Pd-based alloys as catalysts for the conversion of carbon dioxide to renewable fuels

Lawes, Naomi 2023. Pd-based alloys as catalysts for the conversion of carbon dioxide to renewable fuels. PhD Thesis, Cardiff University. Item availability restricted.

	PDF - Accepted Post-Print Version Restricted to Repository staff only until 10 May 2025 due to copyright restrictions. Download (11MB)
	PDF (Cardiff University Electronic Thesis and Dissertation Form) - Supplemental Material Restricted to Repository staff only Download (124kB)

Abstract

The conversion of carbon dioxide to methanol — a key chemical commodity, alternative fuel, and energy carrier — has been investigated using Pd-based catalysts. Initially, PdZn catalysts with varying Zn/Pd molar ratios, supported on P25 TiO2 were tested at 20 bar and at temperatures between 230 - 270 °C. Further studies explored the relationship between the formation of the 1:1 β-PdZn alloy and the influence of excess ZnO on methanol productivity. Altering the Zn/Pd ratio led to significant changes in product selectivity, particularly impacting methane production, which is undesirable in industry. Using Pd/TiO2 resulted in substantial methane production (25 - 50%). However, introducing small quantities of Zn suppressed methane production in favour of CO desorption. A Zn/Pd ratio of 0.5 yielded the highest CO selectivity (92%), with methanol selectivity sharply rising beyond a Zn/Pd ratio of 1. Methanol productivities reached 2068 mmol kgcat -1 h -1 for Pd1Zn20/TiO2. Additionally, it was found that an excess of ZnO resulted in higher methanol selectivity. Emphasising the complex interplay of Zn/Pd ratios in governing selectivity and productivity, the study highlighted the crucial role of PdZn and ZnO in tailoring methanol selectivity during CO2 hydrogenation. Investigations were extended to Ga2O3 and In2O3 as supports for both Pd and PdZn, using the solvent-free chemical vapour impregnation method, as used initially with TiO2. Alloying Pd with Zn, Ga or In increased methanol production rates compared to unalloyed Pd. For the Ga2O3-based catalysts, the 1:1 β-PdZn alloy was formed on PdZn/Ga2O3, whereas Pd2Ga was formed for the Pd/Ga2O3 catalyst, as verified by in situ X-ray diffraction (XRD) experiments and STEM-EDX data. The role of relative oxide stability in alloy formation was highlighted to further understand the absence of other alloy phases of PdZn-based catalysts. In contrast, the PdZn/In2O3 catalysts did not show the 1:1 β-PdZn alloy but revealed the presence of a Pd2In3 alloy.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Chemistry
Date of First Compliant Deposit:	10 May 2024
Last Modified:	10 May 2024 08:20
URI:	https://orca.cardiff.ac.uk/id/eprint/168816

Actions (repository staff only)

Edit Item