Impact of catalyst support on water-assisted CO oxidation over PdO/MO2 (M = Sn, Ti, and Si) catalysts: experimental and theoretical investigation

Abstract

This study examines the impact of different supports, SnO₂, TiO₂, and SiO₂, on the catalytic performance and water resistance of PdO-based catalysts for CO oxidation. By merging experimental data with DFT calculations, we reveal the distinct characteristics exhibited by each catalyst. Specifically, PdO/TiO₂ stands out with exceptional CO oxidation activity, attributed to its minute Pd grain size, robust CO adsorption capacity, and optimal Pd dispersion on the TiO₂ surface. In stark contrast, PdO/SnO₂ demonstrates heightened activity in the presence of water vapor, whereas PdO/SiO₂ experiences minimal effects, as evidenced by quantitative H₂O-TPD analysis and DFT simulations of surface interactions. Water vapor exerts differential impacts on the catalytic performance of these catalysts by modulating the energy barriers associated with the CO oxidation mechanisms. On PdO/TiO₂, the presence of H₂O or H–OH elevates the energy barrier for CO to abstract surface oxygen, thereby diminishing catalyst activity under humid conditions and gradually leading to deactivation due to accumulated surface H₂O and OH species. Conversely, on PdO/SnO₂, when H₂O is present in the form of OH, the energy barrier diminishes, augmenting CO oxidation activity owing to the beneficial effects of surface OH groups.