The aim of the present proposal is to investigate the mechanism of CO oxidation over hydrous palladium oxide, both directly and indirectly. For the direct route, the sample will be dosed with CO at 77K, where it will physisorb but not react and then stepwise warm to room temperature, with the aim of stabilising the intermediate before the reaction goes to completion. A complementary route is to dose with CO2 since on Pd(1%)/Al2O3 (Föttinger et al, Chem. Commun. 2008, 320) it has been shown that this leads to enhanced quantities of the bicarbonate intermediate. For an indirect approach, the intention is to generate a surface adsorbed formate intermediate from formic acid and monitor its decomposition.