Combustion of Methane over Palladium-Based Catalysts: Catalytic Deactivation and Role of the Support

Palladium-based catalysts supported on metal oxides are attractive for methane combustion at low temperature. However, at temperatures below 450 °C, their tendency to deactivate hinders their usefulness. Catalytic deactivation in this temperature regime has been attributed to a water/hydroxyl inhibition effect. We investigated this effect to better understand the mechanism for catalytic deactivation. Comparative in situ FTIR transmission spectroscopy experiments at 325 °C revealed that hydroxyl accumulation occurs on the oxide supports during catalytic methane combustion and deactivation. The water/hydroxyl accumulation on the support is slow to desorb at this temperature. In light of our recent finding that oxygen from the support is utilized in the methane combustion process, we propose that hydroxyl/water accumulation on the support impedes the catalytic combustion reaction by hindering oxygen mobility on the support. We support this hypothesis by demonstrating that the presence of water on the catalyst inhibits oxygen exchange with the oxide support.