From recovered metal waste to effective catalysts for C–C bond formation
File(s)
Author(s)
McCarthy, Sean
Type
Thesis or dissertation
Abstract
Catalysts containing palladium or gold are ubiquitous in modern synthetic chemistry. However, unrelenting demand for the finite natural reserves of palladium has resulted in supply deficits and record prices. Palladium production is also plagued with the environmental impact of mining and refining processes. The production of gold bears similar economic and environmental challenges. As a result, palladium and gold consumption in their current forms is unsustainable and improvements to the lifecycle of the metals are needed. For both palladium and gold, there exists significant quantities of metal-enriched waste that is typically destined for landfill. These waste streams – waste electronic and electrical equipment, and automotive three-way catalytic converters – offer an valuable ‘urban mine’ of metals for catalytic applications. This has led to the research of this thesis, which demonstrated the application of molecular palladium and gold compounds which are recoverable from waste as homogeneous catalysts. The molecular gold compounds were explored in chapter two as catalysts for a variety of transformations which broadly covered the mechanistic modes of gold catalysis. Molecular palladium compounds were explored in chapters three and four as catalysts for one of the largest industrial scale Suzuki-Miyaura cross-coupling reactions. The catalytic studies in chapter three were underpinned by a ‘Design of Experiments’ optimisation, which revealed a non-linear influence of the catalyst loading on the performance of the catalyst. Strategies to isolate and recover palladium for reuse as catalysts have also been presented in chapter three. Kinetic and mechanistic analysis of the recovered palladium compounds presented in chapter four revealed a novel chloride anion mediated catalyst inhibition mechanism alongside aggregation of the active catalyst. The chemical understanding reported in this thesis aims to incentivise increased recycling of metal waste and thus support the transition to a ‘closed-loop’ consumption of palladium and gold in the chemical industry.
Version
Open Access
Date Issued
2024-05-10
Date Awarded
2024-09-01
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Wilton-Ely, James
Braddock, Christopher
Sponsor
Engineering & Physical Sciences Research Council
Grant Number
EP/S023232/1
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)