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Water Molecules Facilitate Hydrogen Release in Anaerobic Oxidation of Methane to Methanol over Cu/Mordenite
journal contribution
posted on 2019-10-17, 15:49 authored by Dennis Palagin, Vitaly L. Sushkevich, Jeroen A. van BokhovenDevelopment
of a suitable mild-condition process for direct conversion
of methane to methanol faces multiple challenges, the principal ones
being the higher reactivity of the primary oxidation products and
the need for temperature swings in the typically employed chemical
looping procedures. To circumvent these problems, the use of water
as a mild oxidant has been recently suggested, leading to the concurrent
formation of molecular hydrogen. By means of ab initio calculations,
we address the experimentally observed features of the reaction to
identify possible reaction pathways of such hydrogen release. We propose
that, along with a strong stabilizing effect of water, short-lived
[Cu–H] intermediate species play a crucial role in the mechanism
of the reaction. Proton transfer from the Brønsted acid site
of the zeolite framework via an adsorbed water molecule to the CuI species generates a [Cu–H] intermediate, which then
facilitates the release of molecular hydrogen. This allows the reaction
to proceed over a relatively low-energy transition state configuration.
At the same time, excess of water leads to increased complexity of
the concerted transition state, which results in hindering of the
hydrogen transfer and increase of the corresponding energy barrier.
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water Molecules Facilitate Hydrogen Releasechemical looping proceduresspeciestransition statewater moleculeProton transferzeolite frameworkAnaerobic Oxidationtemperature swingshydrogen transferenergy barrieroxidation productsBr ønsted acid sitereaction pathwaysab initio calculationsmild-condition processhydrogen releaselow-energy transition state configurationCu
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