Formation of Uniform Mesopores in ZSM-5 Zeolite through Treatment in Alkaline Solution

Ogura, Masaru; Shinomiya, Shin Ya; Tateno, Junko; Nara, Yasuto; Kikuchi, Eiichi; Matsukata, Masahiko

doi:10.1246/cl.2000.882

Cited by 273 publications

(175 citation statements)

References 6 publications

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“…[15] Nevertheless, for several decades, such type of post-synthetic treatments did not find great scientific interest due to an incomplete understanding of mesopore formation mechanism. Recently, explicit evidence of mesopore formation in ZSM-5 crystals by NaOH treatment has been reported, [16] which opens up promising potential for acid catalysis with bulky substrates. Currently, desilication is the most widely used method to introduce disordered mesopores into microporous zeolite frameworks and it is accepted that the long-range order and Brønsted acidity of the zeolites is retained upon alkaline treatment.…”

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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Section: Introductionmentioning

confidence: 99%

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

et al. 2016

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“…The formation of mesoporous zeolites has been actively sought as a way to overcome the diffusion limitation of reagents and products. There are several approaches for synthesizing mesoporous zeolites, such as the use of carbon particles as hard templates 50) , the use of organosilane surfactants as soft templates 51) , and, more recently, the desilication method 52) . Therefore, the interzeolite conversion method provides a new route for creating mesopores in zeolites, although the need for two steps (synthesis of starting zeolite and hydrothermal conversion) and the lower product yield presents major problems.…”

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High Potential of Interzeolite Conversion Method for Zeolite Synthesis

Sano

Itakura

Sadakane

2013

J. Jpn. Petrol. Inst.

101

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Many types of zeolites such as beta (hereinafter, BEA), CHA, LEV, RUT, and MFI were successfully synthesized by interzeolite conversion of FAU, BEA, and LEV type zeolites as starting materials under various hydrothermal synthesis conditions. The crystallization rates of zeolites using such starting zeolites were notably elevated compared to rates observed in conventional hydrothermal syntheses using amorphous aluminosilicate gels. This characteristic enhancement in the crystallization rate results from the generation of locally ordered aluminosilicate species (nanoparts) through the decomposition/dissolution of the starting zeolite, resulting in assembly and evolution into another type of zeolite. The structural similarity between the starting zeolite and the final crystallized zeolite is a crucial factor for interzeolite conversion. These findings strongly indicate that the interzeolite conversion route is an attractive strategy for zeolite synthesis and zeolite design will be possible after methods to selectively assemble the nanoparts are established.

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“…Desilication, that is, extraction of framework Si, is an efficient methodology to create intracrystalline mesoporosity in MFI-type zeolites. 3,4 The Si extraction and related mesopore formation is controlled by framework Al, and an optimal bulk Si/Al ratio of 25-50 has been identified. 5 A high framework Al concentration prevents Si extraction, while a low Al concentration leads to excessive extraction and formation of large pores.…”

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confidence: 99%

Creation of Hollow Zeolite Architectures by Controlled Desilication of Al-Zoned ZSM-5 Crystals

et al. 2005

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Zeolites are crystalline aluminosilicates that possess an exceptional combination of properties such as high thermal stability, Brønsted acidity, and microporosity. Accordingly, these materials are frequently practiced in industrial processes, for example, fluid catalytic cracking (Y), cumene production (mordenite), and toluene disproportionation and xylene isomerization .The presence of regular micropores of molecular dimensions is responsible for the zeolites' unequaled shape selectivity in catalytic conversions and separations, but this feature also poses diffusional limitations due to the restricted transport of molecules to and from the active sites. As a consequence, generation of mesoporosity in microporous crystals is attracting significant research interest. 1,2 The created mesopores facilitate physical transport and should lead to a more effective use of these materials. Desilication, that is, extraction of framework Si, is an efficient methodology to create intracrystalline mesoporosity in MFI-type zeolites. 3,4 The Si extraction and related mesopore formation is controlled by framework Al, and an optimal bulk Si/Al ratio of 25-50 has been identified. 5 A high framework Al concentration prevents Si extraction, while a low Al concentration leads to excessive extraction and formation of large pores. However, how the porosity is distributed throughout the crystals and the effect of crystal size is practically ignored. This information is indispensable to rationally devise potential applications of alkaline-treated zeolites.The occurrence of Al zoning, that is, an Al-rich external surface as compared to the bulk aluminum concentration, is well-known in large ZSM-5 crystals. 6,7 Accordingly, it can be anticipated that this Al gradient will affect the Si extraction throughout the zeolite particle. Dessau et al. 8 have observed the nonuniform dissolution of large ZSM-5 crystals (5-10 µm) upon prolonged treatment at high concentrations of alkaline solution. This was speculatively attributed to the nonuniform concentration of Al in the crystals. However, a systematic study on the impact of Al gradients and the effect of crystal size to tailor the porosity development under optimized treatment conditions has not yet been accomplished.Here we show that by controlled desilication of both large and small ZSM-5 crystals we have been able to address and make use of the impact of Al-zoning on the mesoporosity development. The presented approach provides a thus-far unused method to tailor the fabrication of hollow zeolite crystals, offering clear advantages to other methodologies pursuing hollow zeolite entities. 9,10 Our results are of fundamental interest in materials science and may open auspicious uses of alkaline-treated zoned ZSM-5 zeolites.Two procedures were applied to synthesize ZSM-5 zeolite with small (SZ) and large (LZ) crystals in the optimal bulk Si/Al range of 25-50. The alkaline treatment was performed as described in the Supporting Information. The chemical composition and textural properties of the n...

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Formation of Uniform Mesopores in ZSM-5 Zeolite through Treatment in Alkaline Solution

Abstract: Treatment of ZSM-5 in alkaline solution dramatically changes morphology of the ZSM-5, leading to the formation of mesopores whose size is almost uniform without destruction of microporous structure.

Cited by 273 publications

References 6 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

High Potential of Interzeolite Conversion Method for Zeolite Synthesis

Creation of Hollow Zeolite Architectures by Controlled Desilication of Al-Zoned ZSM-5 Crystals

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