Oxidation of CO by Oxygen on a Stepped Platinum Surface: Identification of theReaction Site

摘要

The coadsorption of oxygen and carbon monoxide on the stepped Pt (112) surfacehas been studied using electron stimulated desorption-ion angular distribution (ESDIAD), temperature programmed desorption (TPD), and low energy electron diffraction (LEED). It has been possible to preferentially adsorb different isotopic CO molecules on step and terrace sites, respectively, following oxygen adsorption on step sites to partial coverage. Transient kinetic experiments show that below approx. 200 K, isotopic CO present exclusively on terrace sites is more effectively involved in CO2 production, compared to less reactive CO on the step sites. Above approx. 200 K, site exchange between step and terrace CO species prevents the measurement of the relative reactivity of the two kinds of chemisorbed CO. The results show that the elementary step producing CO2 from adsorbed CO and adsorbed oxygen is structure sensitive, even though the overall catalytic reaction between CO and 02 is generally classed as a structure insensitive reaction.