Metal-organic framework catalysis in the upgrading of ethanol for advanced biofuels

Jepson, Harry 2023. Metal-organic framework catalysis in the upgrading of ethanol for advanced biofuels. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

The work presented in this thesis focusses on the Guerbet reaction for the upgrading of ethanol to n-butanol, in particular researching heterogenous catalytic routes for this transformation. The use of metal-organic frameworks as heterogeneous Lewis acid catalysts for the aldol condensation of acetaldehyde in the Guerbet reaction of ethanol was initially explored, with homogeneous transfer hydrogenation catalysts. Reaction optimisation using UiO-66(Zr) as an aldol catalyst with [RuCl2(dppm)2] showed that this combination of catalysts were active for the synthesis of n-butanol from ethanol, while further study was conducted on changing the nature of the MOF, and the homogeneous ruthenium catalyst in the reaction. System recyclability experiments shows that over multiple cycles, the combination of UiO-66(Zr) and [RuCl2(dppm)2] evolved to give a catalyst mixture that was more active and selective for n-butanol synthesis from ethanol than the initial catalysts. A combination of these catalysts initially catalysed the conversion of ethanol to n-butanol to a 10.7 % yield of the desired product. Through subsequent recycling steps, where liquid product was removed from the reaction mixture under vacuum, the residual catalyst mixture demonstrated a significant improvement in activity over subsequent cycles, where n-butanol yield improved to 21.1 % after 6 cycles. As UiO-66(Zr) was shown to be an active aldol catalyst in the upgrading of ethanol to n-butanol, attention turned to synthesising a single, heterogeneous catalyst for the upgrading of ethanol. Initially, the immobilisation of homogeneous complexes into the linkers of the zirconium derived UiO-67(Zr) was attempted in search of a heterogeneous Guerbet catalyst. The main body of this work consisted of the immobilisation of [RuCl(cymene)(bipy-COOH)]Cl into the linkers of UiO-67. UiO-67(Zr) was demonstrated to be an active aldol catalyst in the Guerbet upgrading of ethanol, and under certain reaction conditions [RuCl(cymene)(bipy-COOH)]Cl was demonstrated to be an active transfer hydrogenation catalyst. And while the immobilisaiton of [RuCl(cymene)(bipyCOOH)]Cl in the linkers of UiO-67(Zr) was not demonstrated, the work conducted on this area forms a strong foundation for further research into immobilised catalysis in the ii Guerbet reaction., Further preliminary work into the immobilisation of pincer complexes into zirconium MOFs was also conducted. The concept of utilising etched derivatives of UiO-66(Zr) as a support for homogeneous transfer hydrogenation catalysts was explored. With primary work focused on the synthesis of new ruthenium complexes bearing ligands with pendant carboxylate groups, that could be used for complex immobilisation on the nodes of UiO-66(Zr). Different methods of synthesisng complexes with this desired functionality were probed, and a detailed in-situ transfer hydrogenation catalyst formation study with phosphino azomethinylate ligands in the Guerbet reaction was conducted. Combinations of phosphino azomethinylate ligands with [RuCl2(cymene)]2 were shown to be active hydrogenation catalyst precursors in the Guerbet upgrading of ethanol with sodium ethoxide, where the formation of both mono- and bischelate complexes were targeted. Further work into designing a catalytic system to utilise these transfer hydrogenation catalysts in combination with metal-organic frameworks is warranted,

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Chemistry
Date of First Compliant Deposit:	17 October 2024
Last Modified:	17 Oct 2024 12:56
URI:	https://orca.cardiff.ac.uk/id/eprint/172977

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