Platinum Metal Group Availability

The platinum group metals are usually found as sulfides, arsenides or as the native metal, usually in conjunction with base metals. The concentration is almost always too low to justify mining for the precious metals alone, and the worldwide availability of the precious metal component tends to be determined by the demand for the other metal. For example, platinum is most commonly associated with nickel and copper sulfide deposits, and it is the extraction of the base metals from their ores that provides an economic route to the precious metal. In a typical operation in the US, 10 lbs copper can be extracted from a ton of ore, but the content of palladium is 0.000029 tr.oz and the platinum content is only 0.0000029 tr.oz. Significant quantities are only available in South Africa, Canada, Russia and the United States. 

Spent honeycomb exhaust catalysts contain a relatively high concentration of the precious metal, and these can be recycled. It is certain that they will become an important and economic source of the metals as the use of automobiles continues to increase. About 15% platinum and 5% rhodium were recycled in 1990. The predicted demand for the metals to be used in autocatalysts, compared with the potentially available supplies, is shown in Table 11.12.  

Different catalysts or combinations of catalysts can be used as outlined in the basic principles  

Year World Catalyst use World Catalyst World Catalyst 

Detailed information is never released by the catalyst supplier, as it is very difficult to guarantee adeqnate protection of proprietaiy information. Metal loadings vary depending on the engine size and the required performance. The catalyst monolith in a 1.8 liter car would have a volume of about 1.25 liters with 400 channels per square inch, or 60 chaimels per square centimeter. Up to 300 grams of an alnmina washcoat containing 30% ceria and about 1% precious metals would be used, corresponding to about 0.1wt% of metal in the monolith. Some monoliths contain about 600 channels per square inch or 90 chatmels per square centimeter. 

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It is in the catalyst preparation and recycling that the clear superiority of the platinum catalyzed reductive alkylation method becomes obvious. In the succeeding methods using Raney nickel, one is dependent upon a supply of aluminum-nickel alloy for making Raney nickel. To make platinum catalyst, one needs only obtain platinum metal and one group of a series of readily available chemicals. The basic metal itself, platinum, is easily obtained from coin or other precious metal dealers. The underground chemist thereby shields himself from suspicion by using the cloud of dust... 

Rhodium. Rhodium is the most commonly plated platinum-group metal. In addition to its decorative uses, rhodium has useful properties for engineering appHcations. It has good corrosion resistance, stable electtical contact resistance, wear resistance, heat resistance, and good reflectivity. The use of rhodium for engineering purposes is covered by an ASTM specification (128). Typical formulas are shown in Table 15. The metal content is obtained from prepared solutions available from proptietary plating supply companies. Replenishment is requited because anodes are not soluble. Rhodium for decorative use may be 0.05—0.13 p.m thick for industtial use, it maybe 0.50—5.0 p.m thick. 

A large number of papers has been devoted to the influence of substituents upon the reactivity of benzene nucleus. Extensive studies concerning various benzene derivatives and catalysts from the platinum group metals have been published by H. A. Smith and his co-workers (for a summary see 36). The most consistent sets of data on alkylbenzenes are available from him and other groups of authors. Table VI summarizes the influence of the structure of a single alkyl group Table VII (94, 95, 97-103) summarizes the influence of the number and position of the methyl groups. Both series show very similar behavior on all metal catalysts, a decrease in rate with the size... 

A 1987 review surveys the methods available for the determination of Os and other platinum group metals (13), with a more recent review examining the use of thiourea complexes in the determination of Os (14). In the following text, reviews on more specific topics will be referred to where appropriate. 

Because of the creative minds contributing to the field, the tools of C-H bond transformation available to synthetic chemists are actively expanding [1], Among these, coordination-directed C-H bond-activation has long preserved its appeal, because it enables selective functionalization of a particular C-H bond in the presence of other functional groups. This can be achieved by using a heteroatom (FG = functional group shown in Scheme 1) in the substrate structure to direct the metal complex to the proximity of the specific C-H bond. Even unactivated sp3-centered C-H bonds tend to react in a cyclometalation step with palladium, platinum [2], and ruthenium catalysts [3]. 

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