Adsorption and decomposition of methanol on Rh(111) studied by electron energy loss and thermal desorption spectroscopy

F. Solymosi, A. Berkó, T. I. Tarnóczi

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100 Citations (Scopus)

Abstract

Methanol adsorbs readily on the Rh(111) surface at 100 K., with a high sticking probability, which decreases only slightly up to monolayer coverage. The adsorption occurs in a random fashion, as no long-range order was found by LEED measurements. Four adsorption states can be distinguished: a condensed layer which exhibits fractional kinetics (Edes = 37 kJ mol), a physisorbed layer (Edes = 39 kJ mol), and two chemisorption states. The methanol is initially adsorbed dissociatively to the accompaniment of the appearance of a loss feature at 13.7 eV in the EEL spectrum of Rh(111) in the electronic range. This process is followed by an associative chemisorption of methanol with a bonding energy of 48 kJ mol; the corresponding loss feature in the EEL spectrum is at 12.1-11.2 eV. The surface concentration of chemisorbed methanol at monolayer formation is ~ 7 × 1014 molecules cm2. The methoxy species is not stable on the Rh(111) surface; some of it reacts with adsorbed hydrogen and desorbs as methanol at 210-250 K, in a second-order process with an activation energy of 58 kJ mol. The remaining methoxy decomposes at around 200 K to produce CO and H on the surface. This process is indicated in the EEL spectra by the appearance of a loss at 13.1 eV due to chemisorbed CO. There are no indications of the formation of stable methoxy species.

Original languageEnglish
Pages (from-to)533-548
Number of pages16
JournalSurface Science
Volume141
Issue number2-3
DOIs
Publication statusPublished - Jun 2 1984

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry

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