(597c) Microwave-Driven Non-Oxidative Methane Coupling Using Mo/CeO2 catalyst for Ethylene Production: Insight into the Effect of Metal Promoters.

With the growing need to transition to cleaner and more sustainable energy sources, the battle for efficient hydrocarbon conversion technologies has reached a critical point. Methane, a key component of natural gas (∼95%) and shale gas (∼70%), has become a focus for innovative solutions due to its abundance and environmental concerns (Xiao & Varma, 2018). Therefore, the strategic conversion of methane to ethylene, the key building block in the chemical industry, is critical to the long-term use of natural gas and shell gas utilization and the global move to net zero emission (Gao et al., 2019). Currently, ethylene is produced through the generation of syngas and methanol, which are then converted into ethylene. However, this approach is expensive and environmentally unfriendly, as it produces undesirable byproducts such as CO and CO₂, contributing to greenhouse gas emissions. As a result, direct conversion of CH₄ can potentially reduce the production complexity and minimize the environmental effects. Non-oxidative methane coupling (NOCM), which avoids traditional oxidative procedures, opens up new possibilities for developing CH4 conversion technologies to produce more sustainable and environmentally friendly products. In addition, it also has the potential to improve selectivity and energy efficiency.

Despite its economic and environmental benefits, direct, NOCM to value-added compounds has major thermodynamic limits. Therefore, designing an effective catalyst is crucial to resolving methane conversion difficulties. Furthermore, employing microwave irradiation to heat the catalyst is an effective technique to reduce energy consumption. A well-designed catalyst increases methane conversion efficiency by allowing selective chemical reactions, lowering unwanted byproducts, and increasing desired outcomes.
Microwave irradiation for catalyst heating is a concentrated and energy-efficient strategy. Unlike other heating methods, microwave irradiation selectively heats the catalyst, resulting in efficient energy transfer at the reaction sites. This application of microwave technology in NOCM not only improves methane conversion and ethylene selectivity, but it also solves environmental issues by enabling for operation on intermittent renewable energy sources. Such focused energy delivery can significantly reduce the overall energy input required for bond cleavage in methane coupling, addressing the high energy demand of strong carbon-hydrogen bonds.

In this study, we conducted NOCM using a Mo/CeO₂ catalyst under microwave irradiation at relatively moderate temperatures (700°C). Various metal promoters were introduced into the primary catalyst system, Mo/CeO₂, to assess their impact on the direct conversion of methane and ethylene production. The findings revealed that catalysts containing metal promoters exhibited higher ethylene selectivity compared to the unpromoted Mo/CeO₂. Among them, Cs-Mo/CeO₂ emerged as the most efficient catalyst for ethylene and C₂-selectivity, achieving rates of 60% and 90%, respectively, with a reasonable CH₄ conversion rate of approximately 22%. The catalyst's properties were studied using diverse physicochemical characterization methods, including CO chemisorption, temperature-programmed reduction (TPR), X-ray diffraction (XRD), and Brunauer–Emmett–Teller (BET) surface area analysis.