Quantum mechanics

Methane

Catalysis

Reactivity (psychology)

Biology

Yield (engineering)

Metallurgy

Materials science

Extended X-ray absorption fine structure

Methanol

Inorganic chemistry

Vanadium

Evolutionary biology

Anaerobic oxidation of methane

Alternative medicine

Redox

X-ray absorption spectroscopy

Physics

Organic chemistry

Genetic algorithm

Mordenite

Oxygen

Zeolite

Environmental chemistry

Medicine

Chemistry

Absorption spectroscopy

Pathology

ACS Catalysis

The proton form of Cu-exchanged mordenite (Cu-H-MOR) was prepared via ion-exchange, and the nature of the active Cu species in the cyclic oxidation of CH4 to CH3OH was investigated by high-pressure reactivity testing, X-ray absorption spectroscopy (XAS), and H2 temperature-programmed reduction (TPR). Increasing the CH4 pressure from 1 to 35 bar and the reaction time from 4 to 20 h increased the product yield from 0.30 to 0.42 mol (mol Cu)−1, suggesting that at lower pressures and shorter reaction times, the CH4 activation reaction is not complete and the active site for CH3OH formation likely contains fewer than three Cu atoms. Linear combination fitting of the Cu K-edge X-ray absorption near edge spectra showed that 83% of the Cu in freshly prepared Cu-H-MOR can be autoreduced in He at 723 K. Analysis of the extended X-ray absorption fine structure of Cu-H-MOR after activation in O2 at 723 K resulted in an oxygen coordination number of 2.9. The product yield normalized by the redox-active Cu fraction was 0.50. All of these findings are consistent with a dicopper active site. The same fraction of nonreducible Cu was observed by autoreduction in He and TPR in H2, suggesting that redox-inert Cu is inactive toward CH4 oxidation.

Insights into the Speciation of Cu in the Cu-H-Mordenite Catalyst for the Oxidation of Methane to Methanol