Structural Evolution of Pd-Zeolite Catalyst and Its Consequence in the Activation and Deactivation for Methane Combustion

Abstract

Understanding the dynamic evolution of heterogeneous catalysts under harsh conditions is critical for controlling active site activation and deactivation. In this work, we investigate the hydrothermal evolution and reaction-driven dynamics of Pd confined within CHA zeolite. The confinement effect of the CHA framework successfully stabilizes Pd as subnanometer clusters, even after severe hydrothermal aging at 850 °C. Utilizing this robust system, we elucidate the structural transformations of Pd species during methane combustion to establish the structure–reactivity relationship. We find that ∼10 nm Pd nanoparticles exhibit higher activity relative to subnanometer clusters and larger aggregates (>20 nm), a trend consistent across CHA, MCM-22, MOR, and ZSM-5. Notably, Pd sintering under reaction conditions is driven by CO, a key intermediate in methane activation. Furthermore, steam exacerbates this CO-mediated sintering by enhancing methane activation and accelerating catalyst deactivation. These findings provide fundamental insights into the evolution of zeolite-confined metal catalysts, guiding the design of durable catalytic systems.