Real-time observation of the dehydrogenation processes of methanol on clean Ru(001) and Ru(001)-p(2x2)-O surfaces by a temperature-programmed electron-stimulated desorption ion angular distribution/time-of-flight system

Decomposition processes of methanol on clean and oxygen-precovered Ru(001) surfaces have been visualized in real time with a temperature-programmed (T P) electron-stimulated desorption ion angular distribution (ESDIAD)/time-of -flight (TOF) system. The mass of desorbed ions during temperature-programm ed surface processes was identified by TOF measurements. In the case of met hanol (CH3OD) adsorption on Ru(001)-p(2 x 2)-O, a halo pattern of H+ from t he methyl group of methoxy species was observed at 100-200 K, followed by a broad pattern from the methyl group at 230-250 K and by a near-center patt ern from O+ ions originating from adsorbed CO above 300 K. The halo pattern is attributed to a perpendicular conformation of the C-O bond axis of the methoxy species, leading to oh-normal C-H bond scission. On the other hand, methanol adsorbed on clean Ru(001) did not give any halo pattern but a bro ad pattern was observed along the surface normal, indicating that the confo rmation of the methoxy species is not ordered on the clean surface. Compari son between the ESDIAD images of the oxygen-precovered surface and the clea n surface suggests that the precovered oxygen adatoms induce ordering of th e methoxy species. Real-time ESDIAD measurements revealed that the oxygen a toms at the Ru(001)-p(2 x 2)-O surface have a positive effect on selective dehydrogenation of the methoxy species to CO+H-2 and a blocking effect on C -O bond breaking of the methoxy species. (C) 1999 Elsevier Science B.V. All rights reserved.