Structural analysis of hierarchically organized zeolites

Mitchell, Sharon; Pinar, Ana B.; Kenvin, Jeffrey; Crivelli, P.; Kärger, Jörg; Pérez‐Ramírez, Javier

doi:10.1038/ncomms9633

Cited by 225 publications

(163 citation statements)

References 117 publications

(186 reference statements)

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“…Recently, hierarchical zeolites, which combine micro and mesopores in a multilevel pore network, strongly emerged as novel materials for catalytic applications to overcome typical drawbacks of traditional microporous materials such as poor mass-transfer and hindered diffusion. [1,2] Direct benefits of the incorporation of micropores and mesopores within a single porous architecture have been demonstrated in key catalytic processes for petroleum refining, catalytic cracking of hydrocarbons, isomerization and fine chemical applications. [3][4][5] Many synthetic strategies (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…The alkali treatment adopted to produce hierarchical H-ZSM-5 can modify these OH sites, in terms of their localization, concentration and acid strength. [2] To get information on the nature, strength and accessibility of the acid sites after the alkaline treatment, a detailed physico-chemical characterization using FTIR spectroscopy of adsorbed molecules together with SS MAS-NMR was performed. In addition, structural and textural properties of the hierarchical zeolites were also explored by means of XRD and volumetric analyses.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2016

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“…It is obvious that in addition to the development of novel synthetic strategies and thorough characterization of the resulting materials (as nicely discussed in ref. 13), the evaluation of the novel catalysts in one or more suitable test reactions is required.…”

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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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“…27 For materials used as adsorbents and catalysts, hierarchical organization of porosity at the micro-, meso-, and macrolevel can impact performance characteristics such as activity, selectivity, and stability. 28 In his article, Snyder discusses various synthesis strategies based on direct synthesis, post-synthetic modifi cations, and combinations thereof that are being developed. In their article, Valtchev and Mintova discuss hierarchical zeolites (ordered microporous materials incorporating meso-and macropores) that fi nd uses in industrial applications such as crude oil cracking catalysts.…”

Section: Hierarchical Materials For Energy Storage and Conversion Admentioning

confidence: 99%

Hierarchical materials: Background and perspectives

Mishnaevsky

Tsapatsis

2016

MRS Bull.

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Starting from steel swords with complex structures to mud and straw-based buildings in Mali to ancient mortars and concrete, efforts to enhance the properties of materials by changing their structures have always been at the center of technological development. Composites, materials consisting of two or more dissimilar constituents with different properties, emerged from such efforts. While the possibilities of composite materials seemed infi nite at fi rst, two observations came into focus: (1) the composite constituents have their own, sometimes complex, structures that can in turn be modifi ed, and (2) the potential for improving the properties of composite materials by adding or rearranging reinforcements is often limited-while some properties (e.g., stiffness) can be improved by increasing the volume content of hard reinforcements, other properties (e.g., fracture toughness) degrade. This motivated modifi cations of structure and properties of composite constituents and their control at several scale levels. 1At the same time, the extraordinary properties of materials found in nature, including wood, nacre, bone, and other biological materials, attracted the interest of the scientifi c community. It was observed that one of the main sources of such extraordinary properties of biocomposites is their complex hierarchical structure. In his classic paper, Lakes 2 summarized the main ideas of hierarchical materials as a "basis for synthesizing new microstructures, which give rise to enhanced or useful physical properties." This provided the impetus for the development of new, bioinspired materials based on biomimicry principles. 3 With the continuing advances and development of nanotechnology, new possibilities emerged to enable the manufacture of hierarchical materials with constituents modifi ed on the nanoscale. Biological hierarchical materials: Variety of structures and biomimickingNatural biological materials often demonstrate extraordinary strength, damage resistance, and hardness. For instance, nacreous mollusk shells, which consist of 95% CaCO 3 by volume, have double the strength and exhibit a work of fracture that is 3000 times higher than that of monolithic CaCO 3 . 4 Numerous studies have been devoted to the analysis of the sources of such extraordinary properties of biological materials. Several features have been identifi ed, including the staggered brick-and-mortar structure and interlocked platelets of nacre (see Figure 1 ), 5 -8 the layered structure with randomly distributed layer thicknesses found in the spicules that provide structural support in certain sea sponges, the functionally graded structures (graded distributions of reinforcement) of bamboo 9 and tooth, 10 and features of wood such as a cellular multilayered structure and fi ber/fi brils with varied distribution Hierarchical materials: Background and perspectives Leon Mishnaevsky Jr. and Michael Tsapatsis , Guest EditorsHierarchical design draws inspiration from analysis of biological materials and has opened new possibilities for ...

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Structural analysis of hierarchically organized zeolites

Cited by 225 publications

References 117 publications

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

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

Catalytic test reactions for the evaluation of hierarchical zeolites

Hierarchical materials: Background and perspectives

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