Spectroscopic Definition of the Copper Active Sites in Mordenite: Selective Methane Oxidation
- 7 May 2015
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 137 (19), 6383-6392
- https://doi.org/10.1021/jacs.5b02817
Abstract
Two distinct [Cu-O-Cu](2+) sites with methane monooxygenase activity are identified in the zeolite Cu-MOR, emphasizing that this Cu-O-Cu active site geometry, having a ∠Cu-O-Cu ∼140°, is particularly formed and stabilized in zeolite topologies. Whereas in ZSM-5 a similar [Cu-O-Cu](2+) active site is located in the intersection of the two 10 membered rings, Cu-MOR provides two distinct local structures, situated in the 8 membered ring windows of the side pockets. Despite their structural similarity, as ascertained by electronic absorption and resonance Raman spectroscopy, the two Cu-O-Cu active sites in Cu-MOR clearly show different kinetic behaviors in selective methane oxidation. This difference in reactivity is too large to be ascribed to subtle differences in the ground states of the Cu-O-Cu sites, indicating the zeolite lattice tunes their reactivity through second-sphere effects. The MOR lattice is therefore functionally analogous to the active site pocket of a metalloenzyme, demonstrating that both the active site and its framework environment contribute to and direct reactivity in transition metal ion-zeolites.Keywords
Funding Information
- Division of Graduate Education (DGE-11474)
- Division of Chemistry (CHE-0948211)
- Achievement Rewards for College Scientists Foundation
- National Science Council Taiwan
- Fonds Wetenschappelijk Onderzoek (G.0596.11)
- KU Leuven
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