Base metal oxides have long been of interest as catalysts for oxidation of small molecules such as CO, NO, or SO2. As an example, Ru metal becomes active for catalytic oxidation only after partial surface oxidation. The (110) surface of RuO2 is a convenient model for the oxidized metal surface because it is active for CO oxidation and well characterized.[1] In this study we employ plane-wave, supercell DFT calculations to examine the mechanism of oxygen activation on RuO2(110) surface. The energetic and electronic properties of the (110) surface as a function of two types of surface oxygen coverages are explored. We find that higher molecular oxygen coverage becomes accessible if strong oxidants such as NO2 or O3 are present. Molecular adsorbed oxygen might play a role as an intermediate in catalytic reactions such as CO oxidation.

Practical applications of most catalysts are limited by surface poisoning, so it is important to understand and ultimately to learn to bypass surface poisoning. Experimental observations have suggested that the excellent oxidation activity of RuO2 can be poisoned under some conditions by the formation of a surface carbonate.[2] Therefore, we also probe the formation of carbonate on an RuO2(110) surface by DFT calculations and determine its implications for surface poisoning. In general, carbonate adsorbs weakly and, based on equilibrium calculations, competes ineffectively with oxygen adsorption. The more favorable kinetics of carbonate formation are likely important to the observed high carbonate coverages [3] at high O2 pressures.

[1]: H. Over et al., Science 287, 1474 (2000).

[2]: A. Lafosse, Y. Wang, and K. Jacobi, J. Chem. Phys., 117, 2823 (2002).

[3]: M. Rossler, S. Giinther, and J. Wintterlin, J. Phys. Chem. C, 111, 2242 (2007).