The adsorption and oxidation of methanol on thin palladium films

The adsorption of methanol (MeOH) on clean and oxygen covered Pd films, deposited on a multicrystalline Re substrate, has been studied using TPD, XPS and ISS. Significant differences in the chemistry are seen between thin (1 monolayer) and multilayer (> 10 monolayers) films, the thicker film behaving in a very similar way to the Pd{ l l l } surface and showing a higher reactivity to MeOH decomposition, but also exhibiting higher desorption temperatures for the decomposition products when compared to the thin layer case. This behavionr is described in terms of charge transfer between the Re substrate and the Pd overlayer. The preadsorption of oxygen leads to significant structural differences in the Pd film as determined by XPS and ISS depending on the preparation temperature, and this in turn leads to significant differences in the reactivity of MeOH. When the oxygen-covered film is prepared at 300 K and exposed to MeOH, no formaldehyde is formed on desorption, whereas following a preparation temperature of 1000 K, significant amounts of formaldehyde are evolved.