Selective Isomerization of Hydrocarbon Chains on External Surfaces of Zeolite Crystals

Martens, Johan A.; Souverijns, W; Verrelst, Wim H.; Parton, Rudy F.; Froment, Gilbert F.; Jacobs, Pierre

doi:10.1002/anie.199525281

Cited by 200 publications

(139 citation statements)

References 15 publications

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“…Process-with selectivity similar to traditional Friedel-Crafts catalysis [29,30], which implies that it is not a case of shape selectivity. Only the shape-selective hydroconversion of long n-alkanes at the exterior surface of TON-, MTT-, ERI-, and CHA-type zeolites [4,[6][7][8][9][10][11][12][13][14][15][16][17] remain under discussion. In the present paper, we critically review exterior surface catalysis and suggest that TON-and MTT-type zeolites do not exhibit shape-selective exterior surface catalysis, whereas ERI-and CHA-type molecular sieves do exhibit exterior surface catalysis that might be shapeselective.…”

Section: Introductionmentioning

confidence: 99%

“…Intersecting-pore MFI-type zeolites enhance formation of alkanes with proximate methyl groups (and thereby the extent of hydrocracking), because the MFI-type intersections afford a snug fit with these precursors, thereby decreasing the Gibbs free energy of formation of these hydrocracking precursors [40,41]. Tubular-pore zeolites impede the formation of alkanes with proximate methyl groups and thus impede hydrocracking in favor of hydroisomerization [4][5][6][7][8][9][10][11][12][13][14][24][25][26][27][42][43][44]. How the nonintersecting tubular TON-and MTT-type pores impede formation of alkanes with proximate methyl groups remains incompletely understood.…”

Section: Introductionmentioning

confidence: 99%

“…How the nonintersecting tubular TON-and MTT-type pores impede formation of alkanes with proximate methyl groups remains incompletely understood. One possible explanation is that they impede formation of alkanes with proximate methyl groups, because these alkanes fit poorly inside the narrow TON-, MTT-, MTW-, or ZSM-48-type pores [24][25][26][27][41][42][43][44][45]; another possibility is that they impede formation of alkanes with proximate methyl groups, because not even an alkane with a single methyl group fits inside TON-or MTT-type pores [4][5][6][7][8][9][10][11][12][13][14][15].…”

Section: Introductionmentioning

confidence: 99%

“…The hypothesis that no methylalkane fits inside TON-type zeolite pores led to the postulation of "pore mouth" and "keylock" catalysis-reaction schemes all occurring in a layer of alkane isomers adsorbed epitaxially at the exterior TONand MTT-type zeolite crystals [4][5][6][7][8][9][10][11][12][13][14][15]. Originally, a molecular graphics assessment formed the basis for the key hypothesis that methylalkanes are too large to fully enter TONtype pores [6].…”

Section: Introductionmentioning

confidence: 99%

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Shape-selective n-alkane hydroconversion at exterior zeolite surfaces

Maesen

Krishna²,

Baten³

et al. 2008

Journal of Catalysis

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A critical review of the adsorption and catalysis of n-and methylalkanes demonstrates that the interior surface of TON-and MTT-type zeolites dominates both adsorption and catalysis, and that the contribution from the exterior surface is negligible. For both n-and methylalkane isomers, the experimental Henry constants at the interior TON-type zeolite surface are more than an order of magnitude greater than those at the exterior surface. Molecular simulations on exclusively interior TON-type silica surface reproduce the adsorption isotherms of n-and methylalkane isomers remarkably well and suggest that even an isomer as bulky as 2,3-dimethylpentane could have access to the interior TON-type zeolite surface. Only the reference state used in solution thermodynamics affords an equitable comparison between internal and external surface thermodynamics. It indicates that methylalkanes adsorb in a structured fashion at the exterior TON-type zeolite surface when the interior surface is inaccessible. But the entropic penalty for this organized exterior surface "pore mouth" or "key-lock" adsorption is high, so that methylalkanes prefer adsorption at the interior surface when it is accessible. We speculate that CHA-and ERI-type sieves exhibit exterior surface catalysis in long n-alkane conversion, but the database remains too small to allow investigation of the full potential of shape selectivity in exterior zeolite surface catalysis.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Shape-selective n-alkane hydroconversion at exterior zeolite surfaces

Maesen

Krishna²,

Baten³

et al. 2008

Journal of Catalysis

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“…The commensurate dimethylalkanes combine a low free energy of adsorption with a high free energy barrier to diffusion, whereas the incommensurate molecules combine a high free energy of adsorption with a low free energy barrier to diffusion [56]. Therefore, only the latter type of dimethylalkanes are found in the hydrocracking product slate [56,133]. However, this nice example of the importance of the Frenkel-Kontorowa effect to catalysis remains the subject of debate [22,56].…”

Section: Fig 11mentioning

confidence: 99%

Computer Simulations of Shape Selectivity Effects

Smit¹,

Maesen

2008

Handbook of Heterogeneous Catalysis

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Introduction Today, almost every gasoline molecule has seen the interior of a zeolite and experienced the effect of shape selectivity. Given the economical importance [1][2][3][4][5] implied by this statement, one would expect that we have a very good understanding of the mechanisms underlying shape selectivity. Clearly, we do have a very good understanding of the chemical reactions that take place inside the pores of a zeolite. In addition, many mechanisms have been proposed to explain the various product distributions that have been observed experimentally. However, we are still very far away that by looking at a zeolite structure we can provide a prediction of the products.Let us consider as a simple example the conversion of n-decane in an acid zeolite. The chemistry tells us that isomerization reactions take place giving mono-, di-, and tribranched isomers. These isomerization reactions compete with cracking, and this results in a large number * Corresponding author.

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Shape Selectivity in Hydrocarbon Conversion

et al. 2001

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Molecular sieves with three-dimensional framework structures find many applications in catalysis. [1, 2] A comprehensive and fundamental understanding of the product selectivity associated with these catalytic processes remains a formidable challenge of considerable practical significance. [3] Herein we focus on conversion reactions of alkanes. We demonstrate that molecular sieves favor the formation of reaction intermediates that have a shape commensurate with their pore shape. Bis(bidentate) catecholamide ligands (Scheme 2) were synthesized according to previously published procedures. [26] Libraries were obtained following a simple procedure: H 4 -L 2 (33.1 mg, 0.077 mmol), H 4 -L 3 (39.0 mg, 0.077 mmol), Et 4 NCl, (4.3 mg, 0.026 mmol), and [Ga(acac) 3 ] (acac acetylacetonate) (37.1 mg, 0.102 mmol) were suspended in methanol (20 mL). A 0.5 n NaOH solution (620 mL) in H 2 O was added slowly, and a clear solution was obtained. After the mixture had been stirred for 2 h, the solvent was reduced to 4 mL, and excess acetone was added to precipitate the product, which was collected by ultracentrifugation, washed with acetone and dried (quantitative yields). The same library was obtained by mixing solutions of [Ga 4 L 2 6 ' (Et 4 N)] 11À and [Ga 4 L 3 6 ' (Et 4 N)] 11À at pD 7.5 after heating for several hours at 60 8C.

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Selective Isomerization of Hydrocarbon Chains on External Surfaces of Zeolite Crystals

Cited by 200 publications

References 15 publications

Shape-selective n-alkane hydroconversion at exterior zeolite surfaces

Shape-selective n-alkane hydroconversion at exterior zeolite surfaces

Computer Simulations of Shape Selectivity Effects

Shape Selectivity in Hydrocarbon Conversion

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