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Title: Greener catalyst preparation
Author: Casabán Julián, José
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2013
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Heterogeneous catalysts which consist of metal (nano)particles dispersed on a support material are conventionally prepared in multi-step procedures. Commonly, the metal precursor is in the form of a soluble metal nitrate salt and several calcination, dissolution, precipitation and reduction steps are required to form the active metal catalyst. This processing releases significant NOx and is also wasteful in terms of the number of process steps required to produce the catalyst. The main objective of this work was to examine alternative more direct catalyst preparation methods. Two more direct deposition methods were proposed, which may be performed electrochemically or electrolessly. Specifically, a base metal in elemental form could be oxidized (stripped) into solution and then deposited onto a support material in the same vessel. In this way, the ionized form of the metal is generated only transiently and no nitrate is consumed. Depending on the metal, the support, and the conditions applied, the oxidation and deposition steps may be induced electrochemically or may even occur spontaneously under appropriate conditions. In order to facilitate the overall process, the characteristics of such a system could be tuned through the preparation parameters but also by adding ligands to the solution which would ideally be recyclable, acting as shuttles to provide the solubilised metal in the form of a complex of a desired stability. The stability of the complex is sufficiently low that the ligands can be released back into solution upon metal deposition. The development of such a system was investigated for copper using aqueous ligand solutions. Stripping and electrodeposition processes were investigated using ethylenediamine. The recyclability of the ligand was successfully proved when Cu-graphite materials were synthesised by stripping-electrodeposition processes combined in the same vessel. Alternatively, in the presence of oxide supports, stripping and electroless deposition were combined in the same vessel using aqueous ammonia solutions and active water gas shift Cu-AI20 3 catalysts were prepared by this new ligand-assisted route from Cu metal and Cu ores. These new copper-alumina materials showed enhanced catalytic activity in comparison with standard impregnated catalysts and greater stability when compared against commercial WGS catalysts. Active water gas shift Cu/Al20 3 catalysts were also prepared by solvent-free mechanochemistry using a ball mill. Similar catalytic activity was observed using a Cu/Ab03 catalyst prepared by ball milling (from CuO as the copper source), compared with a conventionally prepared Cu/Ab03 catalyst (wet impregnation)
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available