Platinum Metals Review - Volume 54, Issue 2, 2010

The technique known as ‘ossification’ has emerged as one of the most promising approaches for immobilisation of metal complexes, generating highly selective, stable and recyclable heterogeneous counterparts of homogeneous catalysts.‘Ossification’ involves modifying the ligand(s) in a metal complex catalyst to achieve inherently insoluble forms of the metal complexes, without destroying the configuration responsible for their catalytic properties. The ossified catalysts have been demonstrated to show high catalytic activity and selectivity for a number of industrially important reaction classes such as palladium-catalysed carbonylation and Suzuki coupling and rhodium-catalysed hydroformylation. The characterisation of these catalysts has also shown that the key features of their homogeneous metal complex analogues are retained on immobilisation. The approach is very useful for the design and development of immobilised catalysts with specific features and functionality for various applications. It is also advantageous for catalyst–product separation. This article reviews the recent work on ossification involving platinum group metal complex catalysts in our research group.

Low-energy ion scattering (LEIS) can be used to selectively analyse the atomic composition of the outer atomic layer of a catalyst, i.e., precisely the atoms that largely determine its activity and selectivity. It is shown how a new development in LEIS significantly improves its mass resolution. Using this advanced separation and quantification of signals from platinum and gold, the atomic composition of the outer surface of a realistic supported platinum-gold bimetallic system can be determined for the first time.

The crystallographic properties of iridium at temperatures from absolute zero to the melting point are assessed following a review of the literature published during the period 1907 to date. However, the theoretical values above 2000 K are considered to be tentative because of the poor quality of the experimental thermal expansion data in this region. Selected values of the thermal expansion coefficient and measurements of length change due to thermal expansion have been used to calculate the variation with temperature of the lattice parameter, interatomic distance, atomic and molar volumes, and density. This data is presented in the Tables. Comparison of the data available in the literature with the selected values presented in this paper is shown in the Figures. The density of iridium at 293.15 K (20°C) is 22,562 kg m^–3.

Under the Platinum Development Initiative, platinum-based alloys were being developed for high-temperature and special applications for good corrosion and oxidation resistance. Parts I–III of the present series of papers dealt with the development of the ternary and quaternary Pt alloys (1–3). In this final paper (Part IV), the corrosion behaviour of selected Pt alloys treated with sodium sulfate salt was compared with that of coated and uncoated CMSX-4^®nickel-based superalloy (NBSA). Scanning electron microscopy (SEM) results showed that protective alumina scales of different integrities formed on the Pt alloys, whereas the NBSAs failed rapidly even with an additional Ptaluminide protective coating. Although there were pits on the Pt alloys, they were minor and not visible to the unaided eye. The potential for application of these Pt alloys in the aerospace gas turbine industry was assessed based on their hot corrosion performance.