How Surface Reactivity Depends on the Configuration of Coadsorbed Reactants: CO Oxidation on Rh(100)

Abstract

LEED, TPRS, and RAIRS experiments combined with DFT calculations have been used to study CO oxidation on Rh(100) from preadsorbed O and CO and to unravel how the reaction kinetics is influenced by the configuration of the adsorbed reactants. At least four different regimes are identified in increasing order of reactivity: near zero coverage, isolated CO and O species react with the highest activation energy observed in this work (105 ± 4 kJ/mol). In the second regime, oxygen is present in a p (2 × 2) structure and reacts with bridge bonded CO, with an activation energy of 77 ± 8 kJ/mol. In the third regime, the reactivity is associated with on-top CO in defects of a c (2 × 2) oxygen layer, at an estimated activation energy of 58 ± 10 kJ/mol. In the last and most reactive regime, the oxygen adlayer has (2 × 2)- pg order with the top metal layer reconstructed. According to DFT calculations, CO adsorption lifts the reconstruction. Oxygen occupies 4-fold hollow and bridge sites; the latter react with bridged CO. The general trend is that if the reactants become destabilized by repulsive lateral interactions, the rate of reaction to CO 2 increases.