Greener catalyst preparation

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)EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Tribocorrosion behavior and ions release of CoCrMo alloy coated with a TiAlVCN/CNx multilayer in simulated body fluid plus bovine serum albumin

While the CoCrMo biomaterial is currently employed in artificial joints, there are medical concerns regarding its metal ion release and material loss caused by tribocorrosion. In this work, a TiAlVCN/CNx multilayer coating has been employed to improve the tribocorrosion-resistance of the CoCrMo substrate. During the tribocorrosion test, with the sample immersed in a simulated body fluid containing bovine serum albumin, open-circuit potential measurements showed more noble potential as well as a reduction of both the friction coefficient and wear-rate during the sliding phase. Inductive coupled plasma results demonstrate that the multilayer coating effectively blocked the emigration of metallic ions.Funding Agencies|CONACYT [FOMIX Jal-2010-10-149472]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; Tecnologico de Monterrey research seed fund</p