New directions in Guerbet catalysis for the upgrading of ethanol to advanced biofuels

Jones, Osian Wyn 2025. New directions in Guerbet catalysis for the upgrading of ethanol to advanced biofuels. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

The Guerbet reaction, first reported by Marcel Guerbet over a hundred years ago converts shorter chain alcohols into β-branched longer-chain alcohols. Recent focus has turned to the upgrading of ethanol via the Guerbet reaction to various butanol isomers which possess idyllic properties as a replacement for gasoline. Industrial systems for this process have primarily utilised heterogeneous catalytic systems, which require harsh conditions and typically exhibit low selectivity towards butanol. Homogeneous catalytic systems have been developed which increase the selectivity towards butanol and run at milder conditions however some key challenges remain. The production of insoluble inert waste solid such as acetate limits the application of a homogeneous catalytic system at an industrial scale. This thesis aims to develop the upgrading of ethanol to butanol via the Guerbet reaction by investigating a set of Ru(II) complexes as catalysts, in addition to exploring alternative co-catalysts for the reaction with the aim of suppressing the inert waste solid formation. Chapter 2 aimed to build on very promising work within the Wass group on Guerbet systems utilising a Ru(II) phosphinophenoxide catalyst. Initially the catalytic conditions were optimised before various analogues of the phosphinophenoxide ligand were investigated. Investigations were conducted to probe the active species via base activation of the complex. Chapter 3 explored Lewis acid co-catalysed Guerbet chemistry while seen as a potential alternative to a base co-catalyst. Initial work within the Wass group found Zr(OEt)4 to be an active aldol condensation catalyst within the Guerbet upgrading of ethanol to n-butanol. The scope of Lewis acid co-catalysts was widened, the system optimised and a study on the aldol condensation reaction probed with a range of different Lewis acids. However, analysis of the post reaction mixture suggested formation of Zr(OH)4, recycling studies suggested the post-reaction solid was still an active co-catalyst within the reaction. Chapter 4 followed a natural progression investigating a co-catalytic system which consisted of a homogeneous transfer hydrogenation catalyst and the heterogeneous aldol condensation catalyst Zr(OH)4. Various samples of Zr(OH)4 were synthesized and characterised, a relationship between weak acidic site density and selectivity towards Guerbet alcohol formation was proposed. Less than 1% of the post-reaction solid was found to be acetate. An investigation into the evolution and role of each co-catalyst was conducted followed by a conditions optimisation.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Chemistry
Date of First Compliant Deposit:	11 May 2026
Last Modified:	11 May 2026 15:51
URI:	https://orca.cardiff.ac.uk/id/eprint/186897

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