Coordinatively unsaturated sites in zeolite matrix: Construction and catalysis

Li, Weijie; Sun, Lanan; Xie, Linjun; Deng, Xin; Guan, Naijia; Li, Landong

doi:10.1016/s1872-2067(19)63381-4

Cited by 32 publications

(21 citation statements)

References 206 publications

(236 reference statements)

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“…In most cases, extraframework cations in different states coexist in zeolites prepared by ion exchange, and they also undergo dynamic changes under various treating conditions. 17 The main reason is the weak electrostatic interaction between the extraframework cations and the negatively charged zeolite framework and the mobility of cations thereof. The complexity and mobility of extraframework cations can be tactfully utilized in certain catalytic reactions but are generally not good for the identification of active sites and the establishment of the structure−activity relationship in catalysis.…”

Section: Extraframework Cation Sitesmentioning

confidence: 99%

“…The extraframework cations are confined in the zeolite structure due to electrostatic attraction, which is affected by the spatial constraint. In most cases, extraframework cations in different states coexist in zeolites prepared by ion exchange, and they also undergo dynamic changes under various treating conditions . The main reason is the weak electrostatic interaction between the extraframework cations and the negatively charged zeolite framework and the mobility of cations thereof.…”

Section: Construction Of Zeolite Catalysts Via Confinementmentioning

confidence: 99%

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Confinement in a Zeolite and Zeolite Catalysis

et al. 2021

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Conspectus Zeolites, accompanied by their initial discovery as natural mines and the subsequent large-scale commercial production, have played indispensable roles in various fields such as petroleum refining and the chemical industry. Understanding the characteristics of zeolites, in contrast to their counterparts with similar chemical compositions and the origin thereof, is always a hot and challenging topic. Zeolites are known as intrinsic confined systems with ordered channels on the molecular scale, and structural confinement has been proposed to explain the unique chemical behaviors of zeolites. Generally, the channels of zeolites can regulate the diffusion of molecules, leading to a visible difference in molecular transportation and the ultimate shape-selective catalysis. On the other hand, the local electric field within the zeolite channels or cages can act on the guest molecules and change their energy levels. Confinement can be simply interpreted from both spatial and electronic issues; however, the nature of zeolite confinement is ambiguous and needs to be clarified. In this Account, we make a concise summary and analysis of the topics of confinement in a zeolite and zeolite catalysis from two specific views of spatial constraint and a local electric field to answer two basic questions of why zeolites and what else can we do with zeolites. First, it is shown how to construct functional sites including Brønsted acid sites, Lewis acid sites, extraframework cation sites, and entrapped metal or oxide aggregates in zeolites via confinement and how to understand the specific role of confinement in their reactivity. Second, the multiple impacts of confinement in zeolite-catalyzed reactions are discussed, which rationally lead to several unique processes, namely, Brønsted acid catalysis confined in zeolites, Lewis acid catalysis confined in zeolites, catalysis by zeolite-confined coordinatively unsaturated cation sites, and a cascade reaction within the confined space of zeolites. Overall, confinement effects do exist in zeolite systems and have already played extremely important roles in adsorption and catalysis. Although confinement might exist in many systems, the confinement by zeolites is more straightforward thanks to their well-ordered and rigid structure, deriving unique chemical behaviors within the confined space of zeolites. A zeolite is a fantastic scaffold for constructing isolated sites spatially and electrostatically confined in its matrix. Furthermore, zeolites containing well-defined transition-metal sites can be treated as inorganometallic complexes (i.e., a zeolite framework as the ligand of transition-metal ions) and can catalyze reactions resembling organometallic complexes or even metalloenzymes. The local electric field within the confined space of zeolites is strong enough to induce or assist the activation of small molecules, following the working fashion of frustrated Lewis pairs. The tactful utilization of structural confinement, both spatially and electronically, becomes the key to ...

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Section: Extraframework Cation Sitesmentioning

confidence: 99%

Section: Construction Of Zeolite Catalysts Via Confinementmentioning

confidence: 99%

Confinement in a Zeolite and Zeolite Catalysis

et al. 2021

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“…Zeolites are a group of crystalline aluminosilicate materials with microporous structures and are widely investigated as supports of the Ni-based catalysts of the CRM reaction because of their advantages of abundant microporous channels, good thermal stabilities, large specific surface areas, and big pore volumes (Martínez Galeano et al, 2019;Kumar et al, 2020;Zhu et al, 2020). The Si/Al ratio of zeolite reflects the number of charge compensating ions and can modify the surface acidity (Li W. et al, 2019). In view of these advantages, the zeolites have been widely investigated as catalytic supports of metal or oxide clusters in many catalytic processes owing to the high metal dispersions and excellent stabilities (Xie et al, 2019).…”

Section: Zeolite Supportsmentioning

confidence: 99%

Recent Progresses in the Design and Fabrication of Highly Efficient Ni-Based Catalysts With Advanced Catalytic Activity and Enhanced Anti-coke Performance Toward CO2 Reforming of Methane

Chen

et al. 2020

Front. Chem.

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CO 2 reforming of methane (CRM) can effectively convert two greenhouse gases (CO 2 and CH 4) into syngas (CO + H 2). This process can achieve the efficient resource utilization of CO 2 and CH 4 and reduce greenhouse gases. Therefore, CRM has been considered as a significantly promising route to solve environmental problems caused by greenhouse effect. Ni-based catalysts have been widely investigated in CRM reactions due to their various advantages, such as high catalytic activity, low price, and abundant reserves. However, Ni-based catalysts usually suffer from rapid deactivation because of thermal sintering of metallic Ni active sites and surface coke deposition, which restricted the industrialization of Ni-based catalysts toward the CRM process. In order to address these challenges, scientists all around the world have devoted great efforts to investigating various influencing factors, such as the option of appropriate supports and promoters and the construction of strong metal-support interaction. Therefore, we carefully summarized recent development in the design and preparation of Ni-based catalysts with advanced catalytic activity and enhanced anti-coke performance toward CRM reactions in this review. Specifically, recent progresses of Ni-based catalysts with different supports, additives, preparation methods, and so on, have been summarized in detail. Furthermore, recent development of reaction mechanism studies over Ni-based catalysts was also covered by this review. Finally, it is prospected that the Ni-based catalyst supported by an ordered mesoporous framework and the combined reforming of methane will become the future development trend.

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“…Although an acceptable aldol condensation activity was achieved with these catalysts, catalyst deactivation occurs rapidly, especially in the presence of bio-based acids like acetic acid [19][20][21][22]. Lewis acidic heteroatom substituted zeolites, including Sn-Beta, Ti-Beta, Zr-Beta and Ta-Beta, were recently developed for this reaction [15,16,[23][24][25][26][27][28][29]. It was reported that two types of framework heteroatoms might exist, the so-called closed and open sites [30][31][32][33].…”

Section: Introductionmentioning

confidence: 99%