Tailoring Pt/TiO2 catalysts: particle size and support modifications for enhanced oxidation reactions

Tigwell, Max 2024. Tailoring Pt/TiO2 catalysts: particle size and support modifications for enhanced oxidation reactions. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This work focuses on the valorisation of glycerol, a by-product of biodiesel, by selective oxidation using heterogeneous catalysis for lactic acid production over Pt/TiO2. Specifically, the relationship between catalytic properties and pathway selectivity, in particular, with respect to oxidative dehydrogenation versus dehydration is investigated. The present work has evidenced that both the size of platinum nanoparticles and the phase of the TiO2 support are critical for pathway selectivity. Larger platinum particles favour the ODH pathway, while the LA selectivity is enhanced by smaller particles. In addition, it was observed that the anatase phase of TiO2 significantly increases LA selectivity, associated with variations of electron density and binding energy. The conclusion of this work identifiesthat there is a close relationship between LA selectivity and the surface residence time of intermediates, thereby giving new insights for designing catalysts with improved selectivity in glycerol oxidation. Furthermore, volatile organic compounds are a significant threat to ecosystems and human health; therefore, more efficient ways of their removal have been developed to fulfil ever-growing demands for tightening emission limits. Previous literature has identified support acidity as one of the key factors that the catalytic performance of Pt/TiO2-based catalysts in propane total oxidation. In this work, through synthesising a series of Pt/Si-TiO2 catalysts and characterising them with a series of methodologies indicates that small quantities of silicon can significantly improve the dispersion of platinum and as such, form single-atom platinum sites with reduced C-H bond activation. Among the prepared catalysts, Pt/Si-TiO2 (4%) displays the best activity due to the synergistic effect of highly dispersed small platinum clusters, single-atom sites, and nanoparticles. Similarly, Pt/Si-TiO2 (4%) exhibited higher activity in the presence of moisture, while the conversion at 300 °C for 70 h was maintained at 64%; with slight deactivation observed attributed to oxidised platinum species, PtO. Additionally, the study investigated the preparation methodologies using Chemical Vapour Impregnation (CVI) and sol-gel techniques to obtain TiO2-doped supports for propane oxidation. The literature has identified the active phases of Co, Mn, and Fe and as such, a number of new synthesis techniques have been applied to maximise catalyst performance. This work prepared a set of Pt/TiO2 catalysts using the two techniques of sol-gel and CVI. iii Catalysts were tailored through the addition of Co, Mn, and Fe onto the catalyst surface via CVI, and within the TiO2 matrix via sol-gel. Comparing the effects of surface and bulk species provided insight into the further optimisation of doped Pt/TiO2 catalysts. Consequently, detailed characterisations indicated that PtFe/TiO2 having surface Fe2O3 was the most active catalyst showing 50 % conversion at 311 °C, while the species Co and Mn were synthesised in their least active form, CoO and MnO, respectively. The addition of dopant metals affected the Pt particle size and catalyst reducibility, but only PtFe/TiO2 outperformed the standard Pt/TiO2. CVI is a developing methodology, therefore, this study is important and can provide insight into the design of catalysts for enhanced activity with respect to the total oxidation of propane, although further optimisation concerning synthesis methodologies needs to be considered.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Chemistry
Subjects:	Q Science > QD Chemistry
Date of First Compliant Deposit:	17 March 2025
Last Modified:	17 Mar 2025 16:38
URI:	https://orca.cardiff.ac.uk/id/eprint/176926

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