Comparison of redox isotherms for vanadia supported on zirconia and titania
By Shah, P.R.; Baldychev, I.; Vohs, J.M. & Gorte, R.J.
Published in Applied Catalysis A: General
NULL
2009
Abstract
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/nm2 showed that reduction occurred in a single step at a P O 2 of 10-22 atm, corresponding to a ΔG 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 O 2 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.
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