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Subject: search.filters.subject.Heterogeneous catalysis

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    Methanation of CO2 on Supported Ru Catalysts
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1981, 77 (05), 1981) Solymosi, Frigyes; Erdohelyi, Andras; Kocsis, Maria
    The transformation of C in the form of CO2 into hydrocarbons was investigated on supported Ru catalysts. Special attention was paid to the surface processes occurring during the removal of the O atoms of CO2 by H2 and on the identification of surface species formed during the reaction. Infrared spectroscopic measurements revealed that chemisorbed CO and formate ion are formed during the coadsorption of H2+ CO2 at 373 K and also during the methanation of CO2 at higher temperatures. The CO formed produced a weak absorption band at lower frequencies (1990–2000 cm–1) than did the CO alone (2030–2040 cm–1). This shift was attributed to the effect of hydrogen adsorbed on the same Ru atoms and to that of surface C formed during the reaction. Evidence is presented to show that formate ion forms on the Ru but migrates rapidly onto the supports. It is considered as an inactive species in the methanation of CO2. The hydrogenation of CO2 on Ru/Al2O3 occurred at a measurable rate above 443 K yielding almost exclusively CH4. The formation of surface carbon was detected during the reaction at a level ca. 1.5 orders of magnitude less than in the H2+ CO reaction. The rate of CH4 formation is described by the expression NCH4= 2.7 × 106 exp (–16.1/RT)×PH2× 0.47 PCO2. It is proposed that the synthesis of CH4 from H2+ CO2 occurs via the formation of surface C and its subsequent hydrogenation.
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    Selectivity of a Heterogeneous Rhodium Catalyst for the Carbonylation of Monohydric Alcohols
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (12), 1977) Christensen, Bjarne; Scurrell, Michael S
    The carbonylation activity of a heterogeneous rhodium-zeolite catalyst has been examined for the reactions of methanol, ethanol and propan-2-ol. A marked contrast in the behaviour of these three alcohols is seen. Selectivity for the carbonylation of methanol is high (>90 %) at all temperatures, whereas the sole reaction product with propan-2-ol is propene. Ethanol shows intermediate behaviour, exhibiting high selectivity (approaching 100%) for carbonylation at low temperatures, but very poor selectivity at higher temperatures. The results are consistent with the relative ease with which dehydration of the reactants occurs on polar catalysts.
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    Effect of Lead Compounds on Heterogeneous Oxidation Catalysts
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (08), 1978) Bucknell, James G.; Cullis, Charles F.; Hucknall, David J.
    Studies have been made of the structure, physicochemical characteristic and catalytic activity of a number of unsupported and alumina-supported transition metal oxides as well as of alumina-supported platinum. Measurements have also been made of the effects on these properties of varying amounts of lead bromide and lead chloride, which were introduced onto the surface of the catalysts by means of a fluidised-bed reactor and in all cases caused a reduction in activity. X-ray and thermal studies showed that the observed decrease in catalytic activity could not be attributed to the formation of a new catalytically inactive phase. With unsupported nickel (II) oxide, manganese (IV) oxide and possibly copper (II) oxide, the poisoning effect of the lead halides can, however, be satisfactorily accounted for in terms of the formation of a monolayer of the lead compound on the catalyst surface. The results obtained with unsupported cobalt (II, III, III) oxide are less readily explained. At low temperatures, lead (II) chloride in monolayer amounts caused complete deactivation, but at higher temperatures considerably greater quantities of this compound were needed to eliminate catalytic activity. Under all conditions used, a large excess of lead (II) bromide was required to deactivate this oxide completely. With supported catalysts, the lead halides appeared to be preferentially adsorbed on the alumina support. Again, however, Co3O4/Al2O3 catalysts behaved atypically, in that no such preferential adsorption took place and even sub-monolayer amounts of lead (II) chloride caused complete elimination of catalytic activity.