Evidence for X-ray-amorphous zeolites

Jacobs, Peter A.; Derouane, Éric G.; Weitkamp, Jens

doi:10.1039/c39810000591

Cited by 222 publications

(127 citation statements)

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“…As the thermodynamic adsorption data relate to the shape selective properties that are intrinsic to a zeolite structure, we develop a criterion to identify catalytic data that are unimpaired by mass transport or hydrogenation rate limitations. A subsequent scrutiny of the published n-C 7 (8,18) and n-C 10 (5,(19)(20)(21)(22)(23) hydroconversion data using this criterion shows intrinsic differences in paraffin hydroconversion between MFI-and MEL-type zeolites. Simulated C 10 adsorption data are then used to explain the observed differences in the hydroconversion of n-C 10 and of complex feedstocks and the absence of such differences in a publication (8) on the hydroconversion of n-C 7 .…”

Section: Fig 1 Sketch Of the Mfi-(a)mentioning

confidence: 99%

Differences between MFI- and MEL-Type Zeolites in Paraffin Hydrocracking

Maesen¹,

Schenk

Vlugt

et al. 2001

Journal of Catalysis

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A critical evaluation of published paraffin hydroconversion data shows that MEL-type zeolites preferentially hydrocrack paraffins where two methyl groups are separated by a methylene group, whereas MFI-type zeolites prefer paraffins with geminal methyl groups (preferably at the central carbon atom). Due to this difference in hydrocracking pathway, MEL-type zeolites will hydroisomerize a higher percentage of the feed than MFI-type zeolites at low temperature, while the reverse is true at high temperature. The free energies of adsorption calculated by means of configurational bias Monte Carlo (CBMC) molecular simulations are used to explain these differences in selectivity. They show that the MEL-and MFI-type zeolites favor the formation and hydrocracking of the dimethyl paraffins that have a shape commensurate with that of their pores. They indicate that the higher paraffin hydroisomerization selectivity of the MEL-type zeolites can also be explained by their higher selectivity for adsorbing linear rather than branched paraffins at high paraffin loading. At low paraffin loading this difference in adsorption selectivity disappears. Both temperature and loading effects could resolve a disparity in the literature between n-decane and n-heptane hydroisomerization selectivity data.

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Section: Fig 1 Sketch Of the Mfi-(a)mentioning

confidence: 99%

Differences between MFI- and MEL-Type Zeolites in Paraffin Hydrocracking

Maesen¹,

Schenk

Vlugt

et al. 2001

Journal of Catalysis

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“…With regard to the Jacobs et al (1981) claim to have synthesized ZSM-5 consisting of 'very small nuclei, with sizes below the X-ray detection limit', we emphasize that there is no intrinsic lower size limit below which zeolite crystals become inherently undetectable. Any object (particle), whether crystalline or non-crystalline, and regardless of size, has a diffraction pattern.…”

Section: Introductionmentioning

confidence: 99%

“…This assumption of infinite size is adequate for 50-unit-cell crystals but not for 4-unit-cell crystals. An objective assessment of the Jacobs et al (1981) claim to have prepared a 4-unit-cell ZSM-5 exhibiting no discernible ZSM-5 X-ray diffraction pattern requires a method for calculating the X-ray powder patterns that is considerably more realistic than the procedures generally used.…”

Section: Introductionmentioning

confidence: 99%

“…Because intracrystalline diffusion may be the ratelimiting step for a variety of catalyzed industrial reactions, there has always been a limited but sustained interest in the preparation ofultrasmall (0.005 to 0.01 ~tm diameter) crystalline zeolites (Jacobs, Derouane & Weitkamp, 1981;Gabelica, Nagy, Debras & Derouane, 1985). A crystal size of 50-100 A corresponds to 2 to 4 unit cells for faujasite and roughly 2.5 to 5 unit cells for ZSM-5.…”

Section: Introductionmentioning

confidence: 99%

“…Various groups have reported the synthesis of even smaller (ultrasmall) zeolite crystals. For example, Jacobs, Derouane & Weitkamp (1981) report the synthesis of X-ray amorphous zeolites 'which exhibit infrared and catalytic properties typical for ZSM-5... and therefore must contain ZSM-5 crystals of less than 8 nm size in an amorphous matrix'. Although they marshal X-ray, infrared and catalytic evidence to support this claim, it must be regarded as subject to some doubt.…”

Section: Introductionmentioning

confidence: 99%

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Computed X-ray Powder Diffraction Patterns for Ultrasmall Zeolite Crystals

Schlenker¹,

Peterson²

1996

J Appl Crystallogr

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Theoretical X-ray diffraction pattems have been calculated for powders of very small faujasite (FAU) and ZSM-5 (MFI) crystallites. These calculated patterns give the first realistic picture of the expected appearance of X-ray powder diffraction patterns of ultrasmall crystals of these well known commercial zeolites. The X-ray patterns were calculated using SKIP-small-crystal interference program-a program originally written to assist in the interpretation of X-ray diffraction patterns of synthetic zeolites and layered materials. The results are somewhat surprising in that they suggest that the crystallite size of faujasite must fall to below 4-5 unit cells before the resulting pattern diverges significantly from the asymptotic pattern. In contrast, the calculated X-ray pattern of ten-unit-cell ZSM-5 crystallites is scarcely recognizable.

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ZeolitesBased in part on the article Zeolites by Alan Dyer which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.

Williams

2005

Encyclopedia of Inorganic Chemistry

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This work looks at the natural formation of zeolites in our environment. It details the steps required in the laboratory to successfully manufacture zeolites, producing both novel and nature identical crystal forms. The classification of zeolites based on their aluminium content, pore/channel size is also covered in some detail. Finally the various physical and chemical properties that make zeolites so useful to everyday life are examined. These include their absorptive properties, ion‐exchange properties, desiccant properties, and catalytic properties.

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Evidence for X-ray-amorphous zeolites

Cited by 222 publications

References 0 publications

Differences between MFI- and MEL-Type Zeolites in Paraffin Hydrocracking

Differences between MFI- and MEL-Type Zeolites in Paraffin Hydrocracking

Computed X-ray Powder Diffraction Patterns for Ultrasmall Zeolite Crystals

ZeolitesBased in part on the article Zeolites by Alan Dyer which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.

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