Catalytic Methane Mitigation Over Mesoporosity-Engineered Hierarchically Porous Pd/SSZ-13 Zeolites

Abstract

Palladium-zeolites are active catalysts for abating methane (CH₄), the second largest greenhouse gas contributing to climate change, via catalytic combustion. Yet, it remains challenging to improve the activity of Pd-zeolites in CH₄ combustion, in particular under humid conditions. Here, using small-pore SSZ-13 zeolite as a showcase, we demonstrate mesoporosity engineering as an effective approach to boost the CH₄ combustion performance of Pd-zeolites. A newly designed gemini quaternary ammonium surfactant, namely C_18–4N₂MP, was fabricated using inexpensive reagents and employed as a mesoporogen in the hydrothermal synthesis of hierarchically micro–meso–macro–porous SSZ-13 product. High-dispersion Pd catalysts were achieved by using the hierarchically porous SSZ-13 zeolites as supports. Physicochemical characterization and reaction kinetics disclosed that rational mesoporosity engineering of the hierarchically porous SSZ-13, simply by optimizing C_18–4N₂MP addition in the precursor gel prior to hydrothermal crystallization, favored the formation of highly dispersed PdO_x active phase and, in turn, the CH₄ combustion without noticeable accumulation of carbonaceous intermediates on the surface. Additionally, mesoporosity-optimized Pd/SSZ-13 displayed improved durability and outstanding moisture resistance during CH₄ combustion. This study sheds new light on the fabrication of high-performance Pd-zeolite catalysts for CH₄ emission abatement by facile engineering of zeolite mesoporosity.