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/ZrO 2 catalysts to tune the monoclinic ( m -) and tetragonal ( t -) phase ratio and boost the catalytic performance. The introduced Si–O–Zr structure in ZrO 2 not only reduced the grain size, but also produced oxygen vacancies due to lattice distortion, which greatly improved the stability of t -ZrO 2 in high-temperature (800 °C) calcined catalysts. However, the excessive Si-addition caused the blockage of oxygen vacancies by amorphous SiO 2 , facilitating the transformation from t -ZrO 2 to m -ZrO 2 . In the Pd/0.05Si–ZrO 2 catalyst with a relatively high t -ZrO 2 ratio, the presence of abundant oxygen vacancies stimulated the formation of surface-active oxygen and Pd 2+ 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–ZrO 2 exhibit superior catalytic activity, stability and water-resistance to catalysts with low t -ZrO 2 ratio. The revealed Si-promotion effect could be generalized to design phase-regulated Pd-based catalysts with optimized surface property for catalytic oxidation reactions.
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