Advances in the synthesis and catalysis of solid and hollow zeolite-encapsulated metal catalysts

Dai, Chengyi; Zhang, Anfeng; Chen, Song; Guo, Xinwen

doi:10.1016/bs.acat.2018.10.002

Cited by 18 publications

(7 citation statements)

References 102 publications

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“…The confined environment of zeolites could provide the spatial restriction for the small metal entities, which can improve the metal stability against sintering and leaching of active metal species during catalysis. 1,2 Additionally, such a successful encapsulation can afford site proximity between metal and acid sites, which could improve catalytic performance owing to providing synergistic effects between the different functional sites. 3−12 The impregnation and ion-exchange methods are traditional approaches widely employed for achieving metal species highly dispersed into zeolite cavities.…”

Section: Introductionmentioning

confidence: 99%

“…The encapsulation of metal clusters within zeolite micropores or cavities is an attractive and efficient strategy for the preparation of ultrafine metal nanoparticles. The confined environment of zeolites could provide the spatial restriction for the small metal entities, which can improve the metal stability against sintering and leaching of active metal species during catalysis. , Additionally, such a successful encapsulation can afford site proximity between metal and acid sites, which could improve catalytic performance owing to providing synergistic effects between the different functional sites. − The impregnation and ion-exchange methods are traditional approaches widely employed for achieving metal species highly dispersed into zeolite cavities. − However, both methods have their own limits and are either not suitable or effective for the metal encapsulation into small-pore zeolites (8-member ring zeolite, e g., LTA zeolite, 0.42 nm in aperture size) and medium-pore zeolites (10-member ring zeolite, e g., MFI zeolite, 0.55 nm in aperture size) . Notably, previous studies have shown some successful examples of metal encapsulation into MFI zeolites via different approaches. − However, most MFI zeolites in those cases were related with purely siliceous MFI zeolites (silicate-1) and TS-1.…”

Section: Introductionmentioning

confidence: 99%

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Enhanced Catalytic Performance through In Situ Encapsulation of Ultrafine Ru Clusters within a High-Aluminum Zeolite

et al. 2022

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Zeolite-encapsulated metal clusters have been shown to be an effective bifunctional catalyst for tandem catalysis. Nevertheless, the efficient encapsulation of nanometric metal species into a high-aluminum ZSM-5 zeolite still poses a significant challenge. In this contribution, we have prepared well-dispersed and ultra-small Ru clusters encapsulated within a high-aluminum ZSM-5 zeolite (with a Si/Al ratio of ∼30–40) via an in situ two-stage hydrothermal synthesis method. Small Ru clusters with an average size of ∼1 nm have been identified by scanning transmission electron microscopy and hydrogen chemisorption. Shape-selective hydrogenation experiments with different probe molecules reveal a predominant encapsulation (∼90%) of metal clusters within the MFI zeolite cavities, which significantly enhances thermal stability of metal clusters against sintering. 27Al magic angle spinning nuclear magnetic resonance and Brønsted acid site (BAS) titration experiments show the successful incorporation of aluminum species (>99%) into the zeolite framework and build-up of intimacy between the Ru clusters and BASs at a sub-nanometric level. The resulting Ru@H-ZSM-5 shows an enhanced activity and stability for the crucial hydrodeoxygenation (HDO) of phenol to cyclohexane, in biomass valorization. This synthesis strategy could be of great help for the rational design and development of zeolitic bifunctional catalysts and could be extended to other crystalline porous materials.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Enhanced Catalytic Performance through In Situ Encapsulation of Ultrafine Ru Clusters within a High-Aluminum Zeolite

et al. 2022

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“…Alternatively, host–guest systems have provided a more modular approach for engineering outer-sphere interactions, and host–guest systems that do not feature covalent interactions between the host and the guest provide more degrees of freedom for the guest catalyst to interact with the host. Promising host–guest systems have been developed using supramolecular cages , and zeolites − that have shown enhanced activity and selectivity for a variety of reactions catalyzed by transition metal complex-based catalysts. However, systematic engineering of the hosts for further improvement in performance is often synthetically demanding: modifying supramolecular cages requires lengthy bottom-up synthesis of new organic ligands, and modification of zeolites is often difficult due to the harsh conditions required to modify their exceptionally stable structures .…”

Section: Introductionmentioning

confidence: 99%

Engineering Second Sphere Interactions in a Host–Guest Multicomponent Catalyst System for the Hydrogenation of Carbon Dioxide to Methanol

Rayder

Bensalah

et al. 2021

J. Am. Chem. Soc.

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Many enzymes utilize interactions extending beyond the primary coordination sphere to enhance catalyst activity and/or selectivity. Such interactions could improve the efficacy of synthetic catalyst systems, but the supramolecular assemblies employed by biology to incorporate second sphere interactions are challenging to replicate in synthetic catalysts. Herein, a strategy is reported for efficiently manipulating outer-sphere influence on catalyst reactivity by modulating host–guest interactions between a noncovalently encapsulated transition-metal-based catalyst guest and a metal–organic framework (MOF) host. This composite consists of a ruthenium PNP pincer complex encapsulated in the MOF UiO-66 that is used in tandem with the zirconium oxide nodes of UiO-66 and a ruthenium PNN pincer complex to hydrogenate carbon dioxide to methanol. Due to the method used to incorporate the complexes in UiO-66, structure–activity relationships could be efficiently determined using a variety of functionalized UiO-66-X hosts. These investigations uncovered the beneficial effects of the ammonium functional group (i.e., UiO-66-NH3 +). Mechanistic experiments revealed that the ammonium functionality improved efficiency in the hydrogenation of carbon dioxide to formic acid, the first step in the cascade. Isotope effects and structure–activity relationships suggested that the primary role of the ammonium functionality is to serve as a general Brønsted acid. Importantly, the cooperative influence from the host was effective only with the functional group in close proximity to the encapsulated catalyst. Reactions carried out in the presence of molecular sieves to remove water highlighted the beneficial effects of the ammonium functional group in UiO-66-NH3 + and resulted in a 4-fold increase in activity. As a result of the modular nature of the catalyst system, the highest reported turnover number (TON) (19 000) and turnover frequency (TOF) (9100 h–1) for the hydrogenation of carbon dioxide to methanol are obtained. Moreover, the reaction was readily recyclable, leading to a cumulative TON of 100 000 after 10 reaction cycles.

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“…80 In recent work, colleagues have incorporated Pt particles in hollow zeolite crystals for similar purposes. 110 It reveals the potential of core-shell alumina spheres to serve as a model catalyst support. the similarity in the morphology and size of the zeolite and the alumina particles and the convenience of mixing the powders.…”

Section: X-ray Diffractionmentioning

confidence: 99%

Spherical core–shell alumina support particles for model platinum catalysts

et al. 2021

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Advances in the synthesis and catalysis of solid and hollow zeolite-encapsulated metal catalysts

Cited by 18 publications

References 102 publications

Enhanced Catalytic Performance through In Situ Encapsulation of Ultrafine Ru Clusters within a High-Aluminum Zeolite

Enhanced Catalytic Performance through In Situ Encapsulation of Ultrafine Ru Clusters within a High-Aluminum Zeolite

Engineering Second Sphere Interactions in a Host–Guest Multicomponent Catalyst System for the Hydrogenation of Carbon Dioxide to Methanol

Spherical core–shell alumina support particles for model platinum catalysts

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