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Selective oxidation of alkyl aromatics by bimetallic heterogeneous catalysts

Giles, Cicely 2018. Selective oxidation of alkyl aromatics by bimetallic heterogeneous catalysts. PhD Thesis, Cardiff University.
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This thesis reports the selective oxidation of alkyl aromatic substrates under mild ‘green’ conditions, with a particular emphasis on developing alternatives to established gold-based catalysts. Three alkyl aromatics were chosen for investigation: toluene, ethylbenzene and 2-ethylnapthalene; so differences due to increased alkyl chain length and extended aromaticity could be explored. The oxidation of toluene using tertiary-butyl hydroperoxide (tBHP) was carried out with a ruthenium-palladium catalyst. This catalyst was found to be highly active, more so than a gold-palladium equivalent, and further optimised in terms of molar ratio of Ru : Pd, wt.% metal loading, reducing temperature and support material. The resulting catalyst was found to be reusable with little loss of conversion, though selectivity changed significantly. This was the case despite notable metal leaching. Finally, the catalyst was explored via experiments varying substrate : metal molar ratio and time-on-line studies, revealing unusual behaviour. The ruthenium-palladium catalyst was also applied to the oxidation of 2-ethylnapthalene with tBHP. Extensive comparisons were drawn between this catalyst and gold-palladium equivalents. Sol immobilisation, conventional impregnation and modified impregnation were tested as preparation methods. Once again, the ruthenium-palladium bimetallic catalyst proved to be more active than the gold-palladium, even at very low wt.% loadings. Finally, an iron-palladium catalyst was applied to the oxidation of ethylbenzene with molecular oxygen. High molar ratios of substrate : metal were explored, and conversion found to be highly dependent on this factor. The catalyst was optimised in terms of molar ratio of Fe : Pd, wt.% metal loading, preparation method and reducing temperature. The resulting iron-palladium catalyst achieved activity exceeding that of gold-palladium in similar conditions. This activity was attributed to radical chemistry, explored via studies with initiators and scavengers.

Item Type: Thesis (PhD)
Date Type: Submission
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Funders: ERC: After the Goldrush
Date of First Compliant Deposit: 16 October 2018
Last Modified: 31 Mar 2021 14:02

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