Fundamental study of the oxidation of butane over vanadyl pyrophosphate

Pepera, Marc A.; Callahan, James L.; Desmond, Michael J.; Milberger, Ernest C.; Blum, P.; Bremer, Noel J.

doi:10.1021/ja00303a012

Cited by 181 publications

(60 citation statements)

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“…The weakest C-H bond in alkanes and alkenes is usually cleaved in the initial step of oxidation reactions; [38][39][40] thus, C-H bonds at the secondary carbon and allylic C-H bonds in propene are expected to be involved in rate-determining C-H activation steps. This was also confirmed by the observed kinetic isotopic effects when comparing reactions of CH 3 CH 2 -CH 3 /O 2 and CH 3 CD 2 CH 3 /O 2 .…”

Section: Resultsmentioning

confidence: 99%

Kinetics and Mechanism of Oxidative Dehydrogenation of Propane on Vanadium, Molybdenum, and Tungsten Oxides

2000

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The effect of cation identity on oxidative dehydrogenation (ODH) pathways was examined using two-dimensional VO x , MoO x , and WO x structures supported on ZrO 2 . The similar kinetic rate expressions obtained on MoO x and VO x catalysts confirmed that oxidative dehydrogenation of propane occurs via similar pathways, which involve rate-determining C-H bond activation steps using lattice oxygen atoms. The activation energies for propane dehydrogenation and for propene combustion increase in the sequence VO x /ZrO 2 < MoO x /ZrO 2 < WO x /ZrO 2 ; the corresponding reaction rates decrease in this sequence, suggesting that turnover rates reflect C-H bond cleavage activation energies, which are in turn influenced by the reducibility of these metal oxides. Propane ODH activation energies are higher than for propene combustion. This leads to an increase in maximum alkene yields and in the ratio of rate constants for propane ODH and propene combustion as temperature increases. This difference in activation energy (48-61 kJ/mol) between propane ODH and propene combustion is larger than between bond dissociation enthalpies for the weakest C-H bond in propane and propene (40 kJ/mol) and it increases in the sequence VO x /ZrO 2 < MoO x /ZrO 2 < WO x /ZrO 2 . These results suggest that relative propane ODH and propene combustion rates depend not only on C-H bond energy differences but also on the adsorption enthalpies for propene and propane, which reflect the Lewis acidity of cations involved in π bonding of alkenes on oxide surfaces. The observed difference in activation energies between propane ODH and propene combustion increases as the Lewis acidity of the cations increases (V 5+ < Mo 6+ < W 6+ ).

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Section: Resultsmentioning

confidence: 99%

Kinetics and Mechanism of Oxidative Dehydrogenation of Propane on Vanadium, Molybdenum, and Tungsten Oxides

2000

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“…The following types of hypothetical active sites have been proposed to exist on the surface (200) plane (8) According to a recent model (9) the vanadyl dimers from clusters on the surface (200) planes, each composed of four vanadyl dimers, which are isolated from other clusters by terminal pyrophosphate groups. This so-called site isolation in VPO catalysts, which requires only the local ordering in surface structure for the selectivity as well as the inertness of the bulk of the catalyst in n-butane oxidation (11), is analogous to supported metal oxide catalysts (12). In order to investigate the analogy between the bulk VPO and supported metal oxide catalysts we have performed a kinetic and physicochemical study of model supported vanadia catalysts in the n-butane oxidation.…”

Section: Introductionmentioning

confidence: 99%

Fundamental Studies of Butane Oxidation over Model-Supported Vanadium Oxide Catalysts: Molecular Structure-Reactivity Relationships

Wachs

Jehng

Deo

et al. 1997

Journal of Catalysis

137

102

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The oxidation of n-butane to maleic anhydride was investigated over a series of model-supported vanadia catalysts where the vanadia phase was present as a two-dimensional metal oxide overlayer on the different oxide supports (TiO 2 , ZrO 2 , CeO 2 , Nb 2 O 5 , Al 2 O 3 , and SiO 2 ). No correlation was found between the properties of the terminal V= =O bond and the butane oxidation turnover frequency (TOF) during in situ Raman spectroscopy study. Furthermore, neither the n-butane oxidation TOF nor maleic anhydride selectivity was related to the extent of reduction of the surface vanadia species. The n-butane oxidation TOF was essentially independent of the surface vanadia coverage, suggesting that the n-butane activation requires only one surface vanadia site. The maleic anhydride TOF, however, increased by a factor of 2-3 as the surface vanadia coverage was increased to monolayer coverage. The higher maleic anhydride TOF at near monolayer coverages suggests that a pair of adjacent vanadia sites may efficiently oxidize n-butane to maleic anhydride, but other factors may also play a contributing role (increase in surface Brønsted acidity and decrease in the number of exposed support cation sites). Varying the specific oxide support changed the n-butane oxidation TOF by ca. 50 (Ti > Ce > Zr ∼ Nb > Al > Si) as well as the maleic anhydride selectivity. The maleic anhydride selectivity closely followed the Lewis acid strength of the oxide support cations, Al > Nb > Ti > Si > Zr > Ce. The addition of acidic surface metal oxides (W, Nb, and P) to the surface vanadia layer was found to have a beneficial effect on the n-butane oxidation TOF and the maleic anhydride selectivity. The creation of bridging V-O-P bonds had an especially positive effect on the maleic anhydride selectivity.

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“…Oxygen reactant is used to heal the oxygen atom defects at the surface. 19,20 This explains how TPD can help to elucidate some aspects of the interaction of the hydrocarbon with the catalyst surface. The aspects that should be noted include the ability of surfaces to interact with hydrocarbon, the relative quantiÐcation of centres capable of interaction with hydrocarbon, the temperature of desorption of such molecule and whether this desorption is a redox process or not.…”

Section: Discussionmentioning

confidence: 99%

TPD, XPS and ESR Studies of the Surface Processes Involved in the Oxidation ofn-Pentane on a (VO)2P2O7 System

Granados

Coronado

Fierro

et al. 1997

Surf. Interface Anal.

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Fundamental study of the oxidation of butane over vanadyl pyrophosphate

Cited by 181 publications

References 0 publications

Kinetics and Mechanism of Oxidative Dehydrogenation of Propane on Vanadium, Molybdenum, and Tungsten Oxides

Kinetics and Mechanism of Oxidative Dehydrogenation of Propane on Vanadium, Molybdenum, and Tungsten Oxides

Fundamental Studies of Butane Oxidation over Model-Supported Vanadium Oxide Catalysts: Molecular Structure-Reactivity Relationships

TPD, XPS and ESR Studies of the Surface Processes Involved in the Oxidation ofn-Pentane on a (VO)2P2O7 System

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