Future of nano-/hierarchical zeolites in catalysis: gaseous phase or liquid phase system

Yan, Yueer; Guo, Xiao; Zhang, Yahong; Tang, Yi

doi:10.1039/c4cy01114g

Cited by 87 publications

(45 citation statements)

References 122 publications

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“…This improvement enables higher activities and/or improved kinetics of catalytic and sorptive processes which is kind of the ''driving force'' for the growing interest in hierarchically porous materials in general. [34][35][36][37] In the following, zeolite-based hierarchical materials shall be discussed according to their compositional, textural and structural properties as well as according to the underlying preparation principles.…”

Section: Preparation Of Porous Materials In Generalmentioning

confidence: 99%

Hierarchy concepts: classification and preparation strategies for zeolite containing materials with hierarchical porosity

et al. 2016

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'Hierarchy' is a property which can be attributed to a manifold of different immaterial systems, such as ideas, items and organisations or material ones like biological systems within living organisms or artificial, man-made constructions. The property 'hierarchy' is mainly characterised by a certain ordering of individual elements relative to each other, often in combination with a certain degree of branching.Especially mass-flow related systems in the natural environment feature special hierarchically branched patterns. This review is a survey into the world of hierarchical systems with special focus on hierarchically porous zeolite materials. A classification of hierarchical porosity is proposed based on the flow distribution pattern within the respective pore systems. In addition, this review might serve as a toolbox providing several synthetic and post-synthetic strategies to prepare zeolitic or zeolite containing material with tailored hierarchical porosity. Very often, such strategies with their underlying principles were developed for improving the performance of the final materials in different technical applications like adsorptive or catalytic processes. In the present review, besides on the hierarchically porous allzeolite material, special focus is laid on the preparation of zeolitic composite materials with hierarchical porosity capable to face the demands of industrial application.

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Section: Preparation Of Porous Materials In Generalmentioning

confidence: 99%

Hierarchy concepts: classification and preparation strategies for zeolite containing materials with hierarchical porosity

et al. 2016

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“…As a consequence, hierarchical materials have been used to achieve these tasks by increasing the external surface area, maximizing the rate of intracrystalline diffusion, and reducing the deactivation rate and thereby improving catalyst lifetime. 10 Despite all such promising applications and properties, the utilization of most of the hierarchical zeolites in large (industrial) scale is still a challenge. Laborious and very expensive synthesis procedures could be among the main reasons limiting the scale up of these materials into large scale production although hierarchical zeolites are described as industrial reality in a recent review.…”

Section: Wilhelm Schwiegermentioning

confidence: 99%

Catalytic test reactions for the evaluation of hierarchical zeolites

2016

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Catalytic test reactions for the evaluation of hierarchical zeolitesStudies on the synthesis, characterization and catalytic performance of hierarchical zeolites and related porous materials are currently revitalizing the mature field of zeolite research. This review discusses the challenges in evaluating the catalytic performance of a hierarchical zeolite catalyst compared to its parent zeolite. zeolites and the facilitated access and transport in the additional meso-or macropore system. In this tutorial review, we discuss several test reactions that have been explored to show the benefit of the hierarchical pore system with respect to their suitability to prove the positive effects of hierarchical porous zeolites. It is important to note that positive effects on activity, stability and less frequently selectivity observed for hierarchically structured catalysts not necessarily are only a consequence of the additional meso-or macropores but also the number, strength and location of active sites as well as defects and impurities. With regard to these aspects, the test reaction has to be chosen carefully and potential changes in the chemistry of the catalyst have to be considered as well. In addition to the determination of conversion, yield and selectivity, we will show that the calculation of the activation energy and the determination of the Thiele modulus and the effectiveness factor are good indicators of the presence or absence of diffusion limitations in hierarchical zeolites compared to their parent materials. Key learning pointsHierarchical zeolites are an emerging technology in the mature field of industrial catalysts. Several test reactions are suggested to prove the advantage of their hierarchical structure. In addition to an increase in activity and selectivity suppression of coke formation is often observed. Concept of the Thiele modulus and the effectiveness factor is required to judge the presence of diffusion limitations in hierarchical catalysts.

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“…[17] The hierarchical zeolites have shown enhanced catalytic performances with respect to the microporous analogues in diffusion-constrained reactions or those carried out in the liquid-phase at low temperatures. [11,18] In the present study, a post-synthetic desilication strategy in alkali media was followed to achieve hierarchical H-ZSM-5 ( Fig.1), starting from parent MFI zeolites with different Si/Al ratio. H-ZSM-5 is a wellknown microporous zeolite with a cross-section of straight channels (5.1 Å x 5.5 Å) intersected by zig-zag channels (5.3 Å x 5.6 Å) and it is widely used as a heterogeneous acid catalyst in a large number of reactions.…”

Section: Introductionmentioning

confidence: 99%

Creating Accessible Active Sites in Hierarchical MFI Zeolites for Low‐Temperature Acid Catalysis

et al. 2016

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A versatile desilication design strategy for the creation of hierarchical H-ZSM-5 catalysts with different Si/Al ratio has been demonstrated. The nature, strength and the accessibility of the acid sites after the alkaline treatment was elucidated by employing a range of physico-chemical characterization tools; notably probebased FTIR spectroscopy along with SS MAS-NMR. In addition, structural and textural properties of the hierarchical zeolites were also explored and compared to their corresponding microporous analogues. CO was used to probe the acidic properties of the hierarchical zeolites with the concomitant deployment of a bulky molecular probe, 2,4,6-trimethylpyridine (collidine), which is too large to access the micropores, to specifically investigate the enhanced accessibility of the active sites. The hierarchical zeolites were evaluated in the industrially relevant, acid-catalyzed Beckmann rearrangement of cyclohexanone oxime to -caprolactam, the precursor for Nylon-6, in liquid phase and at low-temperatures. The catalytic findings with the hierarchical catalysts reveal a significant enhancement in the production of -caprolactam, compared with the parent microporous H-ZSM-5 zeolite, thereby highlighting the merits of our design approach in facilitating enhanced diffusion and masstransfer.

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Future of nano-/hierarchical zeolites in catalysis: gaseous phase or liquid phase system

Abstract: This perspective highlights the catalytic characteristics and future prospects of nano-/hierarchical zeolites in gaseous phase and liquid phase reactions.

Cited by 87 publications

References 122 publications

Hierarchy concepts: classification and preparation strategies for zeolite containing materials with hierarchical porosity

Hierarchy concepts: classification and preparation strategies for zeolite containing materials with hierarchical porosity

Catalytic test reactions for the evaluation of hierarchical zeolites

Creating Accessible Active Sites in Hierarchical MFI Zeolites for Low‐Temperature Acid Catalysis

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