The adsorption of acetic acid on Au/Pd(111) alloy surfaces

The adsorption of acetic acid is studied as a function of gold content by temperature-programmed desorption and reflection-absorption infrared spectroscopy on Au/Pd(111) alloys formed by depositing 5 ML of gold onto a Pd(111) surface and heating to various temperatures. For mole fractions of gold greater than similar to 0.5, acetic acid adsorbs molecularly and desorbs intact with an activation energy of similar to 52 kJ/mol. This acetic acid is present as catemers, where the nature of the caterner is found to depend on gold concentration. When the relative gold concentration is less than similar to 0.33, adsorption of acetic acid at 80 K and heating to similar to 207 K forms ill-acetate species on the surface. On further heating, these can either thermally decompose to eventually evolve hydrogen, water and oxides of carbon, or form eta(2)- acetate species, where the coverage of reactively formed eta(2)-acetate species increases with decreasing gold concentration in the near surface region. (c) 2006 Elsevier B.V. All rights reserved.