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DFT Exploration of Active Site Motifs in Methane Hydroxylation by Ni-ZSM-5 Zeolite


The O2-activated Ni-ZSM-5 zeolite is a promising catalyst for the selective oxidation (hydroxylation) of methane to methanol. While XPS and EXAFS analyses (Shan et al. Langmuir 2014, 30, 8558–8569) have proposed a bent mono(μ-oxo)dinickel [Ni2(μ-O)]2+ as the active site in Ni-ZSM-5 zeolite, calculations based on density functional theory (DFT) have shown that methane activation on such an active site motif leads to a very high activation barrier, which makes the reaction impossible to proceed at low temperatures (<150 C). Thus, explorations of other possible motifs of Ni active site in ZSM-5 zeolite are indispensable. In the present study, we employed DFT+U method to calculate methane hydroxylation on various motifs of Ni-oxo active species, including [NiO]2+, [Ni2(μ-O)]2+, [Ni2(μ-O)2]2+, and [Ni3(μ-O)3]2+, in the periodic structure of ZSM-5 zeolite. On the basis of agreement between the previously reported experimental and presently calculated activation energies, we suggest the [Ni2(μ-O)2]2+ and [Ni3(μ-O)3]2+ motifs as two possible candidates for the actual structure of active sites in Ni-ZSM-5. Different from [Cu2(μ-O)]2+-exchanged zeolites extensively studied in recent years, the [Ni2(μ-O)2]2+- and [Ni3(μ-O)3]2+-ZSM-5 are predicted to activate methane and desorb the formed methanol with low activation and desorption energies, respectively, providing a new direction for a low-temperature, high-selectivity, and isothermal-operation methane hydroxylation by metal-exchanged zeolites.

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Publication details

The article was received on 11 Jul 2018, accepted on 03 Oct 2018 and first published on 04 Oct 2018

Article type: Paper
DOI: 10.1039/C8CY01441H
Citation: Catal. Sci. Technol., 2018, Accepted Manuscript
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    DFT Exploration of Active Site Motifs in Methane Hydroxylation by Ni-ZSM-5 Zeolite

    M. H. Mahyuddin and K. Yoshizawa, Catal. Sci. Technol., 2018, Accepted Manuscript , DOI: 10.1039/C8CY01441H

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