Novel Insight in the CO Oxidation on RuO2(110) by in Situ Reflection−Absorption Infrared Spectroscopy

In situ reflection−absorption infrared spectroscopy (RAIRS) experiments identify the most abundant surface species during the CO oxidation on RuO2(110) in a wide pressure range from 10−7 mbar to 10−3 mbar. Under reaction conditions with highest catalytic activity most of the undercoordinated (bridging) surface O atoms of the RuO2(110) surface are shown to be replaced by bridging CO molecules, thereby modifying the operating catalyst. The observed replacement of bridging O by bridging CO contradicts recently published ab initio kinetic Monte Carlo (k-MC) simulations on the same catalytic system. The C−O stretching frequency depends not only on the adsorption site but also on the local adsorption environment on the surface. This allows us to gain unprecedented information about the distribution and local configuration of the adsorbed reactants on the catalyst’s surface during the CO oxidation reaction, which may serve as benchmarks for future k-MC simulations. Under reaction conditions the catalyst surface exposes areas which are catalytically active and areas which are poisoned by densely packed bridging CO and on-top CO. The actual reaction proceeds via the so-called Langmuir−Hinshelwood mechanism in that neighboring on-top O and on-top CO preferentially recombine to form CO2. The thermally induced restoration of the mildly reduced RuO2(110) surface was studied in situ on the atomic scale.