Bridging adsorption analytics and catalytic kinetics for metal-exchanged zeolites

Xie, Pengfei; Pu, Tiancheng; Aranovich, G. L.; Guo, Jiawei; Donohue, Marc D.; Kulkarni, Ambarish; Wang, Chao

doi:10.1038/s41929-020-00555-0

Cited by 46 publications

(42 citation statements)

References 88 publications

(142 reference statements)

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“…The channel system of MFI zeolite is composed of the interconnected straight and sinusoidal 10-membered ring channels, which intersect to form larger void spaces (Figure f). The arrangement of aluminum sites could either influence the proceeding of reactions due to the channel space limitation , or the configurations of metal sites due to distinct proximities of Al sites, − while this is seldom studied in the MTA chemistry.…”

Section: Discussionmentioning

confidence: 99%

Aromatics Production via Methanol-Mediated Transformation Routes

et al. 2021

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The methanol-to-aromatics (MTA) process is regarded as a promising route to produce aromatic commodities through non-petroleum carbon resources, such as biomass, waste, coal, natural gas, and CO2. In contrast with the industrially implemented methanol-to-olefin (MTO) process, most MTA studies are still in the laboratory-scale stage. Recently, a few demonstration plants of MTA have been successfully launched, indicating the importance and the gradual industrial maturity of this technology. However, there are still many fundamental questions and technological challenges that must be addressed. In this Review, we summarize the recent advances in mechanistic understanding on the reaction and catalyst deactivation during MTA, elaborate the available strategies to improve the catalytic performance, and correlate MTA studies with other important catalytic aromatization processes. With this knowledge in hand, we share our views on future research directions in this field.

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Section: Discussionmentioning

confidence: 99%

Aromatics Production via Methanol-Mediated Transformation Routes

et al. 2021

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“…38−40 Combining the information from phase diagrams with knowledge of the anchoring point distribution enables derivation of the site distribution present in the zeolite material under specific experimental conditions. 37,41 In the conversion of methane to methanol using Cu-exchanged zeolites, attempts so far have aimed at describing the relative stability of different Cu sites in mordenite, 42 ZSM-5, 19 or SSZ-13. 29,43 These studies, however, considered only few possible active sites, which does not describe the complex distribution of sites expected to be present in such a zeolite system.…”

Section: ■ Introductionmentioning

confidence: 99%

“…First-principles-based modeling can support and extend these experimental assignments by systematically considering an extensive set of possible active site structures and by calculating their relative thermodynamic stability. , This information can then be summarized in phase diagrams, which reveal the most stable phase under various experimental conditions. − Combining the information from phase diagrams with knowledge of the anchoring point distribution enables derivation of the site distribution present in the zeolite material under specific experimental conditions. , In the conversion of methane to methanol using Cu-exchanged zeolites, attempts so far have aimed at describing the relative stability of different Cu sites in mordenite, ZSM-5, or SSZ-13. , These studies, however, considered only few possible active sites, which does not describe the complex distribution of sites expected to be present in such a zeolite system.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics Perspective on the Stepwise Conversion of Methane to Methanol over Cu-Exchanged SSZ-13

2021

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Transition-metal exchanged zeolites are known to convert methane to methanol with high selectivity, in a stepwise process, involving exposure to oxidants, followed by exposure to methane, and finally by exposure to water vapor. However, a comprehensive theoretical study on the nature of the possible active sites and their respective changes during this stepwise process is still lacking. Here, we use a combination of density functional theory calculations in its generalized-gradient approximation (DFT-GGA) and post-DFT methods to identify the thermodynamically preferred sites in Cu-exchanged zeolite SSZ-13 during the stepwise conversion of methane to methanol. We develop a thermodynamic model for an extensive set of possible active sites, that is, Cu monomers, dimers, and trimers, which are anchored in different ring structures and supported by a series of different local Al distributions. Subsequently, phase diagrams are constructed and used to identify thermodynamically favored sites at each step during the stepwise conversion of methane to methanol. We find that during exposure to O2, hydroxylated dimersCu2O2H2 and, depending on the local Al configuration, Cu2OHare preferred. Upon exposure to methane, site-bound methanol molecules are formed. With the subsequent increase in water vapor pressure, a thermodynamic preference for monoatomic Cu and the release of methanol are observed. Furthermore, we compare our predicted results to experimental measurements published in the literature and find close agreement in terms of Cu coordination number and bond distances for some of the sites considered. We expect that the insights obtained here can be used to improve our understanding of the reaction mechanism and to optimize the stepwise conversion of methane to methanol.

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“…The main NO absorption band on Cu-FER samples consists of two main components at 1911 and 1901 cm −1 . These bands were previously assigned to NO adsorbed on Cu(II)-oxo 36,37 and monomeric Cu(II) 21,38,39 species. The weak band at 1960 cm −1 has been attributed by some authors to oligomeric Cuoxo clusters active in CH 4 oxidation, 21,38,39 while in other reports it was attributed to NO adsorbed on bare Cu(II) cations.…”

Section: ■ Results and Discussionmentioning

confidence: 79%

Speciation of Cu-Oxo Clusters in Ferrierite for Selective Oxidation of Methane to Methanol

et al. 2022

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Cu-oxo nanoclusters in Cu-exchanged zeolites oxidize methane to methanol via a three-step process. Cuexchanged ferrierite shows high reactivity to this selective oxidation at both ambient and elevated methane pressures. The active sites are dimeric Cu clusters located in the eight-membered channels of ferrierite, containing two oxygen atoms with different reactivities. Combining in situ ultraviolet−visible (UV−vis), X-ray absorption spectroscopy (XAS), and Raman spectroscopy, it is shown that the active site is a [Cu 2 O 2 ] 2+ cluster stabilized at pairs of negatively charged aluminum oxygen tetrahedra. This cluster is able to oxidize up to two methane molecules at elevated methane chemical potential.

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Bridging adsorption analytics and catalytic kinetics for metal-exchanged zeolites

Cited by 46 publications

References 88 publications

Aromatics Production via Methanol-Mediated Transformation Routes

Aromatics Production via Methanol-Mediated Transformation Routes

Thermodynamics Perspective on the Stepwise Conversion of Methane to Methanol over Cu-Exchanged SSZ-13

Speciation of Cu-Oxo Clusters in Ferrierite for Selective Oxidation of Methane to Methanol

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