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Lee, Sang-Ok; Sankar, Gopinathan; Kitchin, Simon J.; Dugal, Markus; Thomas, John Meurig; Harris, Kenneth D. M.

doi:10.1023/a:1016626722806

Cited by 10 publications

(6 citation statements)

References 24 publications

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“…It is also true that certain acid-catalyzed reactions in zeolitic solids also have a kinship with enzyme action. Thus, the Brønsted acid catalyzed cyclodimerization of 3-hydroxy-3-methylbutan-2-one (HMB) [89] over a H + form of (synthetic) ferrierite (Si:Al ratio of 40:1) yields only one product, whereas HMB in acidic solution generates a wide variety of products (Scheme 14 a).…”

Section: Methodsmentioning

confidence: 99%

“…[83][84][85][86][87] In each case, cavities in the catalysts impose shape-selectivity that governs the "choice" of reactant species which is to be transformed, and the molecular complementarity and associated factors of the microenvironment at the active site facilitates ensuing chemical conversion. In designing inorganic enzyme mimics, [88][89][90] the key targets are high activity coupled with high selectivity and an ability to function at ambient temperatures and pressures. In general, inorganic enzyme mimics are thermally and mechanically stable, robust, and are usually readily capable of being regenerated when (through "poisoning" of active sites, for example) their performance diminishes.…”

Section: Enzyme Mimicsmentioning

confidence: 99%

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Single‐Site Heterogeneous Catalysts

2005

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Intellectually, the advantages that flow from the availability of single-site heterogeneous catalysts (SSHC) are many. They facilitate the determination of the kinetics and mechanism of catalytic turnover-both experimentally and computationally-and make accessible the energetics of various intermediates (including short-lived transition states). These facts in turn offer a rational strategic principle for the design of new catalysts and the improvement of existing ones. It is generally possible to prepare soluble molecular fragments that circumscribe the single-site, thus enabling a direct comparison to be made, experimentally, between the catalytic performance of the same active site when functioning as a heterogeneous (continuous solid) as well as a homogeneous (dispersed molecular) catalyst. This approach also makes it possible to modify the immediate atomic environment as well as the central atomic structure of the active site. From the practical standpoint, SSHC exhibit very high selectivities leading to the production of sharply defined molecular products, just as do their homogeneous analogues. Given that mesoporous silicas with very large internal surface areas are ideal supports for SSHC, and that more than a quarter of the elements of the Periodic Table may be grafted as active sites onto such silicas, there is abundant scope for creating new catalytic opportunities.

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Section: Methodsmentioning

confidence: 99%

Section: Enzyme Mimicsmentioning

confidence: 99%

Single‐Site Heterogeneous Catalysts

2005

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“…[83][84][85][86][87] In each case, cavities in the catalysts impose shape-selectivity that governs the "choice" of reactant species which is to be transformed, and the molecular complementarity and associated factors of the microenvironment at the active site facilitates ensuing chemical conversion. In designing inorganic enzyme mimics, [88][89][90] the key desiderata are high activity coupled with high selectivity and an ability to function at ambient temperatures and pressures. In general, inorganic enzyme mimics are thermally and mechanically stable, robust, and are usually readily capable of being regenerated when (through "poisoning" of active sites, for example) their performance diminishes.…”

Section: Enzyme Mimicsmentioning

confidence: 99%

“…It is also true that certain acid-catalyzed reactions in zeolitic solids also have a kinship with enzyme action. Thus, the Brönsted-acid catalyzed cyclo-dimerization of 3-hydroxy-3-methylbutan-2-one (HMB) [89] over a H + form of (synthetic) ferrierite (Si/Al ratio of 40) yields only one product, whereas HMB in acidic solution generates a wide variety of products -see Scheme 15…”

Section: Chiral Conversions With Sshcmentioning

confidence: 99%

Single‐Site Heterogeneous Catalysts

Thomas¹,

Raja²,

Lewis³

2005

ChemInform

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Intellectually, the advantages that flow from the availability of single-site heterogeneous catalysts (SSHC) are many. Firstly, they facilitate the determination of the kinetics and mechanism of catalytic turnover-both experimentally and computationally-and render accessible the energetics of various intermediates (including short-lived transition states). These facts in turn offer a rational strategic principle for the design of new catalysts and the improvement of existing ones. Secondly, it is generally possible to prepare soluble molecular fragments that circumscribe the single-site, thus enabling a direct comparison to be made, experimentally, between the catalytic performance of the same active site when functioning as a heterogeneous (continuous solid) as well as a homogeneous (dispersed molecular) catalyst. This also makes it possible to modify the immediate atomic environment as well as the central atomic structure of the active site. From the practical standpoint, SSHC exhibit very high selectivities leading to the production of sharply defined molecular products, just as do their homogeneous analogues. Examples are given of (i) the high regioselectivities of inorganic SSHC enzyme mimics which oxyfunctionalize terminal methyl groups in linear alkanes under mild conditions; (ii) the marked shape-selectivity of SSHC in converting methanol (by Brönsted-acid catalyzed dehydration) preferentially to ethene and propene; (iii) numerous selective hydrogenations with high turnover frequencies (under solvent-free conditions) of polyenes, and also of several enantioselective hydrogenations characterized by high values of ee; and (iv) bifunctional openstructure forms of SSHC in which 'isolated' acid centers and 'isolated' redox centers cooperatively lead to the in situ production of hydroxylamine (from NH 3 and O 2), cyclohexanoneoxime (from cyclohexanone) and (-caprolactam (the precursor to nylon-6). Given that mesoporous silicas with very large internal surface areas are ideal supports for SSHC, and that more than a quarter of the elements of the Periodic Table may be grafted as active sites onto such silicas, there is abundant scope here for creating new catalytic opportunities.

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“…Auch bestimmte säurekatalysierte Reaktionen in zeolithischen Feststoffen zeigen eine Verwandtschaft mit der Wirkungsweise von Enzymen. So entsteht bei der Brönsted‐Säure‐katalysierten Cyclodimerisierung von 3‐Hydroxy‐3‐methylbutan‐2‐on (HMB)89 über einer H + ‐Form von (synthetischem) Ferrierit (Si/Al‐Verhältnis 40) nur ein einziges Produkt (Schema ), während in saurer Lösung eine Vielzahl von Produkten beobachtet wird.…”

Section: Anwendungsbeispieleunclassified

Heterogene Single‐Site‐Katalysatoren

2005

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Die Vorteile heterogener Single‐Site‐Katalysatoren (single‐site heterogeneous catalysts, SSHCs) sind vielfältig. Sie ermöglichen es – sowohl experimentell als auch mit Computermethoden – den Mechanismus und die Kinetik eines katalytischen Umsatzes zu bestimmen, und sie machen die Energetik von Intermediaten einschließlich kurzlebiger Übergangsstadien zugänglich. Dies wiederum bildet die Voraussetzung für ein rationales Vorgehen bei der Verbesserung existierender und der Entwicklung neuer Katalysatoren. Man kann lösliche molekulare Bruchstücke herstellen, die das Einzelatomzentrum enthalten, sodass sich die katalytische Leistung eines aktiven Zentrums in einem heterogenen und in einem homogenen Katalysator experimentell direkt miteinander vergleichen lässt. Mit dieser Information gelingt es, sowohl die unmittelbare atomare Umgebung als auch die zentrale atomare Struktur des aktiven Zentrums zu modifizieren. In der Praxis haben die SSHCs, genauso wie ihre homogenen Analoga, sehr hohe Selektivitäten, was zu genau definierten molekularen Produkten führt. Mesoporöse Siliciumdioxide mit sehr großer innerer Oberfläche sind ideale Träger für SSHCs, und mehr als ein Viertel der Elemente des Periodensystems können als aktive Zentren auf ein solches Siliciumdioxid aufgebracht werden, sodass sich vielfältige Wege für die Erzeugung neuer katalytischer Funktionen ergeben.

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Untitled

Cited by 10 publications

References 24 publications

Single‐Site Heterogeneous Catalysts

Single‐Site Heterogeneous Catalysts

Single‐Site Heterogeneous Catalysts

Heterogene Single‐Site‐Katalysatoren

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