The interaction of methanol with modified Ru(001) surfaces: The effects of oxygen and potassium

Abstract

The adsorption and decomposition of methanol on a Ru(001) surface modified by preadsorbed potassium and oxygen has been investigated with electron energy loss spectroscopy (EELS) and multiple mass thermal desorption spectroscopy (TDS). On ruthenium precovered with a low coverage of atomic oxygen ( θ o = 0.25), methoxy formation is promoted with respect to the clean surface and is found to occur at 85 K. In contrast, on ruthenium modified by “ionic” potassium ( θ K = 0.10), methoxy formation is inhibited, i.e., oxygen-hydrogen bond breaking does not occur until temperatures reach 240 K. On both surfaces, the decomposition of methanol proceeds via O-H and C-H bond breaking and ultimately leads to the formation of CO and H 2. The results differ from those obtained on the clean Ru(001) surface, where methoxy formation is observed at 85 K only when exposed to small amounts of methanol, and where a significant C-O bond-breaking decomposition channel leading to the formation of water and surface carbon is also present. The differences in methanol reactivities on these low-coverage potassium- and oxygen-modified surfaces can be attributed largely to electronic modifications of the metal substrate. At higher coverages of the surface additives, a different behavior is encountered. Oxygen at θ O = 0.60 completely inhibits the formation of methoxy due to physical site blocking, while metallic potassiu, ( θ K = 0.33) reacts directly with methanol to form potassium methoxide.