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  • 11
    ISSN: 1572-879X
    Keywords: Copper/alumina ; crotonaldehyde hydrogenation ; selectivity (butanal) ; chlorine poisoning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of the presence of chlorine on the activity and selectivity of a Cu/Al2O3 catalyst has been examined for the selective hydrogenation of an αβ unsaturated aldehyde, crotonaldehyde. Cu/Al2O3 in the absence of chlorine poisons produced 1-butanol almost exclusively, whereas catalysts pre-dosed with a suitable amount of chlorine compound (CCl4, CHCl3 and CH2Cl2) shifted the product distribution towards formation of butanal. The poisoning effectiveness increased in the order CCl4〈CHCl3〈CH2Cl2≪CH3Cl and methyl chloride was found to totally deactivate the catalyst. The most significant enhancement in butanal selectivity was observed with CCl4 and CH2Cl2. The effect of chlorine as a poison is in contrast to the effect of sulphur which enhances formation of crotyl alcohol and the origins of these effects are discussed.
    Type of Medium: Electronic Resource
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  • 12
    ISSN: 1572-879X
    Keywords: titanium silicalite TS-1 ; hydrogen peroxide as oxidant ; allyl alcohol epoxidation ; glycidol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The epoxidation of allyl alcohol to glycidol using the titanium silicalite TS-1 with hydrogen peroxide as the oxidant is described and discussed in detail. The reaction conditions (alcohol, solvent, temperature) required to obtain 100% selectivity to glycidol are described and this selectivity has been observed at conversions of allyl alcohol of up to 20%. Addition of excess hydrogen peroxide enhances conversion but does not appear to affect selectivity to glycidol deleteriously, whereas addition of hydrogen peroxide over an extended time period is not particularly beneficial. The major side reactions are the oxidation of the alcohol solvent and the ring opening solvolysis of the glycidol that leads to the formation of alkoxy diols. Base treatment of the TS-1 using sodium azide enhances the glycidol selectivity, whereas the incorporation of Brønsted acid sites by addition of aluminium into the framework structure of TS-1 enhances the selectivity to the products of solvolysis ring opening reactions.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Catalysis letters 34 (1995), S. 115-127 
    ISSN: 1572-879X
    Keywords: zeolite Y ; allyl alcohol conversion ; acrolein ; acetone ; propene oxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The reaction of allyl alcohol using zeolite Y as catalyst has been investigated and it is shown that it can be converted into a range of products, including hydrocarbons, acrolein and diallyl ether. Control of product selectivity can be achieved by careful selection and manipulation of the charge balancing cation, a series of catalysts can be prepared which, for the conversion of allyl alcohol, lead almost exclusively to the initial formation of either (a) C2-C6 hydrocarbons and coke (H-NaY), (b) acrolein (H-CsY), (c) propene (Li-NaY) or (d) diallyl ether (Cs-NaY). The effects of addition of H2 and H2O to the reactant are described and discussed with respect to the reaction mechanism and the reaction of potential intermediates (2-propanol and propene oxide) is also described. Mechanisms of formation of the major products are proposed that involve the concerted action of Brønsted acid and basic sites within the zeolite. In particular, since the addition of H2O does not affect the product distribution, it is considered that the mechanism of hydrocarbon formation does not involve the allyl cation as an intermediate.
    Type of Medium: Electronic Resource
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  • 14
    ISSN: 1572-879X
    Keywords: thiophene synthesis ; heterogeneous catalyst ; vapour phase ; chromia–alumina
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A study of the synthesis of thiophene from the reaction of butanol and CS2 over potassium‐promoted Cr2O3/γ‐Al2O3 has been performed by examination of the reactivity of model intermediates. This study indicates that the reaction path involves successive dehydrogenation, O/S exchange and dehydroheterocyclization.
    Type of Medium: Electronic Resource
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  • 15
    ISSN: 1572-879X
    Keywords: Propane aromatization ; zeolite H-ZSM-5
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The aromatization of propane is investigated for Ga2O3, H-ZSM-5 and Ga2O3/H-ZSM-5 catalysts, and the results are discussed for a series of ZSM-5 catalysts containing varying SiO2/Al2O3 ratios. It is apparent that on addition of a gallium phase to H-ZSM-5, the yield of methane is significantly decreased. These results are discussed with respect to the mechanism of formation of the initial reaction product from propane. It is proposed that the synergy observed between the gallium compound and the zeolite can be explained in terms of a mechanism in which the role of the gallium phase is to induce C-H bond polarization in the propane, which leads to attack via the Bronsted acid sites of the zeolite, which leads to initial C-H bond cleavage occurring.
    Type of Medium: Electronic Resource
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  • 16
    ISSN: 1572-879X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 17
    ISSN: 1572-879X
    Keywords: vanadium phosphorus oxides ; VOHPO4.0.5H2O ; catalyst promotion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of the addition of Co2+ and Fe3+ on the catalytic performance and structure of vanadium phosphate catalysts is described and discussed. The catalyst precursor VOHPO4.0.5H2O was prepared using the aqueous HC1 route and Co2+ and Fe3+ were incorporated using the incipient wetness method. Addition of Co2+ improves the selectivity to maleic anhydride, but is found to decrease the specific activity for the formation of maleic anhydride, whereas the addition of Fe3+ increases the specific activity up to a maximum level at ca. 2 mol% Fe. The effects are not due to changes in the specific surface area of the final catalyst, which remains 6.5 ±0.5 m2 g−1 for all the catalysts studied. Part of the effect is due to the formation of VOPO4 phases in the catalyst precursor due to the method of addition of the Co2+ or Fe3+ and this is both related to the effect of the oxidation potential of the additive cation and to the pH of the impregnating solution. It is apparent that the use of the incipient wetness method for the addition of promoter compounds should be used with care for the VPO system at variance with the direct incorporation of the promoter during the preparation of the VOHPO4.0.5H2O precursor.
    Type of Medium: Electronic Resource
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  • 18
    ISSN: 1572-879X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Inhibition of the methanol to gasoline reaction induced by co-feeding of nitric oxide is compared and contrasted with inhibition by ammonia. It is concluded that NO does not act as a catalyst poison by being converted to NH3. A mechanism for inhibition of the reaction by NO based on the Barton reaction is proposed.
    Type of Medium: Electronic Resource
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  • 19
    ISSN: 1572-879X
    Keywords: gallium oxide ; zeolite H-ZSM-5 ; propane aromatization ; synergy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effects of co-feeding excess hydrogen on the propane aromatization reaction over Ga2O3, H-ZSM-5 and physical mixtures of Ga2O3/H-ZSM-5 are described and discussed. For Ga2O2 alone co-feeding excess hydrogen gives a significant increase in the conversion and aromatic selectivity. For H-ZSM-5 alone co-feeding excess hydrogen gives a slight decrease in conversion and increases the selectivity to hydrogenated products. For Ga2O3/H-ZSM-5 physical mixtures co-feeding excess hydrogen leads to a significant decrease in the conversion and aromatic selectivity. We propose that hydrogen can be used as a reactive probe molecule for this reaction. Experiments are also described for propane aromatization over physical mixtures of powdered Ga2O3 and pelleted H-ZSM-5 that provide evidence for the reversible formation of the active site for this reaction.
    Type of Medium: Electronic Resource
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  • 20
    Electronic Resource
    Electronic Resource
    Springer
    Catalysis letters 8 (1991), S. 115-123 
    ISSN: 1572-879X
    Keywords: Propane activation ; zeolite Y ; gallium oxide ; propane cracking ; propane dehydrogenation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The activation of propane using zeolite H-Y and Ga3+ exchanged zeolite Y indicates that in the presence of Ga3+ the mechanism of propane activation is changed from a cracking pathway to a dehydrogenation pathway. The presence of both Ga3+ and H+ are required to achieve this effect.
    Type of Medium: Electronic Resource
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