Atomic-scale structure and catalytic reactivity of RuO2

Abstract

The structure and reactivity of the oxygen phases on Ru(0001) and Ru(100) and the bulk RuO2(101) surface were studied by quantitative LEED I/E analysis, TDS and AES. On Ru(0001), the (2´ 2)-3O phase forms at an O coverage of 0.75 ML. The atomic structure of this phase turned out to be a (2´ 2) vacancy structure of a (1´ 1)-O network on Ru(0001). CO does not adsorb on the (2´ 2)-3O overlayer in sample temperature range of 100 K and 300 K. At O coverages above 2–3 ML, RuO2 grows on Ru single crystals. Under UHV conditions, RuO2(110) is formed on Ru(0001), while on Ru(100), the (100) face of RuO2 is exposed. CO molecules bind selectively and strongly on cus (coordinatively unsaturated sites) Ru atoms of these RuO2/Ru surfaces. The CO molecules on the RuO2(110) and RuO2(100) surfaces can readily recombine with the lattice O atoms to produce CO2. The oxide formation is responsible for the high activity of the O-rich phases of Ru(0001) for the CO oxidation. In addition, the weakly bound O species on the RuO2(110) surface was characterized, which may provide a more efficient reaction pathway of the CO oxidation at 350 K, and stabilize the RuO2 catalyst in that the CO-induced vacancies are healed. The bulk RuO2(101) crystal reveals an equally high activity for the CO oxidation reactions as the RuO2(110) and RuO2(100) surfaces