Effects of single and double active sites of Cu oxide clusters over the MFI zeolite for direct conversion of methane to methanol: DFT calculations

Nunthakitgoson, Watinee; Thivasasith, Anawat; Maihom, Thana; Wattanakit, Chularat

doi:10.1039/d0cp05435f

Cited by 6 publications

(3 citation statements)

References 62 publications

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“…Reaction (1) in Scheme depicts the formation of methanol effected by a single mono-μ-oxo dicopper(II) site, which has been described extensively in the literature and likely proceeds via the “radical rebound” mechanism. ,,,− Spectroscopic studies have provided extensive evidence that methanol formation over Cu zeolites involves the formation of methoxy ,,,,,,− and/or adsorbed methanol ,,,,,− , surface intermediates. The formation of methanol at mono-μ-oxo dicopper(II) sites is supported by our observation of a positive correlation between methanol yield and relative intensity of the Cu-MOR UV–vis spectra at 27 500 cm –1 (Figure ), a feature which we attribute to mono-μ-oxo dicopper(II) species.…”

Section: Resultsmentioning

confidence: 99%

“…We propose that two μ-1,2-peroxo dicopper(II) species are involved in the formation of CO 2 based on the correlation in Figure between the UV–vis peak at ∼22 000 cm –1 (assigned to the μ-1,2-peroxo dicopper(II) species) and the CO 2 yield, as well as the requirement of four oxygen atoms for CO 2 formation from methane. A recent quantum chemical study demonstrated the feasibility of a pair of μ-1,2-peroxo dicopper(II) sites activating methane in Cu-exchanged ZSM-5 …”

Section: Resultsmentioning

confidence: 99%

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Effect of the Co-cation on Cu Speciation in Cu-Exchanged Mordenite and ZSM-5 Catalysts for the Oxidation of Methane to Methanol

et al. 2021

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Copper-exchanged zeolites are promising catalysts for the direct methane-to-methanol reaction, but the design of improved catalysts has been hampered by limited understanding of the active site structures. Here, we show that the identity of the co-cation (H vs Na) in Cu-MOR and Cu-ZSM-5 catalysts significantly affects Cu speciation and the resulting reactivity of the catalysts in the cyclic methane-to-methanol reaction. The combination of reactivity results with spectroscopy and density functional theory (DFT) calculations suggests that the prevailing active site structure depends on the identity of the co-cation. The H-form of the catalysts contains a high concentration of mono-μ-oxo dicopper(II) species, which are selective for methanol formation, whereas the presence of Na appears to shift the Cu distribution toward species with greater oxygen content (attributed to μ-1,2-peroxo dicopper(II) species), which promote overoxidation of methane to carbon oxides. Results from DFT calculations indicate that Cu preferentially forms mono-μ-oxo dicopper(II) species in the 8MR side pockets of MOR, whereas the μ-1,2-peroxo dicopper(II) species is favored in the 12MR main channels of MOR for some Al pair configurations. Competition between Na and Cu for ion exchange sites in the 8MR side pockets results in displacement of some Cu into the 12MR main channels, thus affecting Cu speciation and catalyst selectivity. These findings suggest that the choice of co-cation can be used to control active site structure in transition-metal ion-exchanged zeolites.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Effect of the Co-cation on Cu Speciation in Cu-Exchanged Mordenite and ZSM-5 Catalysts for the Oxidation of Methane to Methanol

et al. 2021

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“…Active site heterogeneity is a key concept in heterogeneous catalysis and a primary challenge is identifying active sites and their distribution. − Active site heterogeneity can stem from differences in ligands and atomic environments, ,− including variations in the nuclearity of metal active sites. − Materials containing a distribution of metal active site nuclearities can show drastic differences in reactivity for reactions including ethylene hydrogenation, − D 2 exchange in CH 4 , and partial methane oxidation (PMO). ,− Copper-exchanged zeolites in particular have shown sensitivity to active site nuclearity for a number of reactions including the selective catalytic reduction (SCR) of NO x ,, catalytic or stepwise PMO, ,, and NO oxidation . Here, we develop condition-dependent computational models for Cu speciation in a wide variety of zeolite topologies and compositions.…”

Section: Introductionmentioning

confidence: 99%

Competition between Mononuclear and Binuclear Copper Sites across Different Zeolite Topologies

Wijerathne,

Sawyer,

Daya

et al. 2024

JACS Au

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A key challenge for metal-exchanged zeolites is the determination of metal cation speciation and nuclearity under synthesis and reaction conditions. Copper-exchanged zeolites, which are widely used in automotive emissions control and potential catalysts for partial methane oxidation, have in particular evidenced a wide variety of Cu structures that are observed to change with exposure conditions, zeolite composition, and topology. Here, we develop predictive models for Cu cation speciation and nuclearity in CHA, MOR, BEA, AFX, and FER zeolite topologies using interatomic potentials, quantum chemical calculations, and Monte Carlo simulations to interrogate this vast configurational and compositional space. Model predictions are used to rationalize experimentally observed differences between Cu-zeolites in a wide-body of literature, including nuclearity populations, structural variations, and methanol per Cu yields. Our results show that both topological features and commonly observed Al-siting biases in MOR zeolites increase the population of binuclear Cu sites, explaining the small population of mononuclear Cu sites observed in these materials relative to other zeolites such as CHA and BEA. Finally, we used a machine learning classification model to determine the preference to form mononuclear or binuclear Cu sites at different Al configurations in 200 zeolites in the international zeolite database. Model results reveal several zeolite topologies at extreme ends of the mononuclear vs binuclear spectrum, highlighting synthetic options for realization of zeolites with strong Cu nuclearity preferences.

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Advances in Catalytic Applications of Zeolite‐Supported Metal Catalysts

2021

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Effects of single and double active sites of Cu oxide clusters over the MFI zeolite for direct conversion of methane to methanol: DFT calculations

Abstract: In this work, we investigate the effect of various species of Cu oxide clusters including single and double active sites incorporated in the MFI zeolite framework for the direct conversion of methane to methanol.

Cited by 6 publications

References 62 publications

Effect of the Co-cation on Cu Speciation in Cu-Exchanged Mordenite and ZSM-5 Catalysts for the Oxidation of Methane to Methanol

Effect of the Co-cation on Cu Speciation in Cu-Exchanged Mordenite and ZSM-5 Catalysts for the Oxidation of Methane to Methanol

Competition between Mononuclear and Binuclear Copper Sites across Different Zeolite Topologies

Advances in Catalytic Applications of Zeolite‐Supported Metal Catalysts

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