Microwave-Driven Nonoxidative and Selective Conversion of Methane to Ethylene over Mn-Based Catalysts

Recent advancements in microwave-driven nonoxidative catalytic synthesis of C₂H₄ from CH₄ coupling offer a promising, energy-efficient, and eco-friendly alternative to conventional methods, where selective heating under microwave irradiation enables comparable conversions at substantially lower bulk temperatures and shorter reaction times. This study explores the performance of an MnO_X-based catalyst supported on CeO₂ and HY zeolite (silica-to-alumina ratio = 5.1) for the nonoxidative coupling of CH₄ (NOCM) under microwave irradiation. Inspired by the well-established efficacy of MnO_X catalyst in oxidative CH₄ coupling (OCM), their application in NOCM has also shown significant performance. The catalytic system achieved 15% CH₄ conversion and 99% selectivity toward C₂ hydrocarbons and maintained 64% selectivity toward C₂H₄ surpassing the yields reported in the literature even at higher temperatures (700-1000 °C). Catalyst performance was correlated with measurements by in situ Raman spectroscopy, and additional characterizations were performed using H₂-temperature programmed reduction , NH₃-temperature programmed desorption, and BET surface area analysis to understand structural changes during the reactions. These findings suggested that Mn functions as active sites for CH₄ activation in nonoxidative environments while also promoting efficient C-C coupling under microwave irradiation.