Methane is an important potential feedstock for the production of value-added chemicals and fuels. However, the activation and conversion of methane remain a great challenge due to its stable tetrahedral structure, high bond energy and low polarizability. To date, the oxidative conversion of methane has been carried out mainly over metal or metal oxide catalysts. Hexagonal boron nitride (h-BN) is emerging as an important metal-free catalyst for oxidative dehydrogenation of ethane, propane and butane, exhibiting higher olefin selectivity with negligible CO2 formation compared to traditional metal-based catalysts. However, the origin of activity h-BN has aroused considerable interest and debate, since h-BN has been widely accepted as catalytically inert material. Investigating the catalytic ability of h-BN in the activation and conversion of methane will result not only in improved catalysts, but will also enhance our fundamental understanding of oxidative dehydrogenation by h-BN at the molecular level. h-BN catalyzes the conversion of methane to valuable products including C2H4, C2H6, CO and H2 (the components of syngas), with minor formation of CO2. In situ IR and isotope-labelling experiments demonstrate that B-OH groups are involved in the activation of methane. In combination with theoretical studies, we demonstrate that B-O-H groups both originally present and generated in-situ during the reaction promote the activation of O2 and CH4. We propose a novel H2O-assisted mechanism, involving mutual and synergistic activation of O2 and CH4. B-O-H groups facilitate the insertion of O2 into the B-N bond to form a transient B-O-O-N intermediate. Subsequent CH4 activation at the B-O-O-N site generates methyl and methoxy radicals, resulting in the formation of partial oxidation and coupling products by a series of gas phase radical and/or surface reaction. This metal-free h-BN catalyst enriches our knowledge of methane activation and might lead to new possibilities for development of more sustainable methane conversion schemes.

Methane activation over a boron nitride catalyst driven by in situ formation of molecular water

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.