Promoting supported noble metal catalysts for enhanced activity and selectivity

Barnes, Alexandra 2024. Promoting supported noble metal catalysts for enhanced activity and selectivity. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

In this thesis two important reactions in the area of heterogeneous catalysis are explored, the chemoselective hydrogenation of 3-nitrostyrene and the direct synthesis of hydrogen peroxide. It was found that by tuning the platinum sites of low loading (0.05 – 0.5wt% Pt/TiO2) through heat treatment that highly active and selective catalysts could be produced for the chemoselective hydrogenation of 3-nitrostyrene to 3-vinylaniline. From a range of characterisation techniques, it was found that by employing an oxidative treatment prior to a second reductive step, a detrimental SMSI (strong metal-support interaction) effect could be prevented, due to the stabilisation of the nanoparticles during calcination. This work resulted in a highly active and selective 0.2wt% Pt/TiO2 (calcination then reduced at 450°C) catalyst. This work also investigated the effect of low-level doping of non-precious transition metals to enhance the performance of AuPd-supported catalysts towards the direct synthesis of H2O2. In particular, 1%AuPd(0.975)X(0.025)/TiO2 (where X = Cu, Ni, Zn) catalysts prepared by sol-immobilisation were found to be particularly active towards the synthesis of H2O2, improving upon the activities seen for the bimetallic analogue 1wt% AuPd/TiO2 without compromising on the H2 selectivity towards H2O2. It was also observed that increasing the concentration of the tertiary metal above 0.025wt% resulted in a substantial decrease in reactivity, with all catalytic performance dropping below that seen for the bimetallic at a dopant loading of 0.1 wt%. Developing upon this a 1%AuPd(0.975)Cu(0.025)/ZSM-5 catalyst prepared by an excess chloride co-impregnation method, was found to give superior activity to the aforementioned catalysts. The success of these trimetallic catalysts was attributed to electronic modification of the Pd species through the introduction of the dopant metal, as well as changes in the surface composition of the nanoalloys.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Cardiff Catalysis Institute (CCI) Chemistry
Date of First Compliant Deposit:	24 January 2025
Last Modified:	24 Jan 2025 09:42
URI:	https://orca.cardiff.ac.uk/id/eprint/175552

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