Mesoporous K- and Ca-Promoted Ni/Al2O3 Catalysts Derived from MIL-53(Al) for Microwave Plasma-Assisted Dry Reforming of Methane into Syngas

Microwave plasma-catalyzed dry reforming of methane (DRM) offers an innovative strategy for the conversion of CO₂ and CH₄ into syngas, highlighting the necessity for the development of novel catalysts. This study investigates the comparative efficacy of alkaline (e.g., K) and alkaline earth (e.g., Ca) promoters in enhancing the catalytic performance. The Ni₅M_2.5/Al_MIL (M = K, Ca) catalysts derived from MIL-53(Al) were synthesized and employed in the plasma-assisted DRM process. Among the catalysts evaluated, Ni₅Ca_2.5/AlMIL exhibited exceptional activity and synergy with plasma, achieving a fuel production efficiency (FPE) of about 36%. This catalyst demonstrated a CO₂ conversion of 53.5%, a CH₄ conversion of 43.4%, a CO selectivity of 56.5%, and a H₂ selectivity of 86.7%, resulting in CO and H₂ yields of 25.9 and 39.1%, respectively. The significant enhancement in catalytic efficiency can be attributed to several factors: improved reducibility, stronger metal–support interactions (MSI), increased basicity, facilitated the formation of oxygen vacancies, and diminished carbon deposition. These attributes collectively facilitate the enhanced adsorption and activation of reactive species, thereby optimizing the synergy between plasma and catalysts in the DRM process. Moreover, the mesoporous Al_MIL support contributes to a larger surface area and improved dispersion of active metals, effectively mitigating the limitations typically associated with conventional supports. Notably, the variation of the H₂/CO ratio from 4.0 to 1.9 can be linked to the modulation of CO selectivity influenced by the MSI and basicity of the catalysts. This study underscores the potential of tailored catalysts in enhancing the efficiency of the microwave plasma-catalyzed DRM process.