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Identifying Cu-exchanged zeolites able to activate C-H bonds and selectively convert methane to methanol is a challenge in the field of biomimetic heterogeneous catalysis. Recent experiments point to the importance of trinuclear [Cu3(μ-O)3]2+ complexes inside the micropores of mordenite (MOR) zeolite for selective oxo-functionalization of methane. The electronic structures of these species, namely, the oxidation state of Cu ions and the reactive character of the oxygen centers, are not yet fully understood. In this study, we performed a detailed analysis of the electronic structure of the [Cu3(μ-O)3]2+ site using multiconfigurational wave-function-based methods and density functional theory. The calculations reveal that all Cu sites in the cluster are predominantly present in the Cu(II) formal oxidation state with a minor contribution from Cu(III), whereas two out of three oxygen anions possess a radical character. These electronic properties, along with the high accessibility of the out-of-plane oxygen center, make this oxygen the preferred site for the homolytic C-H activation of methane by [Cu3(μ-O)3]2+. These new insights aid in the construction of a theoretical framework for the design of novel catalysts for oxyfunctionalization of natural gas and suggest further spectroscopic examination.
Bibliographical noteFunding Information:
K.D.V. would like to acknowledge the University of Tennessee for financial support of this work (start-up grant). G.L. acknowledges financial support from NWO for her personal VENI grant (no. 016.Veni.172.034) and NWO-SurfSARA for providing access to supercomputer resources. E.J.M.H. and E.A.P. acknowledge MCEC, a Gravitation programme of The Netherlands Organization for Scientific Research (NWO) funded by the Ministry of Education, Culture and Science of the government of The Netherlands. E.A.P thanks the Ministry of Education and Science of Russian Federation (GosZadanie no. 11.1706.2017PP). K.D.V. and L.G. thank the Inorganome-tallic Catalyst Design Center, an EFRC funded by the DOE, Office of Basic Energy Sciences (DE-SC0012702). The authors acknowledge the Minnesota Supercomputing Institute (MSI) at the University of Minnesota and the Newton High-Performance Computing program at the University of Tennessee for providing resources that contributed to the research results reported within this paper.
© 2017 American Chemical Society.