Using UV-Vis and resonance Raman spectroscopy, we identify a [Cu2O] 2+ active site in O2 and N2O activated Cu-CHA that reacts with methane to form methanol at low temperature. The Cu-O-Cu angle (120°) is smaller than for the [Cu2O] 2+ core on Cu-MFI (140°) and its coordination geometry to the zeolite lattice is different. Site-selective kinetics obtained by operando UV-Vis show that the [Cu2O] 2+ core on Cu-CHA is more reactive than the [Cu2O] 2+ site in Cu-MFI. From DFT calculations we find that the increased reactivity of Cu-CHA is a direct reflection of the strong [Cu2OH] 2+ bond formed along the H-atom abstraction reaction coordinate. A systematic evaluation of these [Cu2O] 2+ cores reveals that the higher O-H bond strength in Cu-CHA is due to the relative orientation of the two planes of the coordinating bidentate O-Al-O T-sites that connect the [Cu2O] 2+ core to the zeolite lattice. This work along with our earlier study (J.

The direct conversion of methane to methanol would have a wide reaching environmental and industrial impact. Copper-containing zeolites can perform this reaction at low temperatures and pressures at a previously defined O2-activated [Cu2O]2+ site. However, after autoreduction of the copper-containing zeolite mordenite and removal of the [Cu2O]2+ active site, the zeolite is still methane reactive. In this study, we use diffuse reflectance UV–vis spectroscopy, magnetic circular dichroism, resonance Raman spectroscopy, electron paramagnetic resonance, and X-ray absorption spectroscopy to unambiguously define a mononuclear [CuOH]+ as the CH4 reactive active site of the autoreduced zeolite. The rigorous identification of a mononuclear active site allows a reactivity comparison to the previously defined [Cu2O]2+ active site. We perform kinetic experiments to compare the reactivity of the [CuOH]+ and [Cu2O]2+ sites and find that the binuclear site is significantly more reactive. From the analysis of density functional theory calculations, we elucidate that this increased reactivity is a direct result of stabilization of the [Cu2OH]2+ H-atom abstraction product by electron delocalization over the two Cu cations via the bridging ligand. This significant increase in reactivity from electron delocalization over a binuclear active site provides new insights for the design of highly reactive oxidative catalysts.

Atmospheric methane removal (e.g. in situ methane oxidation to carbon dioxide) may be needed to offset continued methane release and limit the global warming contribution of this potent greenhouse gas. Because mitigating most anthropogenic emissions of methane is uncertain this century, and sudden methane releases from the Arctic or elsewhere cannot be excluded, technologies for methane removal or oxidation may be required. Carbon dioxide removal has an increasingly well-established research agenda and technological foundation. No similar framework exists for methane removal. We believe that a research agenda for negative methane emissions—‘removal' or atmospheric methane oxidation—is needed. We outline some considerations for such an agenda here, including a proposed Methane Removal Model Intercomparison Project (MR-MIP). This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 1)'.

Introducing heterovalent cations at the octahedral sites of halide perovskites can substantially change their optoelectronic properties. Yet, in most cases, only small amounts of such metals can be incorporated as...