PROPANE OXIDATION OVER PLATINUM SUPPORTED ON ZIRCONIA

Propane oxidation activity over Pt/zirconia was studied as a function of metal concentration, metal surface area, and temperature. The catalysts, prepared by multiple impregnation of zirconia with chloroplatinic acid, ranged in concentration from 0.02 to 1.5 wt% Pt. A recirculation batch reactor was used for the activity experiments. At a fixed amount of Pt (4 mg), the oxidation rate decreased by a factor of 20 with increasing metal concentration. When calculated per Pt surface atom, as determined by CO chemisorption, the specific oxidation rate initially decreased and then reached a constant value at concentrations above 0.10 wt% Pt. The apparent activation energy remained constant at 17.8 ± 3.5 kcal/mol with Pt concentration. To evaluate the effect of support material, the data were compared to an analogous study in our laboratory over Pt/γ-alumina. Over highly dispersed platinum, propane oxidation activity was two orders of magnitude faster over Pt/zirconla as compared to Pt/γ-alumina. The activity change reflects a difference in interaction between support and catalytic metal. At higher Pt concentrations the influence of the support vanishes and the rate constants on both supports are the same, as expected. At lower Pt concentrations. metal redispersion occurs readily in oxygen at 500°C on γ-alumina, but not on zirconia, according to observed changes in propane oxidation rate. © 1993 Academic Press, Inc.