Direct, Nonoxidative Methane Coupling to Produce Ethylene Using 1M-3Mo/CeO₂ Catalysts under Microwave Irradiation: Insights into the Effect of Metal Loading and Promoters

Methane (CH4), the main component of natural gas, can be directly converted to value-added chemicals, such as ethylene and aromatics, using non-oxidative methane coupling on a molybdenum-ceria-based catalyst. The main challenge to be addressed in non-oxidative methane coupling is the thermodynamic limitations of the reaction to break a very stable C–H bond (434 kJ/mol), low ethylene selectivity, and poor catalyst stability. Herein, we report, for the first time, a comprehensive reaction study of 1M (M = Cs, K, Ni, Cu)-Mo/CeO2 catalysts under microwave irradiation. Microwave irradiation selectively heats the active sites on the catalyst surface, accelerating interfacial chemical reactions and leading to the activation of C–H bonds. The 1Cs-3Mo/CeO2 catalyst formulation enhanced the catalytic performance of the methane coupling reaction by achieving a 23% CH4 conversion and 94% selectivity to C2s. The C2 yield is much higher than those reported in the literature, even at higher temperatures of 700–1000 oC. The microwave reactor performance was correlated to in situ Raman characterization, temperature-programmed reduction, CO-chemisorption, and XPS, which characterized each catalyst system. Results suggested that the Mo surface functions as an active site for methane activation, while the metal promoters play a crucial role in C–C coupling and improving the electronic properties of Mo.