The direct conversion of methane to unsaturated hydrocarbons under mild conditions is a useful type of reaction, but is generally challenging to achieve. The route that is currently used in industry is indirect, and CH₄ is first converted to syngas (a mixture of CO and H₂). Catalysts that can promote the direct conversion of methane are interesting research targets. Metal–organic frameworks (MOFs) can be used as catalyst candidates. In addition, non-thermal plasma (NTP), which can be generated by passing a gas through an electric field, can be useful in this context. NTP features highly energetic electrons, which can activate molecules such as methane under mild conditions and enable challenging reactions.

Martin Schröder, University of Manchester, UK, Sihai Yang, University of Manchester and Peking University, Beijing, China, and colleagues have developed an approach to the direct conversion of CH₄ to C₂H₄ and C₂H₂ under ambient conditions over an iron-based MOF, using a flow chemistry setup and driven by non-thermal plasma. The team used MFM-300(Fe) (MFM = Manchester Framework Material) as the catalyst in a fixed-bed reactor and passed a gas mixture of CH₄ and He through the reactor under NTP activation at 25 °C and 1 atm. They achieved a selectivity for the formation of C₂H₄ and C₂H₂ of 96 %.

The products need to be separated from unreacted CH₄, which the researchers achieved by using a second fixed-bed reactor after the first, packed with MOFs that act as sorbents (HKUST-1 or ZSM-5). The sorbents collect the products, while allowing methane to pass and potentially be reused for another round of conversion. Overall the developed system could provide a solution for the synthesis of chemicals from abundant natural gas.

• Direct Conversion of Methane to Ethylene and Acetylene over an Iron-Based Metal–Organic Framework,
  Yujie Ma, Xue Han, Shaojun Xu, Zhe Li, Wanpeng Lu, Bing An, Daniel Lee, Sarayute Chansai, Alena M. Sheveleva, Zi Wang, Yinlin Chen, Jiangnan Li, Weiyao Li, Rongsheng Cai, Ivan da Silva, Yongqiang Cheng, Luke L. Daemen, Floriana Tuna, Eric J. L. McInnes, Lewis Hughes, Pascal Manuel, Anibal J. Ramirez-Cuesta, Sarah J. Haigh, Christopher Hardacre, Martin Schröder, Sihai Yang,
  J. Am. Chem. Soc. 2023, 145, 20792–20800.
  https://doi.org/10.1021/jacs.3c03935