Microwave-Assisted Methane Conversion on High Microwave-Sensitive Catalysts

Microwave irradiation has been applied to several heterogeneous catalysis reactions. Catalytic materials designed for microwave catalysis becomes crucial due to the unique dielectric effect under microwave irradiation. In this presentation, the potential of microwave-assisted direct methane conversion to ethylene and aromatics on the microwave-sensitive catalysts was explored. The result shows that higher methane conversion was observed at a lower bulk catalyst temperature of 550 ℃ compared with traditional molybdenum-based catalysts under the same reaction conditions. Characterization indicates that the synthesized catalyst has a higher dielectric loss than the traditional molybdenum-based catalyst, which means less electromagnetic energy is required to heat the catalytic materials. Meanwhile, a slower catalyst deactivation was observed.

This research discovered that due to the microwave irradiation, the reaction pathway has been changed, and the coking mechanism is different. Microwave facilitates methane C-H bond activation on catalyst surface and hence improves the production of C2 products (ethane and ethylene). With presence of microwave and high hydrogen concentration from CH₄ activation, heavy hydrocarbons (i.e. aromatics, poly-olefinic coke, etc.) exhibit hydrogenolysis leading to the formation of methane. According to Le Chatelier’s principle, this hydrogenolysis will further favors C2 production. Therefore, high C2 selectivity was observed, and only graphite-like coke was detected. This observation indicates the reaction pathways and coking mechanism of microwave-assisted methane conversion are different with that of direct methane conversion in a thermally heated fixed-bed reactor.

In conclusion, this study demonstrates a novel direct methane conversion process under microwave irradiation with high methane conversion and low catalyst deactivation. Specifically, this research provides an in-depth analysis of the microwave-involved reaction mechanism of direct methane conversion on high microwave-sensitive catalysts. By applying microwave-sensitive catalysts, the energy requirement can be lowered, and better reaction stability can be achieved.