Secondary crystallization of SBA-15 pore walls into microporous material with MFI structure

Campos, Alexandre A.; Martins, Leandro; Oliveira, L.; Silva, Camila Ramos da; Wallau, Martin; Urquieta‐González, Ernesto A.

doi:10.1016/j.cattod.2005.07.007

Cited by 23 publications

(16 citation statements)

References 27 publications

(35 reference statements)

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“…This phenomenon is unique, and quite different from other routes reported previously. [24][25][43][44][45][46][47][48][49][50] As the size of the microporous zeolite crystal formed is similar to that of the starting amorphous aggregate of nanoparticles, this could potentially indicate that each aggregate of nanoparticles was transformed into a zeolite crystal, possibly due to good accessibility for the structure-directing agent and supplementary silica source of the unique mesostructure formed by aggregation of the nanoparticle precursor and the relatively mild glycerol system. This is probably a critical factor in the formation of uniform crystals and maintenance of the mesostructure.…”

Section: Resultsmentioning

confidence: 99%

“…The question then arises whether an atypical hydrothermal process can be used for the synthesis, that is, a method that minimizes the damage to the mesoporous and macroporous structure caused by hydrothermal synthesis. Some successful methods were demonstrated by Kanno et al, Campos et al, Coppens et al, and Kaliaguine et al, [24,25,[43][44][45][46][47][48][49][50] who used glycerol as a medium to directly synthesize zeolites, to recrystallize mesoporous silica to zeolite, to embed zeolite nanocrystals into a well-connected amorphous matrix, and to coat the walls of mesostructured materials with zeolite nanoclusters, respectively. However, the generation of crystalline micro-meso-macroporous aluminosilicates constructed entirely from zeolite nanocrystals with interconnectivity on three length scales still remains a great challenge, since the structures of the mesoporous aluminosilicates would still be easily destroyed during reactions even when using the glycerol system.…”

Section: Introductionmentioning

confidence: 99%

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Well‐Organized Zeolite Nanocrystal Aggregates with Interconnected Hierarchically Micro–Meso–Macropore Systems Showing Enhanced Catalytic Performance

Yang

Tian

Chen

et al. 2011

Chemistry A European J

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Preparation and characterization of well‐organized zeolitic nanocrystal aggregates with an interconnected hierarchically micro–meso–macro porous system are described. Amorphous nanoparticles in bimodal aluminosilicates were directly transformed into highly crystalline nanosized zeolites, as well as acting as scaffold template. All pores on three length scales incorporated in one solid body are interconnected with each other. These zeolitic nanocrystal aggregates with hierarchically micro–meso–macroporous structure were thoroughly characterized. TEM images and 29Si NMR spectra showed that the amorphous phase of the initial material had been completely replaced by nanocrystals to give a micro–meso–macroporous crystalline zeolitic structure. Catalytic testing demonstrated their superiority due to the highly active sites and the presence of interconnected micro–meso–macroporosity in the cracking of bulky 1,3,5‐triisopropylbenzene (TIPB) compared to traditional zeolite catalysts. This synthesis strategy was extended to prepare various zeolitic nanocrystal aggregates (ZSM‐5, Beta, TS‐1, etc.) with well‐organized hierarchical micro–meso–macroporous structures.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Well‐Organized Zeolite Nanocrystal Aggregates with Interconnected Hierarchically Micro–Meso–Macropore Systems Showing Enhanced Catalytic Performance

Yang

Tian

Chen

et al. 2011

Chemistry A European J

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“…A maioria das abordagens está relacionada com uma cristalização (secundária) parcial dos materiais mesoporosos ordenados em uma estrutura zeolítica. 53,55 Geralmente, os materiais obtidos através da moldagem indireta podem ser classificados como cristais suportados de zeólitas e, portanto, não são objeto desta revisão.…”

Section: Materiais Zeolíticos Com Estrutura Hierárquica De Porosunclassified

Zeólitas hierarquicamente estruturadas

Grecco¹,

Rangel²,

Urquieta‐González³

2013

Quím. Nova

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Recebido em 5/3/12; aceito em 3/7/12; publicado na web em 26/11/12 HIERARCHICALLY STRUCTURED ZEOLITES. This review presents the main characteristics and properties of microporous (zeolites) and ordered mesoporous materials, focusing on structural aspects and preparation. In addition, their use as heterogeneous catalysts are also discussed, with emphasis on their advantages and disadvantages. Due to difficulty in application of zeolites in the conversion of bulky molecules, the most relevant strategies of synthesis for the preparation of zeolitic materials with hierarchical pore structure was also analyzed, which allow this limitation to be overcome.Keywords: synthesis of zeolites; mesoporous materials; hierarchical porous structure. INTRODUÇÃOAs zeólitas, materiais cristalinos microporosos, têm se consolidado ao longo da segunda metade do século XX e nesta primeira década do século XXI como importantes catalisadores em processos das indústrias de refino de petróleo, química e petroquímica, assim como no controle ambiental.1 Esse amplo espectro de aplicações está relacionado às propriedades físicas e químicas desses materiais, que podem ser controladas durante a sua preparação, visando uma aplicação específica. Além de seu particular sistema de microporos, as zeólitas apresentam propriedades específicas, que as diferenciam de outros materiais, tais como acidez ou basicidade superficial e capacidade de troca iônica.2 Entretanto, apesar dessas propriedades desejáveis, a presença apenas de microporos nas zeólitas impõe limitações à difusão de reagentes ou produtos volumosos. Embora a limitação difusional seja usada, em alguns casos, para controlar beneficamente a seletividade a um determinado produto da reação catalítica, a difusividade relativamente baixa de moléculas volumosas, nos microporos da zeólita, limita a taxa de reação, devido ao transporte mais lento dos reagentes e produtos, ocasionando um maior tempo de residência e, como consequência, favorecendo a ocorrência de reações indesejáveis.3 Em processos envolvendo hidrocarbonetos, a limitação difusional contribui para a formação do coque, que provoca a desativação da zeólita por obstrução dos canais ou envenenamentos dos sítios ativos. 4 Com a expectativa de superar as limitações difusionais, no fim da década de 80 se deu início à busca por materiais contendo mesoporos, que resultou na síntese de materiais mesoporosos ordenados no início dos anos 90.5-8 Diversas peneiras moleculares mesoporosas com tamanho de poros ajustável têm sido desenvolvidas, apresentando emprego potencial em reações catalíticas. Entretanto, comparado às zeólitas, esses materiais mesoporosos possuem acidez e estabilidade hidrotérmica mais baixas, o que limita as suas aplicações catalíticas. Assim, esforços consideráveis têm sido dedicados ao desenvolvimento de materiais zeolíticos com estrutura hierárquica de poros, que combinam as propriedades intrínsecas das zeólitas com a facilidade de difusão resultante da geração de mesoporosidade.Um número significativo de procedimentos experime...

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“…Another advantage of this chemical crystallization transformation process under glycerin medium is easy to form MFI-type zeolite with uniform particle size because of the slow crystallization process. In fact, some successful attempts were previously demonstrated using glycerin as a reaction medium to directly synthesize silicalite-1 nanocrystals [41], and MFI-type zeolite-coated mesoporous aluminosilicates [42,43], recrystalize mesoporous SBA-15 into microporous ZSM-5 [44] and secondary crystallization of mesoporous walls into microporous materials with MFI structure [45,46], respectively. It is very remarkable that the zeolite nanocrystals in the final products exhibited a uniform particle size of around 500 nm in length and 300 nm in width (Figs.…”

mentioning

confidence: 99%

Multimodal Zr-Silicalite-1 zeolite nanocrystal aggregates with interconnected hierarchically micro-meso-macroporous architecture and enhanced mass transport property

Chen

et al. 2012

Journal of Colloid and Interface Science

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Secondary crystallization of SBA-15 pore walls into microporous material with MFI structure

Cited by 23 publications

References 27 publications

Well‐Organized Zeolite Nanocrystal Aggregates with Interconnected Hierarchically Micro–Meso–Macropore Systems Showing Enhanced Catalytic Performance

Well‐Organized Zeolite Nanocrystal Aggregates with Interconnected Hierarchically Micro–Meso–Macropore Systems Showing Enhanced Catalytic Performance

Zeólitas hierarquicamente estruturadas

Multimodal Zr-Silicalite-1 zeolite nanocrystal aggregates with interconnected hierarchically micro-meso-macroporous architecture and enhanced mass transport property

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