Silicon-induced optimization on phase structure and surface property of Pd/ZrO₂ catalysts for enhanced methane combustion

Palladium-based catalysts are relatively active for eliminating anthropogenic methane emissions through catalytic combustion, while they tend to degrade under drastic conditions. Herein, the silicon promoter was rationally introduced into Pd/ZrO2 catalysts to tune the monoclinic (m-) and tetragonal (t-) phase ratio and boost the catalytic performance. The introduced Si-O-Zr structure in ZrO2 not only reduced the grain size, but also produced oxygen vacancies due to lattice distortion, which greatly improved the stability of t-ZrO2 in hightemperature (800 degrees C) calcined catalysts. However, the excessive Si-addition caused the blockage of oxygen vacancies by amorphous SiO2, facilitating the transformation from t-ZrO2 to m-ZrO2. In the Pd/0.05Si-ZrO2 catalyst with a relatively high t-ZrO2 ratio, the presence of abundant oxygen vacancies stimulated the formation of surface-active oxygen and Pd2+ species, improved the reducibility of PdO and the redox of Pd <-> PdO, meanwhile depressed the accumulation of hydroxyls. These, coupled with the enhanced hydrophobicity by Simodification, made Pd/0.05Si-ZrO2 exhibit superior catalytic activity, stability and water-resistance to catalysts with low t-ZrO2 ratio. The revealed Si-promotion effect could be generalized to design phase-regulated Pdbased catalysts with optimized surface property for catalytic oxidation reactions.