The Insertion of Heterocumulenes into Zn−H and Zn−OH Bonds of Pyrazolylborate−Zinc Complexes

Rombach, Michael; Brombacher, Horst; Vahrenkamp, Heinrich

doi:10.1002/1099-0682(20021)2002:1<153::aid-ejic153>3.0.co;2-k

Cited by 58 publications

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References 32 publications

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“…[1] For example, one of the simple Zn-enzymecatalyzed processes, the hydration of CO 2 by carbonic anhydrase, has led to extensive mechanistic and theoretical studies of the interaction of CO 2 with Zn-OH. [2][3][4][5] Also, in heterogeneous catalysis, a detailed understanding of the surface chemistry of CO 2 is an important issue; interest in this topic ranges from developing new processes for an emplacement of this greenhouse gas to the synthesis of methanol from syngas (CO/CO 2 /H 2 ) over Cu/ZnO catalysts. [6] Numerous studies have been reported on CO 2 adsorption on clean metal surfaces, where frequently activation is found to occur via the formation of a bent CO 2 dÀ species.…”

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CO₂ Activation by ZnO through the Formation of an Unusual Tridentate Surface Carbonate

et al. 2007

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The activation of CO 2 is one of the most important topics in catalysis.[1] For example, one of the simple Zn-enzymecatalyzed processes, the hydration of CO 2 by carbonic anhydrase, has led to extensive mechanistic and theoretical studies of the interaction of CO 2 with Zn-OH. [2][3][4][5] Also, in heterogeneous catalysis, a detailed understanding of the surface chemistry of CO 2 is an important issue; interest in this topic ranges from developing new processes for an emplacement of this greenhouse gas to the synthesis of methanol from syngas (CO/CO 2 /H 2 ) over Cu/ZnO catalysts. [6] Numerous studies have been reported on CO 2 adsorption on clean metal surfaces, where frequently activation is found to occur via the formation of a bent CO 2 dÀ species. [7][8][9] For oxide surfaces much less information is available. This deficit is in part due to the poor electric conductivity of many oxides which severely complicates the application of electron-based spectroscopic methods. In particular, there is a lack of information concerning molecular vibrations from highresolution electron energy loss spectroscopy (HREELS).The application of HREELS on oxide surfaces is-in addition to the electric conductivity problem-severely limited by the presence of intense substrate lattice excitations (FuchsKliewer phonons [10] ) which obscure the relatively weak vibrational modes of adsorbed species.Herein we present the results of a systematic multitechnique experimental and theoretical study on the interaction of CO 2 with the mixed-terminated ZnO(101 0) surface. In contrast to other oxides, ZnO is sufficiently conductive that electron-based methods can be applied without significant difficulties. The results from HREELS, thermal desorption spectroscopy (TDS), low-energy electron diffraction (LEED), He-atom scattering (HAS), and X-ray photoelectron spectroscopy (XPS) reveal a complicated scenario, comprising the presence of two different ordered phases. By employing accurate periodic density-functional theory (DFT) and wave-function-based quantum-chemical cluster calculations it could be shown that the previously proposed bidentate bonding of CO 2 to this ZnO surface [11] has to be revised. Exposure to CO 2 leads-even at temperatures below 100 Kto the formation of an unusual tridentate carbonate species with the two O atoms of the CO 2 molecule being almost equivalently bound to two different Zn surface atoms.In a first set of experiments, the phase diagram of CO 2 adlayers on this ZnO substrate was determined using HAS. This technique uses neutral He atoms with thermal energy so charging problems are avoided. HAS is a highly sensitive surface-analysis method, [12][13][14] and has been successfully used to determine the phase diagram of H 2 O on the same surface.[15] The HAS data show that exposure of the sample to very small amounts of CO 2 in two steps (first with 4 L at 260 K and then 8 L at 120 K; exposures are given in units of langmuir (1 L = 1.33 10 À6 mbar s)) results in the formation of a well-ordered (2 1) phase (Figure 1 ...

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CO₂ Activation by ZnO through the Formation of an Unusual Tridentate Surface Carbonate

et al. 2007

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“…The active site is proposed to contain a Zn atom in a tetrahedral coordination sphere connected to histidine ligands. Model studies [44,45] have so far activated CO 2 , but the process stopped at the bicarbonate complex (''product inhibition''). Figure 17 is an illustration of the Zn-complex from Ref.…”

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Designing Heterogeneous Catalysts by Incorporating Enzyme-Like Functionalities into MOFs

2010

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Everyone who works within the field of catalysis draws inspiration from the amazing functionality of nature's catalysts, the enzymes. It is particularly the mild conditions that these catalysts are able to operate at and the selectivity that they demonstrate that make these materials dream targets for scientists involved in the art of synthesizing homogeneous and heterogeneous industrial catalysts. But enzymes also have their weak points; in particular their low thermal stability and their often too slow reaction rates for an economical industrial process are problems that have to be overcome. The obvious solution would be to copy the catalytic active center into a robust open framework. A key property of an enzyme is its selectivity; this property is partly regulated by steric constraints surrounding the catalytically active site. The microporous zeolite based catalysts in some cases show impressive selectivity based on the geometrical constraints imposed by the size and shape of the regular channels in these crystalline silicate and alumino-phosphate based structures, and enzyme-like properties have been claimed but the pure inorganic nature of the selective internal surface in these materials makes it impossible to mimic many important enzymatic properties. The new generation of microporous materials, Metal Organic Frameworks (MOFs) are hybrids of organic and inorganic structures.This dualistic nature offers an unprecedented flexibility in the possibility to incorporate both organic and metallic functional groups into the ordered crystalline lattice and thereby opening up for a much greater possibility to copy structural motifs known from enzymes into much simpler but also more stable open structures. Several groups are working on development of new catalysts by this approach. Here we will illustrate this approach with structures that mimic anhydrase and C-H activation.

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“…Die Aktivierung von CO 2 ist eines der wichtigsten Themen in der Katalyse 1. So wurden zum Beispiel zur Hydratation von CO 2 durch Carboanhydrase, einem der einfachen durch Zinkenzyme katalysierten Prozesse, umfangreiche mechanistische und theoretische Studien durchgeführt, speziell zur Wechselwirkung von CO 2 mit ZnOH 2–5. Auch in der heterogenen Katalyse ist ein grundlegendes Verständnis der Oberflächenchemie von CO 2 von großer Bedeutung; das Interesse reicht von der Entwicklung neuer Prozesse für eine Einlagerung dieses Treibhausgases bis zur Methanolsynthese aus Synthesegas (CO/CO 2 /H 2 ) über Cu/ZnO‐Katalysatoren 6.…”

Section: Experimentelle Und Berechnete Schwingungsfrequenzen [Cm−1] Dunclassified

CO₂‐Aktivierung durch ZnO unter Bildung eines ungewöhnlichen dreizähnigen Oberflächencarbonats

et al. 2007

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Die Aktivierung von CO 2 ist eines der wichtigsten Themen in der Katalyse.[1] So wurden zum Beispiel zur Hydratation von CO 2 durch Carboanhydrase, einem der einfachen durch Zinkenzyme katalysierten Prozesse, umfangreiche mechanistische und theoretische Studien durchgeführt, speziell zur Wechselwirkung von CO 2 mit ZnÀOH. [2][3][4][5] Auch in der heterogenen Katalyse ist ein grundlegendes Verständnis der Oberflächenchemie von CO 2 von großer Bedeutung; das Interesse reicht von der Entwicklung neuer Prozesse für eine Einlagerung dieses Treibhausgases bis zur Methanolsynthese aus Synthesegas (CO/CO 2 /H 2 ) über Cu/ZnO-Katalysatoren. [6] Frühere Untersuchungen zur CO 2 -Adsorption konzentrierten sich auf saubere Metalloberflächen, auf denen in der Regel eine CO 2 -Aktivierung über die Bildung einer gewinkelten CO 2 dÀ -Spezies erfolgt. [7][8][9] In einer ersten Serie von Experimenten wurde das Phasendiagramm der CO 2 -Adsorbatlagen auf diesem ZnO-Substrat mithilfe von HAS untersucht. Bei dieser Technik werden neutrale He-Atome mit thermischer Energie verwendet, sodass grundsätzlich keine Aufladungsprobleme auftreten. Diese außerordentlich empfindliche Oberflächenanalysen-methode [12][13][14] wurde bereits erfolgreich in früheren Untersuchungen zur Bestimmung des Phasendiagramms von H 2 O auf derselben Oberfläche eingesetzt.[15] Die HAS-Daten zeigen, dass sich nach Belegen der Probe mit einer sehr kleinen CO 2 -Menge in zwei Schritten (zuerst mit 4 L bei 260 K und dann 8 L bei 120 K) eine gut geordnete (2 1)-Phase bildet (Abbildung 1, Kurve b). Nach Sättigung der Oberfläche mit CO 2 verschwindet diese (2 1)-Struktur, und eine (1 1)

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The Insertion of Heterocumulenes into Zn−H and Zn−OH Bonds of Pyrazolylborate−Zinc Complexes

Cited by 58 publications

References 32 publications

CO₂ Activation by ZnO through the Formation of an Unusual Tridentate Surface Carbonate

CO₂ Activation by ZnO through the Formation of an Unusual Tridentate Surface Carbonate

Designing Heterogeneous Catalysts by Incorporating Enzyme-Like Functionalities into MOFs

CO₂‐Aktivierung durch ZnO unter Bildung eines ungewöhnlichen dreizähnigen Oberflächencarbonats

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The Insertion of Heterocumulenes into Zn−H and Zn−OH Bonds of Pyrazolylborate−Zinc Complexes

Cited by 58 publications

References 32 publications

CO2 Activation by ZnO through the Formation of an Unusual Tridentate Surface Carbonate

CO2 Activation by ZnO through the Formation of an Unusual Tridentate Surface Carbonate

Designing Heterogeneous Catalysts by Incorporating Enzyme-Like Functionalities into MOFs

CO2‐Aktivierung durch ZnO unter Bildung eines ungewöhnlichen dreizähnigen Oberflächencarbonats

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CO₂ Activation by ZnO through the Formation of an Unusual Tridentate Surface Carbonate

CO₂ Activation by ZnO through the Formation of an Unusual Tridentate Surface Carbonate

CO₂‐Aktivierung durch ZnO unter Bildung eines ungewöhnlichen dreizähnigen Oberflächencarbonats