829 research outputs found

    Sorption and activation of hydrocarbons by molecular sieves

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    Substantial progress has been made recently in the understanding of sorption and activation of alkanes. This progress reflects the emergence of new theoretical and experimental results, leading to a more quantitative picture of the elementary steps involved in the ordering of alkanes in molecular sieves and their chemical interaction with the acid site. Conversion of n-alkanes over various zeolites is now well understood to depend mainly upon the concentration of reactants sorbed. The sorption enthalpy and entropy of these molecules are linearly related and this relationship is characteristic of a particular molecular sieve (compensation effect). The interfacial chemistry that alkanes and alkenes undergo involves ionic species only in their transition state, whereas the stable intermediates are covalently bound. This leads to a description of the chemical transformations that resemble nucleophilic and electrophilic substitutions

    Liquid phase hydrogenation of crotonaldehyde over Pt/SiO2 catalysts

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    The dependence of the catalytic properties of Pt/SiO2 catalysts for the hydrogenation of crotonaldehyde on the hydrogen pressure, the reaction temperature, the nature of the solvent and the presence of several additives were investigated. Strong deactivation of the catalysts mainly caused by decarbonylation of crotonaldehyde and irreversible adsorption of CO was observed. The initial activity of the deactivated catalysts is regained by oxidation of the adsorbed CO to CO2 by purging with air. The selectivity to crotylalcohol increased with increasing number of turnovers per metal site. This is explained with preferential blocking of the nonselective sites on the metal crystallites by CO and by a slow surface modification of the aging catalyst with organic deposits. The overall rate and the selectivity to the saturated aldehyde are markedly enhanced by an increase in hydrogen pressure and by a decrease in reaction temperature. The addition of modifiers such as potassium acetate, triphenylphosphine and thiophene had only little influence on the activity and the selectivity of the catalysts

    Infra-red studies of the surface acidity of oxides and zeolites using adsorbed probe molecular

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    The use of infrared spectroscopy to probe the surface acidity of oxides and molecular sieves is reviewed. The experimental requirements and the type and nature of probe molecules available are also discussed. Special emphasis is given to the criteria that have to be met to arrive at a characterization of the solid that is useful for its catalytic application

    Synthesis and characterization of mesoporic materials containing highly dispersed cobalt

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    Highly dispersed Co particles in MCM-41 were prepared by direct addition of CoCl2 to the synthesis gel. The small clusters of Co did not sinter during reduction and sulfidation. Incorporation of Co into the MCM-41 lattice was not observed. The addition of Co to the synthesis gel did not alter the structural characteristics of the MCM-41 samples

    Influence of slope of rise and event order of aircraft noise events on high resolution actimetry parameters

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    Zusammenfassung: Starts und Landungen in der Nacht sind bei den meisten Verkehrsflughäfen durch eine Nachtflugsperre eingeschränkt. Die Empfindlichkeit der Bevölkerung, durch Fluglärm im Schlaf gestört zu werden, ist daher zu Randzeiten, also abends und morgens, besonders gross. In einer experimentellen Feldstudie bei Anwohnern in der Umgebung des Flughafens Zürich untersuchten wir die Wirkung von Fluglärmereignissen auf Körperreaktionen vor dem Aufwachen am Morgen. Dabei wurden in den Schlafzimmern der Versuchspersonen zuvor aufgezeichnete Fluglärm-Geräusche abgespielt. Mit einem nichtinvasiven Aufzeichnungsverfahren für schlafphysiologische Parameter (Hochauflösende Aktimetrie-, Herz- und Atemparameter) wurden Körperbewegungen ereigniskorreliert registriert. Die Resultate ergaben, dass vor allem die ersten paar Lärmereignisse am frühen Morgen die stärksten Reaktionen evozierten und diese mit zunehmender Anzahl erlebter Lärmereignisse abnehmen, was vermuten lässt, dass die zuvor erlebte Anzahl Überflüge eine systematische Wirkung hat, insbesondere wenn die Ereignisse innerhalb kurzer Zeitintervalle auftreten. Es zeigte sich auch, dass die Motilität von der Anstiegsgeschwindigkeit des Schallpegels abhängt, steilere Anstiegsflanken - wie sie typischerweise direkt unterhalb von Landeanflugschneisen auftreten - erzeugen stärkere Bewegungsreaktionen. Dies ist im Einklang mit einer neueren Untersuchung über den Zusammenhang zwischen nächtlichem Flug- und Eisenbahnlärm und Aufwachwahrscheinlichkei

    Ways of quality improving of the ceramic bricks made from Novosibirsk region raw clay materials

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    "Likolor" plant is leading enterprises of the Novosibirsk region for the production of ceramic facing bricks. The research is conducted on the technological aspects of this factory to ensure the stability of quality indicators for different batches of products
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