Dresden 2006 – wissenschaftliches Programm
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O: Oberflächenphysik
O 38: Adsorption V
O 38.9: Vortrag
Donnerstag, 30. März 2006, 17:00–17:15, TRE Phys
Complex formation and proton transfer between formic acid and water on Au(111) surfaces under UHV conditions — •Michel Kazempoor and Gerhard Pirug — Institut für Schichten und Grenzflächen (ISG3), Forschungszentrum Jülich GmbH, 52425 Jülich
The coadsorption of formic acid (HCOOH) and water (H2O) on Au(111) single crystal surfaces has been investigated by means of vibrational spectroscopy (HREELS), photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED). Formic acid adsorbs at 90 K molecularly with vibrational modes characteristic for flat lying zig-zag chains and solid formic acid in the monolayer and physisorbed multilayer regime, respectively. Annealing results in a complete desorption at 190 K without any detectable formation of intermediates like formates. Sequential adsorption of formic acid and water at 90 K shows no significant chemical interaction in the vibrational signatures and the core level photoelectron binding energies. Upon annealing the coadsorbed layer to 140 K new vibrational losses appear in the HREEL-spectrum at 190, 590 and 1000 cm−1. Using isotopically labelled adsorbates such as D2O and H13COOD we were able to identify a hydrogen-bonded complex between formic acid and water with a molecular ratio of one. Upon further annealing this complex decomposes leaving only molecularly adsorbed formic acid on the surface at 160 K. This process is accompanied by a proton exchange between formic acid and water. The results will be discussed in the light of recent findings for the electrochemical oxidation of formic acid on Au surfaces.