Mechanistic Complexity of Methane Oxidation with H2O2 by Single-Site Fe/ZSM-5 Catalyst
KAUST DepartmentChemical Engineering Program
KAUST Catalysis Center (KCC)
Physical Science and Engineering (PSE) Division
Online Publication Date2018-07-18
Print Publication Date2018-09-07
Permanent link to this recordhttp://hdl.handle.net/10754/631522
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AbstractPeriodic 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.
CitationSzécsényi Á, Li G, Gascon J, Pidko EA (2018) Mechanistic Complexity of Methane Oxidation with H2O2 by Single-Site Fe/ZSM-5 Catalyst. ACS Catalysis 8: 7961–7972. Available: http://dx.doi.org/10.1021/acscatal.8b01672.
SponsorsWe thank Elena Khramenkova (ITMO University) for carrying out some of the calculations. The Dutch Science Foundation (NWO) is gratefully acknowledged for financial support through the VIDI personal grant MetMOFCat. G.L. acknowledges financial support from NWO for her personal VENI grant (016.Veni.172.034). E.A.P. acknowledges partial support from the Ministry of Education and Science of the Russian Federation (Project 11.1706.2017/4.6). SurfSARA and NWO (The Netherlands Organisation for Scientific Research) are acknowledged for providing access to supercomputer resources.
PublisherAmerican Chemical Society (ACS)