Revealing Active Sites and Reaction Pathways in Methane Non-Oxidative Coupling over Iron-Containing Zeolites |
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Authors: | Hao Zhang Aleksei Bolshakov Raghavendra Meena Gustavo A Garcia A Iulian Dugulan Alexander Parastaev Guanna Li Emiel J M Hensen Nikolay Kosinov |
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Institution: | 1. Laboratory of Inorganic Materials and Catalysis, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands;2. Biobased Chemistry and Technology, Wageningen University & Research, Bornse Weilanden 9, 6708 WG Wageningen, The Netherlands;3. Synchrotron SOLEIL L'Orme des Merisiers, St. Aubin BP 48, 91192 Gif sur Yvette, France;4. Fundamental Aspects of Materials and Energy, Department of Radiation Science and Technology, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands |
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Abstract: | Non-oxidative coupling of methane is a promising route to obtain ethylene directly from natural gas. We synthesized siliceous Fe]zeolites with MFI and CHA topologies and found that they display high selectivity (>90 % for MFI and >99 % for CHA) to ethylene and ethane among gas-phase products. Deactivated Fe]zeolites can be regenerated by burning coke in air. In situ X-ray absorption spectroscopy demonstrates that the isolated Fe3+ centers in zeolite framework of fresh catalysts are reduced during the reaction to the active sites, including Fe2+ species and Fe (oxy)carbides dispersed in zeolite pores. Photoelectron photoion coincidence spectroscopy results show that methyl radicals are the reaction intermediates formed upon methane activation. Ethane is formed by methyl radical coupling, followed by its dehydrogenation to ethylene. Based on the observation of intermediates including allene, vinylacetylene, 1,3-butadiene, 2-butyne, and cyclopentadiene over Fe]MFI, a reaction network is proposed leading to polyaromatic species. Such reaction intermediates are not observed over the small-pore Fe]CHA, where ethylene and ethane are the only gas-phase products. |
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Keywords: | C−C Coupling Iron Methane Non-Oxidative Zeolites |
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