Water-promoted interfacial pathways in methane oxidation to methanol on a CeO ₂ -Cu ₂ O catalyst

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.

Water enables mild oxidation of methane to methanol on gold single-atom catalysts

“…To further identify how P-OH ensembles participated in the reaction, we combined temperature-programmed surface reaction with mass spectroscopy (TPSR-MS) using an isotope label. Especially, we used 18 ( 32 O 2 ) to pre-treat the catalyst in the dark or under light irradiation. TPSR-MS measurements were operated in the dark under CH 4 when the temperature rose from 50 to 300°C.…”

“…26a, b). With regard to pre-treatment under light irradiation, four types of products were detected, including CH 3 18 OH, CH 3 16 OH, H 2 18 O, and H 2 16 O ( Supplementary Fig. 26c).…”

“…TPSR-MS measurements. In all, 100 mg of Au 1 /BP nanosheets were pre-treated by being immersed in 5 mL 18 O-labeled water (H 2 18 O) under O 2 ( 32 O 2 ) flow in…”

“…Mass spectral responses were collected from 50 to 300°C at 5°C min −1 . We detected the mass numbers (m/z) of 33 for CH 3 18 OH, 31 for CH 3 16 OH, 19 for H 2 18 O, 17 for H 2 16 O, 48 for C 18 DFT calculations. Spin-polarized DFT calculations were performed through Vienna ab initio simulation package 32,33 .…”

“…1). The dilemma lies in activation of methane and over-oxidation of methanol [16][17][18] . Methane takes a non-polar tetrahedral structure with high dissociation energy of C-H bond (439.3 kJ mol −1 ), rendering great difficulties for activation [19][20][21] .…”