Mechanistic Insights into Complete Methane Oxidation on Single-Atom Pd Supported by SSZ-13 Zeolite: A First-Principles Study

Complete catalytic oxidation of methane is an effective strategy for greenhouse gas mitigation and clean energy conversion; yet, ensuring both high catalytic activity and stability with palladium-based catalysts remains a challenge. In the present work, we employed a theoretical investigation of methane oxidation over single-atom Pd supported on SSZ-13 zeolite using density functional theory calculations, combined with climbing-image nudged elastic band calculations to determine activation barriers. A systematic assessment of various Al distributions and Pd placements was carried out to identify the most stable configurations for Pd incorporation within the zeolite framework.Further, two mechanistic routes for methane activation were evaluated: (i) direct dehydrogenation under dry conditions, and (ii) O$_2$-assisted oxidative dehydrogenation. Our results demonstrate that the direct (dry) pathway is energetically demanding and overall endothermic, whereas the O$_2$ assisted route facilitates the exothermic energy profile, particularly in the C-H bond cleavage. The formation of stable hydroxyl and CO/CO$_2$ intermediates were also studied. The results emphasize the role of oxygen-rich environments in enabling the complete methane oxidation with improved thermodynamic feasibility. Moreover, we propose an alternate low-energy pathway based on O-assisted and multi-site mechanisms that reduce the overall reaction enthalpy. These insights provide the design principles for highly active and moisture-resistant Pd-zeolite catalysts for sustainable methane utilization.