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Catalytic oxidation of heavy hydrocarbons over Pt/Al2O3. Influence of the structure of the molecule on its reactivity

Paper ID Volume ID Publish Year Pages File Format Full-Text
47476 46473 2010 11 PDF Available
Title
Catalytic oxidation of heavy hydrocarbons over Pt/Al2O3. Influence of the structure of the molecule on its reactivity
Abstract

Deep oxidation of 48 hydrocarbons (HCs), from 6 to 20 carbon atoms, was studied over a 1%Pt/Al2O3 catalyst (105 m2 g−1; mean particle size of Pt: 1 nm). The oxidation reaction (1500 ppm C of HC in air) was carried out by increasing the temperature by step of 5 °C from 100 to 400 °C. The reactivity of HCs was characterized by their T50 (temperature at 50% conversion). The reactivity of n-alkanes increases with the chain length, following the same evolution with n as the ionization potential of the molecule. Isoalkanes are more difficult to oxidize than the corresponding n-alkanes. Hydrocarbon reactivity depends on the nature of carbon in the molecule. The ability to be oxidized is greater with CII and CIII carbons while CI and CIV carbons, still more than CI, are refractory to oxidation. The reactivity of n-alkenes depends relatively little on the number of carbons in the molecule. Light alkenes are much more reactive than light alkanes while the reverse can be observed with long-chain hydrocarbons. Contrary to branched alkanes, isoalkenes or cyclenic hydrocarbons are generally more reactive than the corresponding n-alkenes. Short side-chain alkylbenzenes (toluene, ethylbenzene, …) and polymethylbenzenes are more difficult to oxidize than benzene. When the length of the alkyl group is increased, the behaviour of the hydrocarbon in oxidation resembles more and more to long-chain alkanes with a better oxidability. Polyalkylbenzenes with hindered heavy alkyl groups are quite easy to oxidize. The behaviour of bicyclic or tricyclic hydrocarbons is much more complex. Partial or complete hydrogenation increases their reactivity. For instance, oxidability of bicyclic hydrocarbons is in the order: decaline > tetraline > naphthalene. The reactivity of heavier aromatics also depends on their ability to form partial oxidation intermediates (for instance: fluorene to fluorenone) or to possess extremely rigid internal CC bonds (for instance: acenaphthylene and acenaphthene). These results were discussed in the light of several factors which can affect the reactivity in oxidation: (i) an electron transfer between adsorbed hydrocarbon and adsorbed oxygen species via the surface metal atoms; (ii) the mean C–H bond strength in the molecule and hindrance effects in branched hydrocarbons; (iii) the relative adsorption strength of oxygen and hydrocarbons; (iv) the relative reactivity of hydrocarbons and partially oxidized molecules, intermediates in total oxidation.

Keywords
Hydrocarbon catalytic oxidation; Pt catalysts; Light-off temperatures; Diesel heavy hydrocarbons; Polycyclic aromatic hydrocarbons (PAHs); Structural effects of hydrocarbon molecules
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volume 95, Issues 3–4, 6 April 2010, Pages 217–227
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
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Any Questions? feel free to contact us