CO Oxidation on Pt/α-Al2O3(0001): Evidence for Structure Sensitivity

Abstract

The oxidation of CO by O2 has been studied over model catalysts prepared by vapor deposition of Pt onto an α-Al2O3(0001) crystal. Reaction rates were measured for two particle sizes, 14 and 1.7 nm, in order to determine whether this reaction is structure sensitive and how the rates were affected by changes in the desorption kinetics of CO on small and large particles which had been observed previously (E. I. Altman and R. J. Gorte. J. Catal.110, 191 (1988)). For 10 Torr each of CO and O2, between 560 and 680 K, the turnover frequencies on the 14-nm particles were much higher than on the 1.7-nm particles, and the activation energy, 30 ± 3 kcal/mol, was much lower than that found on the smaller particles, 41 ± 4 kcal/mol. A simple model of the reaction demonstrates that changes in the desorption kinetics of CO with particle size can explain the observed structure sensitivity found in the reaction rates. The results indicate that adsorption studies on model catalysts can be used to understand the properties of real catalysts.