Atomically dispersed palladium-based catalysts obtained via constructing a spatial structure with high performance for lean methane combustion†
Lean methane combustion through efficient catalysis is an intensely important way to reduce environmental pollution. Notably, palladium-based catalysts are promising catalytic materials. The small size of palladium particles is a crucial factor to improve the catalytic activity. In this study, we proposed a new pathway to minimize the size of palladium particles for palladium-based catalysts from the perspective of material preparation. We first built double spatial barriers on the interface between the support and the active species to prepare atomically dispersed palladium species catalysts. To be specific, organo-silane was employed as a surfactant to modify the zirconia support and palladium acetate was selected as the palladium precursor, taking advantage of the spatial structure of alkane chains combined with silicon atoms and palladium acetate in toluene. Under a lean methane reaction environment, 0.23 wt% atomically dispersed palladium species deposited on decorated zirconia (donated as 0.23 wt% Pd/SiO2–ZrO2) displayed high catalytic activity with 100% conversion at a temperature of around 400 °C with gas hourly space velocity (GHSV) of 30 000 ml g−1 h−1, higher than that of pristine zirconia loaded with 0.23 wt% palladium nanoparticles (donated as 0.23 wt% Pd/ZrO2), which removed all lean methane at around 600 °C under the same conditions. As the palladium loading increased on the modified support, the 1.38 wt% Pd/SiO2–ZrO2 catalyst had a comparable catalytic activity and fully converted lean methane at around 330 °C. The lean methane combustion reaction pathway for the 0.23 wt% Pd/SiO2–ZrO2 catalyst was investigated by in situ NAP-XPS and in situ DRIFTS. Hydroxyl groups formed during the reaction were transferred to the silica, which could reduce the formation of the inactive Pd(OH)x species and expose more active sites to improve the catalytic activity. It is hoped that this study will provide a novel method to improve the utilization of palladium species in practical applications.