OXIDATION OF CO BY OXYGEN ON A STEPPED PLATINUM SURFACE - IDENTIFICATION OF THE REACTION SITE

The coadsorption of oxygen and carbon monoxide on the stepped Pt(112) surface has 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 approximately 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 approximately 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 O2 is generally classed as a structure insensitive reaction.