Platinum Metals Review - Volume 44, Issue 2, 2000

Nuclear medicine radiotherapy involves the administration of a radiolabelled drug whose purpose is tissue damage and/or destruction at the point of localisation. Radionuclides useful for this application are those which emit particles (that is alpha, beta or Auger electrons) because they deposit their decay energy over a relatively short range (for example, at the tumour site). Rhodium-105 is a radionuclide with desirable nuclear properties for therapeutic applications (its half-life is 35.4 hours, the maximum α^- energy is 0.56 MeV and it produces a 319 keV γ-ray suitable for imaging). However, this radionuclide is not readily available to most of the interested investigators due to the difficulty in production scale-up. The work reported here was designed to develop a viable method to produce and purify multi-millicurie quantities of ¹⁰⁵Rh for radiotherapy research. Rhodium-105 was produced at the University of Missouri Research Reactor by the nuclear reaction, ¹⁰⁴Ru (n, γ) → ¹⁰⁵Ru (β^- decay) → ¹⁰⁵Rh and a new procedure was developed to chemically separate the no-carrier-added ¹⁰⁵Rh from the neutron irradiated ruthenium target. Rhodium-105 production yields, for 10 runs, averaged about 5 mCi per milligram of ruthenium from a 72-hour irradiation at a thermal neutron flux of 8 × 10¹³ neutrons cm^-2 s^-1. Rhodium-105 was successfully isolated from the ruthenium radionuclides and the non-radioactive ruthenium. This new separation technique was fast (a total time of 3 hours) and highly efficient for removing the ruthenium. The decontamination factor of ruthenium averaged 16,600, indicating that only 0.006 per cent of the ruthenium remained after separation.

Metathesis (from the Greek meta tithemi = change place) describes in chemistry the interchange of atoms between two molecules. The metathesis of olefins is the formal scission of a pair of double bonds, followed by the interchange of their carbon atoms. Metathesis polymerisation of cycloolefins refers to the apparent ring cleavage at the double bond, accompanied by polymerisation to unsaturated polymers (la, lb). Nowadays metathesis is established as a powerful method of synthesis in organic and polymer chemistry (1), and platinum group metal catalysts have played a prominent role in this achievement. Metathesis has resulted in both unique syntheses and novel compounds. In this review metathesis reactions catalysed by platinum group metals are described, specifically the types of catalyst, their metathesis activity and various ring-opening and ring-closing reactions. Part II of this paper will be published in the July issue of this Journal.

The oxidation of ammonia for the production of nitric acid is a well known process which has been in constant use since the 1890s for the manufacture of fertiliser. Ammonia is oxidised on the surface of a woven or knitted catalyst gauze made of noble metals. Fertiliser production throughout the world partly depends on this technology and research is continuously being undertaken aimed at optimising output and reducing the noble metal loss from the catalysts. Here, some investigations carried out in Ukraine on the surface composition of binary (platinum-palladium) and ternary (platinum-palladiumrhodium) alloys used for the ammonia oxidation process are described. Samples of catalyst received different pretreatments, and their activity was then measured in a laboratory reactor, paying particular attention to the composition of the first few nanometres below the surface. Analysis of the experimental data showed that the role of carbon is different to that of other elements and that the activity of the catalyst is a maximum for carbon concentrations in the range 6 to 10 atomic per cent. It seems most probable than the carbon is present as microcrystals embedded in the alloy and concentrated on the faces of the metal crystals.