Si/Al ratio-regulated PdO dispersion determines methane combustion activity over Pd/H-ZSM-5

Methane (CH 4 ) is a potent greenhouse gas, and catalytic combustion offers an effective route for its emission abatement. Although Pd‑based catalysts have been widely studied, the influence of the Si/Al ratio of ZSM‑5 supports on Pd structure and its correlation with methane combustion activity remains poorly understood. Herein, a series of 1 wt% Pd/H‑ZSM‑5 catalysts with Si/Al ratios of 25, 50, and 85 were synthesized, and their activity exhibited a volcano‑shaped dependence on the Si/Al ratio, with 1% Pd/H-ZSM-5 50 achieving 90% CH 4 conversion at 375 °C. Structural, surface electronic, and temperature‑programmed oxidation/reduction characterizations revealed that a moderate Si/Al ratio effectively suppressed PdO particle growth. The resulting highly dispersed PdO species featured coexisting Pd δ⁺ , Pd 2+ , and Pd 4+ surface states. Among them, the low-valence Pd δ+ species, formed exclusively at the highest PdO dispersion (12.11%), was identified as the key active center. Moreover, the optimized PdO dispersion endowed the catalyst with distinct oxygen desorption behavior and enabled methane oxidation at lower temperatures. This work demonstrated that the Si/Al ratio governed CH 4 combustion activity by modulating PdO dispersion and particle size, providing guidance for the rational design of zeolite-supported Pd catalysts.