Mesoporous Nb and Ta Oxides: Synthesis, Mesoporous Nb and Ta Oxides: Synthesis, Characterization and Applications in Heterogeneous Characterization and Applications in Heterogeneous

CatalysisCatalysis

Yuxiang(Tony) Rao

Department of Chemistry and Biochemistry

University of Windsor

Aug 25,2008

1

BackgroundBackground

Mesoporous structure materials

Microporous: pore diameter < 2 nm

Mesoporous: pore diameter 2~50 nm

Macroporous: pore diameter >50 nm

According to the definition of IUPAC:

(International Union of Pure and Applied Chemistry):

2

BackgroundBackground

M41S Family (three subgroups): (Mobil Oil Corporation)

a) Hexagonal (MCM-41)

b) Cubic (MCM-48)

c) Lamellar (MCM-50)

Kresge, C.T.; Leonowicz, M.E.; Roth, W.J.; Vartuli, J.C.; Beck, J.S. Nature 1992, 359, 710

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MCM-41MCM-41

MCM-41 (Mobil Composition of Matter No.41)

Ordered mesoporous siliceous materials

High surface area and porosity (up to 1600 m2/g)

Ordered hexagonal array, uniform pore structure (2-50 nm)

Chemically and thermally stable 4

Mesoporous Transition Metal OxidesMesoporous Transition Metal Oxides

The first non-silica mesoporous material has been reported by using ligand-assisted templating approach in 1995. (Ti,Nb,Ta……)

Silica based Mesoporous materials Mesoporous transition metal oxides

Fixed oxidation state

Si (+4)

Variable oxidaion state

Ti(+4,+3,+2,+1)

Ta,Nb(+5,+4,+3,+2,+1)

D.M. Antonelli, J.Y. Ying, Angew Chem Int Edit 1995, 34, 2014-2017

Excellent electron donor and acceptor

Higher surface acidity

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OutlineOutline

• Synthetic method for mesoporous Nb and Ta Oxides

• Characterization techniques Powder-XRD, Nitrogen adsorption/desorption, SEM, TEM, FT-IR,

Amine Titration, TPD, TG-DTA, DSC and Solid-state NMR

• Heterogeneous catalytic applications Benzylation, Alkylation, Isomerization

• Future work Photocatalysis, more NMR experiments

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Ligand-Assisted Templating (LAT) ApproachLigand-Assisted Templating (LAT) Approach

Step 1: bonds are formed between the inorganic species and the surfactant amine headgroups (S–I)

Scheme 1. Synthesis of Mesoporous Nb Oxide Materials with different pore sizes

n-hexylaminen-octadecylamine

niobium ethoxide

Nb5+O-O-

-O-OO-

n-dodecylamine

NH2

+Nb

OEtEtO

H2NOEtOEt

OEt

H2O

HN

Nb

OEt

OEt

NH

Nb

OEt

OEt

NH

Nb

EtO

OEt

NH

Nb

EtOOEt

NH

Nb

EtO OEt

NH

NbEtO

OEtNH

NbEtO

EtO

NH

Nb

EtO

EtO

NH

Nb

OEt

EtO

NH

Nb

OEtEtO

HN

NbOEt

EtOHN

Nb

OEt

OEt

O

HN

NbO

OEtEtO

O

O

OO

O

NH

Nb

EtO

EtO

O

O O

O

O

O

O

O

Et

OEt

OEt

OEtOEt

OEt

OEt

OEt

OEt

OEt

OEt

OEt

OEt

OEt

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Ligand-Assisted Templating (LAT) ApproachLigand-Assisted Templating (LAT) Approach

Step 2: Template Remove and Surface Acidity Enhancement

HN

Nb

OEt

OEt

NH

Nb

OEt

OEt

NH

Nb

EtO

OEt

NH

Nb

EtOOEt

NH

Nb

EtO OEt

NH

NbEtO

OEtNH

NbEtO

EtO

NH

Nb

EtO

EtO

NH

Nb

OEt

EtO

NH

Nb

OEtEtO

HN

NbOEt

EtOHN

Nb

OEt

OEt

O

HN

NbO

OEtEtO

O

O

OO

O

NH

Nb

EtO

EtO

O

O O

O

O

O

O

O

Et

OEt

OEt

OEtOEt

OEt

OEt

OEt

OEt

OEt

OEt

OEt

OEt

OEt

P-toluene sulfonic acid

S

O

O

HO

1M sulfuric/phosphoric acid

Nb

OEt

OEt

Nb

OEt

OEt

Nb

EtO

OEt

Nb

EtOOEt

Nb

EtO OEt

NbEtO

OEt

NbEtO

EtO

Nb

EtO

EtO

Nb

OEt

EtO

Nb

OEtEtO

NbOEt

EtONb

OEt

OEt

O

NbO

OEtEtO

O

O

OO

O

Nb

EtO

EtO

O

O O

O

O

O

O

O

Et

OEt

OEt

OEtOEt

OEt

OEt

OEt

OEt

OEt

OEt

OEt

OEt

OEt

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CharacterizationCharacterization

Powder XRDPowder XRD

The strong (100) reflection at low angle confirmed the retention of mesoporous structure after acid treatment

Figure 1. Powder X-ray diffraction data for Nb-TSM1 and Ta-TSM1 samples. (From Top to Bottom) a) C12 Meso Nb; b) C12 H2SO4 meso Nb; c) C12 Meso Ta; d) C12 H2SO4 Meso Ta

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CharacterizationCharacterization

Type IV Isotherm further confirmed mesoporous structure after acid treatment

BETBET

Figure 2. N2 adsorption/desorption isotherm of a) C12 Meso Nb and C12 H2SO4 Meso Nb;

b) C12 Meso Ta and C12 H2SO4 Meso Ta

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CharacterizationCharacterization

SEMSEM TEMTEM

Figure 3. SEM & TEM of C12 H2SO4 Meso Nb

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CharacterizationCharacterization

FT-IRFT-IR

Figure 4. FT-IR spectra of pyridine adsorbed on C12 Meso Nb, C12 H2SO4 Meso Nb and

Ta, HY Zeolite and H-ZSM5 Zeolite.

Brønsted acid site: 1538cm-1 Lewis acid site: 1443cm-1

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CharacterizationCharacterization

Amine-TitrationAmine-Titration

Sample Ho Acid amount (mmol/g)

C12 Meso Nb -6.6 2.478

C12 H2SO4 Meso Nb -8.2 31.784

C12 Meso Ta -6.6 0.40

C12 H2SO4 Meso Ta -8.2 19.8

HY Zeolite -6.6 1.55

H-ZSM5 -4.4 16.1

Amberlyst 15 N/A N/A

Table 1. Acid strength and acid amount of solid acid catalysts (Measured by Hammett indicators and n-butylamine titration)

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CharacterizationCharacterization

NHNH33 -TPD -TPD

Figure 5. NH3-TPD profiles of sulfated mesoporous Nb and Ta catalysts. Ramp

rate: 10K min-1 B stand for Brønsted acid sites

L stand for Lewis acid sites 14

CharacterizationCharacterization

TGATGA

Figure 6. TGA curves under N2 for sulfated

mesoporous Nb and Ta catalysts

DSCDSC

Figure 7. DSC curves under N2 for sulfated

mesoporous Nb and Ta catalysts

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CharacterizationCharacterization

XRD for Nb samples heated at different temperaturesXRD for Nb samples heated at different temperatures

Amorphous phase transferring to crystalline phase and mesoporous structure collapse during heating process

Figure 8. X-ray diffraction of C12 mesoporous Nb oxides a) at room temperature; b) Heated at

500 ºC for 2 h; c) Heated at 750 ºC for 2 h

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CharacterizationCharacterization

Solid-state NMRSolid-state NMR

Figure 9. 17O MAS NMR spectra of 17O-enriched sol–gel Nb2O5 a) as formed, and after heating to b)

250 °C, c) 500 °C, d) 750 °C, and e) 1000 °C.

Figure 10. 17O MAS NMR spectra of 17O-enriched mesoporous niobia a) as-synthesized, and after heating to b) 250 °C, c) 500 °C, and d) 750 °C.

Skadtchenko, B.O.; Rao, Y.; Kemp. T.F.; Bhattacharya, P.; Thomas, P.A.; Trudeau, M.; Smith, M.E.; Antonelli, D.M. Angew. Chem. Int. Ed. 2007, 46, 2635

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Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications

Reactor and ReactionsReactor and Reactions Benzylation

Alkylation

Isomerization

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Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications

Benzylation: ReactionBenzylation: Reaction

Anisole Benzyl Alcohol 1-benzyl-2-methoxybenzene 1,1'-[oxybis(methylene) ]di

benzene Catalysts: 0.5g

Temperature: Reflux Temperature

Ratio(Anisole/Benzyl Alcohol): 10:1

Rao, Y.; Trudeau, M.L.; Antonelli, D.M. J. Am. Chem. Soc. 2006, 128, 13996. 19

Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications

Benzylation: ActivityBenzylation: Activity

Figure 11. Percent conversion of benzyl alcohol in benzylation of anisole catalyzed by different

mesoporous Nb oxides.

Figure 12. Percent conversion of benzyl alcohol in the benzylation of anisole catalyzed by different bulk

Nb oxides

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Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications

Benzylation: Surface AreaBenzylation: Surface Area

Sample BET surface area(m2/g)

Volume(cm3/g)

BJH Pore size(A)

Nb2O5 3.63 N/A N/A

H2SO4/Nb2O5 5.29 N/A N/A

H3PO4/Nb2O5 2.96 N/A N/A

Meso Nb 612.63 0.3956 22.7

*Meso Nb (Anisole) 587.90 0.3123 20.6

*Meso Nb (Toluene) 386.04 0.2088 20.6

H2SO4/Meso Nb 519.10 0.3408 20.6

*H2SO4/Meso Nb (Anisole) 84.71 0.1409 37.2

*H2SO4/Meso Nb (Toluene) 3.35 0.004 51.1

H3PO4/Meso Nb 502.81 0.3286 20.7

*H3PO4/Meso Nb (Anisole) 76.38 0.0932 39.5

*H3PO4/Meso Nb (Toluene) 6.41 0.0146 47.0

Table 2.The internal structure and surface properties of catalysts before and after reactions

* Denotes surface areas after reaction with substrate in bracket. 21

Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications

Benzylation: Surface AcidityBenzylation: Surface Acidity

Table 3. The amount of acids as mmole g-1 which was calculated from the n-butylamine titration

Indicator Nb2O5 H2SO4/Nb2O5

H3PO4/Nb2O5

Meso Nb

H2SO4/Meso Nb

H3PO4/Meso Nb

Methyl yellow 0.024 0.338 0.317 2.478 31.784 3.086

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Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications

Alkylation: Reaction and ActivityAlkylation: Reaction and Activity

Figure 13. Olefin conversion in the alkylation of benzene with (a) 1-dodecene and (b) 1-tetradecene over sulfated

mesoporous C12-Ta oxide.

Kang, J.; Rao, Y.; Trudeau, M.L; Antonelli, D.M. Angew. Chem. Int. Ed. 2008, 47, 1.

Catalysts: 4.0 wt%

Temperature: Reflux Temperature

Ratio(Benzene/Olefin): 10:1

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Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications

Alkylation: Distribution and Catalyst Loading LevelAlkylation: Distribution and Catalyst Loading Level

Figure 15. 1-Dodecene conversion and 2-phenyldodecane selectivity as a function of catalyst

loading. Reaction conditions: 80 oC, 0.5 h.

Figure 14. Distribution of phenyldodecane isomers over sulfated mesoporous C12-Ta oxide as a function of reaction time. Reaction condition: 80 oC, catalyst loading = 4.0 wt.%. 24

Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications

Alkylation Alkylation

SO42-/C12-Ta 80 1-dodecene 100 41.62

SO42-/C12-Ta[b] 80 1-dodecene 26.8 52.23

SO42-/C12-Ta 80 1-tetradecene 17.5 50.08

SO42-/C12-Ta 150 1-dodecene 100 38.05

SO42-/C6-Ta 80 1-dodecene 46.9 49.93

SO42-/C12-Nb 80 1-dodecene 1.2 100

H-Y zeolite 80 1-dodecene 100 29.48

H-Y zeolite 80 1-tetradecene 73.6 26.53

H-Y zeolite 150 1-dodecene 100 25.83

H-ZSM5 80 1-dodecene 0

0

Catalyst Temp.(oC)

Olefin Conversion(%)

Selectivity(%)

Amberlyst 15 80 1-dodecene 13.5 55.19

 

Table 4. Catalytic properties of solid acid catalysts in alkylation reactions.[a]

[a] reaction time: 0.5 h. [b] in second run. 25

Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications

Isomerization: ReactionIsomerization: Reaction

 

Rao, Y.; Kang, J. Antonelli, D.M. J. Am. Chem. Soc. 2008, 130, 394 26

Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications

IsomerizationIsomerization

 

Table 5. BET surface area, Pore volume and Pore Size measured by N2 adsorption at 77K.

Sample BET (m2/g)

Pore Volume (cm3/g)

BJH Pore Size (Å)

C6 Meso Nb 519.03 0.4858 17.5*

C12 Meso Nb 612.02 0.3199 20.6

C18 Meso Nb 553.72 0.3595 27.2

C6 H2SO4 Meso Nb 160.35 0.293 16.3

C12 H2SO4 Meso Nb 413.97 0.2423 20.5

C18 H2SO4 Meso Nb 282.58 0.2087 25.6

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Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications

IsomerizationIsomerization

 

Table 5. BET surface area, Pore volume and Pore Size measured by N2 adsorption at 77K.(continue)

Sample BET (m2/g) Pore Volume (cm3/g)

BJH Pore Size (Å)

C6 Meso Ta 253.26 0.1905 17.5*

C12 Meso Ta 582.7 0.3651 18.8

C18 Meso Ta 234.74 0.0538 22.7

C6 H2SO4 Meso Ta 206.4 0.1314 17.0*

C12 H2SO4 Meso Ta 292.19 0.0989 18.2

C18 H2SO4 Meso Ta 188.79 0.0347 22.5

HY Zeolite 779.8 0.116 38.9

H-ZSM5 435.96 0.1076 39

Amberlyst 15 51.86 0.3443 303.1

* The pore size was estimated as 12 Å by using more reliable TEM and XRD on previous work 28

Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications

Isomerization: Confinement EffectsIsomerization: Confinement Effects

 

Figure 16. 1-hexene isomerization conversion rate and selectivity on different pore size sulfated Nb oxides

(a) activity of different pore size Nb oxides (b) selectivity of different pore size Nb oxides

(a) (b)

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Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications

Isomerization: Confinement EffectsIsomerization: Confinement Effects

 

(a) (b)

Figure 17. 1-hexene isomerization conversion rate and selectivity on different pore size sulfated Ta oxides

(a) activity of different pore size Ta oxides (b) selectivity of different pore size Ta oxides

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Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications

Isomerization: Catalysts ComparisionIsomerization: Catalysts Comparision

 

(a) (b)

Figure 18. 1-hexene isomerization conversion rate (A) and selectivity (B) on different catalysts.

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Future Work

Photocatalysis (Mesoporous Ti Oxides:

Amorphous StructureCrystalline Structure)

Research Proposal

Solid-State NMR (17O and 15N Nb and Ta Oxygen Coordination )

Rao, Y.;Kemp, T.F.;Trudeau,M;Smith, M.E.;Antonelli,D.M. submitted to J. Am. Chem. Soc 2008

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Publications(1) Rao, Y., Trudeau, M., Antonelli, D.M. “Sulfated and Phosphated Mesoporous Nb Oxide in the Benzylation of Anisole and Toluene by Benzyl Alcohol.” Journal of the American Chemical Society 2006, 128 (43): 13996

(2) Skadtchenko, B.O., Rao, Y., Kemp, T.F., Bhattacharya, P., Thomas, P.A., Trudeau, M., Smith, M.E., Antonelli, D.M. “A Solid-State 17O NMR Study of Local Order and Crystallinity in Amine-Templated Mesoporous Nb Oxide.” Angewandte Chemie International Edition. 2007, 46:2635

(3) Rao, Y., Kang, J., Antonelli, D.M. “1-Hexene Isomerization Over Sulfated Mesoporous Ta Oxide: The effects of activie site and confinement.” Journal of the American Chemical Society 2008, 130 (2): 394

(4) Kang, J., Rao, Y., Antonelli, D.M. “Sulfated Mesoporous Ta Oxides in the Shape Selective Synthesis of Linear Alkyl Benzene.” Angewandte Chemie International Edition 2008, 47: 4896

(5) Rao, Y., Kang, J., Antonelli, D.M. “Investigation of synthesis and characterization of mesoporous Nb and Ta oxide and application in 1-Hexene isomerization” (Article, submitted to Chemistry of Materials, 2008)

(6) Rao,Y.; Kemp, T.F.; Trudeau, M.; Smith, M.E.; Antonelli, D.M. “17O and 15N Solid State NMR Studies on Ligand-Assisted Templating and Oxygen Coordination in the Walls of Mesoporous Nb, Ta and Ti Oxides” (Article, submitted to Journal of American Chemistry Society, 2008)

(7) Rao,Y.; Antonelli, D.M. “Mesoporous transition metal oxides: characterization and applications in heterogeneous catalysis” (Invited Highlight Paper, submitted to Journal of Materials Chemistry, 2008)

And more coming soon ..…..

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Acknowledgments

Professor David M Antonelli

Antonelli’s Group Members

Dr. Boris O Skadtchenko Dr. Longhui Qiu Dr. Junjie Kang Dr. Xin(Tim) Hu Mr. Ahmad Hamaed Mr. Tuan(Tom) Hoang

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Thank you!

Questions?

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Synthetic Method

Triblock copolymer method

Poly(ethylene oxide)-Poly(propylene oxide)-Poly(ethylene oxide) (PEO-PPO-PEO) as structure-directing agents

• thermally stable (up to 500 ºC)• large pore size (up to 14nm)• thick nanocrystalline pore wall (anatase phase, 4~7nm)

Yang et al. Nature 1998, 396, 152

Modified sol-gel combined with silica-coating pore wall reinforcement method

• high surface area (up to 1000 m2/g)

• small pore size (2~5 nm)

• thin wall thickness (2~3nm)

• crystallized structureKondo et al. Chem. Mater. 2008, 20, 835