Dresden 2009 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 62: Surface chemical reactions II
O 62.6: Vortrag
Freitag, 27. März 2009, 12:30–12:45, SCH A01
Adsorption of Methanol on Ru(0001) — •Pawel Gazdzicki and Peter Jakob — Fachbereich Physik, Philipps-Universität Marburg, D-35032 Marburg, Germany
Infrared Absorption Spectroscopy was used to study the adsorption and reaction of methanol on Ru(0001). From the vibrational modes of the isotopes CH3OH and CH3OD clear evidence for intact adsorption at T=80 K has been found. This finding contradicts previous studies which suggested an OH (OD) bond scission upon adsorption of methanol even at low temperatures as well as recombinative desorption at elevated T. Our conclusion is based on isotopic shifts of vibrational modes associated with the OH (OD) group of adsorbed CH3OH and CH3OD, respectively. The findings are corroborated by TPD experiments of CH3OH with coadsorbed D on Ru(0001). While clearly showing desorption of CH3OH, no desorption of CH3OD caused by the recombination of dissociated CH3OH and D was observed. At low coverages (< 0.1 ML) we suggest the presence of isolated methanol molecules which begin to cluster with increasing density by building hydrogen bonds. This clustering was also observed after annealing a low coverage methanol layer up to 100-120 K. At temperatures T=170-200 K CH3OH decomposes (O-H bond cleavage) to form an upright methoxy species (CH3O). The final reaction products are CO and H which are formed at T>220 K.
In comparison, CH3OH adsorbed on pseudomorphic Cu/Ru(0001) produces the same species as on Ru(0001). Yet, the temperature range of the methoxy species is significantly larger, i.e. 200-300 K.