CO oxidation on ruthenium: The nature of the active catalytic surface

The oxidation of carbon monoxide over metal surfaces, such as ruthenium, one of the most studied catalytic reactions, is analyzed. The measured reaction kinetics at reducing or mildly oxidizing conditions for Pt, Pd, and Rh shows a first order dependence on O2 pressure and a negative first-order dependence on CO pressure, with an apparent activation energy for CO2 formation on each metal approximately equal to the corresponding CO desorption energy. Density functional theoretical (DFT) studies have suggested that a tri-layer RuO2 layer should serve as a transition between chemisorbed oxygen and the oxide phase. XPS, AES, and LEED have been used to study the active phase of Ru for CO oxidation under stoichiometric condition. CO2 formation rate is estimated assuming that each removed surface oxygen atom gives rise to one CO2 molecule. It is concluded that RuO2 cannot be a catalyst for CO oxidation at moderate temperature.