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Spectroscopic Definition of a Highly Reactive Site in Cu-CHA for Selective Methane Oxidation: Tuning a Mono-mu-Oxo Dicopper(II) Active Site for Reactivity

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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 that 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. Am. Chem. Soc, 2018, 140, 9236-9243) elucidates how zeolite lattice constraints can influence active site reactivity.
Tijdschrift: Journal of the American Chemical Society
ISSN: 0002-7863
Issue: 19
Volume: 143
Pagina's: 7531 - 7540
Jaar van publicatie:2021
BOF-keylabel:ja
IOF-keylabel:ja
BOF-publication weight:6
CSS-citation score:2
Auteurs:International
Authors from:Higher Education
Toegankelijkheid:Open