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Selective catalytic oxidation in the liquid phase by gold-palladium catalysts

Rucinska, Emilia Maria 2019. Selective catalytic oxidation in the liquid phase by gold-palladium catalysts. PhD Thesis, Cardiff University.
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Abstract

The selective oxidations of cinnamyl alcohol, trans-stilbene and 3-pyridinemethanol were investigated using Au-Pd catalysts. These reactions were carried out under industrially relevant conditions. The tested monometallic and bimetallic heterogenous Au-Pd catalysts were prepared by sol-immobilisation (SIm) and impregnation (Imp) methods. Oxidation of cinnamyl alcohol performed at elevated temperatures leads to autoxidation hence its role has been examined in the catalytic process using supported AuPd nanoparticles. 0.50 %(wt)Au 0.50 %(wt)Pd/ TiO2 (SIm) catalyst was shown to prevent the autoxidation process while promoting the selective catalytic pathway. 0.50 %(wt)Au 0.50 %(wt)Pd/ TiO2 (Imp) catalyst appeared to only limit autoxidation enabling co-existence of these two processes. Further optimisation of metal ratio revealed that the most active catalyst is 0.75 wt.% Au- 0.25 wt.% Pd/ TiO2 (SIm). Furthermore, this metal ratio was found to be stable under the reactions conditions with only minor change observed over multiple uses, highlighting the synergistic effect. The effectiveness of the Au-Pd system for cinnamyl alcohol oxidation has been contrasted with that of trans-stilbene and 3-pyridinemethanol oxidation due to the different chemical nature of these substrates. 0.50% Au 0.50% Pd/TiO2 (SIm) catalyst demonstrated similar behaviour in the oxidations of cinnamyl alcohol and trans-stilbene regarding excluding undesired non-selective reactions under optimised conditions, despite the difference in the mechanisms of these two processes. This is suggested to be due to the effectiveness of smaller nanoparticles in limiting uncontrolled oxidation pathways. 3-Pyridinemethanol oxidation using Au-Pd supported nanoparticles is extremely difficult due to the chemical stability of this substrate. The presence of N- heteroatom in the structure presumably leads to the catalyst poisoning due to interaction between N and Pd. Despite this, the Au-Pd catalysts were found to be more active than monometallic ones which indicates synergistic effect. Furthermore, optimisation of reactions conditions enabled total selectivity to the desired aldehyde product.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Date of First Compliant Deposit: 13 January 2020
Last Modified: 14 Jan 2020 10:00
URI: http://orca-mwe.cf.ac.uk/id/eprint/128461

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