Misconceptions and challenges in methane-to-methanol over transition-metal-exchanged zeolites

Abstract

Direct methane functionalization and, in particular, the selective partial oxidation to methanol, remains an eminent challenge and a field of competitive research. The conversion of methane to methanol over transition-metal-containing zeolites using molecular oxygen is a promising and extensively studied process. Herein, we scrutinize some oft-cited assumptions in this topic—which include the labelling of the process as biomimetic, the debate regarding the industrial viability of direct methane-oxidation systems and the claim that methane is difficult to activate—and delineate the extent to which these are scientifically robust. We highlight both the merits and pitfalls of such statements and point out the hazards associated with their improper use. By examining these misconceptions, we build an outlook for future research, highlighting the need to optimize materials and process conditions for the stepwise approach and to further explore catalytic processes that explicitly employ strategies for the preservation of methanol.

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Fig. 1: Methanol selectivity versus methane conversion.
Fig. 2: Enzymatic versus zeolite-based partial oxidation of methane.
Fig. 3: Evaluation of the established approaches for methane-oxidation using a triangular model.

Data availability

The authors declare that the data supporting the findings of this study are available within the paper.

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Acknowledgements

The authors acknowledge the ESI platform, Paul Scherrer Institute and ETH Zurich for financial support. DP is grateful for the Swiss National Supercomputing Centre for providing the computational facilities.

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J.A.vB devised the overall idea of the perspective and M.Rav. wrote the manuscript in close consultation with all the other authors. All authors contributed insights, provided feedback and edited the manuscript. V.S gave specific inputs on aspects of industrial viability, kinetic measurements and benchmarking as discussed in the manuscript. A.J.K. and M.A.N added to the discussion on the biomimetic descriptor and compiled data from literature for computing the space–time yield under Table 1. M.A.N., A.J.K. and A.B.P. contributed to sections of the manuscript that deal with X-ray based techniques and active site structure. D.P. gave inputs on computational methods used in this chemistry. M.Ran. provided inputs on sections of the manuscript that deal with benchmarking and catalytic processes for methane to methanol.

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Correspondence to Jeroen A. van Bokhoven.

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Supplementary Data 1

Calculations of maximal methanol selectivity for chemical looping system based on reaction stoichiometry

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Ravi, M., Sushkevich, V.L., Knorpp, A.J. et al. Misconceptions and challenges in methane-to-methanol over transition-metal-exchanged zeolites. Nat Catal 2, 485–494 (2019). https://doi.org/10.1038/s41929-019-0273-z

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