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

Abstract

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 high-temperature (800 °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 Si-modification, 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 Pd-based catalysts with optimized surface property for catalytic oxidation reactions.