A scanning tunneling microscopy study of the oxidation of CO on Cu(110) at 400 K: Site specificity and reaction kinetics

Scanning tunneling microscopy (STM) was used to study the oxidation of CO with O-precovered Cu(110) in the steady state at 400 K at the atomic level. There is a strong preference for CO to react with oxygen along the p(2 x 1) oxygen rows. The reaction appears to occur initially at the outer edge of an oxygen island, creating kink defects in the overlayer structure. Once created, these defects are more reactive than non-defect sites and play a dominant role in sustaining the reaction. The equilibrium distribution of adsorbed oxygen is not maintained in the reactive steady state. Monte Carlo simulations suggest that defect sites are 500-1000 times more reactive than non-defect sites. A model is presented in which adsorbed oxygen, formed by -Cu-O- chain scission at these defect sites, is reactive to CO, while p(2 x 1) oxygen atoms in the chain are not reactive. Copper atoms that make up the p(2 x 1) oxygen overlayer structure add to terrace edges after oxygen is reacted away and do not form small Cu islands that could eventually lead to surface roughening.