Kinetics of CO Oxidation over Ru(0001)

Article abstract of DOI:10.1021/j100398a031

The oxidation of CO over a model Ru(0001) single-crystal catalyst has been studied in a high-pressure reaction-low-pressure surface analysis apparatus.Steady-state catalytic activity as a function of temperature and partial pressure of CO and O2 was measured.Both the specific rates and the relative activity (Ru > Pd, Rh) obtained in this study compare very favorably with the results on high area supported catalysts.Surface concentrations of oxygen were monitored following reaction and found to be dependent on the partial pressures of the reactants.Further, the highest rates of rection corresponded to reaction on a ruthenium surface covered with a monolayer of oxygen as detected subsequent to reaction by AES.The kinetics measured at various reactant partial pressures (leading to various surface oxygen coverages following reaction) suggest that a chemisorbed atomic oxygen species present at high oxygen coverages may be a crucial reaction intermediate, largely responsible for the optimum reaction rates.Reaction rates under less than optimum conditions (θ₀ < 1) may be limited by different processes and/or involve a different reaction mechanism: notably, the reaction of adsorbed CO with a less active form of chemisorbed oxygen.These results possibly explain the altered relative activity (Pd,Rh > Ru) observed in ultrahigh vacuum measurements on clean surfaces.