Platinum group metals (PGMs) exhibit a strong tendency to form complexes. Typically they are found within the same mineral ores. The largest known primary deposit in the South Africa Bushveld complex. The complex is also the world's largest chromium and vanadium deposit, and has large deposits of nickel, copper, cobalt, tin, iron, fluorspar and alusite, magnesite, and asbestos. The deposits were discovered by the geologist Hans Merensky (1871-1952) in 1925.

Some of the engine and combustion variables that affect vehicle emissions are the fuel-air ratio, ignition timing, turbulence in the combustion chamber and exhaust gas recirculation. In the latter category, catalytic convertors process exhaust gases so as to remove pollutants. Three-way catalysts are formulated so as to reduce carbon monoxide, hydrocarbons and nitrogen oxides from exhaust fumes.

In a tri-metal catalyser the surface layer of precious metals includes palladium, to facilitate the cat to begin working within a very short time of the engine starting. The platinum and rhodium, which are both highly heat resistant are arranged in upper layers to protect the less heat-resistant palladium. This catalytically active layer is a coating provided on a washcoat. The wash coat typically consists of aluminium oxide, rare earth oxides and other metal oxides to provide thermal stability, and to compensate for fluctuations in air fuel ratio.

The surface layer of platinum group metals is recovered for reuse: and, as 68 per cent of platinum and 90 per cent of rhodium used in Western Europe goes into the production of catalysts, this business is extremely viable. The ceramic casing is also recovered as a powder for refining.

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Image of Chemistry of the Platinum Group Metals: Recent Developments (Studies in Inorganic Chemistry)
Author:
Publisher: Elsevier Science (1991)
Binding: Hardcover, 642 pages