Solid-state NMR for metal-containing zeolites: From active sites to reaction mechanism

Zhao, Xiaohui; Xu, Jun

doi:10.1007/s11705-019-1885-1

Cited by 22 publications

(10 citation statements)

References 146 publications

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“…Tin-containing zeolites are, actually, Lewis acids in which the strength and arrangement of acid sites can be controlled within a wide range [93]. This has enabled researchers to extensively use [Sn]BEA tin-silicate in a variety of reactions, such as aldol and aldol-crotonic condensation [94], Baeyer-Villiger oxidation of carbonyl compounds [95], and various sugar decompositions [96].…”

Section: Synthesis Of Isomorphously Substituted Zeolitesmentioning

confidence: 99%

Interzeolite Transformations as a Method for Zeolite Catalyst Synthesis

2021

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This review presents the achievements of the last 10-15 years in interzeolite transformations as a method for synthesizing high-performance zeolite catalysts. The main regularities and mechanisms of interzeolite transformations are analyzed. The paper describes a variety of examples where interzeolite transformations ensured a successful synthesis of zeolite structures which either could not be prepared from amorphous sources or required the use of expensive templates. The advantages of zeolite catalysts synthesized by interzeolite transformation, compared to those obtained from amorphous sources, are demonstrated.

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Section: Synthesis Of Isomorphously Substituted Zeolitesmentioning

confidence: 99%

Interzeolite Transformations as a Method for Zeolite Catalyst Synthesis

2021

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“…Spectroscopic techniques like X-ray diffraction (XRD), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), infrared (IR), and resonant Raman have been extensively used to study copper-exchanged zeolites. Additionally, UV–vis/NIR spectroscopy has been used to study the evolution of the copper-oxo active sites during their activation and reaction with methane. − By activation, we mean high-temperature processes for forming the copper-oxo active sites from Cu 2+ ions that are typically introduced into the zeolite by ion-exchange methods.…”

Section: Introductionmentioning

confidence: 99%

Copper-Oxo Active Sites for Methane C–H Activation in Zeolites: Molecular Understanding of Impact of Methane Hydroxylation on UV–Vis Spectra

2021

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Here, we analyze changes in the optical spectra of activated copper-exchanged zeolites during methane activation with the Tamm–Dancoff time-dependent density functional theory, TDA-DFT, while using the ωB2PLYP functional. Two active sites, [Cu2O]2+ and [Cu3O3]2+, were studied. For [Cu2O]+, the 22 700 cm–1 peak is associated with μ-oxo 2p → Cu 3d/4s charge transfer. Of the [Cu2O]2+ methane C–H activation intermediates that we examined, only [Cu–O(H)(H)–Cu] and [Cu–O(H)(CH3)–Cu] have spectra that match experimental observations. After methane activation, the μ-oxo 2p orbitals lose two electrons and become hybridized with methanol C 2p orbitals and/or H 1s orbitals. The frontier unoccupied orbitals become more Cu 4s/4p Rydberg-like, reducing overlap with occupied orbitals. These effects cause the disappearance of the 22 700 cm–1 peak. For [Cu3O3]2+, the exact structures of the species formed after methane activation are unknown. Thus, we considered eight possible structures. Several of these provide a significant decrease in intensity near 23 000–38 000 cm–1, as seen experimentally. Notably, these species involve either rebound of the separated methyl to a μ-oxo atom or its remote stabilization at a Brønsted acid site in exchange for the acidic proton. These spectral changes are caused by the same mechanism seen in [Cu2O]2+ and are likely responsible for the observed reduced intensities near 23 000–38 000 cm–1. Thus, TDA-DFT calculations with ωB2PLYP provide a molecular-level understanding of the evolution of copper-oxo active sites during methane-to-methanol conversion.

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“…The absorbance at 652 nm was monitored for 200 s for the oxidized TMB, and the rate constants were obtained by linear plotting of the maximal absorbance versus time. 32 In this experiment, the concentration of Au−PtNCs-GMP was fixed at 20 μg mL −1 ; the increasing rate of intensity at the initial 60 s is used as the rate constant for the catalysis. In parallel, the catalytic assay of Au−PtNCs-GMP was also conducted under anaerobic conditions.…”

Section: Methodsmentioning

confidence: 99%

“…For that, different amounts of Au–PtNCs-GMP (0–240 μg mL –1 ) were added to the acetate buffer (0.1 M × 1.0 mL, pH = 4.0) containing 0.5 mM TMB. The absorbance at 652 nm was monitored for 200 s for the oxidized TMB, and the rate constants were obtained by linear plotting of the maximal absorbance versus time . In this experiment, the concentration of Au–PtNCs-GMP was fixed at 20 μg mL –1 ; the increasing rate of intensity at the initial 60 s is used as the rate constant for the catalysis.…”

Section: Methodsmentioning

confidence: 99%

Gold–Platinum Bimetallic Nanoclusters for Oxidase-like Catalysis

Zhang

Gao

et al. 2020

ACS Appl. Nano Mater.

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Guanosine monophosphate (GMP)-protected bimetallic nanoclusters of gold and platinum, Au–PtNCs-GMP, were prepared through an improved hydrothermal method under basic conditions, which show high catalytic activity for the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) under ambient conditions. Further systematic optimization of synthesis provides the best catalyst by feeding the materials 0.8 mM HAuCl4, 0.2 mM H2PtCl6, 4.0 mM NaOH, and 3.0 mM GMP, which reacted at 120 °C for 30 min, which show an initial maximum velocity (V max) of 253.8 × 10–8 M s–1 for TMB as the substrate. Such a value is at the top among the oxidase mimetics reported, which is essentially attributed to the synergistic effect between two metals in the small nanocluster. Moreover, the achieved Au–PtNCs-GMP show a short reaction time of 60 s for the oxidation of substrates, which is much faster than the previously reported ones. The in-depth mechanistic studies by 1H and 31P NMR spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy of the optimized Au–PtNCs-GMP reveal them to be of ultrasmall size with a unique ligand structure, particularly the synergistic effect between the two metals endow the product with a high catalytic performance. Therefore, the present study not only provides a novel bimetallic nanocluster as a good catalyst with highly efficient oxidase mimetics but also opens a way for the development of other oxidase mimetics.

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Solid-state NMR for metal-containing zeolites: From active sites to reaction mechanism

Cited by 22 publications

References 146 publications

Interzeolite Transformations as a Method for Zeolite Catalyst Synthesis

Interzeolite Transformations as a Method for Zeolite Catalyst Synthesis

Copper-Oxo Active Sites for Methane C–H Activation in Zeolites: Molecular Understanding of Impact of Methane Hydroxylation on UV–Vis Spectra

Gold–Platinum Bimetallic Nanoclusters for Oxidase-like Catalysis

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