MOLECULAR-BEAM STUDIES OF ETHANOL OXIDATION ON PD(110)

The adsorption and decomposition of ethanol on Pd(110) has been studie d by use of a molecular beam reactor and temperature programmed desorp tion. It is found that the major pathway for ethanol decomposition occ urs via a surface ethoxy to a methyl group, carbon monoxide and hydrog en adatoms. The methyl groups can either produce methane (which they d o with a high selectivity for adsorption below 250 K) or can further d ecompose (which they do with a high selectivity for adsorption above 3 50 K) resulting in surface carbon If adsorption occurs above 250 K a h igh temperature (450 K) hydrogen peak is observed in TPD, resulting fr om the decomposition of stable hydrocarbon fragments. A competing path way also exists which involves C-O bond scission of the ethoxy, probab ly caused by a critical ensemble of palladium atoms at steps, defects or due to a local surface reconstruction. The presence of oxygen does not significantly alter the decomposition pathway above 250 K except t hat water and, above 380 K, carbon dioxide are produced by reaction of the oxygen adatoms with hydrogen adatoms and adsorbed carbon monoxide respectively. Below 250 K, some ethanol can form acetate which decomp oses around 400 K to produce carbon dioxide and hydrogen.