from the base one, working in a prevailing oxidized state. Combining operando XANES experiments with catalytic tests of ethylene conversion in pulse reactors and with IR experiments of adsorbed CO, it is concluded that the active phase of the of the KCl/CuCl2/γ-Al2O3 or CsCl/CuCl2/γ-Al2O3 systems is a mixed chloride (KxCuCl2+x or CsxCuCl2+x) phase, which reduces the ability of the active surface to adsorb ethylene and/or transfer two Cl atoms to each ethylene molecule. The formation of the double compound, although not detectable by XRD owing to too small crystal size [2], was suggested by IR spectroscopy of adsorbed CO. The important contribution of S. Vidotto, B. Cremaschi, A. Marsella (INEOS Porto Marghera (Ve), Italy) of G. Leofanti (consultant) and of A. Zecchina, G. Spoto, C. Prestipino and L. Capello (Torino University) is gratefully acknowledged.

References [1] G. Leofanti, M. Padovan, M. Garilli, D. Carmello, A. Zecchina, G. Spoto, S. Bordiga, G.T. Palomino and C.

Lamberti, J. Catal., 189 (2000) 91. [2] G. Leofanti, M. Padovan, M. Garilli, D. Carmello, G.L. Marra, A. Zecchina, G. Spoto, S. Bordiga and C.

Lamberti, J. Catal., 189 (2000) 105. [3] G. Leofanti, A. Marsella, B. Cremaschi, M. Garilli, A. Zecchina, G. Spoto, S. Bordiga, P. Fisicaro, C.

Prestipino, F. Villain and C. Lamberti, J. Catal., 205 (2002) 375. [4] G. Leofanti, A. Marsella, B. Cremaschi, M. Garilli, A. Zecchina, G. Spoto, S. Bordiga, P. Fisicaro, G. Berlier, C.

Prestipino, G. Casali and C. Lamberti, J. Catal., 202 (2001) 279. [5] .C. Lamberti, C. Prestipino, F. Bonino, L. Capello, S. Bordiga, G. Spoto, A. Zecchina, S.D. Moreno, B.

Cremaschi, M. Garilli, A. Marsella, D. Carmello, S. Vidotto and G. Leofanti, Angew. Chem. -Int. Edit., 41 (2002) 2341.


Program Section: 2) Preferred form of presentation: Poster

Dehydration of Glycerol to Acrolein on Heteropolyacids: Assessing Structure-Reactivity Relationships by Operando-EPR

Silke Erfle, Udo Armbruster, Andreas Martin, Angelika Brückner

Leibniz-Institut für Katalyse e. V., Außenstelle Berlin, P.O.Box 961156, D-12474 Berlin


The rapidly rising production of biodiesel from vegetable oils, which leads to a surplus of glyc-erol as the main byproduct, calls for alternative options of its use. Recently, supported H4SiW12O40 was found to be a promising catalyst for the gas-phase dehydration of glycerol with acrolein selectivities above 60 % [1,2]. Unfortunately, deposition of carbon leads to rather fast activity loss. Therefore we tried to slow down deactivation by 1) introducing Mo and V as redox-active elements in the heteropolyacid structure and 2) admixing small amounts of oxygen to the feed. It is the aim of this work to elucidate the influence of feed composition and support on the structure and valence state of V and Mo species as well as on the nature of C species by monitor-ing with operando EPR as a basis for further catalyst optimization.


H3PMo12O40 · 26 H2O (HPMo) and H4PVMo11O40 · 11 H2O (HPVMo) were supported by wet impregnation on two commercial SiO2-Al2O3 supports with Si/Al = 0.21 and 0.32 as well as on Al-MCM-41 (Si/Al = 10) to achieve a loading of 20 wt.-%. UV-vis diffuse reflectance spectra indicate that the Keggin anions of the acids are destroyed upon impregnation leaving behind mo-lybdate fragments, the size of which decreases with the specific surface acidity of the support. Operando-EPR spectra in X-band were monitored for 4h at 280 °C in a home-made plug-flow reactor implemented in the cavity of the spectrometer from 125 mg catalyst particles in a total gas flow 44.8 ml/min with a ratio of glycerol/N2/H2O/O2 = 1/14.1/36.8/0.68 or 1/14.1/36.8/0. The total spin concentration was determined by comparing integral intensities with that of VOSO4/K2SO4 spin standard. The percentage of Mo5+ and V4+ in HPVMo samples was derived from these values by EPR spectra simulation.

For HPMo samples, an Mo5+ EPR signal appeared with time on stream comprising 20-21 % (on Si-Al-0.32 and MCM) and 73 % (on Si-Al-0.21) of the total Mo content after 4h in the presence of O2. When O2 is absent, the Mo5+ percentage is slightly smaller suggesting deeper reduction to M(5+)-x and/or antiferromagnetic coupling of more abundant reduced Mo species, that might di-minish spectral intensities. Moreover, a carbon radical signal grows on the line of Mo5+ with time on stream which is much more intense and narrower in the presence of O2, although carbon de-posit formation is more pronounced without O2 in the feed, as evident from TG/DTA analysis of


Program Section: 2) Preferred form of presentation: Poster

used catalysts. This suggests that, in the presence of O2, less condensed carbon deposites with negligible antiferromagnetic coupling are formed. This agrees with the results of long-term cata-lytic tests in which deactivation could be effectively suppressed by adding a small amount of O2.

In HPVMo samples, a VO2+ signal dominates in the first 30 min on stream and then diminishes gradually. Simultaneously, an Mo5+ signal gains intensity (Fig. 1). While VO2+ is still properly seen after 4h on stream in the presence of O2, it disappeared almost completely when the feed contains no O2, probably due to deeper reduction. This indicates that V5+ is faster reduced than Mo6+. However, the total spin concentration is markedly higher in all HPVMo catalysts compared to HPMo both with and without O2 in the feed. This indicates that the presence of V might hinder deep reduction of the catalyst. Moreover, the carbon deposits remain probably less condensed and deactivating as suggested by the much stronger radical signal even in the absence of O2. This agrees with the catalytic performance observed along with the spectral behavior. Glycerol con-version was slightly higher for HPVMo samples while acrolein selectivities were lower due to more pronounced CO2 formation.

Fig. 1. Operando-EPR spectra of HPVMo/Si-Al-0.21 without O2 (left) and with O2 (right)

Conclusions

Both the presence of vanadium in the catalysts as well as some O2 in the feed helps to suppress catalyst deactivation by keeping the metal ions in a more oxidized and the carbon deposits in a less condensed state. Highest acrolein selectivities were obtained with HPMo and HPVMo sup-ported on Al-MCM-41 which showed the highest surface area, lowest surface acidity and highest molybdate dispersion.

References [1] H. Atia, U. Armbruster, A. Martin, J. Catal. 258 (2008) 71. [2] E. Tsukuda, S. Sato, R. Takahashi, T. Sodesawa, Catal. Comm. 8 (2007) 1349.

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g =1.890

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g =1.943C radicalg = 2.006

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B / G


Program Section: 2 Preferred form of presentation: oral

Comparing UV and visible operando Raman:

An effective tool for reduced catalyst analysis

Xavier SECORDELa, Elise BERRIERa, Sylvain Cristola, Mickaël CAPRONa,

Jean-François PAUL, Edmond PAYEN

a Unité de Catalyse et de Chimie du Solide, Université des Sciences et Technologies de Lille;

Bât C3 Cité Scientifique 59655 Villeneuve d’Ascq Cedex, France

[email protected]


The Raman spectra can strongly differ according to the excitation wavelength owing to resonance effects or surface light-induced modifications. Oxidized metal oxides often exhibit ligand-to-metal charge transfers in the UV range, allowing enhanced UV Raman signal and better descrip-tion of a supported active phase. In the opposite, because reduced oxides often have a strong ab-sorption in the visible range, the reduction of the active phase is likely to produce resonance ef-fects in visible Raman. Recently, a thoughtful study devoted to TiO2 supported oxorhenate cata-lysts has discussed the differences between UV and visible Raman spectra of Re/TiO2 materials. However, the strong absorption of titania in the UV range made it difficult to get genuinely im-proved spectra. The present study is dedicated to alumina supported Mo and Re oxides we have subjected to methanol oxidation for operando studies. Because of its optical properties, alumina was preferred and we have modified its properties by calcination at different temperatures.


The compared visible and UV spectra of a 15% MoO3/γ-Al2O3 catalyst presented in Fig. 1 exhibit differences in intensity assigned to enhancement of νS (Mo=O) modes upon UV excitation. In addition, a shoulder is detected in the UV Raman spectrum at 880 cm-1. This feature was previously assigned to UV–resonant out of plane M-O-M modes.

The catalysts were subjected to a series of feed mixes including methanol with or without oxygen. The main reaction product was found to be strongly dependent on the acidity of the alumina: the higher the calcination temperature (600-1200°C), the lower Lewis acidity and the higher selectivity in methylal (Re-based catalysts) or formaldehyde (Mo-based catalyst) is found at the expense of dimethylether (DME). Concerning the spectroscopic point of view, alumina has a pronounced tendency to give rise to a strong fluorescence in the visible range upon reaction conditions.

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λEXC

632nm

λEXC

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Raman shift / cm-1

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266nm

Fig. 1 : Compared UV and visible Raman spectra of fresh 15% MoO3/γ-Al2O3


Program Section: 2 Preferred form of presentation: oral

Hence, UV Raman was a real benefit in studying working catalysts as depicted in Fig. 2. Reduc-tion of the Re/Al2O3 catalysts under methanol in helium led in both cases to a complete loss of the Raman intensity between 750 and 1000 cm-1. This effect classically accompanies the reduc-tion of the catalyst.

Interestingly, no additional scattering is detected at 800 cm-1, but an intense line was observed at 1600 cm-1 in both spectra. This band is accompanied by another one centred at 1330 cm-1 in the visible Raman spectrum. These features certainly come from laser induced heavy carbon species (coke). When allowing oxygen in the feed, the fluorescence in the visible region made it impossi-ble to record any Raman signal. Conversely, the UV Raman spectrum shows a half recovering of the νS(Re=O) mode. The structure of α-Al2O3 supported catalyst was fairly different, as the spe-cific surface is much lower. In both visible and UV Raman spectra, a broad scattering was de-tected at 800 cm-1 and was found to be highly dependent on the excitation energy and the envi-ronmental conditions. The same procedure with supported oxomolybdate catalysts led to slightly different results, the visible Raman spectra recorded under working conditions exhibited an in-tense scattering around 800 cm-1 which is not present in the UV Raman spectrum anymore. These modes we have assigned these modes to νS (Mo-O) in small clusters are weak by nature and can only be detected when enhanced by resonance effects.

Conclusions

Our results show the complimentarily of operando visible and UV Raman spectroscopies in studying supported metal oxides submitted to redox cycles. The coordinated enhancement allows to deeply studying both oxidized (UV Raman) and reduced states (visible Raman). Moreover, the combination of multiple spectroscopic data strongly suggests the presence of rhenium oxide clus-ters at the surface of low BET surface catalysts.

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Fig. 2 : Compared UV (left) and visible (right) spectra of a 7% Re/γ-Al2O3 catalyst upon successive treatments


Program Section: 2 Bridging the gap between…. Preferred form of presentation: oral

Operando fluorescent X-ray spectroscopy studies on the role of noble metal sensitizers in tin dioxide based gas sensors

D. Kozieja, M. Hübnerb, J.-D. Grunwaldtc, N. Barsanb, U. Weimarb

aETH Zürich, Department of Materials, CH-8093 Zürich, e-mail: [email protected] , bUniversity of Tübingen, Institute of Physical Chemistry, Auf der Morgenstelle 15, Germany,

cDepartment of Chemical and Biochemical Engineering, Technical University of Denmark

(DTU), DK-2800 Kgs. Lyngby


SnO2 based sensors have found applications in many industrial trades such as automotive, chemical, environmental control, food, medicine, military and safety applications. Incorporating small quantities of noble metals into sensitive layers is an effective way to eliminate the crucial drawbacks of metal oxide gas sensors. Namely, it enhance the stability, response and recovery times of metal oxide gas sensors. Further, it decreases the cross sensitivity to water vapor (Pd) and decreases the operating temperature (Au, Pt) of gas sensors. Although already some spectroscopic techniques have been adjusted to fulfil the requirements of sensors experiments in operando condition, the role of nobel metal senitizers, is still a matter of debate.[1-4] XAS is an excellent technique for deriving structure-function relationships, which has been especially applied in catalysis.[5] Recently, simultaneous measurements of XAS and conductivity of the model sample (4.8 % mol Pd:SnO2) were also reported under condition close to operando.[3]

However, the best sensing performance is shown by sensors with relatively low metal loadings (lower than 0.5 wt. %). Recently, we sucessfully bridged the gap between studies on model sensors with 2 - 3 wt. % Pd and on real 0.2 wt. % Pd:SnO2

sensors under real sensor conditions.[6] Here we additionally report the structure of minute quantities of Au (0.2 % wt.) in a heavily X-ray absorbing SnO2 matrix on a 50 μm thick layer and track it changes during sensing of carbon monoxide and hydrogen in air under sensing operation temperatures (200°C-400°C). Note that due to the presence of Pt as electrode material and in order to record high-resolved AuL3-XAS spectra, we used used a horizontal-plane Roland circle spectrometer and measured the resistance simultaneously.

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syn.air at 300°C 50ppm CO/syn.air at 300°C 30 ppm H2/syn.air at 300°C syn.air at RT

Figure 1: XANES spectra of 0.2 wt. % Au:SnO2

sensor under real operation conditions– 50ppm CO and 30ppm H2 each in synthetic air at 300°C.


Program Section: 2 Bridging the gap between…. Preferred form of presentation: oral

Results

Fig. 1 and 2 show XANES spectra of sensors under operating conditions. Au is present in the me-tallic form at the surface of tin dioxide particles, whereas Pd particles are in oxidized state. Inter-estingly, Au as well as PdO particles are not changing their oxidation state during exposure of carbon monoxide and hydrogen in the presence of air, whereas at the same time high sensor sig-nals are recorded. It is possible to reduce PdO to Pd only if the hydrogen is exposed in oxygen free atmosphere. At this condition, the reduction is possible already at 150°C (Fig. 3).

Conclusions

We have successfully determined the structure of gold- and palladium- in the SnO2 matrix in the presence of Pt electrodes using a novel in situ spectroscopic cell. Au is present in metallic state at the surface of tin dioxide particles, whereas Pd is in oxidized state. This was possible due to the high resolution fluorescence detection where the Pt-fluorescence is not disturbing. Moreover, it was possible to monitor the oxidation state of the noble metal under operando conditions. These bring important insights into the role of surface sensitizers in gas sensing mechanism.

References

[1]. Barsan, N., Koziej, D.,Weimar, U., Sens. Act. B 121, (1), 2007, 18-35. [2]. Koziej, D., Barsan, N., Shimanoe, K., Yamazoe, N., Szuber, J.,Weimar, U., Sens. Act. B 118, (1-

2), 2006, 98-104. [3]. Safonova, O., Neisius, T., Chenevier, B., Matko, I., Labeau, M.,Gaskov, A. In 13th Int. Cong. on

Cat., France, (2004); France. [4]. Cabot, A., Dieguez, A., Romano-Rodriguez, A., Morante, J. R.,Barsan, N., Sens. Act. B 79, (2-3),

2001, 98-106. [5]. Grunwaldt, J. D.,Clausen, B. S., Topics in Catalysis 18, (1-2), 2002, 37-43. [6]. Grunwaldt, J.-D., Koziej, D., Hübner, M., Barsan, N.,Weimar, U., Operando fluorescence XAS

measurements on Pd metal doped SnO2. In preparation, 2008.

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Figure 2: XANES spectra of 0.2 wt.% Pd:SnO2 FSP sensor under real operation conditions – 300ppm CO and 125ppm H2 each in synthetic air at 300°C.

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Figure 3: XANES spectra of 0.2 wt.% Pd:SnO2

FSP sensor under reducing atmosphere-1000ppm H2 in He during heating stepwise from RT up to 250°C.



Electrical conductivity of M2-type MoVTeNbO oxide during the gas phase

partial oxidation of propylene: an operando approach M. Caldararu a*, M. Scurtu a, C. Hornoiu a, C. Munteanu a, T. Blasco b and J. M. López Nieto b*

a Institute of Physical Chemistry “Ilie Murgulescu” of the Romanian Academy, Spl.

Independentei 202, 060021 Bucharest, Romania ; bInstituto de Tecnología Química, UPV-CSIC,

Avda. de los Naranjos s/n, 46022 Valencia (Spain).


Efficient Mo-V-Te-Nb-O catalysts in the selective oxidation of propane/propene to acrylic acid consist of at least two main crystalline phases, the so-called M1(orthorhombic) and M2 (pseudo-hexagonal or orthorhombically distorted) [1-4]. M1-type oxide activates olefins and parafins, whereas M2 phase is effective only in the oxidation of olefins [5].

High excess of oxygen in the gas phase supplied during testing leads to overoxidation molybde-num from the oxide surface and waste formation; however, sufficient oxygen should be fed to prevent excessive reduction. Therefore, oxidation/reduction of oxide surfaces plays an important role in catalysis. Here, we present the results on the electrical conductivity of a Mo-V-Te-Nb-O model catalyst of M2-type, active and selective in propylene oxidation to acrylic acid, measured under inert and oxidant atmospheres as well as in reaction conditions. This gives information on the degree of reduction/oxidation state of the surface [4].


Figure 1 shows the Arrhenius plot of the electrical conductivity of MoVTeNbO mixed oxide catalyst, presenting pure M2 phase, measured under dry He (DHex) and subsequent reaction feed (CTx) (propylene-oxygen-He, with a molar ratio of 2/8/90). In every run, the temperature was progressively increased between ambient and a maximum of 300 ºC, 350 ºC or 400 ºC in experi-ments 1 (DHe1, CT1), 2 (DHe2, CT2) and 3 (DHe3, CT3), respectively. The conductivity plots are shown in Figure 1. Previous experiments carried out on M2-oxide showed that the conductiv-ity above 530 K is of n-type. In run DHe1, the increase conductivity at low temperatures (below 360 K) must be associated with water molecules, which are desorbed at increasing temperatures. Analysis of the results on the oxide conductivity indicate that the surface is reduced/re-structured under the reaction condition in the temperature range 623-673 K, despite oxygen is present in the gas mixture (Figure 1). This is evidenced by a dramatic conductivity increase in the subsequent treatment in DHe (not shown).



Gas chromatography was used to analyse the reaction products (see scheme in Figure 1) evolved in the CT experiments depicted above. The higher propylene conversion is obtained at tempera-tures in the range 423-473 K, in where the surface reduction/re-structure occurs. Meanwhile the evolution of the selectivity to acrylic acid with the reaction temperature for the runs CT1, CT2 and CT3 are displayed in Figure 1. As shown there, the better selectivity is obtained in run CT3 in the temperature range 423-473 K, where the oxide surface is reduced/re-structured and the conversion (not shown) reaches a maximum.

Additional experiments have been carried out to investigate the effects of treatments with oxygen flow before the catalytic tests. The results obtained showed again that the oxide must be treated at a temperature above 423 K under oxygen to oxidize the surface of the M2 catalyst. Thus, both surface reduction and oxidation requires a temperature higher than 423 K.

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CT3(400)

MoVTeNbOM2

G.C.

C3H6/O2

ECC

Fig. 1. Electrical conductivity measure-ment (determined in home-made de-signed electrical conductivity cell, ECC) and selectivity to acrylic acid (deter-mined by gas chromatography, GC) obtained during partial the oxidation of propylene over M2-type MoVTeNbO mixed oxides catalyst.

Conclusions

The electrical conductivity of a Mo-V-Te-Nb-O of phase M2 indicates that oxidizing/reducing the oxide surface requires temperatures above 423 K, as for the catalytic reaction. The oxide sur-face is partially reduced under reaction conditions in the same temperature range. The conductiv-ity results under different atmospheres and in operando conditions are correlated with the cataly-lic performance.

References [1] Ushikubo, K. Oshima, A. Kayo, T. Umezawa, K. Kiyono, I. Sawaki, EP Patent 0,529, 853 A2 (1992), assigned

to Mitsubishi. [2] T. Ushikubo, K. Oshima, A. Kayou, M. Hatano, Stud. Surf. Sci Catal. 112 (1997) 473.

[3] P. Botella, E. García-González, J.M. López Nieto, M.I. Vázquez, J. González-Calbet, J. Catal. 225 (2004) 428.

[4] O. V. Safonova, B. Deniau, J-M. Millet, J. Phys. Chem. B 110 (2006) 23962.

[5] P. Botella, J.M. López Nieto, B. Solsona, Catal. Lett. 78 (2002) 383.


Program Section: Preferred form of presentation: Poster

Molecular structure and reactivity of MoO3/TiO2 catalysts for the

oxidative dehydrogenation of ethane

George Tsilomelekis and Soghomon Boghosian

Department of Chemical Engineering, University of Patras and

FORTH/ICE-HT, GR-26500 Patras, Greece


The oxidative dehydrogenation (ODH) of light alkanes is an attractive route to synthesise light alkanes. Supported transition metal oxide catalysts, particularly based on Mo or V, have been investigated for the ODH reaction. The catalyst performance is related to the surface composition, the local structure and the distribution of the MOx species, the nature of the support and the catalyst preparation procedures. Laser Raman spectroscopy is a very useful tool for in situ studies of catalytic materials under working conditions. This work aims at investigating the MoO3/TiO2 catalysts for ethane ODH by means of operando Raman spectroscopy. The evolution of the molecular structure of the molybdena phase is studied under working conditions together with the catalytic performance. The effect of catalyst composition, temperature, gas atmosphere, and reactants residence time on both Raman spectra and catalytic performance is studied.


Supported MoO3/TiO2 catalysts (1.4–18.5 Mo/nm2)were prepared by wet impregnation of TiO2 (Alfa, 127 m2/g) using ammonium heptamolybdate as the precursor in aqueous solutions (pH 4–5). The calcination was performed at 480°C for 4h. A home made in situ cellwas used as a fixed bed reactor–optical cell for Raman and catalytic measurements [1]. In situ Raman spectra under O2 were recorded at temperatures 420–500°C and operando Raman–GC data were collected in a wide range of residence time (W/F, in the range 0.20–1.35 g.s/cm3) at the same temperatures.

1200 1000 800 600 400 200

35%

21%

9%

15%

6%

Inte

nsity

, a.

u.

Raman Shift ,cm-1

MoO3 / TiO2

O2 , 430°C

3%

Fig. 1 shows the in situ Raman spectra of MoO3/TiO2

catalysts under flowing O2 at 430°C as a function of molybdena loading. At loadings up to monolayer (15 wt%, 5.8 Mo/nm2) a well-defined band (with a slight

Figure 1. In situ Raman spectra of MoO3/TiO2 catalysts


Program Section: Preferred form of presentation: Poster

0.7

0.8

0.9

1.0

asymmetric character) is seen at 997 cm-1 (Mo=O), of which the intensity increases with increasing loading and its position has a tendency for a red shift. With increasing loading a weak broad feature, located at 900–930 cm-1 (Mo–O–Mo functionalities) becomes visible, indicating a partial association of surface MoOx and formation of polymolybdates. However, contrary to the case of MoO3/Al2O3 [1] and MoO3/ZrO2 [2], a low extent of association between MoOx units on TiO2 becomes evident. At higher loadings, the spectra are dominated by bands due to crystalline MoO3. Raman bands of the anatase carrier are seen at 390, 510 and 630 cm-1. The molecular structure of the molybdena phase responds to changes in the catalyst gas environment. The various sites are perturbed/reduced to different extents depending on their nature and catalystloading. Fig. 2 shows, e.g. the variation in the relative normalized intensity of the Mo=O band for three different reactor environment conditions for the catalyst samples with sub-monolayer coverage. Fig. 3 shows the behavior of the catalyst selectivity at various conversion levels achieved in the W/F range 0.20–1.35 g.s/cm3 for all samples. The apparent turnover frequencies of ethylene production as a function of Mo surface density are discussed in relation to the evolution of the structural properties of molybdena domains and to the possible identity of the reactive site, in relation to which the Mo–O–Ti linkages appear important.

Conclusions

Raman spectra show that isolated monomolybdate species are formed on TiO2, whereas partial association occurs at high loadings, below monolayer. The catalytic results point to the importance of Mo–O–Ti linkages for the ODH of ethane.

References [1] A. Christodoulakis, E. Heracleous, A. A. Lemonidou and S. Boghosian, J. Catal. 242 (2006) 16. [2] A. Christodoulakis and S. Boghosian, submitted for publication.

C2H6C2H6 + O2

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ativ

e no

rmal

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of M

o=O

ban

d

0 5 10 15 200

20

40

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3% MoO3/TiO2 6% MoO3/TiO26% MoO3/TiO2 9% MoO3/TiO29% MoO3/TiO2 15% MoO3/TiO215% MoO3/TiO2

O2

21% MoO3/TiO2

35% MoO3/TiO2

Ethy

lene

Sel

ectiv

ity ,

%

Ethane Conversion , %Figure 3. Ethylene selectivity as a function of ethane conversion at 500°C

Figure 2. Relative normalized intensity of Mo=O band at different conditions


Program Section: Application of reporter molecules to image catalytic activity Preferred form of presentation: Oral

An Operando UV-vis study on the activity of Cu-ZSM-5 in the decomposition of N2O and the selective oxidation of CH4.

Pieter J. Smeetsa, Marijke H. Groothaerta, Emiel J.M. Hensenb, Bert F. Selsa and Robert A. Schoonheydta.

aCenter for Surface Chemistry and Catalysis, K.U.Leuven, Heverlee 3001, Belgium; bSchuit Insti-tute of Catalysis, Eindhoven University of Technology, MB Eindhoven 5600, The Netherlands.


Cu-ZSM-5 is promising in the decomposition of N2O [1,2] and the selective oxidation of CH4

into CH3OH [3]. The activity in these reactions, both key reactions in today’s sustainable indus-try, has been suggested to be linked to the presence of a peculiar absorption band in the UV-vis spectrum. With Operando UV-vis, the activity of Cu-ZSM-5 is monitored in relation with this band, and information on the reaction mechanism, and the role of water and NO will be dis-cussed.


Cu-ZSM-5 is capable of activating oxidantia such as N2O and O2 at low temperatures with con-comitant formation of an active intermediate with characteristic absorption at 22 700 cm-1. The formation, stability and reactivity of this species were monitored on-line using the Operando UV-vis set-up, presented in Figure 1.

22000 cm-1

0.1% NO + 0.5% N2O at 400°C

0.02% NO + 0.5% N2O at 400°C

0.5% N2O at 400°C

Wavenumber (cm-1)

40000 35000 30000 25000 20000 15000

0.1 a.u.

Abs

orba

nce

(a.u

.)

Figure 1 (left): Operando UV-vis set-up; Figure 2 (right): Operando UV-vis spectra recorded dur-ing the decomposition of N2O over a Cu-ZSM-5 catalyst in the presence and absence of NO.

We previously reported that the peculiar catalytic activity of Cu-ZSM-5 to decompose N2O is associated with the presence of the 22 700 cm-1 band in the catalytic cycle [1,2]. During the N2Odecomposition this core is formed and allows O2 desorption already at low temperatures, which is the rate determining step in Cu-zeolites. Addition of NO and H2O both affects the reaction rate according to a different mechanism. As revealed from in-situ FTIR studies, NO assists the N2Odecomposition by transporting the activated ‘O’ atom from the catalyst surface to the gas phase.


Program Section: Application of reporter molecules to image catalytic activity Preferred form of presentation: Oral

An intensity reduction of the diagnostic band is indeed observed, along with an elimination of the fast O2 desorption route (Figure 2). In particular Cu-ZSM-5 catalysts with low Cu contents bene-fit from the role of NO, while Cu-rich samples seem uninfluenced by the presence of NO. Addi-tion of H2O is generally known to have a detrimental effect on the catalytic decomposition of N2O. This is indeed what we have noticed for our highly loaded Cu-ZSM5 samples. Moreover, the presence of water completely eliminates the crucial intermediate (with the 22 700 cm-1 char-acteristic band). Surprisingly, for low Cu contents, water assists the N2O decomposition resulting in a rate enhancement. Moreover, as will be shown and explained with spectroscopic evidence, the effect of H2O is fully reversible.

A second reaction, the selective hydroxylation of CH4, was monitored on the same set-up shown in Figure 1. After its formation from N2O or O2, the active intermediate (with the characteristic 22 700 cm-1 band) disappears upon reaction with CH4 at about 100°C [3]. Evaluating the decay of the 22 700 cm-1 band allows an estimate for the reaction rate and activation energy. After full conversion of the active species, mainly CH3OH was analyzed as product. Reaction rates with CD4 were found to be 2 times lower than with CH4 (Figure 3), corresponding to a difference in activation energy of about 13 kJ/mol.

t=0

Wavenumber(cm 1)

Absorptio

nun

its(a.u.)

15000 20000 25000 30000

t=0

Wavenumber(cm 1)

Absorptio

nun

its(a.u.)

15000 20000 25000 30000

Figure 3: Operando UV-vis spectra of a calcined Cu-ZSM-5 catalyst (450°C in O2) recorded at 175°C during reaction with CH4 (left) and CD4 (right). Time interval between two spectra is 15 s.

Conclusions

Operando UV-vis is a powerful tool for investigating the role of the parent Cu-ZSM-5 in the N2Odecomposition and the selective oxidation of CH4. Monitoring active intermediates at work pro-vides detailed information relevant to unravel the reaction mechanism, and ultimately assist in the design of even more active/selective catalysts.

References [1] M.H. Groothaert, P.J. Smeets, B.F. Sels, P.A. Jacobs, R.A. Schoonheydt, J. Am. Chem. Soc., 127 (2005) 1394. [2] P.J. Smeets, M.H. Groothaert, R. M. van Teeffelen, H. Leeman, E.J.M. Hensen, R.A. Schoonheydt, J. Catal.,

245 (2007) 358. [3] P.J. Smeets, B.F. Sels, R. M. van Teeffelen, H. Leeman, E.J.M. Hensen, R.A. Schoonheydt, J. Catal., 256 (2008)

183.


Program Section: Poster presentation

Effect of alkaline ions on the selectivity for SCR of NO with CH4: a compari-son between Co-Na-MOR and Co-H-MOR catalysts

Daniela Pietrogiacomi, Maria Cristina Campa, Valerio Indovina

Department of Chemistry, “Sapienza” University of Rome, P.le Aldo Moro 5, 00185-Rome (Italy)


Co high-silica zeolites (MFI, FER, MOR) are active catalysts for the selective catalytic reduction (SCR) of NO with CH4 in the presence of O2. Studying the coadsorption of NO+O2 on Co-containing catalysts, the presence of thermally stable nitrates of various structures has been evi-denced by FTIR [1]. An IR band at 1530-40 cm 1 was ascribed to monodentate nitrates adsorbed on dispersed cobalt [1] and invoked as a key compound in determining the activity for SCR with methane, being these nitrates able to react with methane in the temperature range 373–473 K [2, 3]. For Co-Na-MOR, in which in situ FTIR measurements evidenced isolated Co2+ and [Co-O-Co]2+, we have concluded that [Co-O-Co]2+ species alone were not the active sites for SCR and suggested that the active sites for SCR with CH4 were isolated Co2+ in the main MOR channels [4]. Comparing Co-H-MOR with Co-Na-MOR samples, we have clarified that the specific reac-tion rate per Co2+ did not depend on the amount of protons or alkaline ions, which were present in the samples as balancing atoms [5]. In the present investigation we focus our attention on the possible role of Na or H species in determining the selectivity of Co-MOR. In this study we per-form our investigation by means of operando FTIR methodologies, to compare Co-MOR samples with the same Co amount. Samples were prepared by the conventional ion-exchange method from Na-MOR (Si/Al=9.2, Co-exchange 61%) or H-MOR (Si/Al=9.2, Co-exchange 66%). These samples were portions of those previously used in the in situ FTIR characterization [5]. FTIR spectra were obtained in a stainless steel IR reactor-cell and recorded at various reaction tempera-tures. The IR cell was connected to a flow apparatus, fed with a NO+CH4+O2 mixture, having the same composition of that used for catalytic measurements ([NO]=0.4%, [CH4]=0.4%, [O2]=2%, balance He (total flow = 50 ccNTP/min).


In spite of the similar NO conversion observed on Co-Na-MOR-61 and Co-H-MOR-66, that we ascribed to the amount of isolated Co2+ in the main channel of MOR [5], CH4 conversion was higher, and selectivity SSCR lower, on Co-Na-MOR-61 than on Co-H-MOR-66. Specifically, in the temperature range 423-773 K, selectivity SSCR (percent ratio between the rate of SCR reaction and the rate of total CH4 consumption) decreased with temperature from 75% to 45% on Co-Na-MOR-61 and from 100% to 80% on Co-H-MOR-66. In the same temperature range, a much


Program Section: Poster presentation

higher selectivity SSCR was observed on Co-H-MOR-24 (from 100% to 80%) than on Co-Na-MOR-23 (from 60% to 40%). Operando FTIR studies by flowing NO+O2+CH4 showed that, increasing the temperature from 323 K to 773 K, the amount of surface NOx species progressively decreased. Above 500 K, the interaction of CHx and NOx was evidenced by the presence of weak bands of nitriles (2210 cm-1)and of Co-isocyanate (2250-60 cm-1). More information were obtained by flowing NO+O2 and therefore studying the reactivity with CH4 of surface species in reaction conditions. After saturating the sample by flowing NO+O2 at 573 K, on Co-H-MOR-66, (i) bridged nitrates

0.1

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0.4

0.5

140016001800200022002400

Abs

orba

nce

/ a.u

.

Wavenumber / cm-1

123

1'2'3'

Fig. 1. FTIR spectra of surface spe-cies formed after 30 min under NO+O2 flow (spectra 1 and 1’), and after 8 min under He flow at 573 K (spectra 2 and 2’), or after 8 min under CH4 flow (spectra 3 and 3’).

on the matrix (FTIR band maxima at 1630 and 1590 cm-1),(ii) Con+-nitrosyls (1930 cm-1) and (iii) NO2

+ (or NO+) spe-cies (2200-2100 cm-1 region) formed. In the same condi-tions, on Co-Na-MOR-61, (i) monodentate nitrates on iso-lated Co2+ (1515 and 1300 cm-1) was the most abundant spe-cies, (ii) bridged nitrates were more abundant than on Co-H-MOR-66, (iii) nitrosyls and NO2

+-NO+ were hardly detect-able (compare spectra 1 and 1’ in Fig. 1). At 573 K, on both samples, all surface species desorbed faster by flowing CH4

than by flowing He (compare spectra 3 and 3’ with spectra 2 and 2’ in Fig. 1), suggesting their participation to the SCR process. In contrast, under the same conditions, these species were not detected on H-MOR and Na-MOR. Under CH4

flow, bridged nitrates, more abundant on Co-Na-MOR-61 than on Co-H-MOR-66, reacted faster on the former than on the latter (compare spectra 3 and 3’ in Fig. 1).

Conclusions

The different SSCR selectivity of Co-Na-MOR and Co-H-MOR arises from the different surface species present on the two samples under reaction conditions. The alkaline ions favour the forma-tion of nitrates rather than nitrosyls or NO2

+-NO+. Among the various nitrates, bridged nitrates, more abundant and reacting faster on Co-Na-MOR than on Co-H-MOR, are possibly the species involved in the NO-assisted CH4 oxidation.

References

[1] K. Hadjiivanov, Catal. Rev. – Sci. Eng. 42 (2000) 71 [2] K. Hadjiivanov, B. Tsyntsarski and T. Nikolova Phys. Chem. Chem. Phys. 1 (1999) 4521 [3] B. Tsyntsarski, V. Avreyska, H. Kolev, Ts. Marinova, D. Klissurski and K. Hadjiivanov, J. Mol. Catal. A:

Chemical 193 (2003) 139 [4] V. Indovina, M.C. Campa, D. Pietrogiacomi, J. Phys. Chem. C 112 (2008) 5093 [5] M.C. Campa, I. Luisetto, D. Pietrogiacomi, V. Indovina, Appl. Catal. B 46 (2003) 511


Program Section: 2-bridging the gap between model and technical conditions Preferred form of presentation: oral

Catalytic activity of In,H- and In,Pd,H-zeolite catalysts in the NOx-SCR reaction by methane

Hanna Solt, Ferenc Lónyi and József Valyon

Institute of Nanochemistry and Catalysis, Chemical Research Center, Hungarian Academy of

Sciences, Pusztaszeri u. 59-67, 1025 Budapest, Hungary


The selective catalytic reduction of NOx in the presence of oxygen (NOx-SCR) is a feasible process to reduce the NOx emission, especially the emission of boilers and engines, fuelled by natural gas [1]. Recent studies suggest that indium-containing zeolites are active in the NOx-SCR by methane [2 - 6]. The activity and selectivity were shown to depend on the structure, Si to Al ratio, and acidity of the zeolite, and also on the concentration and properties of the indium species in the zeolite matrix. Some In-zeolites showed high activity and selectivity [5, 6], while some less active In-zeolite preparations became highly active in the presence of a promoting metal, such as Co or Ir [3, 4, 7]. The effects of the different parameters on the catalytic property are not fully understood yet.

It is important to identify of reaction surface intermediates and active sites to get deeper understanding of the reaction mechanism and to direct catalyst development. The present study concerns the redox properties of In-zeolites and the mechanism of the NOx-SCR reaction with methane over In-zeolite catalysts by taking advantage of the operando DRIFTS-MS method.


Indium-containing H-mordenite (In,H-M, Si/AlF = 6.7, where AlF stands for Al T-atom) and H-ZSM-5 (In,H-ZSM-5, Si/AlF= 33) zeolite samples with an AlF/In ratio of 3 and 6 were prepared by the reductive solid state ion-exchange method [8]. Samples containing 0.5% Pd (In,Pd,H-M and Pd,H-M) were prepared by impregnating the In,H-M and H-M samples with the Pd(NH3)4NO3)2 solution and heating samples in O2 flow at 300 0C. The catalytic activities were determined between 300 and 600 oC at GHSV= 30,000 h-1 with a gas mixture, containing 4000 ppm NO, 4000 ppm CH4 and 2 % O2 in helium. The conversion of NO was relatively low on the In,H-M sample and became practically zero at temperatures above 450 oC (fig. 1.). The observed low NO conversion can be attributed to the undesired methane oxidation reaction with molecular oxygen, which consumes most of the reducing agent methane above 450 0C. In contrast, much higher and more stable NO conversion was observed over the In,H-ZSM-5 sample in a much wider temperature range. Over this catalyst the methane oxidation speeds up only at temperatures higher than about 500 0C.


Program Section: 2-bridging the gap between model and technical conditions Preferred form of presentation: oral

The DRIFT-TPR results suggest that the oxidation of In+ to InO+ species with molecular oxygen takes place below 100 oC in the In,H-M and above 400 oC in the In,H-ZSM-5 catalyst, while the same oxidation with NO proceeds well below 100 oC for both catalysts. The facile competitive oxidation of In+ sites in the In,H-M sample with O2 at low temperatures resulted in a very high CH4 oxidation activity, and therefore low deNOx activity and selectivity. The significantly improved catalytic properties of the In,Pd,H-M sample (fig.1) is probably related to the concerted action of the In+/InO+ and Pd0/PdO redox couples, which facilitate the oxidation of NO to the better oxidizing agent NO2. The results of the DRIFTS-MS measurements suggest that the NOx-SCR reaction proceeds via the reaction of adsorbed NH3 and NO+ intermediates.

Conclusions

The zeolite structure and composition was shown to have significant effect on the redox properties of the In-form of the zeolite. In zeolites of high Si/Al ratio the In+ resist oxidation by O2 up to high temperatures while become readily oxidized by NO. This is one of the zeolite properties that seems to determine the catalytic selectivity of NO reduction by methane in the presence of oxygen.

References [1] V.I. Parvulescu, P. Grange, B. Delmon, Catal. Today 46 (1998) 233. [2] M. Ogura, M. Hayashi, E. Kikuchi, Catal. Today 42 (1998) 159. [3] A. Kubacka, J. Janas, E. Wloch, B. Sulikowski, Catal. Today 101 (2005) 139. [4] A. Kubacka, J. Janas, B. Sulikowski, Appl. Catal. B: Environmental 69 (2006) 43. [5] T. Maunula, J. Ahola, H. Hamada, Appl. Catal. B: Environmental 64 (2006) 13. [6] O.A. Anunziata, A.R. Beltramone, E.J. Lede, F.G. Requejo, J. Mol. Catal. A: Chemical 267 (2007) 272. [7] M. Ogura, M. Hayashi, E. Kikuchi, Catal. Today 42 (1998) 159. [8] H. Solt, F. Lónyi, R.M. Mihalyi, J. Valyon, J. Phys. Chem. C 112 (2008) 19423.

Figure 1. NO (left) and CH4 (right) conversion of the reaction mixture 4000 ppm NO/4000 ppm CH4/ /2 % O2/He over In,H-M (Δ), In,H-ZSM-5 (○), Pd,H-M (▲) and In,Pd,H-M (▼) catalysts. GHSV= 30,000 h-1.

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NO

to N

2 con

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, %



Highly Dispersed WOx Species on Titania Nanotubes Surface by In-Situ Thermo-Raman Study

M.A. Cortés-Jacomea, C. Angeles Chavez, E. López Salinasa and J. A. Toledoa

a Instituto Mexicano del Petróleo/Programan de Ingeniería Molecular, Eje Central Lázaro

Cárdenas 152, D.F., 7730, México.


Tungsten oxide has been used for several catalytic applications such as alcohol dehydrogena-tion, n-alkanes isomerization, oxidative desulfurization, cracking and others [1-3]. WO3 is generally dispersed on different supports (Al2O3, SiO2, ZrO2, Nb2O5 and TiO2) [2]. The high acidity, redox and fotocatalytic properties of WOx/TiO2 catalysts open possibilities of appli-cations on selective catalytic reduction of NOx, olefins conversion and partial hydrocarbon oxidation. Recently, TiO2 with nanotubular morphology has been developed with improved textural properties [4]. In this work WOx species has been homogeneously dispersed on tita-nia nanotubes with concentrations 5, 10, 15 y 20 wt % of W. The materials were in situ an-nealed in a LinKam cell at 500, 700 y 800 °C in air flow. Structural evolution of WOx species on the surface of titania nanotubes was followed by in situ thermo-Raman spectroscopy, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS).


Titania nanotubes were synthesized by an alkali hydrothermal treatment following the proce-dure published elsewhere [5]. The starting support dried at 100°C had a specific surface area of 310 m2/g. The residual amount of Na+ ions contained in the nanotubular support was about 2 wt %. The hydrous titania nanotubes support was impregnated by an aqueous solution of (NH4)2WO4, thereafter sample was dried at 100°C. The amount of impregnating solution was adjusted to obtain samples with 5, 10, 15 y 20 wt % of W. The samples then were annealed in a Linkam cell at different temperatures in air flow. Raman spectra of the titania nanotubes used as support and the impregnated samples are presented in Figure 1. The Raman spectra of titania nanotubes used as support is made up of four main characteristic bands at 277, 448, 700 and 915 cm-1, these bands correspond with reported vibrations at 280, 448, 668 and 917 cm-1 for titanate nanotubes where the bands at 450 and 668 cm-1 were assigned to a Ti–O–Ti vibration and the band at 917 cm-1 was related to Ti–O–Na vibrations in the interlayer regions of the nanotubes walls [6]. After the impregnation, one additional band was observed at 962 cm-1

, which has been assignated to terminal W=O vibration [2]. Depending on the tungsten content on the support, different evolutions of tungsten species were observed at 800oC, sam-ples with W concentrations lower than 10 wt %, Figure 2, showed a main peak centered at 923 cm-1, attributed to the symmetric and asymmetric vibration of W=O bonds in tetrahedral coordination in Na2WO4 phase originated from a solid-state reaction between WOx speciesand Na+ ions released from the nanotubular interlayer space, during the structural transforma-tion of the nanotubes [7]. WOx species with octahedral coordination appear at W content as



high as 15 wt %, with Raman shift at 951 cm-1. At W content of 20 wt %, the concentration of octahedrally coordinated W increased and other less intense bands appear at 828 and 877 cm-

1. The band at 923 cm-1 shifted at 933 cm-1 indicating that small amount of WOx species re-mains in tetrahedral coordination. On the other hand, the increase of W content favors the anatase transformation into rutile phase.

200 400 600 800 1000

668

915

150

830

380 192

700 44

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.)

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.)

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20 %

15 %10 %

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.)

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5 %

Figure 1. Raman spectra of titania nano-tubes containing tungsten dried at 110oC

Figure 2. Raman spectra of titania nano-tubes containing tungsten at different con-centration annealed at 800oC

Conclusions

WOx species highly dispersed on TiO2 nanotubes surface were obtained by impregnation of hydrous titania nanotubes with ammonium metatungstate solution. After annealing samples at 800°C, the WOx species remained in tetrahedral coordination with a Raman shift centered at 923 cm-1 at W content < 10 wt %, at increasing W concentration, the WOx species octahe-drally coordinated appear, with a Raman shift at 951 cm-1, suggesting the coexistence two of tungsten species with different coordination. HRTEM showed WOx species with dimensions lesser than 2.0 nm.

References [1] M. Hino, K. Arata, J. Chem. Soc. Chem. Commun., (1987) 1259. [2] I. E. Wachs, T. Kim, E. I. Ross, Catal. Today 116 (2006) 162. [3] T. Kim, A . Burrows, C.J. Kiely, I.E. Wachs, J. Catal. 246 (2007) 370. [4] T. Kasuga, M. Hiramatsu, A. Hoson, T. Sekino, K. Niihara, Langmuir, 14 (1998) 3160. [5] M.A. Cortés, G. Ferrat, L.F. Flores, C. Angeles, E. López, J. Escobar, M.L. Mosqueira, J.A. Toledo, Catal. Today, 126 (2007) 248. [6] D.V. Bavykin, J.M. Friedrich, A.A. Lapkin, F.C. Walsh, Chem. Mater. 18 (2006) 1124. [7] J.A. Toledo, M.A. Cortés, M. Morales, C. Angeles, L.F. Ramirez, E. López, Chem. Mater. 19 (2007) 6605.


Program Section: Application of reporter molecules to image catalytic activity; Preferred form of presentation: Poster

Dehydrogenation of propane over chromium catalysts: New insights into the nature of active chromium species

M. Santhosh Kumara, N. Hammera, M. Rønninga, A. Holmen a, De Chena, J.C. Walmsleyb, G. Øyec aDepartment of Chemical Engineering, bDepartment of Physics, cUgelstad Laboratory; Norwe-

gian University of Science and Technology (NTNU), N-7491 Trondheim, Norway.

E-mail: [email protected]


Dehydrogenation of propane (DHP) is one of the on-purpose propylene production technologies that have the potential to make-up the shortfall of propylene supply left by conventional crackers [1-4]. Typically, the Cr-Al2O3 catalyst system is used for industrial processes. Major challenges associated with this catalytic system are cracking of hydrocarbons and coke formation. Consider-able research has been devoted to gain fundamental knowledge on the structure – reactivity rela-tionships of Cr species in dehydrogenation of alkanes by various characterization techniques [2-4]. However, the nature of active Cr species in Cr catalysts during DHP remains elusive and is still a subject of debate due to the complex nature of the catalytic system [2-4]. The objective of this work is to gain a better understanding on the nature of active Cr species in the catalysts by complementary multi spectroscopy approach.

To this end, a series of xCr-SBA-15 and xCr-Al2O3 (x denotes Cr content) catalysts with varying Cr content (0.5 – 10 wt.%) was prepared by incipient wetness impregnation. The catalysts were characterized by BET, XRD, UV-Raman, STEM–EDXS, XANES and EXAFS. The behaviour of Cr species during DHP was monitored by in situ XAS. DHP was carried out in a TEOM reactor at 853 K in a flow of C3H8 (5 ml/min in 45 ml/min of He) and the space velocity was 11.78 h−1.


N2-physisorption data of the Cr catalysts show that the structure of the support is virtually intact even after Cr loading onto the support followed by subsequent pre-treatments (drying and calci-nation). The Cr speciation is dependent on the nature of the supports and Cr loading as evidenced by XRD, STEM – EDXS, UV-Raman, XANES and EXAFS. At ≤ 1 wt.% Cr loading Cr species were well dispersed on both the supports SBA-15 and Al2O3. In particular, on SBA-15 they were merely isolated Cr(VI) in Td coordination while on Al2O3 formation of oligomers (including dimers) also was evidenced by the Raman bands (Fig.1). At ≥ 5 wt.% Cr loading, the dispersion of Cr decreases implying the formation of α-Cr2O3 crystals at the expense of isolated sites on SBA-15 while on Al2O3 the dispersion was still high and no detectable crystals were formed. In DHP, xCr-SBA-15 catalysts containing exclusively isolated Cr species (i.e., ≤ 1 wt.% Cr) ex-hibited higher activity and selectivity with respect to per mole Cr than the catalyst dominating


Program Section: Application of reporter molecules to image catalytic activity; Preferred form of presentation: Poster

with crystalline α-Cr2O3 particles (≥ 5 wt.% Cr). The intrinsic activity of these isolated Cr species was higher than those observed on γ-Al2O3 (≤ 1 wt.% Cr) (Fig.1). Remarkably, xCr-Al2O3 (≥ 5 wt.% Cr) catalysts dominating with oligomeric Cr species exhibited high activity indicating the importance of these species in the reaction.

Fig. 1 Raman spectra of the catalysts recorded at room temperature (above): a) 0.5, b) 1.0, c) 5.0 and d) 10.0 wt.% Cr and dehydrogenation of propane over the catalysts (below): 0.5 (♦), 1.0 (▲) and 5.0 (■): In situ XANES studies evidenced that isolated Cr(VI) species in Td coordination were immedi-ately reduced to Cr(III) and their coordination number increased (> 4) upon interaction with C3H8. Increased coordination number of Cr species was also shown by in situ EXAFS, though a definitive conclusion on the coordinating atom (C or O) could not be made due to coke.

Based on in situ and catalytic data, it can be concluded that active Cr sites are generated on site during DHP. In xCr-SBA-15, isolated Cr(III) species with coordination number greater than four that originate from isolated Cr(VI) in Td coordination, which were observed on the fresh catalyst, are more active, selective and stable than Cr sites on the surface of Cr2O3. In contrast, oligomeric Cr species are more active and selective than isolated Cr sites in xCr-Al2O3. Oligomeric Cr spe-cies are sensitive to regeneration than the isolated sites as evidenced by in situ XANES and DHP. References

[1] M. Santhosh Kumar, De Chen, J. C. Walmsley, A. Holmen, Catal. Commun. 9, 747, 2008. [2] R. L. Puurunen, B. M. Weckhuysen, J. Catal. 210, 418, 2002. [3] B. M. Weckhuysen, Phys. Chem. Chem. Phys. 5, 4351, 2003. [4] Y. Wang, Y. Ohishi, T. Shishido, Q. Zhang, W. Yang, Q. Guo, H. Wan, K. Takehira, J. Catal. 220, 347, 2003.


Program Section: Preferred form of presentation: POSTER

Support effect on the sulfidation of Ni-Mo hydrotreatment catalysts

M. Olga Guerrero-Pérez a ,Aida Gutierrez-Alejandre b, Jorge Ramirez b, Miguel A. Bañares a

a CATALYTIC SPECTROSCOPY LABORATORY, Instituto de Catalisis y Petroleoquímica, CSIC, Madrid, Spain ([email protected])

bUNICAT, Departamento Ingeniería Química, Facultad Química, UNAM Mexico ([email protected])

Introduction and Objectives The results reported in the literature indicate that adequate design of the characteristics of the catalytic support is of great importance in the development of better hydrotreating catalysts. It was shown that by means of an adequate support design it is possible to increase significantly the HDS, HYD and HDN functionalities of hydrotreating catalyst phases. Alumina supports modi-fied by SiO2 can facilitate the sulfidation of the active species, leading to better-promoted type II active sites with increased HDS and HYD catalyst functionalities. However, the method of SiO2incorporation can lead to changes in the sulfidation behaviour of the catalyst. The aim of the pre-sent work is to determine the effect of silica incorporation to the alumina support when preparing NiMo/Al2O3–SiO2(x) catalysts for the hydrotreatment reactions. The structural transformations and the role of the support characteristics were analyzed during sulfidation by means of in situ Raman spectroscopy.

ExperimentalCommercial -Al2O3 was surface modified with SiO2 using the following procedure: tetraethy-lorthosilicate (TEOS) of 99.5 wt% purity was slowly added to a suspension of -Al2O3 in anhy-drous ethanol in order to obtain the required SiO2 wt%. The suspension was agitated at 351 K during 12 h. After that, the support was filtered under vacuum, then dried at 373 K for 24 h and finally calcined at 823 K for 4 h. Supports were labelled as SAC X, where X represents the wt% SiO2 (0 and 10%). NiMo–SAC catalysts were synthesized by successive impregnation (pore vol-ume method) of Mo (2.8 Mo atoms/nm2) and Ni in a ratio Ni/(Ni + Mo) = 0.3, respectively. Here after, the catalysts will be labelled NiMo–SAC X, where X represents the wt% of SiO2 in the support [1,2]. This series was compared with NiMo/Al2O3–SiO2 catalysts prepared by the pH swing method (NiMo/(x)ASA). The catalysts were sulfided in a continuous flow operando reac-tor [3-5] operating at atmospheric pressure and 673 K for 4 h using a 15% H2S/H2 gas mixture, and heating stepwise from room temperature to 400 ºC. The operando reactor was loaded with 200 mg of catalyst using a flow of 40 ml/min of the sulfiding mixture.

Results and Discussion The results indicate that supported Ni-Mo oxide phases at low coverage do not form bulk nickel molybdate phases, but exhibit the Raman bands of surface modified molybdenum oxide species. The Raman spectra during sulfidation, Fig 1, show only the progressive transformation of Mo oxide species, which are more active in Raman. In the initial sulfidation stages, below 300 ºC, oxysulfides and less reduced molybdenum sulfide phases -probably MoS3- are apparent. Most samples exhibit no clear Raman features at 300 ºC during the sulfidation process. Strong Raman bands of nanocrystalline MoS2, which Raman bands appear in Fig. 2, become apparent above this temperature. The Raman spectra show that there is an initial sulfidation process up to 300 ºC, and


Program Section: Preferred form of presentation: POSTER

a rearrangement into MoS2 above 300 ºC. The specific support oxide affects this general trend. The activity of the catalysts in the hydrodesulfurization of 4,6-dimethyldibenzothiophene changed according to the above observed changes.

Figure 1. Raman spectra during sulfidation of NiMo/50ASA

Figure 2. Reference MoS2

Conclusions The use of in situ Raman allowed to observe the structural transformations of Mo oxide phases during the activation (sulfidation) of the catalysts. The observed changes in the nature of the sul-fided species were reflected on the activity displayed by the catalysts during the hydrodesulfuri-zation of 4,6-dimethyldibenzothiophene.

Acknowledgements The authors are indebted to the bilateral CSIC-CONACYT collaboration project (2005MX0031), this project was

partially funded by the Spanish Ministry of Science and Innovation (project CTQ2005-02802/PPQ). MOGP is indebted to CSIC for an I3PDR-8–02 postdoctoral fellow position.

References 1. Felipe Sánchez-Minero, Jorge Ramírez, Aída Gutiérrez-Alejandre, César Fernández-Vargas, Pablo Torres-

Mancera, Rogelio Cuevas-García, Catal. Today 133 (2008) 267 2. P. Rayo, Mohan S. Rana, J. Ramírez, J. Ancheyta and A. Aguilar-Elguézabal., Catal. Today 130 (2008) 283 3. M. V. Martínez-Huerta, PhD Dissertation, Universidad Autónoma de Madrid, Madrid, Spain 2001 4. Guerrero-Pérez, M. A. Bañares, Chem. Commun. (2002) 1292 5. M. O. Guerrero-Pérez, M. A. Bañares, J. Phys. Chem. C, 111 (2007) 1315 6. M. V. Martinez-Huerta, G. Deo, J. L. G. Fierro, M. A. Bañares, J. Phys. Chem. C, 112 (2008) 11441


Preferred section: Application of reporter molecules to image catalytic activity – Preferred form of presentation: Oral

Study of Au/CeZrO4 catalysts for the low temperature Water Gas Shift reaction;

identification of the active Au species

H. Daly, F. C. Meunier†, R. Pilasombat, R. Burch, A. Goguet* and C. Hardacre CenTACat, Queen’s University Belfast, Belfast BT9 5AG, U.K.

* [email protected] †Current address: LCS, Univ. Caen, CNRS, 6 Bd Maréchal Juin, F-14050 Caen, France.

Introduction and objectives

The importance of the preparation method of gold-oxide supported catalysts in achieving highly active catalysts for reactions such as WGS is widely known. Au supported on CeZrO4 has been found to be one of the most active catalysts for the WGS reaction [1] although there is still an issue with the stability of these catalysts which is hindering their practical application. While there is an understanding of how to produce active catalysts for the WGS reaction there is no consensus on the nature of the active Au with positively charged [2] and metallic gold [3] all proposed to be the active state of the gold.

Infrared spectroscopy has been widely employed to characterise the state of the Au through analysis of the Au-CO band position and in this study, we have carried out an in-situ DRIFTS-GC analysis of 1%Au/CeZrO4 for the WGS reaction. We have investigated the deactivation of the catalyst due to elevated reaction temperature and the amount of water in the feed and studied the evolution of the Au-CO bands during the reaction to assess the nature of the active Au.


The Au species identified on the catalyst under the WGS feed at 150°C are assigned to Au0-CO, band observed at 2095 - 2100 cm-1, Au + at 2125 cm-1 (shoulder on main band) and Au - at 2050-1965 cm-1 [4]. As the catalyst deactivates, there is a decrease in the Au-CO bands with loss of the Au +-CO bands at a faster rate than the Au0-CO bands. However, the catalyst is still active when there is no Au +-CO bands observed. Au + species are reduced under the feed and are not the active species for the WGS reaction. With time on stream, Au --CO bands are observed to increase at ~2050 – 1965 cm-1. These Au species are increasing while the catalyst is still deactivating so these species cannot be active for the WGS reaction. The change in the Au0-COband correlates with the deactivation rate of the catalyst under the different WGS feeds. The same trend regarding changes to the Au-CO bands is observed under


Preferred section: Application of reporter molecules to image catalytic activity – Preferred form of presentation: Oral

the 1% water feed except the change in the Au0-CO band is slower in line with the slower deactivation. The changes to the Au-CO bands are more dramatic following reaction at 400°. After 1 hour at 400°C, the activity has halved and there is a corresponding decrease in the Au0-CO band intensity. Au +-CO bands are fully depleted during the treatment at 400°C. The subsequent rate of change in the Au0-CO bands further maps the deactivation with time on stream. Interestingly, no Au --CO bands form following reaction at 400°C.

Figure 1: DRIFTS spectra of 1% Au/CeZrO4 under the WGS feed (7.5% H2O) at 150°C (a) normalized conversion and (b) evolution of Au-CO band intensity with time on stream.

Conclusions

Investigation of the deactivation of a 1%Au/CeZrO4 catalyst using in-situ DRIFTS-GC allowed clarifying the role of Au0, Au + and Au - species in Au/CeZrO4 low temperature WGS catalysts. Au + and Au - could be discarded as possible active sites while the results are consistent with metallic gold being the active Au species

References

1. Burch, R., Physical Chemistry Chemical Physics 2006, 8, 5483.

2. Fu, Q.; Salzburg, H.; Flytzani-Stephanopoulos, M., Science 2003, 301, 935.

3.Tibiletti, D.; Fonseca, A. A.; Burch, R.; Chen, Y.; Fisher, J. M.; Goguet, A.; Hardacre, C.; Hu, P.; Thompsett, D., J. Pys. Chem B., 2005, 109, 22553.

4. F. Menegazzo, M. Manzoli, A. Chiorino, F. Boccuzzi, T. Tabakova, M. Signoretto, F. Pinna and N. Pernicone, J. Gatal., 2006, 237,2, 431.


Program Section: (3) New applications in liquid-phase processes …. Preferred form of presentation: Poster

Combined on-line transmission FTIR spectroscopy and BTEM studies for

monitoring consecutive base-catalyzed aqueous-phase organic reactions

Martin Tjahjono, Effendi Widjaja, Chong Huiheng, and Marc Garland

Institute of Chemical and Engineering Sciences, Agency for Science, Technology and Research (A*STAR), 1 Pesek Road, Jurong Island, Singapore 627833, Singapore

Email: [email protected]_star.edu.sg


Online transmission FTIR spectroscopy and the Band-Target Entropy Minimization (BTEM)1

algorithm are employed in order to monitor the base-catalyzed and consecutive hydrolysis reac-tions of diethyl phthalate (DEP) in aqueous-ethanol solvent mixture (Scheme 1).2 The pure com-ponent spectra of the reactive species involved in this reaction (i.e., DEP, mono-ion intermediate and di-ion product) and their corresponding concentrations are determined. The results from these observations are further used to study the effect of temperature and the solvent mixture composi-tions on these consecutive reaction steps. Online transmission FTIR spectroscopy was chosen over ATR spectroscopy (which is known to possess non-linear optical effects)3 in order to facili-tate the subsequent signal processing steps and multivariate analysis.4

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Scheme 1. The homogeneous base-catalyzed consecutive transformation of diethyl phthalate to mono-ion in-termediate and di-ion product.


The typical transmission infrared spectra of the hydrolysis reaction of DEP measured in etha-nol-water solvent mixtures in the wavenumber range of 1200-1500 cm-1 are presented in Figure 1(a). In order to further highlight the spectra changes due to reactions, the spectral contributions from the solvents (water and ethanol) as well as the sodium hydroxide are subtracted from the reaction spectra (see Figure 1(b)). In the BTEM analyses, three peaks with maxima at 1301 cm-1,1396 cm-1, and 1403 cm-1, were used and retained as targets. They were found to correspond to the reactant, intermediate and the product species, respectively. The reconstructed pure compo-nent spectra and the concentration profiles of the reactant DEP, mono-ion intermediate and di-ion product are shown in Figure 1(c) and (d), respectively.


Program Section: (3) New applications in liquid-phase processes …. Preferred form of presentation: Poster

(a) (b)

(c) (d) Figure 1. Infrared spectra of the base-catalyzed hydrolysis reaction of DEP in ethanol-water (50:50, %v/v) solvent mixtures and at 293 K. (a) before and (b) after solvent + NaOH spectra subtractions, (c) Pure com-ponent spectra of (i) DEP (ii) mono-ion intermediate (iii) di-ion product and (d) their concentrations. [Note: DEP = 0.285 g; NaOH= 0.8 g in 50 mL mixture solvents] Cell path length was 25 micron.

The effects of temperature (293, 298, 303, 308, and 313 K) and solvent mixtures (etha-nol/water, 40, 50, 60, 70, 80% v/v) on the reaction rates for both consecutive steps were investi-gated. The results showed that both consecutive reaction rates were consistently increasing with higher temperature. However, interesting phenomena was observed when the solvent mixtures were varied. The reaction rates first decreased and then increased with increasing ethanol content, with a rate minimum in circa 60% ethanol. Emphasis is given to the use of transmission FTIR to monitor this aqueous base-catalyzed reaction as well the advanced signal processing steps used.

Conclusions

Combined online transmission FTIR spectroscopy and BTEM analysis were successfully ap-plied to study base-catalyzed aqueous-phase reactions. This allowed elucidation of the reactive species and their respective concentration profiles during reactions. The unusual use of online transmission FTIR spectroscopy for studying this aqueous phase reaction (with 25 micron path length) facilitated the subsequent spectral reconstructions and multivariate analyses.

References [1] Widjaja, E., Li, C.Z., and Garland, M. Organometallics 2002, 21, 1991-1997; Chew, W., Widjaja, E., and Gar-land, M. Organometallics 2002, 21, 1982-1990; Widjaja, E., Li, C.Z., Chew, W., and Garland, M. Anal. Chem. 2003,75, 4499-4507. [2] Venkatasubramanian N. and Rao G.V., Tetrahedron Lett.1967, 52, 5275-5280. [3] Yamamoto K. and Ishida H., Vib. Spectrosc. 1994, 8, 1-36. [4] Garland, M. Processing Spectroscopic Data. In Mechanisms in Ho-mogeneous Catalysis: A Spectroscopic Approach; Heaton, B., Ed.; Wiley-VCH: Weinheim, 2005, ch.4.


Program section : New applications in liquid-phase processes including homogeneous catalysis and catalyst synthesis

Preferred form of presentation: Poster

Combination of Mid-Infrared Spectroscopy and chemometric factorization tools to study the oxidation of lubricating base oils

N.Graciaa,b,c, S. Thomasa, L. Duponchelb, F. Thibaut-Starzyka, O. Leraslec.

a Laboratoire Catalyse et Spectrochimie, ENSICAEN, Université de Caen, CNRS,

6 Bd Maréchal Juin, F-14050 Caen

b Laboratoire de Spectrochimie Infrarouge et Raman (LASIR), CNRS-UMR 8516,

Université des Sciences et Technologies de Lille (USTL), bât C5, F-59655 Villeneuve d’Ascq

c Centre de Recherche de Solaize, TOTAL, BP22 – F-69360 Solaize Cedex.

Introduction and objectives

Maintaining the quality of lubricants is essential because of their key role in machine duration and performance. Oxidation is one of the main causes of oil degradation. To prevent and reduce the consequences of this phenomena in the best possible way, mecanisms must be determined and well understood.

The objective is to set-up an experimental system to reproduce, in a lab-scale and in an accelerated mode, the oxidation process of lubricating base oils under temperature close to those existing under working conditions (addition of metal salts). Mid-infrared spectroscopy has been chosen for on-line monitoring of the chemical changes happening along the process. To understand the oxidation evolution and the action of iron as catalyst, the spectroscopic data recorded have been analysed with factorization techniques such as Principal Component Analysis (PCA).

Results and discussion

Oxidation experiments consist in the heating of a certain amount of lubricating oil with oxygen bubling during 8 hours. Continuous sampling is allowed by a circulation through a transmission cell in a FTIR spectrometer (Figure 1).

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Figure 1: experimental set-up. A: oil sample. B: electromagnetic pump. C: IR transmission cell.


Program section : New applications in liquid-phase processes including homogeneous catalysis and catalyst synthesis

Preferred form of presentation: Poster

The obtained spectra (Figure 2.a) showed that infrared spectroscopy is suitable to detect the molecules issued from the oxidation (alcools, ketones, carboxylic acids, esters) [1,2].

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Figure 2: a) Spectra recorded during oxidation process with iron salt – 1 spectrum/h.

b) Evolution of the integration of νO-H bands along time.

Evolution of the carbonyls band νC-O (1650-1820 cm-1) exhibited no major differences wether the oxidation is carried out with or without catalyst. On the other hand, the evolution of the integration of the band between 3100 and 3600 cm-1 showed that the presence of catalyst (Figure 2.b) induces an acceleration in the formation of alcohols and the esterification reactions.

The Principal Component Analysis (PCA) permits to extract the underlying factors [3] responsible of the evolution of the spectra during oxidation process. PCA showed the differences induced in the oxidation by the presence of iron catalyst, on alcohols formation and consumption in particular. It exhibited the fact that the first Principal Component, expressing more than 97% of the variance of the system, corresponds to the constant formation of oxidized molecules.

Conclusions

Combination of Mid-Infrared spectroscopy and chemometric factorization tools allowed to exhibit the differences induced by the presence of iron salts in oxidation mechanisms for lubricants.

References [1] Adhvaryu A., Perez J.M., Singh I.D. and Tyagi O.S.: Spectroscopic studies of oxidative degradation of base oils,

Energy and Fuels, 1998, 12, 1369-1374. [2] Coates J.P. and Seti L.C.: Infrared spectroscopic methods for the study of lubricant oxidation products, ASLE

Transactions, 1985, 29, 3, 394-40. [3] Joliffe, I.T.: Principal Component Analysis, 2nd Edition, 1986, New York Springer.


Program Section: (3) Preferred form of presentation: Poster

Combination of Spectroscopic Measurements: in situ NMR and UV/Vis Spec-troscopy to understand the Formation of Group 4 Metallacyclopentanes from

the corresponding Metallacyclopropenes

Torsten Beweriesa, Christian Fischera, Stephan Peitza, Vladimir V. Burlakovb, Perdita Arndta,Wolfgang Baumanna, Anke Spannenberga, Detlef Hellera*, and Uwe Rosenthala*

a Leibniz-Institut für Katalyse e.V. and der Universität Rostock, Albert-Einstein-Straße 29a, 18059 Rostock, Germany, b INEOS, Vavilov Street 29, 117813 Moscow, Russia.


First hafnocene alkyne complexes of the type Cp’2Hf(L)( 2-Me3SiC2SiMe3) have been reported recently.1 Upon reaction of these complexes with unsaturated substrates such as olefins, metalla-cycles are formed, which can serve as model compounds for catalytic processes, e.g. for the se-lective oligomerization of ethylene to 1-butene, 1-hexene and 1-octene.

Results and Discussion2

At ambient temperature, the hafnocene alkyne complex 1-Hf reacts with ethylene under forma-tion of a hafnacyclopentene 2-Hf. This species is formed in a consecutive reaction, consisting of two pseudo-first-order-reactions. Most likely, in the first step olefin association and formation of a bis- -complex (A) takes place.

Support for this reaction sequence can be found in the results from UV/Vis spectroscopy: both rate constants (1-Hf A and A 2-Hf) depend on the concentration of ethylene; the constants are direct proportional to the concentration of ethylene. At higher temperature, the hafnacy-clopentane 3-Hf is formed by dissociation of the alkyne and coupling of two molecules of ethyl-ene.


Program Section: (3) Preferred form of presentation: Poster

In contrast, at room temperature the zirconium complex 1-Zr reacts with ethylene under dissocia-tion of the alkyne to give a zirconacyclopentane 3-Zr. This reaction can be described as a pseudo-first-order-reaction, as indicated by an isosbestic point in the UV/Vis reaction spectra.

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We have found a significant gradation in reactivity in the reaction of the alkyne complexes 1-Mwith ethylene and investigated this reaction behavior with in situ NMR methods and UV/Vis spectroscopy. The complexes 1-Zr and 1-Hf form stable metallacycles. However, the formation of the metallacycles proceeds at different temperatures, indicating the stronger complexation of the alkyne in 1-Hf.

Conclusions

The use of UV/Vis spectroscopy made it possible to observe a reactive intermediate in the reac-tion of 1-Hf with ethylene. The assumed -complex has not been observed before by common NMR methods and first hints for the existence of such a complex were found.

References [1] a) T. Beweries, V. V. Burlakov, M. A. Bach, P. Arndt, W. Baumann, A. Spannenberg, U. Rosenthal, Or-

ganometallics 2007, 26, 247. b) T. Beweries, V. V. Burlakov, S. Peitz, P. Arndt, W. Baumann, A. Spannenberg, W. Baumann, U. Rosenthal, Organometallics 2008, 27, 3954.

[2] T. Beweries, C. Fischer, S. Peitz, V. V. Burlakov, P. Arndt, W. Baumann, A. Spannenberg, D. Heller, U. Rosen-thal, submitted.

reaction time

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COUMARINS SYNTHESIS MONITORING BY RAMAN SPECTROSCOPY TO CON-

TROL THE PREPARATION OF PHARMACEUTICALS

V. Calvino-Casilda a, M. A. Bañares a and E. Lozano-Diz b

a Catalytic Spectroscopy Laboratory, Inst. de Catálisis y Petroleoquímica (CSIC), C/ Marie Curie2, E-28049 Madrid ([email protected])

b Perkin-Elmer, Chalfont Road, seer Green HP92FX, UK


Coumarins and their derivatives are important compounds in the synthetic organic andmedicinal chemistry and are used for the preparation of coumarino-pyrones, furocumarins,chromenes, and 2-acylresorcinols. These compounds find applications in synthesis of pharmaceu-ticals, fragrances, agrochemicals, and insecticides. The Hymecromone, 7-hydroxy-4-methylcoumarin or 7-hydroxy-4-methyl-2H-1-benzopyran-2-one, is used commercially as laserdye, as biliary antispasmodic, and it is also the starting material for the production of the insecti-cides. Pechmann reaction is an efficient simple method to synthesize coumarins. In a classicalway, the reaction consists of the condensation of phenols with ¢-ketoesters. This contribution re-ports the synthesis of coumarins, especially of 7-hydroxy-4-methylcoumarin (Hymecromone) viaPechmann condensation between resorcinol and ethyl acetoacetate [1,2].

Raman spectroscopy is ideally suited for process monitoring reaction control. It offers anon-destructive, non-contact method of analysis suitable for both laboratories based and plantbased applications. The high information content of the Raman spectrum provides a unique fin-gerprint to identify and monitor chemical reactions and processes [3,4]. The model reaction stud-ied was the synthesis of coumarins from the condensation between resorcinol and ethyl acetoace-tate with acid solids as catalyst under conventional thermal heating; homogeneous and heteroge-neous acid catalysts are compared for this reaction.


The Pechmann reaction for the synthesis of coumarins was run in a batch reactor underthermal activation at 60 ºC and under continuous stirring. The reaction was monitored by Ramanspectroscopy in a Perkin-Elmer Raman Station 400-F system using 100 mW of 785 nm excitationline and 6 seconds acquisition time. A comparison of the Raman bands intensity with off-line GCanalyses allow for quantitative reaction monitoring and insight into the reaction mechanism. Fig-ure 1 illustrates representative Raman spectra acquired every 5 minutes during reaction.



The Raman bands of the reaction product grow stronger as the reaction progresses; con-comitantly, those of the reactants -resorcinol and of ethylacetoacetate- decrease in intensity. Forinstance, representative Raman bands, like those in the 1600–1100 cm�1 frequency range due tothe C-O-C and methyl alkene stretching vibrations in the alpha-pirone ring of the product growstronger, while those of the of C-H stretching at 998 and 740 cm-1 decrease in intensity with reac-tion time coordinate, reflecting the conversion of resorcinol to the product. Accordingly, the con-sumptions of C=O stretching mode at 1736cm-1 and C-C-O stretching mode at 1304cm-1 reflect-ing the progressive consumption of ethyl acetoacetate to the product.

Figure 1. Raman spectra of the Pechmann reaction between resorcinol and ethyl acetoacetate at60 ºC using HCl as catalyst for the synthesis of 7-hydroxy-4-methylcoumarin (Hymechromone).

References

[1] R.O’Kennedy and R.D. Thornes, Coumarins: Biology, Applications and mode of Action (John Wiley) Sons,Chichester, 1997.

[2] C. Gutiérrez-Sánchez, V. Calvino-Casilda, E. Pérez-Mayoral, R. M. Martín-Aranda, A. J. López-Peinado, M.Bejblová and J. £ejka. Catalysis Letters (2008), in press

[3] T. Becker, B. Hitzmann, K. Muffler, R. Pörtner, K. F. Reardon, F. Stahl R.Ulber, Adv Biochem En-gin/Biotechnol 105 (2007) 249

[4] M. A. Bañares, G. Mestl, Adv. Catal. 52 (2009) in press



In-situ spectroscopic (FTIR and UV-Vis) investigation of the acid-catalysed oligomerization of unsaturated (methyl-acetylene) and aromatic (pyrrole,

thiophene and furane) monomers inside the NAFION membrane.

Jain Sagar Motilal, Svetoslava Vankova, Elena Groppo, Adriano Zecchina and Giuseppe Spoto

Dipartimento di Chimica IFM e NIS Centre of Excellence of the Torino University

Via P. Giuria 7, I-10125 Torino, Italy - E-mail: [email protected]


Conductive polymeric membranes are key components of solid electrolyte membrane fuel cells (PEMFC) (which are expected to represent in the near future an important source of clean energy for transportation, stationary and portable applications) and are therefore extensively studied [1]. Those based on Nafion are at the present the most effective for proton conductivity in devices operating in the 60-80 °C temperature range, although they suffer of some drawbacks like low mechanical and chemical stability, high permeability to methanol and other fuels, and strong de-pendence of the proton conductivity on the humidity. It has been shown that hybridization can represent a route to solve some of these problems. It has been for instance reported that incorpo-ration of sulphonated single-walled carbon nanotubes meliorates the Nafion proton conductivity as well as the chemical and mechanical properties [2]. Methanol crossover is on the contrary ex-tensively reduced (ca. 40%) in poly(1-methylpyrrole)/Nafion hybrid systems [3]. As far as the class of polyaromatic/Nafion hybrid systems is concerned, it is worth underlining that polymeri-zation can be performed in situ because of the strong Brønsted acidity properties of Nafion [4]. It is so conceivable that a detailed knowledge of the polymerization mechanism can help to control the process and finally the physical-chemical properties of the resulting hybrid membrane. For this reason, we have investigated the polymerization of a variety of unsaturated (methyl-acetylene) and aromatic (pyrrole, thiophene and furane) inside Nafion by in situ IR and UV-Vis spectroscopies under operando conditions.


For all the investigated molecules (methyl-acetylene, pyrrole, thiophene and furane) the spectro-scopic measurements were performed using self-supporting Nafion films (prepared following the procedure described in [5]) suitable for IR and UV-Vis transmission measurements. In all cases the Nafion membrane was placed in a cell allowing outgassing of the membrane at 100 °C under vacuum and dosage of the studied molecule from the gas phase. The experiments were therefore performed in absence of water or oxygen contamination. After dosage of the molecule under in-vestigation, the oligomerization reaction was spectroscopically studied as a function of the con-



tact time (up to 24 hrs) and of the temperature (up to 100 °C). As an example, in Figure 1 are shown the spectra obtained with pyrrole before (full line) and after (dashed line) pyrrole dosage at room temperature and after heating in pyrrole atmosphere at 100 °C (all the intermediate spec-tra are omitted for clarity).

2000 1800 1600 1400 1200 1000 8000.0

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Figure 1: IR (left) and UV-Vis spectra of the pyrrole/Nafion system. Full line: Pure Nafion outgassed at 100 °C. Dashed line: After dosage of pyrrole from the gas phase. Dotted line: After heating at 100 °C in pyrrole atmosphere.

Without enter into details for sake of brevity, we only mention that the spectral modifications ob-served in Figure 1 testify the following reaction steps:

-SO3H – C4H5N -SO3- + (C4H5N)H+ (full line dashed line)

(C4H5N)H+ + nC4H5N (C4H5N)nH+ (dashed line dotted line)

where n=3-5. The conclusion that we are dealing with charged reaction products is demonstrated by the fact that dosage of NH3 deeply modify the IR as well as the UV-Vis spectrum.

Conclusions

In situ FTIR and UV-Vis spectroscopy under operando conditions of unsaturated and aromatic monomers/Nafion systems allows the detailed investigation of the acid-catalized polymerization, leading to hybrid proton conductive membranes with potential application in solid electrolyte fuel cells.

References [1] Vishnyakov, V.M. Vacuum 2006, 80, 1053 and references therein.. [2] Kanna, R. et al Angew. Chem. Int. Ed. 2008, 47, 2653. [3] Ja, N et al. Electrochem. Solid State Lett. 2000, 3, 529. [4] Zecchina, A. et al. Phys. Chem. Chem. Phys. 2005, 7, 1627. [5] Buzzoni, R. et al. J. Phys. Chem. 1995, 99, 11937.


Program Section: Bridging the gap between model and technical conditions Preferred form of presentation: Poster

In Situ Monitoring of Turbid Immobilized Enzymatic Systems: Lipase-

Catalyzed Esterification of Oleic Acid Using Fiber-Optic Raman Spectroscopy

Erick Elfansoa, Marc Garlandb, Kai Chee Loha, M. M. Rahman Talukderb, Effendi Widjajab

aDepartment of Chemical and Biomolecular Engineering, National University of Singapore, 4

Engineering Drive 4, Singapore 117576bInstitute of Chemical and Engineering Sciences, Agency for Science, Technology and Research

(A*STAR), 1 Pesek Road, Jurong Island, Singapore 627833

[email protected]

[email protected]


Owing to the advantages offered by enzymes as catalysts in organic solvent, the interest in lipase-catalyzed reactions, such as esterification, inter-esterification, and trans-esterification has vastly grown.1 It has also triggered chemical industries to exploit the catalytic characteristics of lipases isolated from various microbial sources. One of the most common analytical techniques em-ployed to investigate the kinetics of enzymatic reactions is to use off-line chromatographic in-strumentation. This conventional technique generally requires more sample preparation, longer analysis time, and it is also invasive. Alternative analytical techniques, such as in situ spectros-copy is certainly preferred, since it can be readily carried out and the progress of the reaction can be monitored in real time.2 In the present study, we investigated the use of fiber-optic Raman spectroscopy to monitor the lipase-catalyzed synthesis of ethyl oleate by the esterification of oleic acid and ethanol. The effects of reaction temperature and molar ratio of substrates were studied.


The fiber optic probe was immersed in a 3-neck 25-ml jacketed and thermostated glass reactor. Stirring was achieved with a magnetic stirrer controlled at 200 rpm. The Raman spectra were col-lected using a near infrared laser (785 nm) over the range 1300-1800 cm-1 with a resolution of circa 1.2 cm-1. The collected in situ Raman spectra were then processed and analyzed to deter-mine the percentage conversion of substrates to ethyl oleate ester using a calibration approach. Figures 1a and 1b show the concentration profile of ethyl oleate with time for various reaction temperatures. These reactions with various temperatures were carried out with a molar ratio of ethanol to oleic acid of 1.2 and 0.4 grams of Candida antartica lipase in 10 ml of iso-octane sol-vent. The solution is turbid during reaction due to the insolubility of the immobilized lipase.


Program Section: Bridging the gap between model and technical conditions Preferred form of presentation: Poster

Figure 1. Concentration profiles of ethyl oleate as a function of reaction time, (a) T = 25, 30, 35, 40, 50 C, (b) T = 50, 60, 65 C

The time-dependent concentration profiles of ethyl oleate were then used to calculate the initial reaction velocity. Figures 2a and 2b show the plots of initial reaction velocity obtained from varying reaction temperatures and molar ratio of substrates.

Figure 2. Initial reaction velocity obtained from: (a) temperature variations, (b) molar ratio varia-tions

The effect of reaction temperature suggested that the optimal reaction temperature was 60oC (Fig. 2a). Beyond this temperature, the rate started to decrease due to thermal denaturing of the lipase. The effect of the ethanol to oleic acid molar ratio suggested that the initial reaction rate reaches a maximum at a ratio 1.2, after which it decreases (Fig. 2b). The decrease in reaction rate at higher ratio indicates that the excess ethanol inhibits Novozym 435 activity. This inhibitory effect was found to follow the Ping-Pong Bi-Bi mechanism.

ConclusionsPresent study shows that in-situ fiber-optic Raman spectroscopy can be successfully applied to turbid enzyme-catalyzed organic-phase reactions. The rates of organic product formation can be successfully monitored. References [1] Krishna SH, Karanth NG. Catal Rev 2002, 44, 499-591. [2] Haberkorn M, Hinsmann P, Lendl B. Analyst 2002, 127, 109-113. [3] Bell WC, Booksh KS, Myrick ML. Anal Chem 1998, 70, 332-339.

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Program Section: (3, 4)? Preferred form of presentation: lecture

On-line NMR Spectroscopy of Technical Samples – Challenges and Solutions

Michael Maiwald

BAM – Federal Institute of Materials Research and Testing Division I.4: Process Analytical Technology

Richard-Willstaetter-Str. 11, D-12489 Berlin, Germany Tel.: +49 30 81 04-11 40, Fax: +49 30 81 04-11 47

[email protected], www.bam.de


The development of on-line (flow) techniques has tremendously increased the value of nuclear magnetic resonance (NMR) spectroscopy for process development applications and became very attractive as non-invasive methods. Quantitative high-resolution on-line NMR spectroscopy can meet these demands when flow probes are directly coupled to process equipment like reactors for process monitoring – from laboratory size up to industrial scale [1]. There is a need to study com-plex multicomponent mixtures and gain insight into their behaviour in the real process.


There are important restrictions in most engineering applications of NMR spectroscopy, e.g., to work completely without deuterated solvents (cost, isotope effects). For most technical samples also sample preparation generally is not possible. This has several consequences, e.g., on shim-ming or lock. Suitable techniques for solvent signal suppression have to be applied under quanti-tative aspects. Radiation damping for concentrated nuclei lead to line broadening, non-linear phase shifts, errors in determining T1 and T2 times and pulse width calibration, and other effects. The use of extremely small pulse angles or mismatching the rf circuit (“detuning”) can be a solu-tion in some cases.

Among various applications, quantitative results from NMR studies of autocatalyzed as well as homogeneously and heterogeneously catalyzed esterification kinetics are discussed with empha-sis on the analytical method and its experimental challenges and solutions.


Program Section: (3, 4)? Preferred form of presentation: lecture

Conclusions

On-line NMR spectroscopy is the method of choice for the investigation of complex fluid mix-tures with analytically similar compounds, where other analytical methods (e.g., optical spectros-copy such as UV/VIS, infra-red (IR), Raman, or fluorescence spectroscopy) suffer from insuffi-cient differentiation of components. In addition the high value of NMR in determining chemical structure and accurate quantitation, more subtle features such as speciation (e.g. protonation) are clearly indicated. Many samples are sensitive to changes in concentration, pH, temperature, or pressure, so that chromatographic methods may be ruled out. A major advantage of NMR spec-troscopy is that no calibration is needed for quantification in most cases, and the method features a high linearity between absolute signal area and species concentration. Furthermore, on-line NMR spectroscopy allows investigations under elevated pressures, e.g., to prevent the solutions from boiling [1, 2], for studies under process conditions, or supercritical fluid conditions [3]. The use of self-shielding magnet technology allows compact magnets with low stray fields to be used in miniplant environments, and provides new opportunities for high-field, high-resolution ex-periments.

References [1] Maiwald, M.; Fischer, H. H.; Y.-K. Kim; Albert, K.; Hasse, H.: Quantitative High-resolution On-line NMR

Spectroscopy in Reaction and Process Monitoring, J. Magn. Reson. 166 (2004), 135–146 [2] Maiwald, M.; Grützner, T.; Ströfer, E. Hasse, H.: Quantitative NMR spectroscopy of complex technical mix-

tures using a virtual reference: chemical equilibria and reaction kinetics of formaldehyde–water–1,3,5-trioxane, Anal. Bioanal. Chem. 385 (2006), 910–917

[3] Maiwald, M.; Li, Hongping; Schnabel, T.; Braun. K.; Hasse, H.: On-line 1H NMR Spectroscopic Investigation of Hydrogen Bonding in Supercritical and Near Critical CO2-Methanol up to 35 MPa and 403 K, Journal of Su-percritical Fluids, 43 (2007) 267–275


Program Section: New reactor cells and coupling techniques. Preferred form of presentation: Poster

Experimental Systems for Convenient and Robust In-Situ Liquid-Phase

Spectroscopic Studies.

Feng Gao, Chuanzhao Li, Cheng Shuying, Marc Garland

Institute of Chemical and Engineering Sciences, 1 Pesek Road, Jurong Island, Singapore 627833


In situ liquid phase studies of homogeneous (and even heterogeneous) catalytic systems are be-coming much more common. However, there are a considerable number of experimental / equipment issues that must be addressed for successful studies, as well as a number of experi-mental / equipment issues which can greatly enhance the convenience and robustness of such studies.

In the present contribution, we review the current experimental set-ups being used at our insti-tute. The necessary equipment items include cheap and easy-to-machine (a) high pressure reac-tors and (b) FTIR / UV-VIS cells as well as (c) hermetically sealed gear pumps with interchange-able heads, which can be used separately for each catalytic metal studied, in order to avoid cross-contamination [1]. In addition, we are using high pressure (d) injection / sampling blocks to fa-cilitate pulse additions / withdraw of reactants as well as (e) syringe pumps for semi-continuous infusion of reactants.

Our present set-ups, which can be used up to 5.0 MPa and more, provide unusual contacting patterns for the addition of reactants. This flexibility in the sequence and frequency of reactant addition greatly facilities better experimental designs and this greatly benefits further signal proc-essing work such as spectral reconstruction [2].


Fig 1 shows a schematic diagram of the general experimental system used for in-situ FTIR stud-ies. This general system contains all the parts mentioned previously in the introduction. In addi-tion, on-line measurements of the liquid-phase during a heterogeneous catalytic reaction is easily implemented by installing a fixed-bed-reactor in-line with the other components. This has been performed for heterogeneous catalytic reactions.[3] Fig 2 shows photographs of some in-house designed and constructed equipment items. These include the reactor with built-in stirrer and internal heat exchanger, a typical flow-through cell for 40 mm diameter by 15 mm thick windows (also with internal heat exchanger) and the injection / sampling block constructed with multi-port valves (also with internal heat exchanger). Detailed information, including gas-liquid mass transfer characteristics, mixing information and technical drawings can be found in reference 1.


Program Section: New reactor cells and coupling techniques. Preferred form of presentation: Poster

Fig 1. Typical experimental system for high pressure liquid phase studies up to circa 5.0 MPa. (1) stirred tank (2) high pressure hermetically sealed gear pump (3) mid-infrared cell with CaF2, KBr, or ZnSe windows (4) far-infrared cell with CVD diamond windows (5) multi-port inject and sampling block (6) syringe pump (7) fixed bed reactor (optional for heterogeneous catalytic studies [3]). [connections for gases, vacuum etc not shown]

Fig 2. Photographs of the thermostated reactor (left), spectroscopic cell (center) and injection / sampling block (right)

Commercial components include a hermetically sealed gear pump (MicroPump) and a stainless steel syringe pump assembly (Harvard Instruments). A hermetically sealed pump is absolutely needed for careful and reproducible work on both homogeneous and heterogeneous systems in order to avoid contamination by moisture and oxygen. The entire system has been extensively used in order to perform robust experimental designs for homogeneous catalyzed reactions whose data were then successfully analysed with various multivariate algorithms [4].

Conclusions

Robust experimental systems enhance the opportunities for in-situ spectroscopic studies. The present system is an example of the flexible set up currently used in our institute.

References [1] F. Gao, KP Ng, C Li, KI Krummel, AD Allian, M Garland Journal of Catalysis 237 2006, 49 [2] M. Garland “Processing Spectroscopic Data” in Mechanisms in Homogeneous Catalysis B. Heaton (Ed) Wiley 2005 [3] F. Gao, AD Allian; HJ Zhang; S Cheng ; M Garland, Journal of Catalysis 241 2006, 189 [4] C Li, L. Chen, M Garland J. Am. Chem. Soc., 129 2007 13327


Program Section: 3 or 4 Preferred form of presentation: poster

Kinetic Investigations on Rhodium Catalyzed Ligand Modified Hydroformylation

Christoph Kubisa, Ralf Ludwigab, Detlef Selenta, Armin Börnerab,Klaus-Diether Wiesec, Dieter Hessc

aLeibniz-Institut für Katalyse e.V. an der Univ. Rostock, Albert-Einstein-Str. 29a, 18059 Rostock bInstitut für Chemie, Universität Rostock, Albert-Einstein-Str. 3, 18059 Rostock cEvonik Oxeno GmbH, Paul-Baumann-Str. 1, 45772 Marl


The study of the kinetics is an important tool for mechanistic knowledge of any catalyzed re-action [1]. For kinetic investigations of the hydroformylation we perform the reactions in a semi-batch autoclave under constant pressures of 10 – 50 bar SynGas (CO/H2 = 1/1) and temperatures between 25 – 120 °C. With the help of an automated sample device [2] for chromatographic

analysis it’s possible to take a variable number of samples under the reaction conditions, Fig. 1. This device allows sampling under inert conditions.

At present time we’re in the process of connecting our experimental apparatus with an external IR transmission cell [3] in order to combine analysis of substrates and products via chromatography with analysis of catalyst species via IR spectroscopy.

Fig. 1: Coupled system in our lab: Semi-batch autoclave and automated sample device

We selected the cyclic olefin (Z)-cyclooctene as substrate, which exclusively give one hydro-formylation product. We performed this reaction with three different phosphite ligands, Fig. 2.

Fig. 2: Hydroformylation of (Z)-cyclooctene and the different phosphite ligands used for this study

PO

O O

P PO O

OCH3 OCH3

O OO

O

P PO O

OCH3 OCH3

OO

OCH3

OCH3

OOO

Ligand A Ligand B Ligand C

OCO/H2

(Z)-Cyclooctene

kobs.

Cyclooctanecarboxaldehyde




The following activity graduation was observed: ligand A > ligand B > ligand C, Fig. 3. For the reaction with ligand C we applied even a higher rhodium concentration and a higher temperature. The observed rate constants were determined by nonlinear-regression of the gas chromatographic data with assumption of first order kinetics with respect to the olefin.

Fig. 3: Determination of the observed first order rate constants for the hydroformylation of (Z)-cyclooctene

Conclusions

In the hydroformylation of (Z)-cyclooctene catalyst systems with monodentate ligands show higher activity compared to bidentate systems [4]. The first order with respect to the olefin indicates a step early in the reaction cycle as rate limiting. In order to prove this the detection of the catalyst carbonyl species and a kinetic study of these with in situ IR spectroscopy, which is a tool of choice for these investigations, is necessary [5]. The connection of our reactor system to an external transmission IR cell is in progress.

References [1] Drexler, H.-J.; Preetz, A.; Schmidt, T.; Heller, D.: Kinetics of Homogeneous Hydrogenations : Measurement and

Interpretation. In: de Vries, J. G.; Elsevier, C. J.: The Handbook of Homogeneous Hydrogenation. Weinheim : WILEY-VCH, 2007.

[2] Construction: amplius GmbH, Friedrich-Barnewitz-Str. 8, 18119 Rostock [3] Construction: Dr. Bastian GmbH Feinwerktechnik, Oberer Grifflenberg 155, 42119 Wuppertal [4] Kamer, P. C. J.; Reek, J. N. H.; van Leeuwen, P. W. N. M.: Rhodium Phosphite Catalysts. In: van Leeuwen,

P. W. N. M.; Claver, C. (Ed.): Rhodium Catalyzed Hydroformylation. Dordrecht : Kluwer, 2000. [5] Zuidema, E.; Escorihuela, L.; Eichelsheim, T.; Carbó, J. J.; Bo, C.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.:

Chem. Eur. J. 2008, 14, 1843-1853.


Program Section: Preferred form of presentation: poster

Operando Raman-GC study of Mo-V-Nb-O catalytic system during the selec-tive oxidation of propane to acrylic acid

Ricardo López-Medinaa, M. Olga Guerrero-Pérezb and M.A. Bañaresa

aCatalytic Spectroscpy Laboratory, Instituto de Catálisis y Petroleoquímica (CSIC); Marie Cu-rie, 2; E-28049-Madrid (Spain), dDepartamento de Ingeniería Química; Universidad de Mála-

ga; Campus de Teatinos; E-29071-Málaga (Spain)


The availability and low cost of alkanes have generated much recent interest in the oxidative catalytic conversion of alkanes to olefins, oxygenates, and nitriles. Mo-V-O oxides are being in-vestigated as catalysts for many oxidation reactions, and they are especially suitable conversion of parafins, like propane, to olefins or to oxygenates, like acrylic acid. When these catalysts are modified with niobium, their selectivity to acrylic acid improves significantly. This contribution reports an operando Raman-GC investigation of alumina supported Mo-V-Nb-O during the par-tial oxidation of propane. The spectroscopic results obtained during reaction show the transfor-mation of surface structures and their relevance for propane oxidation to acrylic acid.


Table 1 shows the activity data obtained during propane ammoxidation at 400 ºC. Figure 1 shows the Raman spectra for fresh and used alumina-supported 4Mo5V4Nb1 and 12Mo5V4Nb1 under ambient (hydrated) and dehydrated conditions (air, 200ºC). The 4 and 12 prefixes indicate the coverage, 4 and 12 Mo+V+Nb atoms/nm2 of Al2O3 support.

Conversion Selectivity

Propane Acrylic Acid Acrolein Propylene CO CO2

4Mo5V4Nb1 19.1 5.4 5.7 8.9 5.5 72.7

12Mo5V4Nb1 30.3 3.9 4.2 2.9 39.8 42.8

The fresh samples exhibit Raman bands near 822 and 370 cm-1 under dehydrated conditions (air, 200 ºC), characteristic of Mo-V-O species (phase I) [1]; new Raman bands appear near 1010 and 230 cm-1 and a broad band at 770 cm-1 in 4Mo5V4Nb1 (spectra b). The Raman bands at 770 and 230 cm-1 have been found before in aged alumina-supported Mo-V-O catalysts and are assigned to AlVMoO7 phase [2].. Raman band near 1024 cm-1 is assigned to the V=O stretching mode of surface vanadium oxide species, this band shifts under hydrated conditions [3]. The band near 996 cm-1 is characteristic of the Mo=O stretching mode of surface monooxo molybdenum oxide species [3]. The presence of V2O5 and/or MoO3 nanocrystals can be excluded since their intense Raman bands are not observed [3].


Program Section: Preferred form of presentation: poster

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Conclusions

Raman spectroscopy is a powerful tool to characterize nanostructurated oxides and their trans-formations during reaction. The present study reports the interaction between Mo and V and ex-clude the presence of crystalline MoO3 and V2O5 oxide phases. Operando Raman-GC experi-ments follow the changes that theses mixed phases undergo during reaction. At low coverage, Mo-V-O phase I is present in fresh samples and AlVMoO7 and surface vanadia and molybdena from during reaction

References [1] M.A. Bañares, S.J. Khatib, Catal. Today 96 (2004) 251 [2] M.O. Guerrero-Pérez, L.J. Alemany, Appl. Catal. A 341 (2008) 119 [3] M.A. Bañares, I.E. Wachs, J. Raman Spectrosc. 33 (2002) 259



Automated Sampling Device for Kinetic Analysis of High Pressure Reactions: An Example from Rhodium Catalyzed Hydroformylation

Christoph Kubisa, Detlef Selenta, Hans-Joachim Stillerb,Armin Börnerac, Ralf Ludwigac, Kerstin Thurowd

aLeibniz-Institut für Katalyse e.V. an der Univ. Rostock, Albert-Einstein-Str. 29a, 18059 Rostock bInstitut für Automatisierungstechnik, Univ. Rostock, Richard-Wagner-Str. 31, 18119 Rostock cInstitut für Chemie, Universität Rostock, Albert-Einstein-Str. 3, 18059 Rostock damplius GmbH, Friedrich-Barnewitz-Str. 8, 18119 Rostock


The sampling of reaction solutions at definite times and under high pressure and temperature is a prerequisite for kinetic analysis via gas or liquid chromatography. Enhanced requirements such as automation and sampling under inert conditions demand sophisticated technologies.

We present a modified automated sampling device which was originally constructed for a bank with five autoclaves for parallel reaction analysis [1]. Sampling is realised with the help of micro- gear-pumps and multi-port-valves, Fig. 1 (left). The reaction solution is circulated through the multi-port-valves and at definite times by switching the valves and flushing with a solvent samples are collected. Reaction start is defined by inserting the substrate from a cylindrical vessel by a magnetic valve. The system is designed for 10 samples per run, by combining more runs it’s possible to take a variable number of samples. A further development of the system was found necessary in order to rigorously exclude contamination of the reaction solution with the flushing medium and to optimize the inert conditions during the sampling [2], Fig. 1 (middle and right).

A connection of such a reactor system to an external transmission IR cell [3] in order to study those reactions at the concentration level of catalysts is in progress. Thereby we combine chroma-tographic analysis of substrates and products with spectroscopic analysis of catalyst species [4].

Fig. 1: Principle of the original sampling process (left, property of [1]), modified principle (middle, property of [2]), device in the lab (right)




The main difference between the two sampling processes is that in the modified version sampling happens with the help of the pressure applied for the reaction. The reaction solution is pressed into the sample loop which was flushed before with argon. By switching the valve the sample ex-pands and is flushed with argon into the vial. Thereafter the capillaries are washed with the sol-vent and the sample is diluted. By blowing out with argon the solvent is removed. To ensure re-presentativeness of the samples the capillaries are flushed several times with actual reaction solu-tion before collecting the sample. The minimum interval between two samplings is 60 seconds.

As an example of application we show the conversion-vs.-time curves of the hydroformylation of (E)-4-octene, Fig. 2.

Fig. 2: Hydroformylation of (E)-4-octene, 20 samples for gas chromatography were collected (X1-X4: an exactly assignment was not possible till yet with the current chromatographic method)

Conclusions

For kinetical analysis via gas or liquid chromatography of high pressure reactions with the demand of automation and inert conditions during the sampling a modified sampling apparatus was presented. Benefits of the modification are the exclusion of contamination with a flushing medium and optimization of the inert conditions. By connecting our reaction apparatus with an external transmission IR cell we’ll get additional information about the catalyst species.

References

[1] Construction: Analytical Instrument GmbH, Friedrich-Barnewitz-Str. 8, 18119 Rostock [2] Construction: amplius GmbH, Friedrich-Barnewitz-Str. 8, 18119 Rostock [3] Construction: Dr. Bastian GmbH Feinwerktechnik, Oberer Grifflenberg 155, 42119 Wuppertal [4] Haynes, A.: The Use of High Pressure Infrared Spectroscopy to Study Catalytic Mechanisms. In: Heaton, B.

(Ed.): Mechanisms in Homogeneous Catalysis : A Spectroscopic Approach. Weinheim : WILEY-VCH, 2005. [5] Selent, D.; Hess, D.; Wiese, K.-D.; Röttger, D.; Kunze, C.; Börner, A.: Angew. Chem. 2001, 113, 1739.


New reactor cells and coupling techniques Poster presentation

New Insight in the Activation-Deactivation Processes of PtSn-based Propane Dehydrogenation Catalysts

Ana Iglesias Jueza, Karin Maaijena, Bert M. Weckhuysena

Group of Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands

Introduction The dehydrogenation of light alkanes is of great interest due to the growing demand of propene for the production of polymers [1]. Pt-based catalysts have been – next to Cr-based catalysts - widely used for alkane dehydrogenation due to its good activity and selectivity. However, this system suffers from fast deactivation due to coke formation and metal sintering. There are several strategies to improve the catalytic properties of Pt. The most promising is the promotion with a second metal, such as Sn, which is known to alter the product distribution for hydrocarbon con-version and thereby enhancing the selectivity and stability in dehydrogenation process [2-3]. However, inadequate Sn proportions can also decrease the alkane conversion values. The mecha-nism by which Sn modifies the catalytic behaviour of Pt remains a matter of debate due to the complicated nature of the Pt-Sn alloy system. On the other hand, during the regeneration process in O2 - to burn the formed coke on the catalyst – Pt segregation can also take place, causing an irreversible deactivation of the catalyst [3]. Another important point is the nature of the support; as the carrier has an influence on these factors. So it is very important to understand the activity-selectivity relationship and deactivation mechanism of these systems.

The aim of this research is to shed detailed insight in the phenomena of activation and deactiva-tion of Pt-Sn-based propane dehydrogenation catalysts. For this purpose, two series of Pt and Pt-Sn catalysts supported on Al2O3 and TiO2 have been investigated making use of a catalytic reac-tor working in similar conditions to the industrial process. The catalysts were subjected to suc-cessive activation-reaction-regeneration cycles. Catalytic activity was analyzed using a gas chro-matograph and, at the same time, in-situ Raman and UV-visible spectra were measured in the fixed bed reactor to obtain information on the formation of coke deposits and correlate it with the catalytic data [4]. Furthermore, the electronic-geometrical effects of Sn (combined with the sup-port) on the Pt species were studied by X-ray absorption spectroscopy as well as IR spectroscopy after adsorption of CO as probe molecule. As a result, new insight in the structure-performance of these catalysts has been obtained.

Results and Discussion Catalytic data shows that Sn improves the catalytic behaviour both in terms of conversion and selectivity for the systems based on Al2O3 as support. The addition of Sn modifies the propane activation mechanism and thus the final product distribution and Pt-Sn/Al2O3 catalysts do not suffer deactivation. However, there is a clear effect of the support as for catalysts based on TiO2the addition of Sn does not modify the propane activation mechanism and the catalysts deacti-vate.

To get insight into the origin of activity and deactivation, a combined in-situ UV-visible/Raman and catalytic data approach was used to follow the coke evolution during successive propane de-hydrogenation cycles: type and amount of coke during formation and burning. After 2 or 3 cycles a decrease of conversion, selectivity is observed and the amount of formed coke decreases along the cycles. However, after 10 cycles a steady state was achieved. At this point, it is possible to


New reactor cells and coupling techniques Poster presentation

analyze the effect of different reaction parameters, such as temperature and the presence of water presence in the feed.

By using in situ EXAFS-XANES measurements under H2 reduction it was possible to gain in-formation on the metal active species during the activation process. The oxidation state changes were followed to examine the evolution of the electronic properties and the local structures of Pt and Sn in Pt-Sn-based catalysts. Different effects on Pt by Sn were observed: geometric (differ-ences in particle size) and/or electronic (alloy formation) effects affecting the propane activation mechanism. In both systems, the addition of Sn reduces the Pt particle size. There is an interac-tion between Sn and Pt. Furthermore, a charge transfer from Sn to Pt is observed. There seems to be Pt-Sn alloy formation in the bimetallic catalysts. However, the support effect is still observ-able. These modifications are confirmed by CO TPD IR spectroscopy experiments. Sn promotion increases the amount of chemisorbed CO on Pt. Sn stabilizes surface CO on Pt at higher tempera-tures. However, the amount of surface CO is lower on TiO2 than on Al2O3 catalysts.

Conclusions Sn promotion modifies the properties of Pt inducing electronic and geometric changes due to al-loy formation. However, there is an influence of the support that alters the final behaviour of the active species. These effects affect the propane conversion and deactivation due to coke forma-tion. The combination of in-situ UV-Vis/Raman appears to be valuable tool to follow the coke evolution and deactivation-regeneration processes.

References

[1] B. Buonomo, D. Sanfilippo, F. Trifiro, in: G. Ertl, H. Knozinger, J. Weitkamp (eds), Hand-book of Heterogeneous Catalysis, vol. 5, VCH, Weinheim, 1997, p. 2140. [2] S.M. Stagg, C.A. Querini, W.E. Alvarez, D.E. Resasco, J. Catal. 168 (1997) 75. [3] J.C. Serrano-Ruiz, A. Sepúlveda-Escribano, F. Rodríguez-Reinoso, J. Catal. 246 (2007) 158. [4] T.A. Nijhuis, S.J. Tinnemans, T. Visser, B.M. Weckhuysen, Chem. Eng. Sci. 59 (2004) 5487.


Program Section: 4 Preferred form of presentation: poster

Reaction monitoring of heterogeneously catalysed hydrogenation of imines via coupled ATR-FTIR/Raman spectroscopy

Leif R. Knöpke, Navid Nemati, Angela Köckritz, Ursula Bentrup, Angelika Brückner Leibniz-Institut für Katalyse e.V. an der Universität Rostock, Außenstelle Berlin

Richard-Willstätter-Str. 12, D-12489 Berlin, Germany


The heterogeneously catalysed enantioselective hydrogenation of C=N-double bonds is still a challenge. Supported noble metals (e.g. Pt, Pd) or Raney nickel combined with chiral modifi-ers are known to be enantioselective catalysts in the asymmetric hydrogenation of C=O dou-ble bonds [1]. The chiral induction in the heterogeneous stereoselective hydrogenation of im-ines or N-heterocycles was transported via chiral auxiliaries [2]. A homogeneous enantiose-lective transfer hydrogenation of imines was described by Rueping et al. using a chiral phos-phorus acid derivative as organocatalyst [3]. We pursue a new approach to identify selective catalysts for the asymmetric hydrogenation of C=N bonds comprising the use of supported noble metal catalysts for the activation of hydrogen in combination with a suitable chiral modifier for introducing enantioselectivity. For elucidating reaction mechanism and kinetics of such hydrogenation reactions under pres-sure a real-time monitoring of the reactions is preferably needed to overcome the disadvan-tages of conventional off-line analytics concerning sampling, possible consecutive reactions and time consuming analysis. Nowadays, the availability of several operando techniques of-fers new possibilities for studying homogeneous and heterogeneous catalysts under working conditions. In particular, the combination of different techniques enables a comprehensive insight into the relevant catalytic system [4]. We report here about simultaneous ATR-FTIR/Raman spectroscopic investigations of the heterogeneously catalysed hydrogenation of imines using a stirred tank reactor (Parr Instru-ment Co., Illinois, USA) with implemented probes for ATR (infrared fiber sensors, Aachen) and Raman (Kaiser Optical Systems, Inc., Michigan, USA) spectroscopic measurements.


Derivatives of simple benzylidene imines were chosen as substrates and 5wt.% Pt /Al2O3 as catalyst for assessing the setup in the hydrogenation reaction. At first, only non-chiral imines were used for testing. The influence of different parameters was studied including the nature of the substrate varied by diverse substituents at the nitrogen atom, the reaction temperature and the substrate-to-catalyst (S/C) ratio.Imines as educts and corresponding amines as products show characteristic bands in the IR- as well as in the Raman spectra which can be attributed to the vibrations of the (C=N),

(C N), and (N-H) groups. While in the Raman spectra the characteristic (C=N) vibrations of the educts could be detected very well, no typical product bands were observable. How-ever, they could nicely be seen in the ATR spectra. Thus, the conversion of the educt was fol-



lowed by Raman spectroscopic measurements and the formation of products simultaneously by ATR spectroscopy.Representative in situ ATR spectra of the hydrogenation of salicylidenaniline are shown in Fig. 1. Besides other new appearing bands, the increasing intensity of the band at 1603 cm-1

indicates the formation of the hydrogenation product. The conversion of different educts demonstrated by changes of the integral intensities of the (C=N) bands (1620 cm-1, N-salicylideneaniline, 1641 cm-1, N-phenyl-(1-phenylethylidene)-amine, and 1653 cm-1, N-benzylidene-tert-butylamine) calculated from the Raman spectra in dependence on time is shown in Fig. 2.

Fig. 1. Hydrogenation of salicylidenaniline: Fig. 2. Dependence of the integral Raman ATR difference spectra in dependence on time. band intensities of different educts on time.

It can be seen that the different substituents affect the reaction rate. The results show a clear trend: The higher reaction rates of the salicylidene- and tert-butyl-derivative indicate that steric limitations are less important than the stabilisation of a positive charge on the substrate when an ionic mechanism is presumed for the hydrogenation. Variations of temperature and S/C ratio showed that higher temperatures and lower S/C ratios increase the reaction rate.

Conclusions

The heterogeneously catalysed hydrogenation of imines has been monitored successfully us-ing combined ATR-FTIR and Raman spectroscopy. While Raman spectra precisely show the conversion of the reactants the ATR spectra show more detailed the structural changes as well as the formation of the products. Due to the complementarity of both methods sophisticated information is available regarding mechanisms and kinetics. The implementation of UV-vis into the established ATR/Raman setup to get more information about the changes at the cata-lyst surface is planned for the future.

References[1] H.-U. Blaser, H.-P. Jalett, M. Müller, M. Studer, Catal. Today 37 (1997) 441. [2] A. Tungler, K. Fodor, Catal. Today 37 (1997) 191. [3] M. Rueping, E. Sugiono, C. Azap, T. Theissmann, M. Bolte, Org. Lett. 7 (2005) 3781.[4] S. J. Tinnemans, J. G. Mesu, K. Kervinen, T. Visser, T. A. Nijhuis, A. M. Beale, D. E. Keller, A. M. J. van

der Eerden, B. M. Weckhuysen, Catal. Today 113 (2006) 3.



An in situ multiple-technique setup to reveal greater insight into catalysts

Matthew G. O’Briena, Andrew M. Bealea, Bert M. Weckhuysena

aInorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science Utrecht Univer-

sity, Sorbonnelaan 16, 3584 CA, Utrecht, The Netherlands


To fully understand the operation of a catalyst, there are a number of conditions that an in situ/operando time-resolved experimental measurement must meet. These include the recording of data under as close to realistic or ‘industrial-like’ conditions as possible, the measurement of variation throughout the catalyst bed and the recording of high quality congruent data from a number of techniques. Combining these conditions is a considerable challenge. However, devel-

opments in synchrotron and detector technology have resulted in the combination of multiple techniques in increasingly realistic environments.1 Despite this, these experiments are often per-formed on capillary setups which offer only a small restrictive sample environment. Thus they do not mimic the larger volume of industrial catalysts, severely limit the possibility of profiling the bed and limit the number of techniques that can be utilized without interference. The objective of this work is to address these issues by developing an experimental setup incorporating all of the

conditions mentioned above. This requires not only the use of specific cell architectures but also correct synchrotron beam characteristics. Here we detail the setup and demonstrate examples in which we profile the catalyst bed and obtain high quality multiple technique data.


The experimental cell (figure a) is based on an open architecture, heated using two heat guns with

specifically designed nozzles resulting in a relatively even temperature gradient. A programmable mass flow control system allows the sample to be treated with various gases in the temperature

range 24 – 450 ºC. ∅ = 4 mm quartz tubes house the sample (considerably wider than for a typi-cal capillary). This allows for (a) a more realistic sample environment (b) the ability to ‘scan’ the various parts of the catalyst (figure b) and (c) the combination of many techniques without sig-nificant loss of data quality. The choice of beam line is also critical and ID15 at ESRF is ideal as it has (a) high flux/brilliance allowing for a high time resolution, (b) high energy (89 keV) result-

ing in better penetration and (c) the ability to obtain inelastic data and although not optimal, fluo-rescence information. The combination of (a) & (b) then allow for the collection of high quality (refineable) data, whilst avoiding problems with sample damage. Initial experiments performed on this cell were on powdered iron molybdate and MoO3 catalysts (methanol to formaldehyde conversion)2. In the first example we have achieved time-resolved congruent multiple technique profiling of an iron molybdate catalyst bed under redox conditions. Here we combined WAXS/UV-Vis/Raman/Fluorescence and online mass spectrometry to monitor structure/activity



2 2.5

relationships. An example of the data is given in (figure b). Here the diffraction data indicates significant differences in the behavior of the catalyst at the top (no regeneration on oxidation) and then further down the bed (regeneration). Similar changes are observed in the Raman and whilst the exact details are not currently fully understood the ability of this setup to observe and profile

such changes in a catalyst are obvious and will be of significant use in the study of many catalytic systems. In the second example we demonstrate how the combination of high quality multiple-techniques can measure subtle changes in the bonding of a catalyst during a time-resolved ex-periment. Here we again combine the techniques above to observe the reduction of MoO3 to MoO2. The high quality of the WAXS data allows for Rietveld analysis revealing subtle changes in one of the three unique Mo-O bond distances within the catalysts. This is confirmed by

changes in Raman with the band for this bond disappearing more rapidly than the others whilst UV-Vis and mass spectrometry allow us to compare this data with the formation of particular surface species and catalyst reactivity. These results suggest the identification of the oxygen most likely involved in the Mars van-Krevelen process. Without such high quality time-resolved in-formation recorded from numerous techniques, such subtle changes could not easily be observed.

Conclusions

In this work we demonstrate a new way of recording data using open cells and high flux/energy which is a considerable step towards achieving the conditions required for a successful in situ or operando experiment. Using this setup we have successfully profiled a catalyst bed in situ, using time-resolved multi-techniques and additionally, with the high quality of the data, measured sub-tle changes in a catalyst, both of which reveal information important for understanding catalyst

operation.

References

[1] Tinnemans, S. J., Weckhuysen, B. M. et al., Catal. Today 2006, 113, 3. [2] Soares, A. P. V.; Portela, M. F., Catal. Rev.-Sci. Eng. 2005, 47, 125.

2 2.5

(a) (b)

Tim

e

No Regeneration

Reduction

Oxidation Reduction Oxidation

Reduction

Oxidation Reduction Oxidation

Angle (2θ)

Regeneration

Tim

e



In-Situ ESR/GC Study of n-, iso- Butanes Hydrogenolysis over Ni-ReCatalysts

E.H.Ismailov, Yu.A.Ganbarova, M.J.Maharramov, D.B.Tagiyev, M.I.Rustamov

Institute of Petrochemical Processes, Azerbaijan National Academy of Sciences, 30, Hojali Ave., AZ1025, Baku, Azerbaijan; tel./fax: (99412) 441 48 75;



In-situ spectroscopy including in situ ESR investigation of catalyst under the reaction conditions gives possibility to get more suitable information about the nature of catalytically active sites and their function. At the Institute of Petrochemical Processes of Azerbaijan National Academy of Sciences the system based on Jeol JES-PE-3X ESR spectrometer, LXM-80 gas chromatograph equipped with TCD and FID detectors and flowing micro-catalytic reactor is constructed and used to obtain the simultaneous kinetic and spectral data directly about magnetic sites of cata-lysts, intermediates and reaction products [1].

In this paper the results of ESR monitoring of the state of active components in combination with simultaneous chromatographic analysis of gas phase products of n- and iso- butanes hydro-genolysis over Ni-Re/ZSM-5+ -Al2O3 with different contents of metallic component to identify the magnetic species and study of their role in this reaction are reported. This catalyst have shown higher activity in hydrocracking of light gasoline fractions at 523K and atmospheric pressure [2] and we considered to examine the activation of C-C bonds of lower alkanes over this catalyst.


Two types signals are observed in ESR spectra for these catalysts: belong to ferromag-netic/superparamagnetic metallic particles with effective g-factor g=2.2-3.6 and line width

H=750-2600 G and paramagnetic carbon deposits with g=2.003 and H= 5-7 G. The tempera-ture dependence of ESR spectra of particles is investigated for catalysts with different contents of Ni, Re in the range 293-843K. The dependence of the signals on contact time H2, n-, iso- butanes and reaction mixture at different temperatures is obtained. It was concluded that the catalytic ac-tivity of samples in hydrogenolysis of n-and iso-butanes due to nano-dispersed magnetic parti-cles. In hydrogenolysis reaction conditions active catalyst are characterized with the symmetrical ESR signal, due to superparamagnetic particles of the size 20-30 Å. The mechanism of reaction with participation of these particles and influence of Re on the state of magnetic particles are dis-cussed. It was established that active catalysts of this reaction are characterized with more sym-metrical narrow ESR signals at reaction conditions and Re/Ni ratio 0.33.



The results of catalytic hydrogenolysis of n- and iso- butanes over Ni-Re/ZSM-5+ -Al2O3 are given in the table.

Table. Gaseous products of the reactions of the mixtures 10 iso-C4H10 + 90 H2 (vol.%) and 10 n-C4H10 + 90 H2 (vol.%) with Ni-Re/ZSM-5+ -Al2O3 catalyst

Selectivity Catalyst Temp., K Contacttime, , s

Conversion, % CH4 C2H6 C3H8

10 iso-C4H10+90H2 (vol.%)

2.8%Re, 4.6%Ni 523 573

5.0 5.0

2.1 34.0

59.0 77.0

13.0 12.8

28.0 9.3

5.6%Re, 4.6%Ni 523 573

5.0 5.0

3.1 72.2

61.7 81.4

12.0 8.9

26.3 10.0

14%Re, 4.6%Ni 523 543

1.0 1.0

54.6 87.1

63.5 85.0

15.0 12.1

21.5 2.9

14%Re, 9.2%Ni 523 573

5.0 5.0

19.2 97.2

68.7 94.4

10.8 4.3

20.5 1.3

10 n-C4H10+90H2 (vol.%)

2.8%Re, 4.6%Ni 523 573

5.0 5.0

3.2 73.3

64.2 80.1

19.1 16.7

16.9 3.2

5.6%Re, 4.6%Ni 523 573

5.0 5.0

5.4 80.0

50.8 62.3

25.5 20.2

23.7 17.5

14%Re, 4.6%Ni 523 573

1.0 1.0

73.0 90.2

49.2 52.8

26.7 30.7

24.1 16.8

14%Re, 9.2%Ni 523 573

5.0 5.0

29.7 98.0

52.1 64.8

23.6 15.2

24.3 20.0

The analysis of the data of the table shows that the conversion of butanes depends on the concen-tration and ratio of the metallic components of catalysts and has the extremal character for ratio Re/Ni; conversion of butanes depends on the reaction temperature and contact time; for the lower reaction temperature and contact time the selectivity on propane and ethane is highest.

Conclusions

1. Presented system is enough effective for investigation of reaction ability, catalytic activity of magnetic particles;

2. Two type of magnetic species exists in Ni-Re catalysts: a) metal, b) coke particles;

3. Catalysts with Re/Ni ratio 0.33 and the size 20-30 Å of metal particles are more active in hydrogenolysis of n- and iso- butanes.

References [1] Ismailov E.H., Tagiyev D.B., Rustamov M.I. Operando - II, Book of Abstracts , pp.142-143, Toledo, Spain,

2006 [2] Patent 1796660 USSR/ M.I.Rustamov, V.M.Akhmedov, G.T.Farkhadova, S.M.Ibragimova, G.F.Samedova,

Yu.A.Martynova.



In-Situ IR Investigations on the Equilibria of Ligand Modified Rhodium Catalyst Species

Enrico Barscha, Ralf Ludwiga,b, Detlef Selenta, Armin Börnera,b

Klaus-Diether Wiesec, Dieter Hessc

aLeibniz-Institut für Katalyse e.V. an der Universität Rostock, Albert-Einstein-Str. 29a, 18059 Rostock bInstitut für Chemie, Universität Rostock, Albert-Einstein-Str. 3, 18059 Rostock cEvonik Oxeno GmbH, Paul-Baumann-Str. 1, 45772 Marl


Hydroformylation is a significant example for a homogeneously catalysed and industrially applied reaction. Because of their outstanding activity and high regio- and chemoselectivity ligand modified rhodium catalysts are in the centre of interest, but till today mainly cobalt catalysts are used for the hydroformylation of internal olefins [1]. Though the reaction conditions for rhodium catalysis are considerably milder compared to the predominantly applied cobalt process there are unsolved problems like the degradation of the complex ligands and the absence of an appropriate catalyst recycling technology. The loss of catalytic active rhodium species to inactive clusters concluding in metal deposition is still a problem. The equilibria between different catalyst species influence the complex kinetics of ligand modified hydroformylation. The aim of this work is to provide a better understanding of the equilibria between rhodium clusters and observable mono-rhodium-complexes with mono- and bidentate phosphorus ligands.


The experiments were performed in a semi-batch autoclave at constant pressures between

10 bar and 50 bar CO/H2 (1:1) and in the temperature range of 25 °C to 120 °C. The reaction solution was continuously pumped through an IR transmission cell with an optical path length of 400 m(Fig.1). The spectra were recorded under typical hydroformylation conditions to achieve an in-situ IR spectroscopy [2]. The system was additionally equipped with a device that allows to inject solutions into the high pressure system and to take samples for GC-analysis.

Fig.1: Autoclave (left) and IR-transmission cell with heated pump and device (right)



A bulky monophosphite and a bidentate phosphite have been examined as ligands for rhodium. We deconvoluted the complex spectra to obtain the pure component spectra of rhodium complexes [3]. To assign these spectra to possible catalyst structures DFT-calculations were performed. Under hydroformylation conditions three major rhodium species have been observed: Rh6(CO)12, mono nuclear rhodium hydride phosphite complexes and depending on the used olefin and ligand an acyl complex. We determined their concentrations at different pressures and temperatures to describe the equilibrium. As an example the IR-spectra of the conversion of the used catalyst precursor Rh(acac)(CO)2 into Rh6(CO)16 and Rh4(CO)12 are shown in Fig.2.

Fig. 2: IR-Spectra of precatalyst conversion into Rh-clusters at 90 °C and 20 bar.

Conclusions

The mononuclear complexes and the rhodium clusters Rh6(CO)16 and Rh4(CO)12 have been examined under different conditions. The description of the catalyst equilibrium is essential for the understanding of the complex hydroformylation kinetics.

References[1] Wiese, K.-D.; Obst, D.: Hydroformylation. Topics in Organometallic Chemistry, 18 (ed. M. Beller); Springer-Verlag Berlin Heidelberg 2006; 1–33. [2] Paul C.J. Kamer, Annemiek van Rooy, Gerard C. Schoemaker, Piet W.N.M. van Leuwen, Coordination Chemistry Reviews, 248 (2004), 2409-2424. [3] Effendi Widjaja, Chuanzhao Li, Marc Garland, Journal of Catalysis, 223 (2004), 278-289.


Program Section: 4 Preferred form of presentation:

The structure of supported vanadium oxide under reaction conditions deter-mined during the oxidation of H2S to sulphur by XAS and Raman

J.P Holgadoa, M.D. Sorianob, J. Jimenez-Jiménezc, A. Jiménez-Lópezc, P. Concepciónb,

A. Caballeroa, E. Rodríguez-Castellónc, J.M. López Nietob

a Instituto de Ciencia de Materiales, Sevilla (Spain); b Instituto de Tecnología Química, UPV-CSIC, Valencia (Spain);c Dep. Química Inorgánica, Universidad de Málaga, Málaga (Spain)


V-containing catalysts seem to be one of the most active and selective in the partial oxidation of H2S to elemental sulfur [1-2]. However, and although the characteristics of metal oxide support and the nature vanadium species strongly influence the catalytic performance of supported vana-dium catalysts, the nature of active and selective sites is still under discussion.

X-ray absorption spectroscopy (XAS) have been used to determine the oxidation state and coor-dination of vanadium-based catalysts [3], while Raman studies have been carried out to deter-mine the structure of vanadium oxide catalysts [4]. In the present paper we present an X-ray ab-sorption spectroscopy (XAS) and Raman study, both working in operando conditions, on the se-lective oxidation of H2S to sulfur using a vanadium oxide supported on a mesoporous zirconium phosphate heterostructure (with 12 wt% of V-atoms, named as 12-MZP) as catalyst. In addition, the reduction or reoxidation of catalyst after the catalytic test has been also studied.


The transmission Vanadium K-edge X-ray absorption spectroscopy (XAS) measurements were performed at the beamline X10DA (superXAS) located at the Swiss Light Source (SLS), Villi-gen, Switzerland. Typically, 50 mg of catalyst powder were used and pressed in a stainless steel sample holder. FT-Raman spectra were recorded with an “in via” Renishaw spectrometer, equipped with a microscope (Olympus). The samples were excited by the 785 nm line of an Ar+

laser (Spectra Physics Model 171) with a lav power of 2.5 mW.

Figure 1 shows the normalised XANES (Fig.1 a) and Raman (Fig. 1b) spectra achieved over sample 12-MZP in a He steam at 200ºC (time on stream, TOS, of 0) and during the selective oxi-dation of H2S (using a with H2S/air/He molar ratio of 1.2/ 5.0/ 93.8, total flow of ml min-1 and a 50 mg of catalyst powder) at TOS of 1 and 2 h. It can be seen that in a He steam at 200ºC the XANES spectrum indicates the presence of V2O5, which is characterized by a Pre-edge position at 5471.5 eV, being the main-edge peak at 5481.4 eV. This is in agreement Raman spectrum (Fig.1b, TOS= 0).

Important modifications of the corresponding spectra of this catalyst are observed, however, when operating in reaction conditions at 200ºC and different time on stream. Thus, a completely


Program Section: 4 Preferred form of presentation:

different XANES spectrum is observed after two hours of time on stream. This is characterized by a pre-edge peak at 5470.2 eV (Fig. 1a).

5,46 5,49 5,52 5,55

Nor

mal

ised

abso

rptio

n(a

.u.)

Energy (KeV)

TOS (h)0.01.02.0

5.466 5.470 5.474

TOS (h)

0.0

1.0

2.0

200 400 600 800 1000Raman Shift (cm-1)

TOS (h)0.01.02.0

Figure 1. a) Normalised absorption spectra for the supported vanadium oxide at different time on stream (for comparison, the pre-edge region of V-O bond is also included at several TOS). A) Raman spectra. Reaction conditions in text.

The Raman spectra of the corresponding samples at TOS of 1 and 2h show a decrease in the in-tensity of the bands related to V2O5 and the appearance of a new band at ca. 904 cm-1, which can be related to the formation of V4O9 [5]. However, the reduction degree of catalyst depends on both the reaction temperature and the composition of the reaction mixture. The nature of active and selective sites in the partial oxidation of H2S to elemental sulphur is also discussed.

Conclusions

According to these results, it is clear that there is a partial reduction of V2O5 during the catalytic tests, which can be followed by XANES and Raman studies in operando conditions. These results are also confirmed by a parallel study of the characteristics of catalyst under reduction and reoxi-dation cycles using several physico-chemical characterization techniques.

Acknowledgments

The authors gratefully acknowledge financial support from CICYT, Spain (NAN20004-09267-C01 and NAN2004-09267-C03-02). We also thank Swiss Light Source (SLS) at the Paul Scherrer Institut (Proposal 20081090). References [1] M.I. Kim, D.W. Park, S.W. Park, X. Yang, J.S. Choi, D.J. Suh, Catal. Today 11(2006) 212. [2] P. Kalinkin, O. Kovalenko, O. Lapina, D. Kjabibulin, N. Kundo, J. Mol. Catal. A 178 (2002) 173-180. [3] G. Silversmit, J.A. van Bokhoven, H. Poelman, A.M.J. van der Eerden, G.B. Marin, M.F. Rayniers, R. De Gry-

se, Appl. Catal. A 285 (2005) 151. [4] G.G. Cortez G.G, M.A. Bañares, J. Catal. 209 (2002) 197 [5] R. Nilsson, T. Limblad, A. Andersson, J. Catal. 148 (1994) 501.


Sections 2&4 – Oral presentation 1

Development of a magnetometer for operando catalyst characterization

Michael Claeysa*, Simon Kellya, Eric van Steena, Kobus Visagieb, Jan van de Loosdrechtb, Igor Krylovc

a Centre for Catalysis Research, Department of Chemical Engineering, University of Cape Town, Private Bag X3,

Rondebosch, 7701, South Africa b Sasol R&D, Sasolburg, 1947, South Africa c Department of Physics, University of the Western Cape, Bellville, 7535, South Africa

*Corresponding author: (fax) +27 21 650 5501, [email protected]

Abstract: This paper describes the development of an in-situ magnetometer which allows following effects of catalyst

oxidation/reduction as well as sintering under fully realistic reaction conditions of temperature and pressure. Although

originally developed for use in Fischer-Tropsch synthesis this novel instrument can be applied to investigate any ferro-

magnetic matter in a controlled environment.

Keywords: in-situ magnetometer, reduction, oxidation, sintering, cobalt.

1. Introduction

High activity of supported metal catalysts is usually obtained by providing high metal surface area or

small metal crystallites respectively. The stability of supported metal catalysts in Fischer-Tropsch synthesis

can be negatively affected as deactivation can result, inter alia, from sintering and phase changes such as

oxidation1,2,3. Characterization of such catalysts, in particular used ones, is notoriously difficult as exposure

to air can cause dramatic changes of their physico-chemical properties. Moreover, they are often surrounded

by a wax layer which can further complicate analysis by conventional techniques such as XRD and TEM

characterization. Ultimately therefore in-situ characterization techniques of these catalysts are becoming

crucially important in order to study the relation of catalyst changes and their performance. This paper

describes the development of an in-situ magnetometer which allows following effects of catalyst

oxidation/reduction as well as sintering under fully realistic reaction conditions of temperature and pressure.

Although originally developed for use in Fischer-Tropsch synthesis this novel instrument can be applied to

investigate any ferro-magnetic matter in a controlled environment.

2. Experimental

Ferromagnetic material such as metallic iron, cobalt and nickel becomes magnetized to a large extent

when exposed to an external magnetic field. It usually shows the phenomenon of hysteresis with a limit of

magnetization at high fields (saturation) and usually residual magnetization upon removal of an external

field (remanence). The latter effect is restricted to crystallites of a certain critical size which depends on the

particular material and temperature (e.g. for cobalt: ca. 12-15 nm at 300 K4). Crystallites smaller than this

size show no remanence, i.e. superparamagnetic behavior, which can be described mathematically. These

properties can be used to determine (a) the amount of metal present in a sample or degree of reduction

respectively (from saturation magnetization), (b) the percentage of ferro-magnetic material (from


Sections 2&4 – Oral presentation 2

remanence), which relates to large crystallites and may indicate effects of sintering, and (c) crystallite size

distributions in purely superparamagnetic samples.

A Weiss extraction magnetometer has been designed and built in which catalysts can be tested in a fixed

bed reactor at realistic conditions (Tmax=500ºC, pmax=50 bar) while the magnetic properties can be monitored.

A previously described in-situ magnetometer did not allow for testing at elevated pressures5. The signal is

generated via low frequency movement of the sample/reactor within the homogenous magnetic field. Field

strengths of up to 2 Tesla allow full magnetic saturation of typical catalyst samples. Details of our set-up

including sample movement, its heating and the control of the instrument will be described in detail.

3. Results and discussion

The set-up has been used to study temperature programmed reduction, temperature programmed oxidation

as well as temporal changes of the degree of reduction (see figure 1) and the percentage of ferro-magnetic

material of a cobalt catalyst while catalytic performance data were collected. Examples of this work will be

discussed in the paper.

Figure 1. Temporal changes of degree of reduction of cobalt catalyst tested at commercial conditions.

4. Conclusions

The novel magnetometer provides a unique new tool for operando characterization of ferromagnetic

catalysts.

Acknowledgment

This project has been conducted in collaboration with Sasol Technology R&D and the financial support is

greatly acknowledged.

References 1. J. Moulijn, A. van Diepen, F. Kapteijn, Appl. Catal. A: Gen. 212 (2001) 3. 2. E. van Steen, M. Claeys, M. Dry, J. van de Loosdrecht, E. Viljoen, J. Visagie, J. Phys. Chem. B 109 (2005) 3575. 3. J. van de Loosdrecht, B. Balzhinimaev, J.A. Dalmon, J.W. Niemantsverdriet, S.V. Tsybulya, A.M. Saib, P.J. van Berge, J.L.

Visagie, Catalysis Today 123 (2007) 293. 4. J.A. Dalmon, “Magnetic measurements and catalysis”, in “Catalysis characterization: Physical techniques for solid materials”,

eds. B. Imelik, J.C. Vedrine, Plenum Press, New York, 1994, p. 585. 5. P.A. Chernavskii, A.Y. Khodakov, G.V. Pankina, J.-S. Girardon, E. Quintet, Appl. Catal. A: Gen. 306 (2006) 108.

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Program Section: 2 or 4 Preferred form of presentation: Poster

Monitoring Reactions of Gases in the NMR tube

Wolfgang Baumanna, Detlef Hellera, Detlef Selenta

aLeibniz-Institut für Katalyse e. V. an der Universität Rostock, Albert-Einstein-Straße 29A, 18059 Rostock.

e-mail: [email protected]


The unsurpassed ability of NMR spectroscopy to provide structural (qualitative) as well as quantitative information from the same experiment makes it attractive for reaction monitor-ing, for mechanistic and kinetic investigations. However, the usual design of the NMR cell hampers severely its use when it comes to reactions in which one of the reaction partners is gaseous. Furthermore, reactions with gases are carried out often at elevated pressure, a fact resulting in experimental difficulties [1]. Mass transfer limitations at the gas-liquid interface (which have been recognised in the scientific community for some time) add further com-plications and lead to a substantial gap between the experiment on an “analytical” and a “preparative” scale.

This contribution describes some developments that have been achieved in Rostock and allow the application of NMR methods to such reactions without the need to purchase and install special NMR hardware, thus enabling a broad community to make use of these powerful methods. The in situ approach which is clearly superior over sampling and offline analytics may be extended in such a way to technically important reactions with gases.


A simple device was constructed first for application under atmospheric pres-sure. The essential part is a 10 mm NMR tube equipped with a hose for the gas feed, in its most simple version as shown on the right. Further peripherals pro-vide for the feeding of solution and gas into the tube as well as for the exhaust of surplus gas. The complete apparatus may be evacuated and purged with an inert gas which is important especially for work with organometallic complexes and catalysts. The homogeneity of the magnetic field is not disturbed severely by the gas bubbles, and loss of resolution even in the proton spectra is not criti-cal when the depicted NMR tube is used. Although gas distribution is effected by diffusion to a certain extent, this device proved useful for monitoring slow reactions. E. g., it is straightforward to determine experimental parameters for the conversion of transition metal complexes (catalyst precursors) into the active species under reaction conditions. Another experimental setup is characterised by extension of the capillary to the bottom of the tube and gas dispersion by a glass frit [2]. This largely improves gas saturation and mixing, however at the cost of reduced resolution in the spectra.


Program Section: 2 or 4 Preferred form of presentation: Poster

This principle of gas distribution was successfully transferred to high-pressure application. A commercially available, pressure-proof sapphire NMR tube was equipped with the necessary tubing for gas feed and outlet (figure left) which is connected with a specially designed circulation pump, thus setting up a closed system suitable also for toxic gases. It features the following advantages [3]:

gas circulation to and from the tube at a gas flow rate of 1…40 ml min–1

and a pressure limit of 50 bar; closed system, may alse be evacuated, i. e.inert conditions are achievable (see sketch below)

fast saturation within few minutes at low flow rates (e. g., about 3 min. for H2 in toluene at 1 ml min–1)

adjustment and control of pressure are possible at any time

changing the reacting gas is possible without accessing the sample

a modified, but commercially available 10 mm sapphire NMR tube can be used inside an unmodified NMR probe (in “standard bore” magnets); sample volume 2-3 ml; temperature up to 120 °C

A successful application of these experimental setups was achieved with several gases (alkenes, hydrogen, and synthesis gas). In particular, rhodium-catalysed hydrogenation and hydroformylation [4] have been studied. Further technical development of the devices is under way.

Conclusions

It is possible to perform and monitor gas-consuming reactions in the NMR tube under “realistic conditions” that approach preparative experiments without the need to have special NMR hardware. This in situ technique is particularly suited to study the chemistry of compounds that are not isolable or that are observable only under special reaction conditions. Examples for such systems are transition metal complexes that act as homogeneous catalysts. Therefore, this technique is a valuable extension of the methodological portfolio in catalysis research.

References [1] Review: G. Laurenczy, L. Helm in B. T. Heaton (ed.), Mechanisms in Homogeneous Catalysis, Wiley-VCH,

Weinheim, 2005.[2] W. Baumann, S. Mansel, D. Heller, S. Borns, Magn. Reson. Chem. 1997, 35, 701. W. Baumann, D. Heller,

DE 102 02 173 C2 (2003).[3] W. Baumann, D. Selent, A. Börner, DE 103 33 143 A1 (2005).[4] D. Selent, K.-D. Wiese, A. Börner in J. R. Sowa (ed.), Catalysis of Organic Reactions vol. 20, Taylor &

Francis Group, Boca Raton, 2005, 459. D. Selent, W. Baumann, K.-D. Wiese, A. Börner, Chem. Commun.2008, 6203.

General Principle: the sapphire tube with gas circulation



Coupling Techniques for operando Catalysis Experiments involving X ray ab-sorption spectroscopy (XAS)

Camille La Fontaine1, Françoise Villain1, Valérie Briois1, François Baudelet1, Quingyu Kong1,Xavier Sécordel2, Anthony Yoboué2, Elise Berrier2, Sylvain Cristol2

1 Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin BP48, 91192 Gif-sur-Yvette Cedex, France

3 Unité de Catalyse et de Chimie du Solide, UMR 8181, USTL, 59655 Villeneuve d'Ascq Cedex, France


The operando approach is a technique of choice in better understanding the activity of a given catalyst. However, it generally appears that one sin-gle spectroscopic technique does not make it possible to spell out the complexity of the catalytic process. Therefore, the use of complementary techniques is mandatory. The direct coupling allows a better availability of the collected data, though implements significant technical problems to fit the needs of all techniques. Our approach is double: the first one consists in using the same operando reactor suitable for a large number of techniques1 (Fig.1).

The second one is the development of a new operando reactor adapted to EXAFS experiments in both transmission and fluorescence modes coupled with Raman spectroscopy. A complete set up involving a multi-purpose gas dosing system, a dedicated reactor and a mass spectrometer is cur-rently being installed on the beamline SAMBA at SOLEIL synchrotron (France) that will make it possible to investigate a broad spectrum of reactions (pressure: 1-20 bars, temperature: RT - 600°C). In addition, the Quick EXAFS technique will be implemented in May 2009 on SAMBA beamline that will give access to time resolution, in so far as 1 EXAFS spectrum will require around 400 ms. The complete operando XAS/Raman system will be assessable to users as it will remains on the SAMBA beamline. Eventually, the use of dispersive EXAFS can be a fair alterna-tive to further improve the time resolution. First examples will be presented that validate our ap-proach in the field of methanol conversion over supported molybdenum and rhenium catalysts.

Fig. 1: Raman/XAS coupling using a commercial operando cell




1. Multi-purpose operando reactor: Methanol conversion over MoO3/TiO2 catalysts

The activity of MoO3/ TiO2 catalysts in methanol conversion to formaldehyde was examined. A commercially available operando chamber, initially designed for DRIFTS and DR-UV visible measurements, then adapted for operando Raman studies1, has been adapted to perform oper-ando XANES or EXAFS studies in fluorescence detection mode with Raman coupling. At low loading (1% MoO3/TiO2), the molybdate phase is essentially made of isolated, monomeric spe-cies in tetrahedral geometry. The 7.5%MoO3/TiO2

catalyst was found to retain a polymolybdate phase with molybdenum clusters involving different coordi-nations. The coupled Raman/XANES operando re-sults converge towards the non-reducibility of tetra-hedrally coordinated species, as confirmed by the non-activity of low loading catalysts.

Reversely, the polymeric phase is reducible from MoVI to MoV under methanol/helium flow as evidenced by XANES (left). In this case, the catalytic activity was found to reach high conversion rates and high selectivity in formaldehyde (>90%). Under real reaction conditions (CH3OH/He/O2), the struc-tural evolutions of the active phase were followed by Ra-man spectroscopy (top).

2. Design of a new operando cell for Raman/XAS coupling

The design, based on Lytle cell2, was validated for dispersive operando Raman/ dispersive EX-AFS (DEXAFS) experiments in studying the reduction of a series of alumina-supported rhenate catalysts by hydrogen. Although, the intensity of the white line was considerably affected by the use of a compacted powder compared to a pellet (explained by a loss of energy resolution due to scattering phenomena occurring through the powder), the EXAFS range of the spectrum allows the precise determination of the reduction temperature. Conclusions

A complete and reliable set up dedicated to a very wide range of applications was designed and tested for coupled Raman/XAS experiments. The ensemble will stay on site at Synchrotron SO-LEIL and offered to users very soon. Our preliminary results confirm the relevancy of this time-resolved, coupled operando analysis of catalysts. References [1] X. Sécordel, E. Berrier and M. Clement, Harrick Scientific application note No. 701204 [2] W. Lytle, P.S.P. Wei, R.B. Greegor, G.H. Via and J.H. Sinfelt, J. Chem. Phys. 70, 4849-4855 (1979)

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Program Section: 4. New reactor cells and coupling techniques Preferred form of presentation: poster

Combination of a multi-channel reactor system with

UV/vis spectroscopy or XRD: proof of principle

M.J.G. Faita, M. Schneidera, E.V. Kondratenkoa, D. Linkea, J. Tilgnerb, A. Bjeoumikhovb, M. Brettschneiderb, U. Rodemercka

aLeibniz Institute for Catalysis e.V., Richard-Willstätter-Str. 12, D-12489 Berlin bInstitute for Scientific Instruments GmbH, Rudower Chaussee 29/31, D-12489 Berlin


Since the middle of the 1990s the high-throughput experimentation (HTE) for the development and optimisation of heterogeneous catalysts has been developed rapidly and is established as thetechnology for an effective catalyst screening. Now, many different reactor concepts are available enabling testing of catalysts for a great variety of reactions in parallel.

However, the combination of HTE with operando characterisation techniques is still a challenge and only a limited number of articles are published up to now. In this contribution a multi-channel reactor system is introduced, which is combined with either operando UV/vis diffuse re-flectance (UV/vis-DR) spectroscopy (36 channels) [1] or with an X-ray diffraction (XRD) pow-der probe (12 channels). The working principles of the complex apparatus are demonstrated in the oxidative dehydration of propane (ODP) over vanadium oxide bulk catalysts (UV/vis-DR spectroscopy) or in the oxidation of V2O3 in air (XRD). The XRD measurements were performed with the aim to decide, which is the optimum incident beam geometry: parallel or orthogonal to the longitudinal axis of the reactor. The X-ray beam is irradiated through a window (10 μm wall thickness). In case of XRD analysis, the analysis of reaction products by gas chromatography and the gas inlet system was omitted to simplify the apparatus and to focus on the XRD part itself.


To demonstrate the reliability of the catalytic data, the propane conversion as well as product se-lectivities were determined at different modified contact times but identical reaction feed compo-sition in three different reactors after ca. 3 h time on stream. Standard deviations between 0.5 and 1.2 % were obtained, i.e. the catalytic data can be measured with good reproducibility. Therefore, the multi-channel reactor is well suited for a rapid screening of catalytic materials.

The UV/vis-DR spectra of V2O5 during ODP differ according to their position along the reactor axis and implies the existence of zones with different composition [2]. The time resolved spectra taken at the inlet of the catalyst bed are characterised by a maximum of the band at 740 nm at ca. 1 min TOS. At this moment, the intensity of the band at 520 nm starts to increase. This means a restructuring of the V2O5 lattice and indicates the formation of reduced vanadium ions [1].


Program Section: 4. New reactor cells and coupling techniques Preferred form of presentation: poster

As exemplified by usage of corundum as reference substance the XRD analysis showed that dif-fractograms can be measured with good reproducibility at different reactor positions from roomtemperature up to 450 °C. This is valid for the parallel beam geometry. The diffractograms of

Fi

V2O3 during the thermal treatment in air for the both geometries are depicted in Fig. 1.

ometries:

(V2O3,

onclusions

e technology for the UV/vis-DR analysis it is possible to identify spatially and time

ture with

eferencesait, R. Abdallah, D. Linke, E.V. Kondratenko, U. Rodemerck, Catal. Today, in press.

g. 1 Diffractograms of V2O3 during thermal treatment in air for different beam ge

25 30 35 40 45 50 55 60 65 70

410 °C

395 °C380 °C360 °C340 °C265 °C165 °C80 °C25 °C

1 cp

s

2 /°25 30 35 40 45 50 55 60 65 70

50 °C

450 °C/18 h

450 °C

430 °C

395 °C

360 °C

300 °C200 °C

100 °C

25 °C

1 cp

s

2 /°

incident beam parallel (left) and orthogonal (right) to the longitudinal axis of the reactor.

For both geometries the powder patterns of the starting substance match to PDF 84-316magenta lines) and of the final to PDF 86-2248 (V2O5, orange lines). The phase transition V2O3

to V2O5 can be traced in high quality with the parallel beam geometry. The reflections at 380 and 395 °C can be interpreted as the coexistence of crystalline V2O3, VO2 (PDF 9-142) and V2O5.However, in case of orthogonal beam geometry no reflections are detectable in the range 395 to 450 °C. V2O5 reflections are visible only after 18 h hold at 450 °C and cool down to 50 °C.

C

Using the fibrresolved spectral changes within the catalyst bed characteristic for catalyst changes during reac-tion. In a similar way time and spatially resolved XRD diffractograms can be acquired.

The XRD measurements showed that diffractograms can be obtained at normal temperaboth incident beam geometries. The set-up with orthogonal incident beam geometry corresponds best with its planned use in the multi-channel reactor system. However, this set-up holds the problem of missing reflections at elevated temperature. Therefore, it necessitates further im-provement of the measurement conditions.

R[1] M.J.G. F[2] B.P. Barbero, L.E. Cadus, L. Hilaire, Appl. Catal. A General 246 (2003) 237.


Combining operando spectroscopy and theoretical studies Poster

Nickel-Catalyzed Isomerization of 2-Methyl-3-Butenenitrile (2M3BN) to 3-Pentenenitrile (3PN)

A Kinetic Study Using in situ FTIR-ATR Spectroscopy

Laura Bini, Evgeny Pidko, Christian Müller, and Dieter Vogt

Department of Chemical Engineering and Chemistry, Schuit Institute of Catalysis, Eindhoven

University of Technology, 5600 MB Eindhoven, The Netherlands.


The DuPont adiponitrile process is so far the only example of an industrial application of the Ni-catalyzed alkene hydrocyanation1. Adiponitrile (ADN) is produced from butadiene in a three step process. In the first step butadiene is hydrocyanated to a mixture of 2-methyl-3-butenenitrile (2M3BN) and 3-pentenenitrile (3PN) typically in a 2:3 ratio (scheme 1). The branched 2M3BN is isomerized to the desired linear 3PN in a second step. The last step is the hydrocyanation of 3PN to ADN. ADN is the precursor of hexane-1,6-diamine, an important building block for the syn-thesis of the Nylon(6,6)2.

Scheme 1. Isomerization of 2M3BN

The Ni-catalyzed isomerization of 2M3BN3 (scheme 1) can be considered as a model for an in

situ study of the mechanism and kinetics of the hydrocyanation reaction. In fact, the Ni0 species is oxidized to Ni2+ upon 2M3BN addition as one of the first steps of the catalytic cycle. In the related hydrocyanation reaction the Ni2+ intermediate is formed via HCN addition to the metal complex. The advantage of this study is the absence of free HCN. HCN is highly toxic and causes rapid deactivation of the Ni catalyst, due to formation of LnNi(CN)2 species.

The tetrahedral coordination geometry of the Ni2+-intermediates causes the presence of paramag-netic species. Therefore, in situ NMR studies of this reaction are very difficult. The characteriza-tion of the Ni complexes by IR spectroscopy has been already reported by Tolman4 and Drulin-der5. We performed the isomerization of 2M3BN and followed the reaction using in situ FT-IR spectroscopy.


The isomerization of 2M3BN was performed in dioxane at 60°C for 4 hours using a triptycene-based phosphine ligand. The final conversion was calculated via GC-analysis as 90%. An IR spectrum was recorded every 10 minutes using an ATR probe connected to a FTIR instrument with a flexible light guide. The light transmission efficiency was less than 20% and subsequently the sensitivity was relatively low. High concentrated samples and long collection times (up to 7 min) were required, implying that fast reactions cannot be monitored with this setup.

CN

3PN

CN

2M3BN

Ni(cod)2, L1

dioxane


Combining operando spectroscopy and theoretical studies Poster

Different regions in the spectra were analyzed. The CN stretch band at 2243 cm-1 shifts gradually to higher wave numbers reaching 2248 cm-1, while the 2M3BN is converted into 3PN. Also the CH bend region and the (C=)CH stretch region show transformations in time. Furthermore, cal-culations on the DFT level have been performed for 2M3BN and trans- and cis- 3PN in order to help identifying the corresponding bands in the spectra of the mixture. Several spectral regions have been transformed to their second derivative. The dynamics in the spectra are calculated and normalised to the end conversion determined by GC. Similar kinetic profiles were obtained from the dynamics of different bands. The average profile is depicted in Figure 1.

0 20 40 60 80 100 120 140 160 180

0

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40

60

80

100

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Figure 1. Absorbance spectra (left) and 2nd derivative spectra (middle) for the CN-region. Ki-netic profile for the isomerization reaction (right), calculated as average of the different band dy-namics in the spectrum.

Conclusions

The isomerization of 2M3BN was followed using in situ FT-IR spectroscopy. The full spectrum for the isomerization was analyzed to obtain a kinetic profile as average of the different band dy-namics, using a “quasi-multivariate analysis technique”. Calculated spectra of the substrate and the products of the reaction support the interpretation of the bands.

References [1] Huthmacher, K.; Krill, S. in Applied Homogeneous Catalysis with Organometallic Compounds, 2nd ed.; Cornils,

B., Hermann, W. A., Eds.; Wiley-VCH: Weinheim, 2002; Vol. 1 pp 465-486.

[2] Kohan, M. I. In Ulmann’s Encyclopedia of Industrial Chemistry: Polyamides, 6th ed.; Wiley-VCH: Weinheim, 2003; Vol. 28, pp 25-53.

[3] Wilting, J.; Müller, C.; Hewat, A.; Ellis, D.; Tooke, D.; Spek, A. L.; Vogt, D. Organometallics 2005, 24, 13-15.

[4] Tolman, C. A.; Seidel, W. C.; Druliner, J. D.; Domaille, P. J. Organometallics 1984, 3, 33-38.

[5] Druliner, J. D. Organometallics, 1984, 3, 205.

2273,7 2240 2216,7cm-1

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Program Section: 5 Preferred form of presentation: Oral presentation

Effects of �i as a promoter atom on sulfidation of �iMo/γ-Al2O3 hydrotreating catalysts

Ana Hrabar a, Johannes A. Lercher a

aLehrstuhl fur Technische Chemie II, TUM, Lichtenbergstr. 4, 85747 Garching, Germany Tel: +49 89 289 13540, Fax: +49 89 289 13544, E-mail: [email protected]


Interest in hydrotreating reactions is continuously growing because of rigid legislations concern-ing the S and N concentration in oil fractions. For improving the process itself, better understand-ing and optimization of NiMo catalyst is needed. Even though many studies were carried out sev-eral questions about the changes in catalyst structure during sulfidation, function of Ni as a pro-moter on active sites formation and thus on the catalyst activity, still remain debated.


The goal of this study is to understand the influence of Ni as a promoter atom on the degree of sulfidation in comparison to catalyst containing only Mo. The kinetics of hydrodenitrogenation and final result of the conversion of oxide catalyst precursor to sulfide is explored with a combi-nation of methods ranging from X-ray diffraction over in situ Raman spectroscopy to kinetic me-thods such as temperature programmed sulfidation where changes in gas streams concentrations are followed by mass spectrometer.

Catalysts sulfidation is performed in gas mixture of H2S/H2/He with an increment of 5˚C/min to 400˚C. Two regions in TPS profile are explored in detail (see Figure 1). In the first, where oxy-gen is exchanged for sulfur on Mo6+ (40 to 245˚C), the catalyst containing only Mo consumes the most H2S. Sulfur consumption drops with increasing Ni concentration. While Ni retards process of oxygen sulfur exchange, the temperature of the maximum H2S consumption remains 120˚C for all catalysts. At this stage H2S consumed reaches 54% of the theoretical values needed for full sulfidation of catalyst containing only Mo. Therefore, it is concluded that only top part of poly-molybdate monolayer is sulfided while bonding with support via oxygen still remains intact. The Mo=O terminal group will be the first to react with H2S causing structural distortion, which will brake Mo-O from Mo-O-Mo bridged groups transforming them into new Mo=O terminal groups. We suggest interaction of oxygen from bridging group with Ni which lowers the possibility of bridged functional group to transform into terminal Mo=O causing retardation of the sulfidation. Raman spectra of studied catalysts, (see Figure 2), indicate the existence of amorphous polymo-lybdate monolayer (3Mo atoms per nm2) with band at 950cm-1 characteristics for vibration of


Program Section: 5 Preferred form of presentation: Oral presentation

Mo=O terminal group and when Ni is impregnated a new band appears at 860cm-1, the intensity of which increases with higher Ni concentration.

In the second region (245 to 285˚C) catalyst containing only Mo eliminates the highest amount of H2S, while with higher Ni concentrations the extent of H2S evolution drops. Evolution of H2S is paralleled / followed by H2 consumption causing the formation of sulfur vacancies. The tempera-ture of the maximum H2S evolution is 270˚C for the catalyst containing only Mo and it shifts to lower values with increasing Ni concentrations. Ni promoted catalysts are concluded to have lower sulfur binding energies in comparison to the unpromoted Mo catalyst. The opposite trend in H2S evolution is expected for fully sulfided catalysts.

Conclusions

Ni is concluded to act in a complex way on the catalyst activation. It retards oxygen sulfur ex-change and lowers the sulfur binding energy in the catalyst.

For catalyst containing only Mo the degree of sulfidation reaches only 50% of the value for MoS2 indicating that bonding with support still remains via oxygen. The persistence of the links to the support is attributed to the high strength of the bond and the steric difficulty of the H2S interac-tion. It is proposed that excess of H2S is needed for breaking the Al-O-Mo bonds and for ex-changing the last oxygen atoms for full sulfidation.

Figure 1. TPS spectra of Mo and NiMo/γ-Al2O3 catalyst precursor

Figure 2. Raman spectra of Mo and NiMo/γ-Al2O3 catalyst precursor


Program Section: Preferred form of presentation:

undoped Li Na K Rb Cs400410420430440450460470480490

2,45

2,50

2,55

2,60

2,65

2,70

2,75

Eads,eV

Tem

pera

rure

,o

C

Fig. 1. Reduction temperature of VOx species(green); Hydrogen adsorption energy in eV (red)where positive value indicates exothermic process.

Combination of theory and experiment to study the effect of alkali additiveson the structure and reactivity of the vanadium catalytic system.

A.E. Lewandowskaa, M. Calatayudb, C. Minotb, M.A. Bañaresa

a Instituto de Catalisis y Petroleoquimica, CSIC, E-28049-Madrid, Spain,[email protected]

b Universite-Paris 06, UMR CNRS 7616 LCT, Paris F-75005, France,


Vanadium supported catalysts are widely applied in selective oxidation reactions [1]. Thecatalytic properties of the supported vanadium oxide species are strongly affected by the vanadialoading, preparation method, nature of the support and type of the promoter. Among catalystspromoters, alkali metals are of particular interest since they are commonly used as promoters forindustrial catalysts. The promoters decrease coke deposits and leads to differentreactivity. The systematic theoretical and experimental studies of the influence of alkali atoms onsurface vanadium oxide species allow observing the gradual effect of the alkali dopants on thestructure and reactivity of catalytic vanadium system. The vanadium supported titania catalystsare modified by the first group metals of periodic system (Li, Na, K, Rb, Cs).


Titania-supported vanadia catalysts exhibit a noticeable dependence on the preparation method,on the coverage of the support and on the characteristics of the promoter [2]. The effect of alkaliadditives on the structure and reactivity of the VOx/TiO2 catalytic system is studied by

combining theoretical modelling (DFT)and experimental in situ Ramanspectroscopy and temperature-programmed reduction (TPR) [2,3].Additionally; the changes in reactivityproperties of the materials are tested inthe methanol temperature programmedsurface reaction (TPSR) [4]. Thevanadium loading are adjusted belowmonolayer coverage since supportedspecies do not form bulk V-alkali-Oaggregates. However, both of thetechniques (experimental and theoretical)


Program Section: Preferred form of presentation:

0 100 200 300 400 500 600960

970

980

990

1000

1010

1020

1030

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undopedNaKRb

V=O

posi

tion

Fig. 2. Changes of the Raman V=O band positionduring hydrogen reduction.

highlight the strong affinity between vanadium oxide species, alkali ions and titania support. Thealkali atoms interact with several vanadia units and support by binding to a bridging oxygen inV–O–Ti and V-O-V and to a terminal oxygen V=O group. At the same time, alkali dopants formbonds with the support oxygen, Ti-O-Ti [5]. This interaction affects the structure, reactivity andreducibility properties of the catalytic system. There is a clear distinct interaction for each of

alkali metal ion. DFT modelling predictsthat the reducibility of the VOx speciesdecreases in the sequence undoped > Li >Na > K > Rb > Cs and withalkali/vanadium atomic ratio. DFT model-ling suggests that the V=O bond is not thepreferred site for reduction with hydrogen,but bridging oxygen. Figure 1 illustratesthe agreement between theoreticalpredictions and experimental results. Theeffect of alkali ions addition on the V=Oband position during reduction process isalso well visible by TPR-Raman study.

Figure 2 presents the shift in the V=O Raman band during reduction of alkali-doped titania-supported vanadia catalysts. The scale and value of the band shift depends directly on the alkalidopants and is related to on site generation of water during reduction at lower temperature.

Conclusions

The alkali ions tend to maximum interaction with all components of the catalyst by interactionwith oxygen sites. The V=O bond elongates in the order H > Li > Na > K > Rb > Cs which is ob-served as a shift to lower frequencies of vanadyl bond in Raman spectra. The reducibility of thevanadium titania supported system depends on the specific alkali additive and on the atomic al-kali/vanadium ratio. The undoped catalyst is more reducible than the doped ones, accordingly tothe order: undoped > Li > Na > K > Rb > Cs. The V=O is not the active site for the studied proc-esses since the V-O-Ti sites are more reducible than V=O.

References[1] M.A. Bañares, Catal. Today 51 (1999) 319[2] H. Si-Ahmed, M. Calatayud, C. Minot, E. Lozano Diz, A.E. Lewandowska, M.A. Bañares, Catalysis Today 126

(2007) 96[3] M. Calatayud, C. Minot, J. Phys. Chem. C 111 (2007) 6411[4] G. Garcia Cortez, J.L.G. Fierro, M.A. Bañares, Catal. Today 78 (2003) 219[5] A.E. Lewandowska, M. Calatayud, E. Lozano-Diz, C. Minot, M.A. Bañares, Catal. Today xxx (2008) in press


Program Section: Bridging the gap between model and technical conditions Preferred form of presentation: Oral

Combining in-situ DRIFTS and BTEM for Heterogeneous Catalytic Studies.

Comparison of Pt/Al2O3 and Pd/Al2O3 systems for CO and NO adsorption.

Srilakshmi Chilukoti,a,b Feng Gao,a Effendi Widjaja,a Huajun Zhang,a Bruce G. Anderson,b J.W. (Hans) Niemantsverdrietb and Marc Garland,a

aInstitute of Chemical and Engineering Sciences, A*STAR, Singapore,bEindhoven University of Technology, Netherlands.


Although a variety of in-situ spectroscopic methods are available for monitoring heterogeneous catalytic systems under operating conditions, few numerical approaches are available for ade-quately processing the subsequent data sets. Herein, we report DRIFTS measurements on the well studied Pt/Al2O3 and Pd/Al2O3 systems for CO and NO adsorption [1,2] and the subsequent analysis of the data using multi-variate techniques. In particular, band-target entropy minimiza-tion (BTEM) [3] is applied in order to reconstruct the spectra of the individual constituents pre-sent.

Circa 30-40 spectral reconstructions are achieved for each system. These include the ob-servations of (1) various nitrates, nitrites, formates, hydroxyls and carbonates on the support sur-face, (2) metal-carbonyls (linear and bridged) and metal-nitrosyls and (3) gas phase species [4,5]. Comparisons are made between the two different systems, and the scope and limitations of the present approach are highlighted. In the present contribution, we review the findings.


A Spectra Tech Collector II DRIFT cell was installed in a Nicolet 460 mid-infrared equipped with an MCT detector. Mass flow controllers were used to regulate the partial pressures of the CO, NO and helium diluent. The Pt/Al2O3 and Pd/Al2O3 catalysts were activated in hydro-gen in-situ before exposure to CO and NO. Hundreds of spectra were collected at various partial pressures and temperatures (50–160°C).

Fig 1a shows typical DRIFTS spectra in Kubelka-Munk representation for the Pt/Al2O3

systems under varying CO: NO ratios. From these selected spectra, it is clear that considerable changes occur in the measured reaction spectra. A few full-range spectral deconvolutions are shown in Fig 1b. These include adsorbed species as well as gas phase species. Some spectral arti-facts are seen as high frequency noise etc.

Fig 2a shows typical DRIFTS spectra in Kubelka-Munk representation for the Pd/Al2O3

systems under varying CO: NO ratios. Although these spectra a quite different from those in Fig 1a, it is again very clear that considerable changes occur in the reaction spectra. Fig 2b shows


Program Section: Bridging the gap between model and technical conditions Preferred form of presentation: Oral

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narrow-range spectral deconvolutions in the Pd-nitrosyl region. These spectral reconstructions possess all have similar band widths and good signal-to-noise ratios.

Fig 1a (left) shows some typical DRIFT spectra of Pt/Al2O3 under varying CO and NO. Fig 1b shows some corresponding full-range spectral reconstructions [4].

Fig 1a (left) shows some typical DRIFT spectra of Pd/Al2O3 under CO and NO. Fig 1b shows some corresponding partial-range spectral reconstructions of the Pd-nitrosyls [5].

Conclusions

The present studies represent the first BTEM analyses of in-situ DRIFTS data and are quite en-couraging. Numerous bands of individual constituents were recovered, and some unexpected chemistry and previously unreported spectra were also revealed. References [1] V. I. Parvulescu, P.Grange, and B. Delmon, Catal. Today, 1998, 46, 233. [2] K. Almusaiteer, S. S. C. Chuang, J. Catal. 1998, 180, 161. [3] W. Chew, E. Widjaja and M. Garland, Organometallics, 2002, 21, 1882. [4] Srilakshmi Chilukoti, Effendi Widjaja, Feng Gao, Huajun Zhang, Bruce G. Anderson, J.W. Hans Niemantsver-

driet, Marc Garland Phys. Chem. Chem. Phys., 2008, 10, 3535 [5] Srilakshmi Chilukoti, Feng Gao, Bruce G. Anderson, J.W. Hans Niemantsverdriet, Marc Garland Phys. Chem.

Chem. Phys., 2008, 10, 5510.


Program Section: Application of reporter molecules to image catalytic activity Preferred form of presentation: oral

In situ Synchrotron-based Infrared Microspectroscopic Study of Styrene and Thiophene Conversion on ZSM-5

Eli Stavitski, Marianne H.F. Kox, Ingmar Swart, Frank M.F. de Groot and Bert M. Weckhuysen

Inorganic Chemistry and Catalysis Group, Department of Chemistry, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands.. E-mail: [email protected]


Recently, a number of in situ spectroscopic techniques featuring micrometer spatial resolution has been developed and successfully applied to investigate heterogeneous catalytic processes taking place in heterogeneous catalysts. These methods, notably, optical absorption micro-spectroscopy [1] and fluorescence microscopy [2] have proven to be capable of elucidating valuable structure-function relationships in acid-base catalytic reactions. Although spatially- and time-resolved mapping of interconversion processes in catalytic solids can be carried out utilizing this approach, only indirect data on the molecular structure of the reaction intermediates and products can be obtained. Therefore, unambiguous identification of the reactive species requires a complimentary, chemically sensitive technique. Vibration spectroscopy, in particular, infrared (IR) microscopy, which is based on the coupling of an IR spectrometer and a microscope is the most suitable candidate to address this challenge.

Here we report on the in situ investigation of catalytic reactions in zeolite crystals by IR microspectroscopy. To improve upon the spatial resolution of the method, synchrotron light with brightness 100-1000 times higher than that of a conventional (globar) source was used. Styrene and thiophene conversion on ZSM-5 zeolite was chosen as probe reactions, where carbocationic reaction intermediates serve as reporter molecules for catalytic activity.


Styrene conversion on ZSM-5 zeolite crystals has been thoroughly studied by means of UV-Vis and confocal fluorescence microspectroscopy in our laboratory [1]. The in-situ IR spectra obtained from a 5 μm ¤ 5 μm region of the ZSM-5 crystal contacted with styrene derivatives reveal a set of bands with the intensities changing in the course of the reaction (Figure 1a-b) [3]. Strong dependence of the intensity of the band at 1534 cm-1 on the IR light polarization suggests that the origin of the latter is a dimeric product aligned within the zeolite channels (Figure 1c). To unravel the chemical structure of the reaction products, DFT calculations for the possible products were carried out. Comparison of the experimental and calculated spectra shows that the main reaction product giving rise to the band at 1534 cm-1 is the dimeric conjugated carbocation, confirming the structure suggested based on the results of UV-Vis microspectroscopy. Spatially resolved measurements demonstrated that a lower concentration of the dimer is obtained at the


Program Section: Application of reporter molecules to image catalytic activity Preferred form of presentation: oral

edges of the crystal, as compared to the center (Figure 1d). This finding was rationalized in terms of the intergrowth structure of the ZSM-5 crystals [4].

Figure 1. (a) Experimental spectra of ZSM-5 crystals exposed to 4-fluorostyrenen (blue) and calculated spectra for 4-fluorostyrene (i) and conjugated carbocationic dimerization product (ii); (b) in situ IR spectra recorded during the reaction; (c) polarization dependence of the IR spectra; (d) intensity of the IR band at 1534 cm-1 mapped over the crystal after reaction and IR spectra taken from the edge and the body of the crystal.

When ZSM-5 crystals were contacted with thiophene derivatives, multiple IR bands in the region 1400-1600 cm-1 could be detected. Polarization dependence of the spectra allows discriminating between the contributions of the reagents and polythiophene reaction products. Reaction mechanism of the thiophene conversion will be discussed based on these findings in conjunction with the results of optical microspectroscopy and micro-focus soft X-rays spectroscopy [5].

Conclusions

Implementation of synchrotron-based IR micro-spectroscopy allows obtaining further insight into the mechanisms of catalytic reaction on acidic zeolites, due to the high chemical sensitivity of the method. The findings complement the data obtained with other microspectroscopic techniques. We believe that the method, as a part of multi-pronged in situ approach or as independent tool is of general applicability and could become a valuable asset in the arsenal of catalyst scientists

References[1] (a) M. H. F. Kox, E. Stavitski, B. M. Weckhuysen, Angew. Chem., Int. Ed. 2007, 46, 3652-3655; (b) E.

Stavitski, M. H. F. Kox, B. M. Weckhuysen, Chem. Eur. J. 2007, 13, 7057-7065.[2] (a) M. B. J. Roeffaers, B. F. Sels, H. Uji-i, F. C. De Schryver, P. A. Jacobs, D. E. De Vos, J. Hofkens,

Nature 2006, 439, 572-575; (b) M. B. J. Roeffaers, B. F. Sels, H. Uji-i, B. Blanpain, P. L'hoëst, P. A. Jacobs, F. C. De Schryver, J. Hofkens, D. E. De Vos, Angew. Chem., Int. Ed. 2007, 46, 1706-1709.

[3] E. Stavitski, M. H. F. Kox, I. Swart, F. M. F. de Groot, B. M. Weckhuysen, Angew. Chem. Int. Ed. 2008,47, 3543-3547.

[4] E. Stavitski, M. R. Drury, D. A. M. de Winter, M. H. F. Kox, B. M. Weckhuysen, Angew. Chem. Int. Ed.2008, 47, 5637-5640.

[5] M. H. F. Kox, E. Stavitski, A. Mijovilovich, B. M. Weckhuysen, in preparation.


Program Section: Preferred form of presentation: ORAL

Enhanced reactivity of chromocene carbonyls confined inside the cavities of

NaY zeolite via an electron transfer mechanism

J. Estephane,a,b E. Groppo,a* A. Damin,a J. G. Vitillo,a D. Gianolio,a C. Lamberti,a S. Bordiga,a

C. Prestipino,c S. Nikitenko,c E. A. Quadrelli,b M. Taoufik,b J. M. Basset,b and A. Zecchinaa

a Department of Inorganic, Physical and Materials Chemistry, NIS Centre of Excellence and INSTM Centro di

Riferimento, University of Turin, Via P. Giuria 7, I-10125 Torino, Italy; bLaboratoire de Chimie Organométallique

de Surface, UMR5265 "LC2P2" - CNRS UCBL1 CPE, 43, Boulevard du 11 Novembre 1918; BP 2077 F-69616

VILLEURBANNE Cedex, France; cESRF, 6 rue Jules Horowitz, BP220, F-38043, Grenoble CEDEX, France


The inclusion of organometallic complexes inside the cavities of host frameworks is particularlyinteresting because of possible application in heterogeneous catalysis or electronic devices andoptical materials.[1] Nowadays this approach is reemerging,[2] because it provides a method formetal incorporation and catalyst immobilisation inside nanoporous scaffolds, alternative toclassical methods, such as ion exchange, ligand exchange or ship-in-the-bottle synthesis. Theorganometallic guests in zeolite hosts become polarized by the electrostatic fields associated withpartly exposed extra-framework cations located in a few well-defined sites of the oxidicframework, and is expected to show substantially enhanced reactivity compared to the parentcompounds.[3]

Metallocenes are organometallic substrates of interest to investigate such potential reactivityenhancement. Besides undergoing a well known variety of thermal and photochemical reactions(which include [2+2] additions and eliminations, oxidative addition and reductive elimination ofsmall molecules, C-H bond activation), they are efficient olefin polymerization catalysts.Therefore, the investigation of their reactivity inside a polar matrix can be extremely useful tounderstand their properties in the polymerization conditions, where they are usually found as partof an ion-pair together with the anionic form of the activator (e.g. MAO). Among metalloceneschromocene, which is the precursor of the Union Carbide olefin polymerization catalyst, is achallenging candidate since the study of its reactivity is complicated by electronic spin-pairingeffects and Cp loss towards small molecules.


We demonstrate that Cp2Cr molecules hosted inside the supercage cavities of the NaY zeoliteundergoes a structural distortion induced by the strong local electric fields generated by chargebalancing counterions. This effect, clearly observed by in situ Cr K-edge EXAFS study, is thekey factor in enhancing the reactivity of Cp2Cr towards CO. The Cp2Cr(CO) adducts initially


Program Section: Preferred form of presentation: ORAL

formed are not as stable as when hosted in non-polar environments, such as toluene solution[4] orpolystyrene.[5] The presence of strong anionic/cationic pairs (Y-/Na+) favors, in CO atmosphere,the loss of a Cp ring driven by an electron transfer mechanism (accompanied by ligand

rearrangement) that results in the formation of charged [CpCr(CO)3]− and [Cp2Cr(CO)]+ carbonyl

species that are stabilized by the Na+ and Y- pairs. The shape selectivity of the supercage cavityof the Y zeolite is necessary for this reaction, as it can host the two Cp2Cr molecules needed forthe disproportionation. Fast FTIR spectroscopy, working in operando conditions (see Figure),allows to follow the time evolution of the IR stretching modes peculiar of reactants and productsand thus to infer a reaction mechanism. Combination of quantum mechanical calculation with insitu EXAFS study supports the hypothesis made on the basis of IR results.

Conclusions

The simultaneous and synergic combination of different spectroscopic techniques, associatedwith quantum mechanical theoretical calculations, allowed us to fully understand the complexreactivity towards CO of Cp2Cr molecules inside the polar cavities of the NaY host, and toadvance a reaction mechanism. The work demonstrates that the zeolitic voids act as “nanoscalereaction chambers”, where the reactivity of guest organometallic complexes can providemolecular insights into the elementary steps of heterogeneous catalysis.

References[1] (a) Ozin, G. A.; Gil, C. Chem. Rev. 1989, 89, 1749; (b) Stucky, G. D.; Macdougall, J. E. Science 1990, 247, 669;

(c) Sachtler, W. M. H.; Zhang, Z. C. Adv. Catal. 1993, 39, 129.[2] (a) Long, J. L. et al. Chem.-Eur. J. 2007, 13, 7890; (b) Davis, M. E. Nature 2002, 417, 813; (c) Kemner, E. et al.

J. Chem. Phys. 2002, 116, 10838; (d) Kaiser, C. T. et al. Chem. Phys. Lett. 2003, 381, 292.[3] Ozin, G. A.; Godber, J. J. Am. Chem. Soc. 1989, 93, 878.[4] van Raaij, E. U.; Brintzinger, H. H. J. Organomet. Chem. 1988, 356, 315-323.[5] Estephane, J.; et al.Phys.Chem.Chem.Phys. 2008, accepted.


Operando Spectroscopy: In-situ Analysis of Supported Pt Catalysts during H2 Oxidation

V.A.Self and P.A.SermonChemistry, FHMS, University of Surrey, Guildford, Surrey, GU2 7XH, UK

Introduction and Objectives.

Our objective was to use in-situ DRIFT to elucidate the mechanism of H2 oxidation of graphite- and oxide-supported Pt, with a view to determining the potential of this approach to the optimisation of electrocatalysts.


Pt was supported on graphite (3%, 5% and 7%), silica (3%), titania (3%), alumina (3%), WO3

(3%) and MoO3 (3%) by impregnation, drying and reduction/oxidation. These were compared with EuroPt-1. Catalysts were characterised for the state of the Pt (by X-ray photoelectron spectroscopy, temperature programmed reduction, etc), Pt dispersion (by transmission electron microscopy, X-ray diffraction line broadening, H2/O2/CO chemisorption, H2-O2

titrations and CO-O2 titrations), texture (by N2 BET adsorption at 77K and Hg porosimetry). During H2-O2 (measured volumetrically and in a flow reactor with GC and H2O sensor analysis at varying reaction time, reaction temperature and H2:O2 that delivered rates of reactant consumption, orders (1 with respect to O2), rates of H2O production, turnover numbers (that were higher for H2 than O2 by a factor of 2) and activation energies) in-situ X-ray diffraction and in-situ DRIFT surface analysis were carried out. TONs with respect to H2

at 303K were significantly higher for graphite-supported Pt than on the oxide-supported Pt (including EuroPt-1).

nH2 ( mol H2/gcat) TONH2 (s-1 at 303K) EuroPt-1 163.0 4.353%Pt/C 16.2 5.205%Pt/C 21.1 5.637%Pt/C 18.7 11.60

For the graphite-supported Pt the DRIFT bands at 1500cm-1, 1600cm-1 and 3500cm-1 rose very rapidly during the reaction (see Figure) and then fell rapidly after the reaction.


Conclusions

This is interpreted in terms of rates of surface OH and H2O formation. In-situ DRIFT provides evidence of mechanistically why the Pt/C is more effective than oxide-supported Pt. It is shown how this multifaceted operando spectroscopy [1] approach is relevant to the optimisation of electrocatalysts (e.g. kinetic analysis of H2 oxidation on Nafion film covered Pt-black electrodes [2]).

[1] J.H.Wilson, C.G.Hill and J.A.Dumesic J.Molec.Catal. 61,333,(1990); M.A.Banares Catal. Today100,71,(2005); [2] R.B.Lin and S.M.Shih J.Chin.Inst.Chem.Eng. 39,475,(2008)



CO Oxidation over Titania Nanotubes Surface by FTIR Study J.A. Toledo Antonioa,*, M.A. Cortes-Jácomea, J. Navarretea, C. Angeles Cháveza, E. López Salinasa , A. Rendon Rivera. a Instituto Mexicano del Petróleo/Programan de Ingeniería Molecular, Eje Central Lázaro Cárdenas 152, D.F., 7730, México. Introduction and Objectives

Titanium oxides have attracted considerable attention because of their multiple potential ap-plications, such as in catalysis, photocatalysis, electronic devises, solar cells, etc. [1,2]. Down-sizing material structures modify their mechanical, optical, magnetic and electronic properties as well as their chemical reactivity, which in turn lead to surprising and unpredictable effects [3]. Thus, the functions of the aforementioned systems can be upgraded when the titanium oxides structure shifts towards nanoscale range, because new and enhanced properties can be developed by the creation of material’s structure in the range of 1-100 nanometers[4]. In this work, the FTIR evolution of CO adsorbed on the surface of Titania with different morpholo-gies, that is, nanoparticles (NP), nanotubes (NT) and nanofibers (NF) is presented. Results and Discussion

Titania nanotubes were synthesized by an alkali hydrothermal treatment following the procedure published elsewhere [5], starting from an anatase precursor Hombifine N supplied by Sachtleben Chemie GmbH. Anatase with nanotubular morphology, see Figue 1a, (NT sam-ple) was obtained by annealing titania nanotubes at 773 K, whereas annealing at 873 yields titania nanofibers, Figure 1b, (NF sample). Titania nanoparticles, Figure 1c (NP samples) were obtained by directly annealing the anatase precursor at 673 and 873 K in order to com-pare FTIR CO adsorption data. Anatase phase in samples with different morphologies was confirmed by microdifraction pattern and Raman Spectroscopy. Specific surface areas were similar for samples NP-673 and NT-773, 196 and 203 m2/g, respectively.

(1 0 1)(0 0 4)(2 0 0)(2 1 1)(2 0 4)

TiO2 anatase

(1 0 1)(0 0 4)(2 0 0)(2 1 1)(2 0 4)

TiO2 anatase

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5nm

(0 1 1)

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[0 1 -1]

(0 1 1)

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(2 1 1)

[0 1 -1]

Figure 1. TEM images and microdiffraction patterns of anatase in NT and NP samples.

Differencial FTIR of CO adsorbed at 100 K in NP, NT and NF anatase samples are shown in Figure 2. In NP-673 sample, after CO adsorption at 100 K, a negative band was observed in the v(OH) region at 3705 cm-1, whereas two intense peaks appeared at 3554 cm-1,as a consequence of the interaction with CO-OH, giving rise to a double hydrogen bonding



Fermi resonance. The v(OH) frequency shift was estimated to ca. – 149 cm-1 and evacuation of CO at higher temperature brings about the restoration of the unperturbed hydroxyl groups. When CO is adsorbed on strongly anisotropic anatase in nanotubular and nanofibrilar mor-phologies, only one CO adsorption band was observed at 2158-2161 cm-1, corresponding to CO interaction with hydroxyls groups. In comparison, no interaction of CO with coordinative unsaturated sites at 2180 cm-1 or with basic O2- ions at 2138 cm-1 as was observed in NP ana-tase (see inset in Figure 2), suggesting that no edges, corners and steps are exposed on the sur-face when anatase are formed as NT or NF. However, the CO adsorbed remain strongly ad-sorbed on hydroxyls groups of NT and NF and after evacuation at 170 K transformed into CO2 by reacting with highly reactive OH groups of NT and NF surface, as can be observed in Figure 3.

2500 2400 2300 2200 2100 20000

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Figure 2. FTIR spectra of CO adsorbed at 100 K on NP, NT and NF samples.

Figure 3. FTIR spectra of the evolution of CO adsorbed on the NT surface after evacuation at the indicated temperature

Conclusions Anatase with nanotubular and nanofibrilar morphology did not expose edges, corners or steps sites for CO adsorption such as anatase nanoparticles. Nevertheles, the highly reactive hydroxyls of nanofibers or nanotubes are able to transform adsorbed CO into CO2 by surface reaction at temperatures as low as 170 K.

References [1] Sakai, N.; Ebina, Y.; Takada, K.; Sasaki, T. J. Am. Chem. Soc. 2004, 126, 5851. [2] Drew, C.; Liu, X.; Ziegler, D; Wang, X.; Bruno, F.F.; Whitten, J.; Samuelson, L.A.; Kumar, J. Nano Lett. 2003, 3, 143.[3] Siegel, R.W.; Hu, E.; Roco, M.C. (Eds.) Nanostructure Science and Technology,Springer (former Kluwer Academic Publishers). Dordrecht, Netherlands. 1999. available at http://www.wtec.org/loyola/nano/). [5] Cortés M.A., Ferrat G., Flores L.F., Angeles C., López E., Escobar J., Mosqueira M.L., Toledo J.A., Catal. Today, 2007,126, 248.


Program Section: 6 Preferred form of presentation: Oral or Poster

In-situ DRIFTS-MS study of preferential oxidation of CO in H2 rich stream over CeO2 coated Cu0.9M0.1O (M = Co, Zn and Sn) catalysts

Parthasarathi Bera, Aitor Hornés, Arturo Martínez-Arias

Instituto de Catálisis y Petroleoquímica, CSIC, C/ Marie Curie 2, 28049 Madrid, Spain



At present fuel cell technology is rapidly growing as a viable alternative source for sus-tainable energy generation and it has been used for both stationary and transportation applica-tions. It offers highly efficient conversion of chemical energy into electrical energy lowering the emission of environmental pollutants (within well-to-wheels analyses), thereby making fuel cells one of the most promising sources of energy generation. At this moment, proton-exchange mem-brane fuel cells (PEMFC) are most studied type of hydrogen based electrical power sources, both for static and mobile power applications. But H2 has its own disadvantage due to the lack of in-frastructure for its distribution and storage. Therefore, processing of hydrocarbon-related fuels is an interesting option for producing H2, in particular when dealing with on-board production for mobile applications.1 Currently, steam reforming, partial oxidation and auto thermal reforming of hydrocarbons and alcohols are the major routes for H2 production. But all these methods produce a large amount of CO along with H2. CO is a pollutant and poisonous for noble metal catalysts in the electrodes of PEMFC. For this reason, water gas shift (WGS) reaction and preferential oxida-tion of CO (CO-PROX) would be required to reduce bulk CO (down to 0.5-1 vol %) and remain-ing CO, respectively, to an acceptable level (below 100 ppm) prior to its introduction into the fuel cell. In this respect, previous work from our group has been dedicated to investigate the proper-ties of combinations between copper and cerium oxides (economically favorable formulations in comparison with those, also active, based on noble metals) for CO-PROX reaction.2,3 On the ba-sis of such works, a new generation of catalysts is being developed in which chemical and struc-tural modifications to the copper oxide component are introduced in order to investigate the ef-fects on the overall CO-PROX performance.

Those previous works have in turn also shown operando-Infrared (IR) spectroscopy as the most useful tool to explore the catalytic details of redox interfacial activity of those type of cata-lysts, which constitutes the main basis to achieve details in the CO oxidation activity, which is the main reaction involved in the whole CO-PROX process.2, 3 In this sense, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) has been employed to obtain in situ spectra of the catalysts under reaction conditions, employing on line mass spectrometry (MS) analysis to identify and quantify gaseous compounds present in the reaction system. The objective of the present study is to investigate the reactive species of CO-PROX reaction over (Cu0.9M0.1O)0.7(CeO2)0.3 (M = Co, Zn, Sn) catalysts by using mainly such experimental system.


Program Section: 6 Preferred form of presentation: Oral or Poster


All the catalysts, including an M-free reference one, were prepared by a microemulsion method based on coprecipitation of the corresponding salt precursors, as detailed elsewhere.2 For this particular case, following extensive stirring of the solid precursor in the microemulsion con-taining the transition metals, the Ce metal salt precursor was added into such microemulsion fol-lowed by addition of the amount of base required for cerium precipitation. The resulting solid part after adequate rinsing was dried overnight at 120 oC and finally calcined at 500 oC for 3 h. All these catalysts were characterized by SBET, ICP-AES, XRD, HREM, Raman, EPR and XPS.

MS analysis shows that in all cases CO oxidation starts around 60 ºC but complete CO oxidation occurs at 245 ºC over (CuO)0.7(CeO2)0.3 and (Cu0.9Zn0.1O)0.7(CeO2)0.3 catalysts, whereas it is 200 and 225 ºC in cases of (Cu0.9Co0.1O)0.7(CeO2)0.3 and (Cu0.9Sn0.1O)0.7(CeO2)0.3.Above these temperatures, H2 combustion predominates over CO oxidation and hence CO signal grows again.

DRIFTS analysis of CO-PROX reaction shows the existence of reductive induction phe-nomena in all cases prior to onset of CO oxidation, evidenced by the formation of copper car-bonyl bands in the 2114-2096 cm-1 range, along with carbonate species already upon first contact with the CO-PROX mixture at 30 oC. Generally speaking, the carbonyl contributions display two bands exhibiting relatively high thermal stability, in spite of their relatively low frequency, which evidence the existence of different interfacial phenomena within the catalysts, according to previ-ous investigation.3 The differences observed in the catalytic behavior of the systems are analyzed on the basis of respective evolutions observed for such carbonyl bands as a function of their chemical composition and structural/morphological characteristics of the modified copper oxide component.

Conclusions

In general terms, the results show that CO-PROX activity can be enhanced with respect to more classical formulations2, 3 due mainly to changes in copper oxide particle size/shape while modifications induced upon doping of this latter component lead essentially to an enhancement of CO oxidation activity but also of H2 oxidation activity (as well as methanation activity in some case) producing various effects on the overall CO-PROX performance as a consequence of the balance between the different reactions taking place.

References

[1] L. F. Brown, Int. J. Hydrogen Energy 26, 2001, 381. [2] D. Gamarra, G. Munuera, A. B. Hungria, M. Fernández-García, J. C. Conesa, P. A. Midgley, X. Q. Wang, J. C. Hanson, J. A. Rodriguez and A. Martínez- Arias, J. Phys. Chem. C 111, 2007, 11026. [3] D. Gamarra, C. Belver, M. Feránadez-García and A. Martínez- Arias, J. Am. Chem. Soc., 129, 2007, 12064.


Program Section: 6 Preferred form of presentation: ORAL

Catalysis Science of Bulk Mixed Metal Oxide Catalysts:

An Operando IR-TPSR Spectroscopic Study

Kamalakanta Routray, Israel E. Wachs

Operando Molecular Spectroscopy and Catalysis Laboratory,

Department of Chemical Engineering

Lehigh University, Bethlehem, PA 18015 USA



Even though bulk mixed metal oxides find wide application in catalysis, there has still been a lack of fundamental understanding of how bulk mixed oxide catalysts function in the literature [1]. In order to obtain insights into how bulk mixed metal oxides function, the model bulk FeVO4

catalyst system was investigated for CH3OH oxidation to HCHO. Special emphasis was placed on obtaining surface information by employing operando IR-temperature programmed surface reaction (TPSR) spectroscopy with the CH3OH chemical probe molecule.

Experimental

The bulk FeVO4 and supported 4% V2O5/Fe2O3 were prepared by co-precipitation and incipient impregnation methods respectively [2, 3]. Bulk V2O5 was synthesized by thermal decomposition of NH4VO3 in flowing air at 300 oC for 4h.

Results

The in situ IR spectra for CH3OH chemisorbed on bulk V2O5, Fe2O3, FeVO4 and supported 4% V2O5/Fe2O3 were collected after adsorbing methanol at 100 oC. Chemisorption of CH3OH on Fe2O3 at 100 oC gives rise to two strong IR peaks at ~ 2924 and 2820 cm-1 characteristic of the C-H stretches for surface methoxy (CH3O*) species and bands at ~2950 and ~2850 cm-1 characteristic of the C-H stretches for intact methanol (CH3OH*) species on Lewis acid sites. Operando IR-TPSR spectroscopy revealed that the intact surface CH3OH* species desorbs as CH3OH (Tp~188 oC) and that the surface CH3O* species reacts to desorb as dimethyl ether (Tp~242oC). For bulk V2O5, methanol adsorption also results in both intact CH3OH* (2962 and 2854 cm-1) and surface CH3O* species (2930 and 2828 cm-1), with the surface methoxy species giving rise to a much a stronger IR signal compared to intact surface CH3OH* species. Both surface species, however, give rise to HCHO (Tp~201 oC) from bulk V2O5. Bulk FeVO4 and supported 4% V2O5/Fe2O3 also form both intact CH3OH* (2956 and 2828 cm-1) and surface CH3O* (2930 and 2828 cm-1), with the surface methoxy species being more dominant. During operando IR-TPSR spectroscopy (shown in Figures 1 and 2), the bulk FeVO4 and 4%


Program Section: 6 Preferred form of presentation: ORAL

V2O5/Fe2O3 catalysts both exclusively yield formaldehyde with Tp~201 oC and ~215 oC, respectively.

Discussion

The methanol chemical probe molecule reacts with surface redox, acidic and basic sites to produce formaldehyde, dimethyl ether (DME) and carbon dioxide, respectively. The formation of DME and absence of HCHO and CO2 from Fe2O3 during CH3OH-TPSR reveals that the Fe2O3

possesses surface acidic sites. In contrast, the vanadia-containing catalysts almost exclusively yield HCHO as the reaction product indicating that they contain surface redox sites. The very similar Tp values, 201-215 oC, for the V-containing catalysts suggest that the bulk FeVO4 catalyst is surface enriched with VOx. This is also supported by the CH3OH-IR spectra only showing the presence of V-OCH3 species on bulk FeVO4.

3100 3000 2900 2800 2700 2600

ννννs(CH

3)

-OCH3

280

260

240Abs

orba

nce

(a.u

.)

Wavenumber (cm-1)

100120140160180200220

FeVO4

2928 cm-12958 cm-1 2828 cm-1

Temp (oC)

L-methanolννννs

(CH3)

-OCH3 2δδδδs

(CH3)

150 200 250 300 350 400

Sig

nal

inte

nsi

ty (

a.u

.)

Temperature (oC)

HCHO 201 oC

CH3OH

DME CO2

CO

FeVO4

Figure 1: Operando IR-TPSR spectra from CH3OH Figure 2: Operando MS-TPSR spectra from CH3OH chemisorbed on bulk FeVO4 in flowing He. chemisorbed on bulk FeVO4 in flowing He.

Conclusions

New insights about the catalytic contributions of the bulk and surface of bulk mixed metal oxide catalysts were obtained for methanol oxidation by the Fe-V-O system with operando IR-TPSR spectroscopy studies. The catalyst surface sites are responsible for the nature of the methanol surface species, surface CH3O* or intact CH3OH*, and their reaction products (HCHO or DME). The presence of surface redox sites for the V-containing catalysts primarily results in the formation of HCHO. Furthermore, since both the monolayer 4% V2O5/Fe2O3 and bulk FeVO4

catalysts give comparable results this suggests that it is the surface characteristics of bulk mixed metal oxide catalysts (surface sites, surface intermediates and their reaction pathways) that dominate the catalytic properties of bulk mixed metal oxide catalysts.

References [1]. I.E. Wachs, Catal. Today, 100 (2005) 79. [2]. I.E. Wachs, L.E. Briand, U.S. Patent 7,193,117. [3]. X. Gao, S.R. Bare, B.M. Weckhuysen, I.E. Wachs, J. Phys. Chem. B 102 (1998) 10842.


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