Role of Water on the Structure of Palladium for Complete Oxidation of Methane

Palladium-based catalysts are attractive for methane combustion on natural gas vehicles at low temperature. By means of ambient pressure X-ray photoelectron spectroscopy, we investigated the reaction on a palladium foil exposed to different mixtures at increasing temperature. Water affects the long-term catalyst stability and blocks the active sites, ascribed to the hydroxyl inhibition effect. We investigated such an effect both under steady state and transient reaction conditions to understand the mechanism of inhibition. The hydroxyl formation on the surface of palladium blocks the sites for methane activation, postponing the formation of the active palladium oxide phase in the bulk.