Comparison of redox isotherms for vanadia supported on zirconia and titania

Zirconia- and titania-supported vanadia catalysts were characterized by coulometric titration, Raman spectroscopy, and rate measurements for methanol oxidation and propane oxidative dehydrogenation (ODH). Redox isotherms obtained at 748 K by coulometric titration of a titania-supported vanadia catalyst with a loading of 2.9 V/nm(2) showed that reduction occurred in a single step at a P-O2 of 10(-22) atm, corresponding to a Delta G of oxidation of -300 kJ/mol; however, reduction of the sample caused changes in the isotherm obtained during re-oxidation consistent with formation of bulk V2O5, which requires higher P-O2 for oxidation, With vanadia-zirconia catalysts, increasing the calcination temperature from 748 to 873 K caused changes in both the Raman spectra and in the 748-K redox isotherm consistent with formation of bulk ZrV2O7. Rate measurements for methanol oxidation and propane ODH on vanadia-titania, vanadia-zirconia, bulk V2O5, and ZrV2O7 showed relatively small differences in specific rates. (C) 2009 Elsevier B.V. All rights reserved.