Platinum replacement

Catalytic Converters Catalytic converters on cars use the metals rhodium and platinum as catalysts to convert potentially dangerous exhaust gases to carbon dioxide, nitrogen, and water. Why don t cars need to have the rhodium and platinum replaced after they are used ... 

Platinum. Replacement of the carbonyl ligand in the reaction between AsPh4-[Pt(C0)O3] and bipyridyl in acidic 95 % aqueous methanol occurs in two stages. The product from the first stage [Pt(COXbipy)Cl][Pt(CO)Cl3] can in fact be isolated and is formed according to the rate law kobs = ki + k2[bipyH+]. Kinetics for the second stage,... 

Three-way catalyst (all or most of the platinum replaced by palladium) platinum/palladium/rhodium ratio of 0-1 8-16 1 with 2-5.5 g of metal per liter of honeycomb volume. 

Earlier processes (e.g. hydroforming) used MoO,i —AI2O3 catalysis but platinum-based catalysts are now extensively used, enabling longer on-stream times before catalyst replacement. 

The carbon is often replaced by a catalyst such as platinized or nickelized carbon or a mixture of carbon, platinum and nickel. 

It is the most corrosion-resistant metal known, and was used in making the standard meter bar of Paris, which is a 90 percent platinum and 10 percent iridium alloy. This meter bar was replaced in 1960 as a fundamental unit of length (see under Krypton). 

This unit, most recentiy defined by the 16th CGPM in 1979, replaced the candle and, later, the new candle and a definition of the candela based on the luminous intensity of a specified projected area of a blackbody emitter at the temperature of freezing platinum. 

To add surface area, the supports are uniformly coated with a slurry of gamma-alumina and recalcined under moderate conditions. The wash coat acts to accept the active metals, typically low levels of platinum and palladium, in a conventional impregnation process. In the United States in passenger car apphcations the spherical catalyst is used almost exclusively, and methods have been developed to replace the catalyst without removing the converter shell when vehicle inspection reveals that emission standards are not met. 

There are, however, technical limitations to substitution. Some materials are used in ways not easily filled by others. Platinum as a catalyst, liquid helium as a refrigerant, and silver on electrical contact areas cannot be replaced they perform a unique function - they are, so to speak, the vitamins of engineering materials. Others - a replacement for tungsten for lamp filaments, for example - would require the development of a whole new technology, and this can take many years. Finally,... 

The contact process which replaced the chamber process reacts the products using a platinum or a vanadium catalyst. 

Contact process for SO3/H2SO4 patented by P. Philips of Bristol, UK (tlie original platinum catalyst was. subsequently replaced by ones ba.sed on V2O5). 

If it is desired to use the biamperometric method for detecting the end point, then the calomel electrode and also the silver rod (if used) must be removed and replaced by two platinum plates 1.25 cm x 1.25 cm. The potentiometer (or pH meter) used to measure the e.m.f. must also be removed, and one of the indicator electrodes is then joined to a sensitive galvanometer fitted with a variable shunt. The indicator circuit is completed through a potential divider... 

The D.M.E. can with advantage be replaced by an S.M.D.E. (Section 16.8), and it is possible to use platinum, graphite, or glassy carbon electrodes, in which case the procedure should be termed voltammetry rather than polarography. 

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