Applied Catalysis A: General 387 (2010) 7586

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Applied Catalysis A: General

journa l homepage: www.e lsev ier .com

Conjug enhydrog ve

Nasima Ca Department ob Department o

a r t i c l

Article history:Received 23 AReceived in reAccepted 5 AuAvailable onlin

Keywords:AluminumAl SBA-15MesoporousIsomerizationRhodiumSafower oilCLA

orousdirec). TheverR mefor al

inmsize ranging from 4 to 7nm, BET-specic surface of 1000m2 g1, and metal nominal total loading of 1%w/w, was revealed as a new active catalyst for the chemocatalytic vegetable oils modication inducinghealth-benecial conjugated linoleic acids (CLA) formation by hydrogenation/isomerization. Time courseproles of (9-cis, 11-trans)-; (10-cis, 12-trans)-octadecadienoic CLA isomers aswell as the other fatty acidstraditionally encountered during the hydrogenation of vegetable oils are presented and discussed for the

1. Introdu

Hydrogeify the melachieve desbility for usHowever, doccurring cisuch as elamerizationlinked to hlowerHigh-occurrencefatty acids alinoleic acid-atherogeni[2].

Conjugaciscis and

CorresponE-mail add

0926-860X/$ doi:10.1016/j.Rh-catalyst supported onAl SBA-15 using Si/Al ratio of 100 under selected process conditions. The resultsshow that it is possible to tailor characteristics of the hydrogenation catalyst in such a way to confer itbifunctional activity: hydrogenation and conjugated isomerization.

2010 Elsevier B.V. All rights reserved.

ction

nation is a widely used hardening technology to mod-ting characteristics and plasticity of vegetable oils toirable techno-functional properties and oxidative sta-e in shortenings, margarines, spreads and frying fats.uring catalytic hydrogenation, some of the naturallys double bonds are isomerized to trans fatty acids (TFA)idic acid as a result of positional and geometrical iso-side reactions. High levels of trans fats in the diet areigher Low-Density Lipoprotein cholesterol (bad) andDensity Lipoprotein cholesterol (good) and then higherof coronary health diseases [1]. Nevertheless, all transre not harmful to health, in particular some conjugated(CLA) isomers are reported to have anti-carcinogenic,

c, -diabetic and lean body mass-enhancing properties

ted linoleic acids (CLAs) in their transcis, cistrans,transtrans congurations are conjugated isomers of

ding author. Tel.: +1 418 656 2131x6511; fax: +1 418 656 3723.ress: khaled.belkacemi@sga.ulaval.ca (K. Belkacemi).

linoleic acid (9-cis, 12-cis C18:2). The later is an important fattyacid in triglycerides composition of some vegetable oils such assunower (4568%) or safower oil (7580%). The CLA are natu-rally present in dairy products and meat from ruminant animalswith concentrations of 38mg/g fat [3]. Vegetable oils contain avery low amount ranging from 0.1mg CLA/g oil for coconut oil to0.7mg CLA/g oil for safower oil [4]. Banni et al. [5] carried outseries of HPLC/UV/MS analyses to characterize the fatty acids withconjugated dienes in partially hydrogenated oil and they detecteda low quantity of conjugated linoleic acid isomers (4.24mg totalCLA/g oil).

CLA isomers are industrially produced by alkaline conjugatedisomerization of linoleic acid from safower or sunower oil withthe total triglycerides hydrolysis [6]. Several studies on CLA enrich-ment of vegetable oils, without the triglycerides hydrolysis, havebeen carried out in the past few years. Jung et al. [7,8] reportedthe effects of catalyst type, catalyst amount, reaction temperature,agitation rate, hydrogen pressure, and different oils on the qualityand quantity of conjugated linoleic acids of hydrogenated soybeanoil using a selective Ni catalyst. They concluded that the gas-liquidmass transfer limitation conditions at low hydrogen pressure, lowstirring rate, high catalyst content, and high reaction temperaturefavored the CLA production in vegetable oils during hydrogena-

see front matter 2010 Elsevier B.V. All rights reserved.apcata.2010.08.006ated linoleic acid formation via heterogenation/isomerization of safower oil o

horfaa,b, Saa Hamoudib, Khaled Belkacemib,

f Chemical Engineering, Universit Laval, Qubec, Canada G1V 0A6f Soil Sciences and Food Engineering, Universit Laval, Qubec, Canada G1V 0A6

e i n f o

pril 2010vised form 30 July 2010gust 2010e 11 August 2010

a b s t r a c t

Aluminum-containing SBA-15mesop10, 20, 50 and 100 were prepared viaisoelectric point of silica (pH=1.9

76 N. Chorfa et al. / Applied Catalysis A: General 387 (2010) 7586

tion and reached 250mg/g oil. However, these hydrogenated oilsalso contained relatively moderate to high quantity (about 810%)of trans C18:1 isomers, mostly elaidic acid, which is known tobe associated with an increased risk of cardiovascular disease [9].During thehydrogen ureported upof CLA isomamounted amers represdeveloped alinoleic melyst for theanalysis, 53verted intoC18:2) and81% of totaestablishedof linoleicof 220mgisomers.

In our phydrogenaton nanostruresulted in lare knownmance for c

Even thopartially hyproductioncis-9, trans-using heter

MoreovemerizationThese catalmetallic sitbe obtainedmetal suppreported fo

Pure siliacidic activever, it is vebecause moous media d

Neverthminum, titaby post-syn[18]. Severaonto the mreported [1to the tremmetal oxide

Yue et aframeworkbutoxide, bspecies whplementaryKumaran etaluminumadjusting thmedium.

The aimthe framewlyst supportimpregnatiThis approa

nique to convert part of the vegetable oils to health-benecial CLAisomers.

erim

ateri

minu(TE

andblocic Ped asP gr

yedsedigh cpro

talys

SBA-agonynthinceere

mental at].

Al SBAl Sia thorouch u0] anch, trriedturesou

inter5, 10sou

roxidorkinevedtion wing lmind thsis, 2Afte35m1.9. TSwasCalcutiosirredh. Thd witopol-conX ishydrogenation of soybean oil by catalytic transfer ofsing non-selective nickel catalyst (N-545), Ju et al. [10]to 120mg CLA/g hydrogenated oil. The composition

ers (9-cis, 11-trans C18:2) and (10-cis, 12-trans C18:2)round 40% of total isomers while transtrans CLA iso-ented60%of total isomers. Andjelkovic et al. [11] havehomogeneous conjugated isomerization approach for

thylated ester and vegetable oils over Wilkinson cata-CLA synthesis. According to the 1H NMR spectroscopic.8% linoleic acid contained in soybean oil was con-

CLA isomers. The twomain isomerswere (9-cis, 11-trans(10-cis, 12-trans C18:2) representing approximatelyl CLA isomer content. Recently, Jain et al. [12] havea pilot plant to produce CLA by photoisomerization

acid contained in soybean oil. They obtained a totalCLA/g linoleic acid, mainly constituted of transtrans

revious works, we have clearly demonstrated thation of vegetable oils over Palladium catalysts supportedctured silica, SBA-15, as an alternative to Ni catalyst,ow transandsaturated fattyacids [1315].Noblemetalsas very active hydrogenation catalysts but their perfor-onjugated isomerization has been scarcely reported.ugh there is an evidence for the occurrence of CLA indrogenated oils, thorough investigation to optimize theof CLA isomers with high biological activities such as11 and trans-10, cis-12 isomers has not been attemptedogeneous catalysts.r, the competition between hydrogenation and iso-could be controlled by using bifunctional catalysts.ysts composed of acidic sites for isomerization andes for hydrogenationdehydrogenation reactions canby adding weak Brnsted acid such as alumina to the

orted catalysts. These catalysts were never yet tested orr CLA production using edible oils.ceous mesoporous SBA-15 materials lack acidity, thuse sites must be introduced into their framework. How-ry difcult to prepare SBA-15 containing heteroatomsst of precursors will dissolve in the strong acidic aque-uring the synthesis procedure [16].

eless, many efforts have been made to incorporate alu-nium and vanadium into the framework of SBA-15,thesis grafting procedures [17] and direct synthesisl post-synthesismethodswhere aluminumwas graftedesoporous wall with various Al sources have been9]. The post-synthesis method drawbacks are linkedendous and complex experimental procedures wheres formation limits the access to the pore channels.l. [20] tried to incorporate aluminum directly into theof SBA-15 through direct synthesis by using Al-tri-tert-ut the product contained extra-framework aluminumere post-synthetic method was necessary as a sup-step to remove them. Recently, Vinu et al. [21] andal. [16] have reported the direct incorporation of high

content (yield >50%) in SBA-15 framework by simplyemolarwater tohydrochloric acid ratio of the synthesis

of this work is to efciently incorporate aluminum intoork of SBA-15 with high yield (80%) and use it as cata-for the hydrogenation/isomerization of safower oil by

ng metals M (M=Ru, Ni, Pd, and Rh) and a nonmetal Se.ch will be investigated as a new chemocatalytic tech-

2. Exp

2.1. M

Alusilicateminumoxide)(Pluronwas usgen UHemplopurchaof its hfor CLA

2.2. Ca

2.2.1.Hex

via a s[22]. Sruns wexperimateri[1315

2.2.2.The

sized vmesopapproaet al. [2approawas caa strucminumin theSi/Al =ing theAl-hydtionwis achicentrathe agethe aluallowesynthewater.Abouta pH=of TEO40 C.Si/Al rawas stfor 24washeblock cThe Alwhereental

als

m tri-sec-butoxide (Aldrich) and tetraethyl ortho-OS) (Aldrich) were used as the sources for alu-silicon, respectively. Triblock copolymer poly(ethylenek-poly(propylene oxide)block-poly(ethylene oxide)123, molecular weight =5800, EO20PO70EO20) (Aldrich)the structure directing template. Hydrogen and nitro-

ade were purchased from Praxair. Deionized water wasduring materials synthesis. Rened safower oil wasfrom local supermarket and used as model-oil becauseontent (7179%) in linoleic acid which is the reactantduction.

t preparation

15ally ordered SBA-15 was synthesized in acidic mediaetic route using Pluronic P123 as a templating agentnumerous experimental hydrogenation/isomerizationcarried out using a same batch of catalyst, a rigorousal methodology was needed to prepare SBA-15 silicalarger scale as reported elsewhere inourpreviousworks

A-15 supportsBA-15 materials with various Si/Al ratios were synthe-e substitution of silicon atoms by aluminum in thes silica SBA-15. This was achieved by direct synthesissing a modied method based on that described by YuedVinuet al. [21] anddeveloped in the laboratory. In thishe incorporation of Al atoms into SBA-15mesostructureout by direct synthesis method using pluronic P123 asdirecting agent, and aluminum tri-sec-butoxide as alu-rce. Indeed, to optimize the aluminum incorporationnal structure of SBA-15 with nominal molar ratios of, 20, 50 and 100, several tests were achieved by vary-rce of aluminum (Al-tri-sec-butoxide, Al-isopropoxide,e) and the concentration of the hydrochloric acid solu-g at 0.1

N. Chorfa et al. / Applied Catalysis A: General 387 (2010) 7586 77

2.2.3. CatalystMetal supported on mesoporous aluminosilicate was pre-

pared by impregnating the nanostructured aluminosilicate support(Al SBA-15, molar ratio Si/Al of 100) with an aqueous solution ofmetal salts.The solid wreduced unature for eawere Ru, Ni

2.3. Charac

Nitrogenwere obtaiAutosorb-1196 C (77degassed fadsorptionamount adswere calcution/desorpmethod [23

Powderan Ultima Iradiation (between 0.angle XRD a

Solid-staAVANCE 30eter, equipSamples weA single pulwas repeatein order to400000 acq

The catatroscopy (Xfrom Kratosray, a sourcan Al sourcwas maintawere recordof 300W. Ttary compoof 160eV anwhich maxresolutionstep energyused for thecalculated wCasaWPS so

Transmitaken on aacceleration

The alumwere analyz200mg of m

2.4. Hydrog

ReactionModel 4560pressure traand an amooil were ch(H2) in the

the reactor was stripped by applying a vacuum and re-establishingatmospheric pressurewithnitrogen (N2). For safety considerations,this procedure was carried out twice, allowing the reactor to oper-ate in the absence of oxygen (O2). The system temperature was

ed gn ext

perctoror thondpresterva3000 C)

actio

and/isoatogl estethe Tchromtionurne). Injerfor 1mmin aa at 1s CLnrmrds. In us

ults

arac

Effects expthe-15.ed

droche surolar

. Thein Fials tecorp

de (ASi/Alourc; while int prehenSi pand

oroueportumtreaThe mixture was dried at room temperature for 24h.as calcined in programmed furnace at 540 C for 5h andder hydrogen ow at predetermined reduction temper-ch investigated metal for 3h. The investigated metals, Pd, and Rh while Se was used as a nonmetal.

terization

adsorption/desorption isotherms of calcined samplesned using a volumetric adsorption analyzer (Model, Quantachrome Instruments, Boyton Beach, FL) atK). Before the adsorption analysis, the samples were

or 3h at 200 C in the degassing chamber of theapparatus. Total pore volume was estimated from theorbed at 0.99 relative pressure. Pore size distributionslated using the desorption branch of the N2 adsorp-tion isotherms and the BarrettJoynerHalenda (BJH)].X-ray diffraction (XRD) patterns were obtained usingII Rigaku Monochromatic Diffractometer using Cu K=1.5406 A). Powder diffraction patterns were obtained

6 and 3 with a scan speed of 1 degree/min, for smallnalysis.te 27AlNMRexperimentswere carriedout onaBRUKER0 (Bruker Biospin Inc., Milton, ON, Canada) spectrom-ped with a 4mm CPMAS NMR probe at 130.32MHz.re spun at 10kHz at magic angle in a 4mm ZrO2 rotor.se sequence 2.1s followed by acquisition of 2k pointsd at a recycle rate of 100ms. The pulse length was /10uniformly irradiate all transitions. Between 50000 anduisitionswere necessary to obtain good quality spectra.lyst surface was studied by X-ray Photoelectron Spec-PS) analysis using an Axis-Ultra system spectrometer(U.K.) equipped with an electrostatic analyzer of large

e of double X-rays AlMg without monochromator ande with monochromator. The pressure in the XPS roomined at 5108 torr during the analysis. All the spectraed with the Al monochromatic source with a powerhe yover spectrum used to determine the elemen-sition was recorded with pass energy in the analyzerd an energy step of 1 eV, using lenses in hybrid mode,

imizes the sensitivity. The detailed spectra with highwere recorded with pass energy of 40 or 20eV, andof 50 or 100meV. The spectra with high resolution arechemical analysis [24]. The adjustment of the envelopeith the experimental spectrum was carried out usingftware from Kratos (U.K.).ssion electron microscopy (TEM) measurements wereJEM-3010 electron microscope (JEOL Japan) with anvoltage of 300kV.inum and silicon content in Al SBA-15(X) materialsed by atomic absorption spectroscopy after dissolvingaterial in 50ml HF aqueous solution (2% vol.).

enation/isomerization reaction

s were carried out in a 600ml Parr Pressure Reactor(Parr Instrument Co., Moline, IL, USA), equipped with ansducer. In a typical experiment, 200g of safower oilunt of catalyst at a concentration of 0.005g metal/100garged into the reactor. Before introducing hydrogenreactor system, dissolved and residual air present in

increaswith athe temthe reavalue fcorrespandH2ular induringand 21work.

2.5. Re

CLAgenateChrommethying toII gasseparaMelbonesseswere pmal fofor 15300kPcis/tranand costandapositio

3. Res

3.1. Ch

3.1.1.It i

role inAl SBAperformin a hywith ththree mditionsshownmaterito an inbutoxifor allsilica scursormiscibthe rssion wthat Al(Al-TSBmesopThey raluminthe preradually andmaintained at preset reaction temperatureernal controller at an agitation speed of 300 rpm. Whenature reached a desired value, H2 was introduced intoat the desired reaction pressure and maintained at thise duration of the reaction. The time zero of reactioned to the moment when desired reaction temperaturesurewere reached. Oil sampleswerewithdrawn at reg-ls for fatty acid analysis and Iodine value evaluation

minof reaction. Two levels of reaction temperature (180and H2 pressure (4 and 7psi) were investigated in this

n sample analysis

d fatty acid composition of the partially hydro-merized safower oil were determined by Gasraphy. The reaction products were converted into theirrs with methanolic-base (sodium methoxide) accord-hompson method [25], and analyzed on a 5890 Seriesatograph (Hewlett-Packard, Palo Alto, CA, USA). GC

was performed on a BPX70 capillary column (SGE,, Australia, 60m0.25mm i.d.0.25m lm thick-ection (split mode) and detection (ame-ionization)rmed at 250 C. Oven temperature was 60 C isother-in, increased to 190 C at 10 C/min, and isothermalt 190 C. The inlet pressure of the carrier gas (H2) was90 C. Identication of individual fatty acids as well asA isomers was achieved based on literature data [26],ed both with commercially available and synthesized

odine value (IV) was calculated from the fatty acid com-ing the AOCS standard method [27].

and discussion

terization of Al SBA-15 materials

of the aluminum sourceected that the source of aluminum plays a criticalmacroscopic growth and the ultimate morphology ofPreliminary tests of Al incorporation into SBA-15 wereby dissolving the aluminum and silicon (TEOS) sourcesloric acid solution 0.7mol l1 (pH=0.15) beforemixingfactant (Pluronic P123). Three sources of aluminumandratios Si/Al = 5, 10 and 20 were tested under these con-aluminum incorporation into the SBA-15 framework isg. 1. We can notice that the aluminum content in all thested is less than1mgAl/gAl SBA-15which correspondsoration yield less than 3%. Furthermore, the Al-tri-sec-l-TSB) seemedtobe themosteffectivealuminumsourceratios. Liquid organic Al-TSB can react with the organice TEOS and form a homogeneous organic AlSi pre-le the other Al sources are not easily dissolved and/orTEOS, resulting in less or no organic Si-Al precursor aftermixing stage. Li et al. [28] arrived to the same conclu-they synthesized Al SBA-15. These authors concludedrecursor by premixing liquid organic Al and Si sourcesTEOS) is a crucial step in obtaining highly ordered

s Al SBA-15 materials with a well-dened morphology.ed that when a solid organic aluminum source is used,is not noticeably incorporated in the AlSi precursor intment process for Si/Al ratios >500. The solid organic Al

78 N. Chorfa et al. / Applied Catalysis A: General 387 (2010) 7586

Fig. 1. Relation between aluminum content in Al SBA-15 materials and aluminumdissolved in TEOS and charged in the gel synthesis at pH=0.15, by varying the molarratio Si/Al and the Al source.

was completely decomposed to Al3+ in the acid solution. Due tothe absence of an AlSi precursor at the beginning of the process,most Al3+ is lost in the sample washing process. They reported alsothat the use of an organic Al source is preferred over an inorganicAl source in terms of obtaining mesoporous Al SBA-15 materialswith a well-ordered structure. Furthermore, among the organic Alsources, only the liquid Al-TSB is superior in terms of Al incorpo-ration which corroborates our nding. These results indicate thatthe Al source plays a critical role in the macroscopic growth ofthe inorganicorganic composite and the ultimate morphology ofAl SBA-15.

Yue et aHowever, thHCl) require

trivalent ionmetal becauseof itshigh solubility. Theseauthorswereconstrained to use a post-treatment step to eliminate aluminumpenta- and octahedral outside de SBA-15 framework. This situationcanbeexplainedby the following reactionpathway,whenusing theisopropoxide aluminum:

Al(C3H7O) + 3H+ Al3+ +3C3H7OH

Al3+ +2H2O Al(OH)2+ +3H+

In view of these reaction steps, it is clear that acidic media solubi-lizes the aluminum source in cationic specie, aluminum hydroxideAl(OH)2+, which does not incorporate into the SBA-15 hexagonalmesophases. Thus, under strongly acidic conditions (pH

N. Chorfa et al. / Applied Catalysis A: General 387 (2010) 7586 79

increase to 2.1 after the formation of the hexagonal mesostruc-ture. This pH value is above the silica isoelectric point, and thesilicon species are then negatively charged and can interact withaluminum hydroxide: Al(OH)2+. However, the aluminum incorpo-ration efciency in the aluminosilicates Al SBA-15 synthesized bythese authors remain less than 50%.

From these observations, it was decided to introduce rst thealuminum source in the gel synthesis containing the surfactant24h after the silicon source when the silicon mesophase is formedand the pH of gel is above the isoelectric point of silica. On theother hand, hydrochloric acid solution with pH=0.15, 1.5 and1.9 have been tested to assess the incorporation of aluminumin the mesoporous silica SBA-15 framework. The results of thesetests are presented in Fig. 3. Therefore, the silicon substitution byaluminum atoms in the mesoporous silica SBA-15 structure is opti-mized through the use of Al-tri-sec-butoxide and a hydrochloricacid solution at 0.0126mol l1 with pH=1.9 very close to the silicaisoelectric point (pH=2). The aluminum incorporation efciency isestimated by silicon and aluminum atomic absorption analysis forthe Al SBA-15 synthesis with a molar ratio Si/Al = 100 as depictedin Fig. 4. It can be observed that the aluminum incorporation yieldreached unprecedented value of circa 80%, corresponding to 4.5mgAl/g Al SBA-15 which has, in the opinion of the authors, never beenreported before for this kind of mesostructured silica materials.Usually the aluminum incorporation in the SBA-15 frameworkdoesnot exceed 50% [29,16].

3.2. Textural characterization

3.2.1. Nitrogen physisorptionTextural properties of the mesoporous solids were obtained

from low-temperature (77K) nitrogen adsorption/desorptionisotherm measurements, which allow calculation of the specicsurface areas, specic pore volumes, and mesopore size distribu-

Fig. 3. pH effects on aluminum content in Al SBA-15 with a molar ratio Si/Al = 100,by using Al-tri-sec-butoxyde.

tions, as summarized in Table 1. For instance, these isotherms andthe corresponding pore size distributions using the BJH theory aredepicted in Figs. 5 and 6, respectively, for SBA-15 as well as forAl SBA-15(100). The shape of SBA-15-like materials isotherm, inFig. 5, corresponds to type IV according to IUPAC classication anddisplayed a broad H1 type hysteresis loop characteristic of largepore mesoporous solids [30]. The initial increase in adsorptioncapacity at low relative pressure is due to monolayer adsorption onmesopores. The upward deviation in the range of P/P0 = 0.40.8 isassociated with progressive mesopores lling. As the relative pres-sure increases, all isotherms display a sharp increase characteristicof capillary

atomic absorption analysis.Fig. 4. Aluminum and silicon content evaluated bycondensation inside uniform mesopores.

80 N. Chorfa et al. / Applied Catalysis A: General 387 (2010) 7586

Table 1The textural parameters of the SBA-15 support as well as the Al SBA-15 samples prepared at different Si/Al molar ratios.

Sample Si/Al molar ratio Synthesis conditions BET surface area (m2 g1) Total pore volume (cm3 g1) Pore size (nm)

Nominal Real T (K) pH

SBA-15 0 0 313 0.1 931Al SBA-15(5) 5 6 313 1.9 996Al SBA-15(10) 10 12 313 1.9 935Al SBA-15(20) 20 25 313 1.9 989Al SBA-15(50) 50 61 313 1.9 1002Al SBA-15(100) 100 123 313 1.9 1006

Fig. 5. Nitroge

In Fig. 5tion isothera wide rangbution (Fig.that this msome blockorption braloop, whichby the BJHtwo pore si(open mesonosilicates

Fig. 6. Pore sipared via direc

In Tabletotal pore vof aluminuratio of 10Al SBA-15(rationof aluvalues. Theimpact on tpore size of

ize dnitiaalumorptitainere. Tain

niforma

copy

Trans7araphn adsorption/desorption of SBA-15 and Al SBA-15(100) materials.

pore sin the iin theN2 adswas obstructulyst rempore uSBA-15micros

3.2.2.Fig.

microgthe capillary condensation step on the nitrogen adsorp-m of Al SBA-15(100) was found to be broad, indicatinge of pore sizes, as conrmed by the BJH pore size distri-6). Indeed, the isotherms of Al SBA-15(100) indicatedaterial has a regular cylindrical mesopore system withed openings [31]. This could be observed from the des-nch of the isotherms and the shape of the hysteresiscorresponds to ink-bottle pores [32]. This is conrmedpore size distribution of Al SBA-15(100) which showze distributions at 4.7nm (ink-bottle pores) and 6.8nmpores) (Fig. 6). Similar results were obtained for alumi-with molar ratios Si/Al = 5, 10, 20, and 50 (see Table 1).

ze distribution of SBA-15 compared with Al-containing SBA-15 pre-t synthesis.

1%Rh/Al SBmaterial (Fpore arrangdescribed b15(100) (Smesoporesonal mesosto 78nm,presentingwhere thepwith the N2(Fig. 7c) shAs clearly dthe mesopooclusters. Tmesopore dmost of theframeworktigation givcrystallitesthe aluminoformation.

3.2.3. X-rayFig. 8 s

tern of silicof well res(200). Thesdimensionaresults arefor SBA-151.20 6.171.12 3.9 and 6.71.21 3.9 and 6.21.2 4.0 and 7.21.18 4.7 and 7.41.85 4.7 and 6.8

1, the BET surface area of SBA-15 is 931m2 g1 with aolume of 1.2 cm3 g1 and 6.17nm pore size. By additionm via direct synthesis, until reaching the Si/Al molar0, the BET surface area increased to 1006m2 g1 for100) and begun to slightly decrease at higher incorpo-mina, corresponding to thedecrease in Si/Almolar ratiorefore, incorporation of aluminum has a consequentialhe BET-specic surface area, specic pore volume andthematerials. All Al SBA-15materials exhibitedbinodalistributions (around 4 and 67nm). With the decreasel Si/Al ratio from 100 to 5 corresponding to the increaseina incorporation into SBA-15, a slight reduction in theon capacitywas observed and less sharp hysteresis loopd. Usingmuchmore Al-TSB seriously affects the poroushe textural properties of 1%Rh/Al SBA-15(100) cata-ed mostly identical to the support Al SBA-15(100). Themity and structural morphology of the synthesized Al-terials can be further veried by transmission electron(TEM).

mission electron microscopyc shows the transmission electron microscopy (TEM)s of SBA-15 silica material, Al SBA-15(100) andA-15(100), respectively. The TEM image of SBA-15ig. 7a) clearly shows the well-ordered 2D hexagonalement and the long-range mesopore architecture asy Zhao et al. [22]. The TEM image of calcined Al SBA-i/Al of 100) material shows ordered hexagonal arrays ofwith one-dimensional channels indicating a 2-D hexag-tructure (Fig. 7b). The average pore size is generally upbut there are some regions in the Al SBA-15 materialcylindricalmesoporous channelswithblockedopeningsore size ismore restricted (size of 34nm) in agreementadsorption measurements. The 1% RhAl SBA-15(100)

ows material grain with a regular array of mesopores.epicted, the Rh crystallites are well dispersed withinrous Al SBA-15 and isolated from each other as nan-heir size (dRh =37nm) does not exceed the averageiameters (4 and 8nm), conrming the suggestion thatmetal crystallites are located within the mesoporouschannels of Al SBA-15(100). Thus, the TEM inves-es a consistent evidence of the presence of the Rhinto the Al SBA-15 pores and the conning effect ofsilicate mesoporous framework during the Rh clustersdiffractionhows the low angle powder X-ray diffraction pat-eous SBA-15 sample. It can be noticed the presence

olved diffraction peaks indexed to (100), (1 10), ande diffraction lines are associated with long-range two-l hexagonal ordering in the p6mm space group. Thesein agreement with the data reported by Zhao et al. [22]material. The XRD patterns of Al SBA-15(100) has pat-

N. Chorfa et al. / Applied Catalysis A: General 387 (2010) 7586 81

tern similar to SBA-15 implying that the mesoporous structure iswell preserved after the incorporation of aluminum. It can also beseen that the (100), (1 10) and (200) peaks became more promi-nent. This indicates improved structural order with the aluminumincorporation in the framework.

3.2.4. 27Al solid-state NMR27Al NMR spectra is well known to give useful information

that enables to ascertain the presence of tetra, penta- and octa-coordinated Al species in various aluminosilicates like zeolites andmesoporous materials. The 27Al NMR spectra of Al SBA-15 alumi-nosilicates with molar ratio Si/Al = 20, 50 and 100 are shown inFig. 9. It can be seen essentially a strong resonance signal around50ppm which is assigned to the aluminum in tetrahedral coordi-nation. This result indicated that under the synthesis conditionsaluminum atoms are incorporated into the mesoporous wall ofSBA-15 material. However, a second peak appears at 0ppm foraluminum in octahedral coordination when there is an importantaluminum amount in the Al SBA-15 gel synthesis for molar ratiosSi/Al < 20 (Table 2). This signal is ascribed to an aluminum oxide

Fig. 7. TEM mSi/Al molar rat

Fig. 8. Low angle XRD proles of calcined SBA-15 and Al SBA-15(100).

outside the SBA-15 framework and tends to block its mesopores.Moreover, aluminosilicates Al SBA-15withmolar ratios Si/Al < 100,show a thirminum oxithat the me1mmol aluexplains thSi/Al is less

Fig. 10 dmolar ratioporated in Sin its hexa-

3.2.5. X-rayIn order

also employ3d, and Si 2on Al SBA-1for the bind2p, Si 2p, an

The bind(Fig. 11a). Aof Al 2p wistudy of O2Al in metalx/y ratios, r

7Al NMR spectra of Al SBA-15 materials with a molar ratio Si/Al = 20, 50 andicrographs of (a) SBA-15 silica material; (b) Al modied SBA 15 withio of 100 (Al SBA-15(100)); and (c) 1% Rh/Al SBA-15(100) catalyst.

Fig. 9. 2

100.d signal at 30ppm assigned to penta-coordinated alu-de species outside the SBA-15 framework. It seemssoporous silica SBA-15 cannot incorporate more thanminum per gram of material as shown in Table 2. Thise formation of aluminum oxide when the molar ratiothan 100.epicts the 27Al-MAS NMR spectra of Al SBA-15 with aSi/Al = 5. It is clearly shown that themajority of Al incor-BA-15 silica material is an extra-framework aluminumcoordinated form.

Photoelectron Spectroscopy (XPS) analysisto get insights into the surface composition, XPS wased in this study. The XPS spectra of Al 2p, 0 Is, C 1s, Rhp were recorded in details for the rhodium dispersed5(100). The C 1s line at 284.6 eV was used as a checking energies. For commodity, only the XPS spectra of Ald Rh 3d are shown in Fig. 11ac, respectively.ing energy (BE) of the Al 2p peak appears at 75.48 eVccording to Pashutski et al. [33], three binding energiesth values of 73.0, 74.5, and 75.4 eV, were found in theadsorption on Al(100), which were assigned to pure

lic state, AlxOy (x/y=3:1 or 1:1) and AlxOy with otherespectively. Accordingly, the value of 75.48 eV for BE in

82 N. Chorfa et al. / Applied Catalysis A: General 387 (2010) 7586

Table 2Aluminum content in Al SBA-15 material with molar ratio Si/Al = 5, 10, 20, 50 and 100.

Designation Al-teta-coordinated(50ppm)

Al-penta-coordinated(30ppm)

Al-hexa-coordinated(0ppm)

Al loading on aluminosilicatematerial (mmol Al/g Al SBA-15)

Al SBA-15(5) 25 9 66 1.00Al SBA-15(10) 46 7 47 0.92Al SBA-15(20) 89 11 0 0.89Al SBA-15(50) 95 5 0 0.38Al SBA-15(100) 100 0 0 0.20

the present study could indicate that the Al phase of the Al SBA-15(100) material can be assigned to alumina in a certain oxidativestate. TheAlmoieties incorporated inside theSi-SBA-15by the reac-tion with silanol groups could be oxidized through the calcinationstep of the Al SBA-15 synthesis. However, it is well documentedthat Al 2p binding energy does not give information to distinguishtetrahedral from octahedral Al [34,35].

On the other hand, the Si 2p signal is symmetrical and centeredat circa 104eV (Fig. 11b). The deconvolution of this signal gives twosignal envelops centered at 104.03 eV and 104.68 eV with respec-tive areas of 66.67% and 33.33%. These signals correspond to theSi 2p3/2 and Si 2p1/2 levels, respectively, ascertaining the oxi-dized state of Si at Si4+ owing to the presence of silanol groupsSiO2.

Rh 3d spin Fig. 11c. Trepresentinprocess. Thwhile the ppeaks haverst bindingsponds to Rstate in thepartial oxidthe contact

3.3. Catalys

Heterognot only facatalyze isopotential ofa heterogenrhodium arisomerizati

Fig. 10. 2

mine the best metal maximizing the hydrogenation/conjugatedisomerization activities.

3.3.1. Effect of the chemical nature of added metals and Se on thecatalyst activity

In the catalyst activity screening process, nickel, palladium,ruthenium, rhodium and selenium have been incorporated by wetimpregnation with the same concentration (1wt.%) in Al SBA-15mesostructured aluminosilicate with a molar ratio Si/Al = 100 toectrum for the Rh/Al SBA-15(100) catalyst is depictedhe experimental curves present awell-dened doubletg Rh 3d5/2 and Rh 3d3/2 after the peak deconvolutione peak for Rh 3d 5/2 core level is centered at 308 38eVeak for the Rh 3d 3/2 is centered at 312.98 eV. Thesean area peak ratio (Area3d 5/2:Area3d 3/2) of 3:2. Theenergy corresponds to Rh0 [36], while the latter corre-

h+1 [37]. Globally, rhodium appears mainly in metalliccatalyst sample, although Rh+1 is also found. Indeed,ation of metallic rhodium must have occurred duringwith air.

t activity

eneous catalysts used for double bond hydrogenationcilitate hydrogenation but also have the tendency tomerization and double bond migration and showed theconjugation of unsaturated fatty acid in edible oil usingeous nickel catalyst [38,39,7]. Palladium, platinum, ande also active catalysts for hydrogenation and possibleon. In the frame of the same idea, it is decided to deter-7Al-MAS NMR spectra of Al SBA-15 with a molar ratio Si/Al = 5.Fig. 11. XPS s2p spectrum;pectra for 1% Rh/Al SBA-15(100) catalyst: (a) Al 2p spectrum; (b) Si(c) Rh 3d spectrum.

N. Chorfa et al. / Applied Catalysis A: General 387 (2010) 7586 83

Table 3Overall activity of the formulated catalysts duringpartial hydrogenationof safoweroil at 210 C under hydrogen pressure of 7psi and agitation of 300 rpm.

Catalyst Final iodine value after300min of reaction, IVf

Overall hydrogenationactivity, mkr 104 (min1)

Ni/Al SBA-15(100) 137 1.0Pd/Al SBA-15(100) 134 2.0Ru/Al SBA-15(100) 119 6.0Se/Al SBA-15(100) 140 0.2Rh/Al SBA-15(100) 134 2.0

test their capacity for the CLA production during the partial hydro-genation/isomerization of safower oil. The reaction conditions forthe temperature and H2 pressure for these tests were 210 C and7psi, respectively.

The overall hydrogenation activity mkr was monitored by thedecay of iodine value IV which indicates the level of non-saturationof double bonds. It is well established that the saturation of doublebounds follows a rst order simple kinetics respective to the IV-decay:

d(IV)tdt

= mkr (IV)t (1)

Table 3 shows the nal iodine value after 300min of partialhydrogenation of safower oil and the overall hydrogenation activ-ity at 210

300 rpm. It itowards parconditionsRh-based ca

The totagenated wicatalytic suwas revealand exhibitization of sby Pakdeecof linoleic a5% rhodiumactive metawork.

3.3.2. EffectIt is kn

exhibits tw

Fig. 12. Fatty[M/Al SBA-15(tions: 7psi H2

Fig. 13. Tota(Rh/Al SBA-15

evidenced bacidic sitesrevealed by

In theirwith low Saluminosiliacidic sites

haveindicAl rah higing, tith

erial

alsoto tahemcataltyperesuC boncarb

4]. Hre esizaticata

20, 5ratioer thn of

limitts hapar

00g oil, at 180 C under agitation of 300 rpm and a hydro-essure of 4psi. The total CLA concentration in the safoweriallyhydrogenated/isomerizedoverRh/Al SBA-15withSi/Alratios of 100, 50, 20 and 10 is depicted in Fig. 13. It is clearlythat Rh/Al SBA-15 with a molar ratio of 100 outperformser catalysts in terms of conjugated isomerization activityup to 70mg CLA/g treated oil were reached after 300min ofC under hydrogen pressure of 7psi and agitation ofs clear that Ru-based catalyst exhibited the best activitytial hydrogenation of safower oil at the same reactionin comparison to other tested catalysts, while Pd- andtalysts showed a similar activity.l CLA concentration in safower oil partially hydro-th the formulated catalysts using Al SBA-15 as thepport is depicted in Fig. 12. The metallic rhodiumed to be very active towards the production of CLAed the highest activity towards conjugated isomer-afower oil. These results corroborate those obtainedhanuan et al. [40] for the conjugation isomerizationcid in soybean oil to produce CLAs using commercial/C as a catalyst. Therefore rhodium is retained as thellic catalyst to carry out the remaining studies of this

of the catalyst support with different Si/Al molar ratioown that doped mesoporous silica with aluminumo kind of acidity: Brnsted acidity and Lewis acidity as

than 1resultlow Si/als witreasonwork was matone.

It isposedthemton theLewis-occursthe Ca givention [4sites aisomer

Theof 10,molarwhethgenatioand acatalysing thewith 2gen proil partmolarshownthe othwhereacid proles of Safower oil during hydrogenation/isomerization100), M=Rh, Pd, Ni, Ru, and Se/Al SBA-15(100)]. Reaction condi-, 210 C, and 300 rpm.

reaction.Gejugated isoma Si/Al ratioThis could bacidic sitessurface witobservationl CLA content in partially hydrogenated/isomerized safowerwith different molar ratio Si/Al, 180 C, 4psi H2, and 300 rpm).

y IR analysis during pyridine adsorption on Brnstedat IR band of 1547 and 1640 cm1 and Lewis acidic sitesIR band of 1455 and 1623 cm1 [41,42].

work on the synthesis of mesoporous aluminosilicatesi/Al ratios, Li et al. [43] reported that the mesoporouscates samples with Si/Al ratios >3 have more Brnstedthan Lewis acidic sites. The sampleswith Si/Al ratios lessless Brnsted acidic sites than Lewis acidic sites. This

ates that the mesoporous aluminosilicates with verytios (Si/Al ratio less than 3) does not result in materi-her amount of the Brnsted acidic sites. Following thishe synthesized Al SBA-15 supports used in this presentSi/Al ratios of 10, 20, 50 and 100 could be regardeds with more Brnsted acidic character than the Lewis

known that the isomerization of linoleic acid is sup-ke place through different reaction pathways amongolecular adsorptionof linoleic acid forminga-complexyst surfacewith a C C bond coordinated to acidic site of. If Brnstedacid sites arepresent, protonationof linoleiclting in carbenium ion intermediate formation whered character is lost. Consequently, a loss of proton fromon atom of linoleic acid, results in double bond migra-owever, it can be understood that both type of acidicsential for the double bond migration via conjugatedon process.lytic activity of Rh/Al SBA-15 with Si/Al molar ratios0 and 100 is investigated to assess the effect of Si/Alon the conjugated isomerization activity and to see

ese materials are catalysts of choice for partial hydro-vegetable oils with a good selectivity for CLA formationed trans fatty acids and stearic acid production. Theseve been testedwith the same operating conditions dur-tial hydrogenation of safower oil: 1 g catalyst reactsnerally, thedecreaseof Si/Almolar ratio lowers the con-erization activity and the formation of total CLAs untilof 20. Beyond this value, the activity starts to increase.e attributed to a relatively higher availability of Lewisfavoring the formation of a -complex on the catalysth a C C bond of linoleic acid, thus corroborating thes or results reported by Li et al. [43]. Indeed, relatively

84 N. Chorfa et al. / Applied Catalysis A: General 387 (2010) 7586

Fig. 14. Fattyat 180 C, agita

high levelsthus leadingto the detricis/trans iso

Table 4 sisomers inRh/Al SBA-after 300misomerizatiAl SBA-15mgeometric islightly augpresence inof Si/Al ratiing siliconnot promotower oil dthe aluminution at the eratio Si/Al