The Role Of Subsurface Oxygen In The Catalytic Co-Oxidation Reaction

The CO/CO2 conversion performed over a Ru(0001) surface shows the decisive role of subsurface oxygen which explains the discrepancy between former UHV results and high-pressure experiments. At oxygen pressure higher than about 10(-3) mbar the oxygen atoms start to penetrate the bulk. This subsurface oxygen has to be considered as a species which accompanies the high-pressure surface reactions where oxygen is involved. This new oxygen phase exhibits unique properties clearly different from adsorbed oxygen as well as from regular ruthenium oxides. The presence of subsurface oxygen raises the yield for CO-oxidation reaction by more than two orders of magnitude. Oxygen atoms forming the subsurface phase seem to be very mobile as can be deduced from the reaction kinetics which show that the CO2 formation is limited only by the thermal diffusion of subsurface oxygen towards the surface.