METHANOL OXIDATION ON CU(110)

The mechanism of reaction and surface structures for the adsorption an d partial oxidation of methanol on the oxygen precovered Cu(110) surfa ce have been studied with a variety of surface sensitive techniques. M olecular beam reaction measurements and TPD have been used to determin e the chemical nature of the adsorbed species and the products formed. LEED and STM have been employed to determine the surface structure of both the oxygen covered surface and the structures formed by reaction with methanol. The kinetics are shown to be dependent on the initial oxygen precoverage and the surface temperature during reaction. The me chanism shows three distinct temperature regimes; at low temperatures (< 330 K) stable methoxy species are formed on the surface in a 2:1 ra tio to preadsorbed oxygen atoms while at intermediate temperatures (33 0-450 K) the stoichiometry is the same, but the methoxy is unstable, d ecomposing to formaldehyde and hydrogen. At high temperatures (> 450 K ) the stoichiometry of reaction changes to 1:1 with no hydrogen produc tion. STM and LEED show a previously unreported (5 x 2) structure for methoxy adsorbed on this surface. It is clear from the combination of techniques that a dual site combination is crucial for high reactivity . This dual site consists of an oxygen atom and a Cu0; the fully oxyge n covered surface with partially oxidised Cu atoms is poisoned in acti vity for the reaction, whereas the partly covered surface is the most active. Tle proposed active sites are located at the short side of the rectangular oxygen islands.