In situ UV-visible spectroscopic measurements of kinetic parameters and active sites for catalytic oxidation of alkanes on vanadium oxides

Morris D Argyle; Kaidong Chen; Enrique Iglesia; Alexis T Bell

doi:10.1021/jp040166c

In situ UV-visible spectroscopic measurements of kinetic parameters and active sites for catalytic oxidation of alkanes on vanadium oxides

J Phys Chem B. 2005 Feb 17;109(6):2414-20. doi: 10.1021/jp040166c.

Authors

Morris D Argyle¹, Kaidong Chen, Enrique Iglesia, Alexis T Bell

Affiliation

¹ Chemical Sciences Division, E.O. Lawrence Berkeley National Laboratory and Department of Chemical Engineering, University of California, Berkeley, California 94720-1462, USA.

PMID: 16851236
DOI: 10.1021/jp040166c

Abstract

In situ diffuse reflectance UV-visible spectroscopy was used to measure the dynamics of catalyst reduction and oxidation during propane oxidative dehydrogenation (ODH) on VOx/gamma-Al2O3. Transients in UV-visible intensity in the near-edge region were analyzed using a mechanistic model of ODH reactions. Rate constants per site for the kinetically relevant reduction step (C-H bond activation) measured using this analysis are slightly larger than those obtained from steady-state ODH rates normalized by surface V. The ratio of these values provides a measure of the fraction of the V surface sites that are active for ODH (0.6-0.7, for V surface densities of 2.3-34 V nm(-2)). This suggests that some of the V atoms are either inaccessible or inactive. Reoxidation rate constants, which cannot be obtained from steady-state analysis, are 10(3)-10(5) times larger than those for the C-H bond activation reduction step.