On the location and disorder of the tetrapropylammonium (TPA) ion in zeolite ZSM-5 with improved framework accuracy

Koningsveld, H. van; Bekkum, H. van; Jansen, J.C.

doi:10.1107/s0108768187098173

Cited by 619 publications

(423 citation statements)

References 11 publications

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“…The channels' intersections, which allow three-dimensional motion of sorbed molecules, are elongated cavities of about 9 Å in diameter. We represented silicalite crystal structure, according to x-ray diffractions studies, 45 in the Pnma space group ͑orthorhombic͒, with unit cell lattice parameters aϭ20.022, bϭ19.899, c ϭ13.383 Å.…”

Section: Zeolite Casementioning

confidence: 99%

A classical molecular dynamics study of recombination reactions in a microporous solid

Delogu

Demontis

Suffritti

et al. 1998

The Journal of Chemical Physics

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Classical molecular dynamics calculations have been applied to the study of the recombination reaction of photodissociated radical species. Within a simplified reaction scheme it has been possible to get qualitative information about the influence of the environment. A comparison has been made between reactions in a liquid solvent and in a complex structured environment, such as a microporous silicate. Marked differences in the recombination yield and in the energy relaxation mechanism have been observed.

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Section: Zeolite Casementioning

confidence: 99%

A classical molecular dynamics study of recombination reactions in a microporous solid

Delogu

Demontis

Suffritti

et al. 1998

The Journal of Chemical Physics

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“…Refs. [7][8][9][10]. This approach would be certainly impractical when there is a substantial degree of disorder.…”

Section: Introductionmentioning

confidence: 99%

Reverse Monte Carlo modeling in confined systems

Sánchez-Gil

Noya

Lomba

2014

The Journal of Chemical Physics

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An extension of the well established Reverse Monte Carlo (RMC) method for modeling systems under close confinement has been developed. The method overcomes limitations induced by close confinement in systems such as fluids adsorbed in microporous materials. As a test of the method, we investigate a model system of 36 Ar adsorbed into two zeolites with significantly different pore sizes: Silicalite-I (a pure silica form of ZSM-5 zeolite, characterized by relatively narrow channels forming a 3D network) at partial and full loadings and siliceous Faujasite (which exhibits relatively wide channels and large cavities). The model systems are simulated using Grand Canonical Monte Carlo and, in each case, its structure factor is used as input for the proposed method, which shows a rapid convergence and yields an adsorbate microscopic structure in good agreement with that of the model system, even to the level of three body correlations, when these are induced by the confining media. The application to experimental systems is straightforward incorporating factors such as the experimental resolution and appropriate q-sampling, along the lines of previous experiences of RMC modeling of powder diffraction data including Bragg and diffuse scattering.

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“…The framework of ZSM-5 had been determined previously by X-ray diffraction 23 and contains 12 non-equivalent T-sites, each occupied by 8 Si/Al atoms per unit cell. The structure is one of the most complex ones.…”

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confidence: 99%

Determining the aluminium occupancy on the active T-sites in zeolites using X-ray standing waves

et al. 2008

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Zeolites are microporous crystalline materials that find wide application in industry, for example, as catalysts and gas separators, and in our daily life, for example, as adsorbents or as ion exchangers in laundry detergents 1 . The tetrahedrally coordinated silicon and aluminium atoms in the zeolite unit cell occupy the so-called crystallographic T-sites. Besides their pore size, the occupation of specific T-sites by the aluminium atoms determines the performance of the zeolites 2 . Despite its importance, the distribution of aluminium over the crystallographic T-sites remains one of the most challenging, unresolved issues in zeolite science. Here, we report how to determine unambiguously and directly the distribution of aluminium in zeolites by means of the X-ray standing wave technique 3 using brilliant, focused X-rays from a thirdgeneration synchrotron source. We report in detail the analysis of the aluminium distribution in scolecite, which demonstrates how the aluminium occupancy in zeolites can systematically be determined.Zeolites are widely used materials with a very wide range of applications. They are used in households in laundry detergents and in industry as catalysts for petrochemical refining and they have become increasingly important in fine-chemical production and in environmental applications; they are used as air and water purifiers and in heating and refrigerating, and they are used in agriculture as selective absorbents. With natural zeolites being discovered more than 200 years ago, intensive research is nowadays aimed at developing new, synthetic zeolites with tailored properties for specific tasks. The functionality of a zeolite is determined basically by just a few parameters: the size and connectivity of the pores and cages, the Si/Al ratio and the placement of the trivalent aluminium atoms at specific crystallographic T-sites. Among them, the placement of aluminium is still unknown for many zeolites because no generally applicable experimental method has been reported to solve this problem. This seriously hampers the understanding of the function of some technologically important zeolites and hinders the development of new zeolites with novel functionalities.In a zeolite, the replacement of a tetravalent silicon atom by a trivalent aluminium atom on a T-site places a negative charge on the framework, which is compensated by non-framework cations. These charge-compensating cations are loosely held in the pores and cages of a zeolite and can be exchanged by other cations. This property makes zeolites good cation exchangers, which are useful in water softening and in the removal of nuclear waste. When the charge-compensating species are protons or elements that are involved in oxidation or reduction reactions, zeolites become catalytically active in Brønsted and redox reactions, respectively. The Si/Al ratio and the aluminium distribution over the framework T-sites thus determine the species and the positions of the chargecompensating cations in a zeolite, which strongly affect its cata...

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On the location and disorder of the tetrapropylammonium (TPA) ion in zeolite ZSM-5 with improved framework accuracy

Cited by 619 publications

References 11 publications

A classical molecular dynamics study of recombination reactions in a microporous solid

A classical molecular dynamics study of recombination reactions in a microporous solid

Reverse Monte Carlo modeling in confined systems

Determining the aluminium occupancy on the active T-sites in zeolites using X-ray standing waves

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