Direct Conversion of Methane to Ethylene and Acetylene over an Iron-Based Metal−Organic Framework

The presence of active sites in porous materials can control and affect significantly their performance in adsorption and catalysis. However, fine tuning of the active sites and elucidation of their role in catalysis remains a challenging task. Metal-organic framework (MOF) materials adopt uniform and well-defined structures, are designable, and can show exceptional structural diversity, enabling the control of active sites at atomic precision.^1-3 Here, we report a comprehensive investigation of the structure and the role of efficient active sites within MOFs for adsorption and catalytic conversion of methane (CH₄).⁴

In this work, direct conversion of methane to ethylene and acetylene is achieved driven by non-thermal plasma under ambient (room temperature and 1 atm) and flow conditions over a metal-organic framework material, MFM-300(Fe). The selectivity for the formation of ethylene and acetylene reaches 96% with a high time yield of 334 µmol∙g_cat⁻¹∙h⁻¹ . At a methane conversion of 10%, the selectivity to C₂₊ hydrocarbons and time yield exceed 98% and 2056 µmol∙g_cat⁻¹∙h⁻¹, respectively, representing a new benchmark for methane conversion. In situ NPD, INS and ssNMR, EPR and DRIFT spectroscopies, coupled with modelling studies, reveal the crucial role of Fe−O(H)−Fe sites in activating methane and stabilising reaction intermediates via the formation of Fe−O(CH₃)−Fe adduct. In addition, a cascade fixed-bed system has been developed to achieve online separation of ethylene and acetylene from unreacted methane for direct use. Integrating the processes of methane activation, conversion, and product separation within one system opens a new avenue for natural gas utility, bridging the gap between fundamental studies and practical applications in this area.

References

1. Han, X. Yang, S. Schröder, M. Porous Metal–Organic Frameworks as Emerging Sorbents for Clean Air. Nat. Rev. Chem. 2019, 3, 108−118.
2. Ma, Y. Schröder, M. Yang, S. et al. Atomically Dispersed Copper Sites in a Metal−Organic Framework for Reduction of Nitrogen Dioxide. J. Am. Chem. Soc. 2021, 143, 10977−10985.
3. Ma, Y. Schröder, M. Yang, S. et al. Direct Observation of Ammonia Storage in UiO-66 Incorporating Cu(II) Binding Sites. J. Am. Chem. Soc. 2022, 144, 8624−8632.
4. Ma, Y. Schröder, M. Yang, S. et al. Direct Conversion of Methane to Ethylene and Acetylene over an Iron-Based Metal-Organic Framework. J. Am. Chem. Soc. 2023, 145, 20792−20800.

Biography

Yujie Ma is working as a postdoctoral research associate in Department of Chemistry, University of Manchester. In 2022, Yujie completed his PhD in Chemistry at the University of Manchester under the supervision of Professor Sihai Yang and Professor Martin Schröder. His research interests lie in multidisciplinary areas of inorganic chemistry and materials chemistry, specifically the design, synthesis and characterisation of porous metal-organic frameworks (MOFs) and MOF-based functional materials for energy and environmental applications. Current focus lies in catalysis and gas adsorption, especially in capture of toxic gases and C1 molecules (such as NO_x, NH₃, CH₄ and CO₂) and catalytic conversion into high value-added chemicals. He uses state-of-the-art experimental and modelling techniques to identify the structures of porous MOF materials and elucidate their roles in gas adsorption and catalysis processes.