Effect of catalyst structure on oxidative dehydrogenation of ethane and propane on alumina-supported vanadia

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The catalytic properties of Al2O3-supported vanadia with a wide range of VOx surface density (1.4-34.2 V/nm2) and structure were examined for the oxidative dehydrogenation of ethane and propane. UV-visible and Raman spectra showed that vanadia is dispersed predominantly as isolated monovanadate species below {approx}2.3 V/nm2. As surface densities increase, two-dimensional polyvanadates appear (2.3-7.0 V/nm2) along with increasing amounts of V2O5 crystallites at surface densities above 7.0 V/nm2. The rate constant for oxidative dehydrogenation (k1) and its ratio with alkane and alkene combustion (k2/k1 and k3/k1, respectively) were compared for both alkane reactants as a function of vanadia surface density. Propene ... continued below

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Argyle, Morris D.; Chen, Kaidong; Bell, Alexis T. & Iglesia, Enrique September 11, 2001.

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The catalytic properties of Al2O3-supported vanadia with a wide range of VOx surface density (1.4-34.2 V/nm2) and structure were examined for the oxidative dehydrogenation of ethane and propane. UV-visible and Raman spectra showed that vanadia is dispersed predominantly as isolated monovanadate species below {approx}2.3 V/nm2. As surface densities increase, two-dimensional polyvanadates appear (2.3-7.0 V/nm2) along with increasing amounts of V2O5 crystallites at surface densities above 7.0 V/nm2. The rate constant for oxidative dehydrogenation (k1) and its ratio with alkane and alkene combustion (k2/k1 and k3/k1, respectively) were compared for both alkane reactants as a function of vanadia surface density. Propene formation rates (per V-atom) are {approx}8 times higher than ethene formation rates at a given reaction temperature, but the apparent ODH activation energies (E1) are similar for the two reactants and relatively insensitive to vanadia surface density. Ethene and propene formation rates (per V-atom) are strongly influenced by vanadia surface density and reach a maximum value at intermediate surface densities ({approx}8 V/nm2). The ratio of k2/k1 depends weakly on reaction temperature, indicating that activation energies for alkane combustion and ODH reactions are similar. The ratio of k2/k1 is independent of surface density for ethane, but increase slightly with vanadia surface density for propane, suggesting that isolated structures prevalent at low surface densities are slightly more selective for alkane dehydrogenation reactions. The ratio of k3/k1 decreases markedly with increasing reaction temperature for both ethane and propane ODH. Thus, the apparent activation energy for alkene combustion (E3) is much lower than that for alkane dehydrogenation (E1) and the difference between these two activation energies decreases with increasing surface density. The lower alkene selectivities observed at high vanadia surface densities are attributed to an increase in alkene adsorption enthalpies with increasing vanadia surface density. The highest yield of alkene is obtained for catalysts containing predominantly isolated monovanadate species and operated at high temperatures that avoid homogeneous reactions (< {approx} 800 K).

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OSTI as DE00836789

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  • Journal Name: Journal of Catalysis; Journal Volume: 208; Journal Issue: 1; Other Information: Submitted to Journal of Catalysis: Volume 208, No.1; Journal Publication Date: 05/15/2002

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  • Report No.: LBNL--49411
  • Grant Number: AC03-76SF00098
  • Office of Scientific & Technical Information Report Number: 836789
  • Archival Resource Key: ark:/67531/metadc781862

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  • September 11, 2001

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  • Dec. 3, 2015, 9:30 a.m.

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  • April 4, 2016, 4:05 p.m.

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Argyle, Morris D.; Chen, Kaidong; Bell, Alexis T. & Iglesia, Enrique. Effect of catalyst structure on oxidative dehydrogenation of ethane and propane on alumina-supported vanadia, article, September 11, 2001; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc781862/: accessed October 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.