Catalytically Active States of Ru(0001) Catalyst in CO Oxidation Reaction

Identifying the composition of the catalytically active state of metal catalysts under dynamic operating conditions is of particular importance for oxidation catalysis. We report here new insights into the chemical identity of different catalytically active states formed on a Ru(0001) catalyst during the CO oxidation at different reaction temperatures. The changes in the surface composition of the Ru catalyst and the CO2 yield under varying reaction conditions in the 10 to 10 mbar pressure range were followed in-situ by synchrotron-based high-pressure x-ray photoelectron spectroscopy and mass spectroscopy. The obtained results reveal that the catalytic activity of a few layers thick ‘surface oxide’ without well defined stoichiometry and structure is comparable with the activity of the stoichiometric RuO2(110) phase. The ‘surface oxide’ forms under reaction conditions when the formation of the RuO2 is kinetically hindered, and can coexist with RuO2 in a wide temperature-pressure range.