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

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 C18-4N2MP, 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 C18-4N2MP addition in the precursor gel prior to hydrothermal crystallization, favored the formation of highly dispersed PdOx 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.