Journal ArticleDOI
DFT Analysis of Methane C−H Activation and Over-Oxidation by [Cu2O]2+ and [Cu2O2]2+ Sites in Zeolite Mordenite: Intra- versus Inter-site Over-Oxidation
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In this paper, the role of dicopper [Cu3 O3 ]2+ sites in methane-to-methanol conversion was investigated using density functional theory (DFT) computations.Abstract:
Methane over-oxidation by copper-exchanged zeolites prevents realization of high-yield catalytic conversion. However, there has been little description of the mechanism for methane over-oxidation at the copper active sites of these zeolites. Using density functional theory (DFT) computations, we reported that tricopper [Cu3 O3 ]2+ active sites can over-oxidize methane. However, the role of [Cu3 O3 ]2+ sites in methane-to-methanol conversion remains under debate. Here, we examine methane over-oxidation by dicopper [Cu2 O]2+ and [Cu2 O2 ]2+ sites using DFT in zeolite mordenite (MOR). For [Cu2 O2 ]2+ , we considered the μ-(η2 :η2 ) peroxo-, and bis(μ-oxo) motifs. These sites were considered in the eight-membered (8MR) ring of MOR. μ-(η2 :η2 ) peroxo sites are unstable relative to the bis(μ-oxo) motif with a small interconversion barrier. Unlike [Cu2 O]2+ which is active for methane C-H activation, [Cu2 O2 ]2+ has a very large methane C-H activation barrier in the 8MR. Stabilization of methanol and methyl at unreacted dicopper sites however leads to over-oxidation via sequential hydrogen atom abstraction steps. For methanol, these are initiated by abstraction of the CH3 group, followed by OH and can proceed near 200 °C. Thus, for [Cu2 O]2+ and [Cu2 O2 ]2+ species, over-oxidation is an inter-site process. We discuss the implications of these findings for methanol selectivity, especially in comparison to the intra-site process for [Cu3 O3 ]2+ sites and the role of Bronsted acid sites.read more
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Journal ArticleDOI
Structure of Selective and Nonselective Dicopper (II) Sites in CuMFI for Methane Oxidation to Methanol
TL;DR: In this paper , the effect of the Si/Al ratio on the selectivity of the active dicopper sites in CuMFI has been investigated, and it has been shown that a higher Si-Al ratio leads to the formation of mono-μ-oxo dicoppers with Cu-Cu separation of 2.9 Å and a UV/vis absorption band at 27 200 cm-1 capable of selective oxidation of methane to methanol.
References
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Journal ArticleDOI
Metal dimer sites in ZSM-5 zeolite for methane-to-methanol conversion from first-principles kinetic modelling: is the [Cu–O–Cu]2+ motif relevant for Ni, Co, Fe, Ag, and Au?
Adam Arvidsson,Vladimir P. Zhdanov,Vladimir P. Zhdanov,Per-Anders Carlsson,Henrik Grönbeck,Anders Hellman +5 more
TL;DR: In this article, the authors used first-principles microkinetic modeling to analyse the methane-to-methanol reaction on the [Cu-O-Cu]2+ motif, for Cu and other metals.
Journal ArticleDOI
On How Copper Mordenite Properties Govern the Framework Stability and Activity in the Methane-to-Methanol Conversion
Michael Dyballa,Michael Dyballa,Dimitrios K. Pappas,Karoline Kvande,Elisa Borfecchia,Bjørnar Arstad,Pablo Beato,Unni Olsbye,Stian Svelle +8 more
TL;DR: In this paper, the authors investigated the activity of copper mordenites in the methane-to-methanol conversion and the material de-and realumination and found that the optimum stoichiometry between silicon, aluminum, and copper leads to a methanol productivity of up to 169 μmol/g.
Journal ArticleDOI
Formation of Active Cu-oxo Clusters for Methane Oxidation in Cu-Exchanged Mordenite
Takaaki Ikuno,Sebastian Grundner,Andreas Jentys,Guanna Li,Evgeny A. Pidko,John L. Fulton,Maricruz Sanchez-Sanchez,Johannes A. Lercher,Johannes A. Lercher +8 more
TL;DR: In this article, the selective oxidation of methane to methanol at moderate temperatures has been studied with the use of the Cu-exchanged mordenite (MOR) system.
Journal ArticleDOI
Pathways of Methane Transformation over Copper‐Exchanged Mordenite as Revealed by In Situ NMR and IR Spectroscopy
TL;DR: Observations are important for understanding the methane partial oxidation mechanism and for the rational design of the active materials for this reaction.
Journal ArticleDOI
Zeolite Surface Methoxy Groups as Key Intermediates in the Stepwise Conversion of Methane to Methanol
Michael Dyballa,Michael Dyballa,Knut Thorshaug,Dimitrios K. Pappas,Elisa Borfecchia,Karoline Kvande,Silvia Bordiga,Gloria Berlier,Andrea Lazzarini,Unni Olsbye,Pablo Beato,Stian Svelle,Bjørnar Arstad +12 more
TL;DR: This article showed that surface methoxy groups (SMGs) located at zeolite Brønsted sites are the key intermediates in the Methane-to-Methanol (MTM) conversion over copper mordenite zeolites.