METHANOL OXIDATION ON CU(110)

The mechanism of reaction and surface structures for the adsorption and partial oxidation of methanol on the oxygen precovered Cu(110) surface have been studied with a variety of surface sensitive techniques. Molecular beam reaction measurements and TPD have been used to determine 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 mechanism shows three distinct temperature regimes; at low temperatures (< 330 K) stable methoxy species are formed on the surface in a 2:1 ratio to preadsorbed oxygen atoms while at intermediate temperatures (330-450 K) the stoichiometry is the same, but the methoxy is unstable, decomposing to formaldehyde and hydrogen. At high temperatures (> 450 K) the stoichiometry of reaction changes to 1:1 with no hydrogen production. 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 oxygen covered surface with partially oxidised Cu atoms is poisoned in activity 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.