Molecular Sieves

Szostak, R.

doi:10.1007/978-94-010-9529-7

Cited by 442 publications

(61 citation statements)

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“…[14][15][16] In the seventies a very large number of organic molecules were tested as structure directing agents in zeolite crystallisation, which resulted in the synthesis of many new structure types and the preparation of high-silica and all-silica zeolites. [17][18][19] The most important discovery in the eighties was the development of a new family of silica-free zeolite-like materials. Aluminophosphate molecular sieves, first synthesised by Union Carbide researchers, were further extended to silicon-and metalcontaining counterparts.…”

Section: Introductionmentioning

confidence: 99%

“…Aluminophosphate molecular sieves, first synthesised by Union Carbide researchers, were further extended to silicon-and metalcontaining counterparts. [19][20][21] Ordered mesoporous materials were synthesised in the nineties, but this family is out of the scope of the present review since the framework walls are amorphous. 22,23 In the dawn of the new millennium, the most important development was the synthesis of microporous materials with extra-large (>1 nm) pores.…”

Section: Introductionmentioning

confidence: 99%

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Tailored crystalline microporous materials by post-synthesis modification

et al. 2013

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Crystalline microporous solids are an important class of inorganic materials with uses in different areas impacting our everyday lives, namely as catalysts, adsorbents, and ion exchangers. Advancements in synthesis have been invaluable in expanding the classical aluminosilicate zeolites to new unique framework types and compositions, motivating innovative developments. However, the inexhaustible post-synthetic options to tailor zeolite properties have been and will continue to be indispensable to realize emerging and to improve conventional applications. Starting from the routine drying and template removal processes that every zeolite must experience prior to use, a wide spectrum of treatments exists to alter individual or collective characteristics of these materials for optimal performance. This review documents the toolbox of post-synthetic strategies available to tune the properties of zeolitic materials for specific functions. The categorisation is based on the scale at which the alteration is aimed at, including the atomic structure (e.g. the introduction, dislodgment, or replacement of framework atoms), the micropore level (e.g. template removal and functionalisation by inorganic and organic species), and the crystal and particle levels (e.g. the introduction of auxiliary porosity). Through examples in the recent literature, it is shown that the combination of post-synthetic methods enables rational zeolite design, extending the characteristics of these materials way beyond those imposed by the synthesis conditions.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Tailored crystalline microporous materials by post-synthesis modification

et al. 2013

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“…The other wide band at about 3300-3600 cm -1 is associated with H bonded, O-H groups (Omegna et al 2004;Miao et al 2016;Sreedhar et al 2009;Toktarev et al 2010). An almost linear decrease was observed in the position of the main T-O-T vibrations at about 1100 cm -1 with increasing Zr content in MFI framework (Szostak 1989). Jin et al (2006) also expressed this idea in their study on the selective synthesis of 2,6-DMN by methylation of 2-MN with methanol over Zr/(Al)ZSM-5.…”

Section: Fourier Transform Infrared (Ftir) Analysismentioning

confidence: 88%

Catalytic performance of Cu- and Zr-modified beta zeolite catalysts in the methylation of 2-methylnaphthalene

2018

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2,6-Dimethylnaphthalene (2,6-DMN) is a commercially important chemical for the production of polyethylenenaphthalate and polybutylene naphthalate. However, its complex synthesis procedure and high production cost significantly reduce the use of 2,6-DMN. In this study, the synthesis of 2,6-DMN was investigated with methylation of 2-methylnaphthalene (2-MN) over metal-loaded beta zeolite catalysts including beta zeolite, Cu-impregnated beta zeolite and Zr-impregnated beta zeolite. The experiments were performed in a fixed-bed reactor at atmospheric pressure under a nitrogen atmosphere. The reactor was operated at a temperature range of 400-500°C and varying weight hourly space velocity between 1 and 3 h -1 . The results demonstrated that 2,6-DMN can be synthesized by methylation of 2-MN over beta type zeolite catalysts. Besides 2,6-DMN, the product stream also contained other DMN isomers such as 2,7-DMN, 1,3-DMN, 1,2-DMN and 2,3-DMN. The activity and selectivity of beta zeolite catalyst were remarkably enhanced by Zr impregnation, whereas Cu modification of beta zeolite catalyst had an insignificant effect on its selectivity. The highest conversion of 2-MN reached 81%, the highest ratio of 2,6-DMN/2,7-DMN reached 2.6 and the highest selectivity of 2,6-DMN was found to be 20% by using Zr-modified beta zeolite catalyst.

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“…Microporous and nanoporous materials are widely used for separating gaseous mixtures, and it would be very advantageous if they could be used for the separation of isotopes by sieving, as an alternative to the conventional methods . However, in many cases the sieving is based on the size or shape of pores and molecules or on electronic effects like polarity . But these effects are negligible for isotopologues, so the separation must be based on mass.…”

Section: Introductionmentioning

confidence: 99%

“…Besides equilibrium factors, one must also consider dynamics, and this study is devoted to dynamics. The importance of quantum effects on the dynamics was studied theoretically by Kumar et al using molecular dynamics simulations. , By analogy to EQS and CAQS, this is called kinetic quantum sieving (KQS), and several studies were performed focusing on hydrogen isotope separation in microporous materials by this effect. ,,,,,− …”

Section: Introductionmentioning

confidence: 99%

Quantum Effects on H₂ Diffusion in Zeolite RHO: Inverse Kinetic Isotope Effect for Sieving

Gao

Zhang

et al. 2019

J. Am. Chem. Soc.

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We use canonical variational theory (CVT) with small-curvature tunneling (SCT) contributions to investigate quantum effects on the H 2 diffusion process in the pure-silica zeolite RHO. At low temperature we find an inverse kinetic isotopic sieving effect in that the heavier isotopic species diffuses faster than the lighter one. Three quantum effects contribute to this kinetic isotope effect (KIE). The first one is quantum mechanical tunneling; thison its ownwould lead to a normal kinetic isotopic sieving effect, in which lighter diprotium diffuses faster than dideuterium. The second factor, which we find to dominate in the present case, is zero-point energy (ZPE). Deuterium has a lower ZPE, which leads to a smaller effective barrier for tunneling because the transition state has a larger ZPE than the precursor stable state; this results in an inverse KIE. The third factor, the thermal vibrational energy (computed from the quantized vibrational partition function), also favors a normal KIE, but it is outweighed by the ZPE effect. The vibrations of the zeolite host framework are found to play an important role at low temperatures, and our calculations consider up to 7296 degrees of freedom at the equilibrium structure and the saddle point and up to 221 degrees of freedom along the reaction path. The importance of quantum considerations on the dynamics is elucidated by comparison to a purely classical treatment.

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Molecular Sieves

Cited by 442 publications

References 0 publications

Tailored crystalline microporous materials by post-synthesis modification

Tailored crystalline microporous materials by post-synthesis modification

Catalytic performance of Cu- and Zr-modified beta zeolite catalysts in the methylation of 2-methylnaphthalene

Quantum Effects on H₂ Diffusion in Zeolite RHO: Inverse Kinetic Isotope Effect for Sieving

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Molecular Sieves

Cited by 442 publications

References 0 publications

Tailored crystalline microporous materials by post-synthesis modification

Tailored crystalline microporous materials by post-synthesis modification

Catalytic performance of Cu- and Zr-modified beta zeolite catalysts in the methylation of 2-methylnaphthalene

Quantum Effects on H2 Diffusion in Zeolite RHO: Inverse Kinetic Isotope Effect for Sieving

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Quantum Effects on H₂ Diffusion in Zeolite RHO: Inverse Kinetic Isotope Effect for Sieving