Methanol oxidation on stoichiometric and oxygen-rich RuO(110).

We used temperature-programmed reaction spectroscopy (TPRS) to investigate the adsorption and oxidation of methanol on stoichiometric and O-rich RuO(110) surfaces. We find that the complete oxidation of CHOH is strongly preferred on stoichiometric RuO(110) during TPRS for initial CHOH coverages below ∼0.33 ML (monolayer), and that partial oxidation to mainly CHO becomes increasingly favored with increasing CHOH coverage from 0.33 to 1.0 ML. We present evidence that an adsorbed CHO species serves as the key intermediate to complete oxidation and that CHO formation is intrinsically facile but becomes limited by the availability of bridging O-atoms on stoichiometric RuO(110) at initial CHOH coverages above 0.33 ML. We show that methanol molecules adsorbed in excess of 0.33 ML dehydrogenate to mainly CHO and desorb during TPRS, with adsorbed CHO groups mediating the evolution of both CHO and CHOH. We find that O-rich RuO(110) surfaces are also highly active toward methanol oxidation and that selectivity toward the complete oxidation of methanol increases markedly with increasing coverage of on-top O-atoms (O) on RuO(110). Our results demonstrate that CHOH species adsorbed within O-rich domains react efficiently during TPRS, in parallel with reaction of CHOH adsorbed initially on cus-Ru sites. The data suggests that the facile hydrogenation of O atoms and the resulting desorption of HO at low-temperature (<∼400 K) provides an efficient pathway for restoring reactive O-atoms and thereby promoting complete oxidation of methanol on the O-rich RuO(110) surface.