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Water-promoted interfacial pathways in methane oxidation to methanol on a CeO2-Cu2O catalyst

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Science  01 May 2020:
Vol. 368, Issue 6490, pp. 513-517
DOI: 10.1126/science.aba5005

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A water boost for methanol synthesis

Model catalysts based on metals and metal oxides can dissociate methane (CH4) at room temperature, converting it directly to methanol (CH3OH). Liu et al. show that for one of these catalysts, an “inverted” CeOx-Cu2O oxide on Cu(111), water tunes the selectivity from forming CO and CO2 to forming surface CH3O groups, as revealed by ambient-pressure x-ray photoelectron spectroscopy. Theoretical modeling showed that adsorbed water blocks O2 dissociation and O2 instead oxidizes the reduced catalyst. Hydroxyl groups from water generate the CH3O species from dissociated CH4, and water then goes on to form and displace CH3OH to the gas phase.

Science, this issue p. 513

Abstract

Highly selective oxidation of methane to methanol has long been challenging in catalysis. Here, we reveal key steps for the pro­motion of this reaction by water when tuning the selectivity of a well-defined CeO2/Cu2O/Cu(111) catalyst from carbon monoxide and carbon dioxide to methanol under a reaction environment with methane, oxygen, and water. Ambient-pressure x-ray photoelectron spectroscopy showed that water added to methane and oxygen led to surface methoxy groups and accelerated methanol production. These results were consistent with density functional theory calculations and kinetic Monte Carlo simulations, which showed that water preferentially dissociates over the active cerium ions at the CeO2–Cu2O/Cu(111) interface. The adsorbed hydroxyl species blocked O-O bond cleavage that would dehydrogenate methoxy groups to carbon monoxide and carbon dioxide, and it directly converted this species to methanol, while oxygen reoxidized the reduced surface. Water adsorption also displaced the produced methanol into the gas phase.

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