Catalytic Methane\nMitigation Over Mesoporosity-Engineered\nHierarchically Porous Pd/SSZ-13 Zeolites

Palladium-zeolites are active catalysts for abating methane\n(CH<sub>4</sub>), the second largest greenhouse gas contributing to\nclimate\nchange, via catalytic combustion. Yet, it remains challenging to improve\nthe activity of Pd-zeolites in CH<sub>4</sub> combustion, in particular\nunder humid conditions. Here, using small-pore SSZ-13 zeolite as a\nshowcase, we demonstrate mesoporosity engineering as an effective\napproach to boost the CH<sub>4</sub> combustion performance of Pd-zeolites.\nA newly designed gemini quaternary ammonium surfactant, namely C<sub>18–4</sub>N<sub>2</sub>MP, was fabricated using inexpensive\nreagents and employed as a mesoporogen in the hydrothermal synthesis\nof hierarchically micro–meso–macro–porous SSZ-13\nproduct. High-dispersion Pd catalysts were achieved by using the hierarchically\nporous SSZ-13 zeolites as supports. Physicochemical characterization\nand reaction kinetics disclosed that rational mesoporosity engineering\nof the hierarchically porous SSZ-13, simply by optimizing C<sub>18–4</sub>N<sub>2</sub>MP addition in the precursor gel prior to hydrothermal\ncrystallization, favored the formation of highly dispersed PdO<i><sub>x</sub></i> active phase and, in turn, the CH<sub>4</sub> combustion without noticeable accumulation of carbonaceous intermediates\non the surface. Additionally, mesoporosity-optimized Pd/SSZ-13 displayed\nimproved durability and outstanding moisture resistance during CH<sub>4</sub> combustion. This study sheds new light on the fabrication\nof high-performance Pd-zeolite catalysts for CH<sub>4</sub> emission\nabatement by facile engineering of zeolite mesoporosity.