Mechanistic Complexity of Methane Oxidation with H2O2 by Single-Site Fe/ZSM-5 Catalyst

Ágnes Szécsényi, Guanna Li, Jorge Gascon, Evgeny A. Pidko

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31 Scopus citations

Abstract

Periodic density functional theory (DFT) calculations were carried out to investigate the mechanism of methane oxidation with HO over the defined Fe sites in Fe/ZSM-5 zeolite. The initial Fe site is modeled as a [(HO)-Fe(III)-(μO)-Fe(III)-(HO)] extraframework cluster deposited in the zeolite pore and charge-compensated by two anionic lattice sites. The activation of this cluster with HO gives rise to the formation of a variety of Fe(III)-oxo and Fe(IV)-oxo complexes potentially reactive toward methane dissociation. These sites are all able to promote the first C-H bond cleavage in methane by following three possible reaction mechanisms: namely, (a) heterolytic and (b) homolytic methane dissociation as well as (c) Fenton-type reaction involving free OH radicals as the catalytic species. The C-H activation step is followed by formation of MeOH and MeOOH and regeneration of the active site. The Fenton-type path is found to proceed with the lowest activation barrier. Although the barriers for the alternative heterolytic and homolytic pathways are found to be somewhat higher, they are still quite favorable and are expected to be feasible under reaction conditions, resulting ultimately in MeOH and MeOOH products. HO oxidant competes with CH substrate for the same sites. Since the oxidation of HO to O and two [H] is energetically more favorable than the C-H oxofunctionalization, the overall efficiency of the latter target process remains low.
Original languageEnglish (US)
Pages (from-to)7961-7972
Number of pages12
JournalACS Catalysis
Volume8
Issue number9
DOIs
StatePublished - Jul 18 2018

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