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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Catalysis letters 12 (1992), S. 105-115 
    ISSN: 1572-879X
    Schlagwort(e): Catalysis ; clean fuels ; reformulated gasoline ; ethers ; oil refining ; natural gas conversion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract New and more stringent environmental legislation is expected to have a major impact on the refining industry. Reformulated gasoline which is currently being introduced into parts of the United States is an example of the shift towards “cleaner” burning fuels. To achieve future government specifications for such fuels significant changes will likely be required in refinery operations to produce products with good combustion characteristics and reduced emissions. Catalysis is expected to play a dominant role in both modifying existing processes and developing new routes to these more environmentally acceptable fuels. Both new and improved catalysts systems which will be required for the production of so-called reformulated gasoline are discussed. For example, oxygenated components in gasoline such as methyl tertiary butyl ether (MTBE) will continue to be required on a large scale necessitating new process and catalyst technology to achieve improved economics. Natural gas can be considered as a “clean” feedstock from which to produce liquid fuels of high quality. A number of new process routes to convert remote natural gas into readily transportable liquid fuels are also discussed. This area of technology offers considerable scope for further major improvements based on innovation in the field of syngas catalysis.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Catalysis letters 12 (1992), S. 147-155 
    ISSN: 1572-879X
    Schlagwort(e): Catalysis ; zeolites ; palladium ; ion exchange ; solid-state ; hydrogenation ; hydroisomerisation ; ethylbenzene
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Bifunctional catalysts containing an acidic as well as a hydrogenation/dehydrogenation function were prepared by solid-state ion exchange. Preparation and properties of Pd-loaded H-ZSM-5 are described in detail. The catalytic behavior of the reduced catalysts was investigated using hydrogenation and hydroisomerisation of ethylbenzene as a test reaction. The catalytic performance of the catalysts could be significantly improved by concomitant incorporation of Ca2+. This was advantageously achieved in a two-step procedure, where first a solid-state ion exchange with CaCl2 and subsequently a second solid-state ion exchange with PdCl2 was carried out. A Ca, H-ZSM-5 with 1.5 wt-% Pd obtained via this two-step procedure and subsequent reduction in H2 exhibited high activity, long life-time and good selectivity with respect to hydrogenation and hydroisomerisation of ethylbenzene to ethylcyclohexane and dimethylcyclohexanes, respectively. Electron micrographs of the reduced catalyst showed finely dispersed palladium with maximum size of about 2.0 nm.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Catalysis letters 14 (1992), S. 101-106 
    ISSN: 1572-879X
    Schlagwort(e): Catalysis ; aromatization ; propane ; ZSM-5 ; hydrogen acceptor ; intermetallic compound ; hydride
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The effect of the hydride-forming intermetallic compound Zr2Fe on the aromatization of propane over high-silica zeolites of CVM type (Russian equivalent of ZSM-5) modified by Zn, Ga or Pt cations has been investigated. Aromatics yield and selectivity of aromatization are shown to increase essentially as a result of releasing hydrogen elimination by the intermetallic acceptor. The effect of hydrogen acceptor on propane conversion and product distribution appeared to be different depending on the composition of the catalyst used. Possible changes in the reaction mechanism in hydrogen removal conditions are discussed.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Journal of molecular evolution 35 (1992), S. 1-6 
    ISSN: 1432-1432
    Schlagwort(e): Sugar synthesis ; Glyceraldehyde ; Iron(III) hydroxide oxide ; Catalysis ; Aldol condensation ; Prebiotic ; Molecular evolution
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Iron(III) hydroxide oxide [Fe(OH)O] efficiently catalyzed the condensation of 25 MM dl-glyceraldehyde to ketohexoses at 25°C (pH 5–6). At 16 days the yields were sorbose (15.2%), fructose (12.9%), psicose (6.1%), tagatose (5.6%), and dendroketose (2.5%) with 19.6% of triose unreacted. Analysis at 96 days showed no decomposition of hexoses. Under these conditions Fe(OH)O also catalyzed the isomerization and rearrangement of glyceraldehyde to dihydroxyacetone and lactic acid, respectively. In these reactions, about 10% of the glyceraldehyde was oxidized to glyceric acid with concurrent reduction of the iron(III) to iron(II). The partial reduction of Fe(OH)O did not noticeably reduce its ability to catalyze hexose synthesis. The relationship of these results to prebiotic sugar synthesis is discussed.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Chromatographia 34 (1992), S. 398-410 
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Reversed-flow technique ; Catalysis ; Hydrodenitrogenation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Many important parameters of surface catalysed reactions can be determined simultaneously, under nonsteady state conditions using Reversed-Flow Gas Chromatography. A simple, slightly modified gas chromatograph is required. The distorted diffusion bands, obtained experimentally for reactant and product(s), can be analysed mathematically, using simple PC programs, to give the pre-exponential factors and the exponential coefficients of a function consisting of the sum of two-four exponential functions of time. From these, and some geometrical and diffusional characteristics of the reaction cell, the values of adsorption, desorption and reaction rate constants, the overall mass transfer coefficients in the gas and in the solid catalyst, and the adsorption equilibrium constant, for both reactant and product(s) can be calculated. The above parameters were determined at various temperatures and over three catalysts for the hydrodenitrogenation of piperidine ton-pentane, an industrially important hydrotreating process. The results obtained can help to understand the mechanism of reactions on solid surfaces and to confirm experimentally theoretical calculations on adsorption and surface reactions.
    Materialart: Digitale Medien
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  • 6
    ISSN: 1040-0397
    Schlagwort(e): Catalysis ; flow analysis ; modified electrodes ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A model for a layer, containing catalytic centers, coated on an electrode and used for the mediation of analyte in a flowing stream is proposed and solved. The model applies to a situation of a Gaussian concentration profile of analyte impinging on the outer edge of the mediating layer. It was found that the important parameters that limit the current magnitude are the diffusion coefficient of the analyte through the layer, the effective electron diffusion coefficient through the layer and the rate of reaction between the mediator and the analyte. On evaluation of literature data, it was found that layers, high catalyst loading and with high rates of electron exchange, lead to linear peak current height versus concentration plots.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Electroanalysis 4 (1992), S. 167-182 
    ISSN: 1040-0397
    Schlagwort(e): Catalysis ; reaction mechanism ; channel electrode ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The shape of the current-voltage curves at a channel electrode have been calculated for the various situations of the catalytic (EC′) mechanism. In particular the halfwave potential and limiting current are found to be highly sensitive to the solution-flow rate and to the concentrations of the mediator and substrate employed. These observations provide a ready method of unambiguously characterizing the different pathways.
    Zusätzliches Material: 22 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 8
    ISSN: 0570-0833
    Schlagwort(e): Proton transfer ; Catalysis ; Enzyme catalysis ; Hydrolysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The proton occupies a special position as a promoter and mediator in chemical reactions occurring in solution. Many reactions in organic chemistry are catalysed by acids or bases; likewise, most enzymes contain active groups which promote acid-base catalysis. To understand the reaction mechanisms involved, it is necessary to identify the elementary steps as well as their course in time. Systematic investigation of these elementary steps as well as their course in time. Systematic investigation of these elementary steps has become possible only with the development of new methods for studying very fast reactions. The present paper reviews the information obtained in this type of investigation. The result is a relatively complete picture of the elementary proton transfer mechanisms and a comprehensive description of the modes and laws of acid-base and enzymatic catalysis.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 93-101 
    ISSN: 0570-0833
    Schlagwort(e): Organometallic catalysts ; Catalysis ; Reaction mechanisms ; Lithium ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Kinetic investigations of the polyreaction of isoprene with organolithium compounds as initiators in n-heptane as solvent indicate the following sequence of reactions: 1. formation of an adduct between a monomeric form of the organolithium compound and the isoprene and 2. reaction of this adduct with an associated form of the organolithium compound with insertion of the isoprene. The adduct formation is considered to be due to chemisorption, and proof of such chemisorption of a monomer (ethylene) is also demonstrated for a homogeneous Ziegler-type catalyst. All the reactions can be formulated in the form of cyclic structures with electron-deficient character. Postulation of such ring structures explains the surprising values obtained for the frequency factors and equilibrium constants.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 185-191 
    ISSN: 0570-0833
    Schlagwort(e): Coordination modes ; Catalysis ; Cyclooctatetraenes ; Reppe chemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The relationship between the structure and the catalytic activity of nickel(II) complexes in the synthesis of cyclooctatetraene by the method of W. Reppe is discussed. The cyclotetramerization of acetylene takes place within labile Ni(II)-acetylene π-complexes. Inhibition tests have made it probable that four molecules of acetylene are grouped around the nickel ion in the transition state, in a configuration which favors the formation of the eight-membered ring.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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