title: In situ UV-visible spectroscopic measurements of kinetic parameters and active sites for catalytic oxidation of alkanes on vanadium oxides.
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.
authors.affiliation: Chemical Sciences Division, E.O. Lawrence Berkeley National Laboratory and Department of Chemical Engineering, University of California, Berkeley, California 94720-1462, USA.
authors.forename: Morris D
authors.initials: MD
authors.lastname: Argyle
authors.forename: Kaidong
authors.initials: K
authors.lastname: Chen
authors.forename: Enrique
authors.initials: E
authors.lastname: Iglesia
authors.forename: Alexis T
authors.initials: AT
authors.lastname: Bell