Surface chemistry and reactivity of ceria–zirconia-supported palladium oxide catalysts for natural gas combustion

The behavior of 2% Pd catalyst supported on ceria–zirconia, prepared by solution combustion synthesis, was investigated in fresh and aged status, after severe hydro-thermal ageing in presence of SO2. A surface chemical characterization study was performed using methane temperature programmed combustion, oxygen temperature-programmed desorption, hydrogen temperature-programmed reduction and infrared spectroscopy of low temperature carbon monoxide adsorption. The fresh catalyst is mostly constituted by partly oxidized very small Pd metal particles and dispersed Pd oxide species. This situation gives rise to high catalytic activity for methane combustion at low temperature. The progressive oxidation of highly dispersed small Pd particles to PdOx, as well as the coalescence of dispersed Pd oxide species result in PdOx particles fully oxidized at least at the surface which are less active (in the low temperature range) with respect to the active species of the original catalyst.