Intracrystalline and Molecular-Shape-Selective Catalysis by Zeolite Salts

Weisz, Paul B.; Frilette, V. J.

doi:10.1021/j100832a513

Cited by 374 publications

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“…421 If a molecule's adsorption is inhibited, it will show up intact in the product slate. If a molecule's desorption is inhibited, it could still form as a reaction intermediate in the adsorbed phase, but only molecules that originate from this reaction intermediate through consecutive reactions will show up in the product distribution.…”

Section: Traditional Shape Selectivitymentioning

confidence: 99%

“…421 It yields only linear and no branched cracking products, because only the former can desorb from the zeolite pores.…”

Section: Product Shape Selectivitymentioning

confidence: 99%

“…8,[416][417][418][419] Weisz and Frilette at the Mobil (now ExxonMobil) oil company coined the term "shape selective catalysis" in the 1950s, when they discovered that only molecules permeable into an LTA-type zeolite were catalytically converted, to the exclusion of others. [420][421][422][423] The concept was rooted in enzymatic catalysis, 421,422 which would suggest that explanations for shape selective catalysis would relate to modifications of the transition state for various reactions. 424 However, explanations for shape selective catalysis gravitated strongly toward mass transport phenomena at Mobil.…”

Section: Introductionmentioning

confidence: 99%

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Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity

2008

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Section: Traditional Shape Selectivitymentioning

confidence: 99%

“…421 It yields only linear and no branched cracking products, because only the former can desorb from the zeolite pores.…”

Section: Product Shape Selectivitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity

2008

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“…5.5.3.2.2 Shape Selectivity: General Principles The original notion of shape selectivity [26] is simply the observation that, if a molecule cannot permeate through the pores of a zeolite, it will not adsorb as a reactant or desorb as a product [6]. If the adsorption of a molecule is inhibited, it will show up intact in the product slate.…”

Section: Figmentioning

confidence: 99%

“…Weisz and Frilette coined the term ''shape selective catalysis'' during the 1950s, when they discovered that only molecules permeable into an LTA-type zeolite were catalytically converted, to the exclusion of others [6][7][8][9]. In a 1971 review Venuto pointed out that, in addition to shape selectivity, there are ''.…”

Section: Introductionmentioning

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‐Selective Catalysis – Heterogeneous

Csicsery

Kiricsi

2002

Encyclopedia of Catalysis

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Molecular sieves have uniform pores. If the pores are small, the fate of the reactants and the probability of forming products are determined by molecular dimensions and configurations as well as by the types of catalytically active sites present. Reactant shape selectivity occurs when some of the molecules in a reactant mixture are too large to enter the pores. Product selectivity occurs when, among all the product molecules formed within the pores, only those with the proper dimensions can diffuse out and appear as products. In restricted transition state type selectivity certain reactions are prevented because the corresponding transition state requires more space than is available inside the pores. Shape selective processes include acid‐ or base‐catalyzed reactions, oxidations, and reductions. Commercial applications of shape selectivity ( 1 ) form desirable isomers instead of undesirable ones, ( 2 ) crack undesirable molecules to smaller, easily removable fragments, or ( 3 ) avoid undesirable competing reactions such as coking and transalkylation. Ordered mesoporous materials, pillared layer structures, heteropolyacids, and carbon molecular sieves and nanotubes extend shape‐selective application to reactions of molecules too large to fit in the pores of aluminosilicate zeolites. Designing new molecular sieves and modifying existing ones can amplify shape selective effects and thus help to meet future challenges: diminishing raw material supplies, more stringent environmental regulations, changing fuel requirements, and the desire for more flexible, more economical, and environmentally more friendly processes.

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Intracrystalline and Molecular-Shape-Selective Catalysis by Zeolite Salts

Cited by 374 publications

References 0 publications

Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity

Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity

Computer Simulations of Shape Selectivity Effects

Shape‐Selective Catalysis – Heterogeneous

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