Active structures and electronic states for adsorption of CO2 and NO on an Na/TiO2(110) surface

Abstract

X.p.s. and u.p.s. studies have shown that submonolayer coverages of Na deposited on a rutile TiO₂(110) surface remarkably enhance the adsorption of carbon dioxide and nitrogen monoxide forming carbonate and nitride, respectively. The amount of adsorbed CO₂ varied with Na coverage showing an S-shaped dependence, where a critical Na coverage of 0.3 monolayer for CO₂ adsorption was observed. This threshold coincides with the onset of a c(4 × 2) structure derived from ordered ‘Na₂O-dimers’, which suggests that the basicity of oxygen atoms on the TiO₂(110) surface is markedly enhanced by the ‘Na₂O-dimer’ ensemble of four Na atoms. Single or paired Na atoms play a negligible role in the basic promotion. In contrast, NO decomposes on the Ti³⁺ cation reduced by Na deposits. The oxidation state of Ti dominates the decomposition of NO.