Electron spectroscopic studies of the methanol adsorption on polycrystalline Ag catalysts

The adsorption and condensation of methanol on polycrystalline Ag catalysts were studied by means of X-ray photoelectron spectroscopy (XPS) and ultraviolet (UV) photoelectron spectroscopy (UPS) at 95 K. The condensed multilayer desorbs between 110 and 140 K, causing a shift of 0.8 eV to lower binding energies in the O Is and C Is XP spectra. In the temperature range between 140 and 160 K monolayer adsorption can be detected. In this range the O Is peak intensity and binding energy are nearly independent of temperature. Above 160 K methanol desorbs without decomposition. The He II UP spectra show five signals, which can be traced back to emissions from the 2a", 7a', 6a'/1a", 5a' and 4a' molecular orbitals of the adsorbed methanol. Work function measurements, the results of the UP spectra and quantum mechanical ab initio calculations suggest a binding of the methanol molecule via the oxygen atom of the hydroxyl group to the polycrystalline Ag surface. (C) 2000 Elsevier Science B.V. All rights reserved.