Automotive catalysts

In the latter twentieth century, spent automotive catalysts have emerged as a significant potential source of secondary Pt, Pd, and Rh. In North America, it has been estimated that 15.5 metric tons per year of PGM from automotive catalysts are available for recycling (22). However, the low PGM loading on such catalysts and the nature of the ceramic monoliths used have required the development of specialized recovery techniques as well as the estabhshment of an infrastmcture of collection centers. These factors have slowed the development of an automotive catalyst recycling iadustry. 

J. P. Day and L. S. Socha, Jr., The Design of Automotive Catalyst Supportsfor Improved Pressure Drop and Conversion Efficieny, SAE 910371, Society of Automotive Engineers, Warrendale, Pa., 1991. 

A catalytic oxidation system may cost 150 per car, but the catalyst cost is estimated to be 30, less than 1% of the cost of an automobile (2). In a few years, the gross sale of automotive catalysts in dollars may exceed the combined sale of catalysts to the chemical and petroleum industries (3). On the other hand, if the emission laws are relaxed or if the automotive engineers succeed in developing a more economical and reliable non-catalytic solution to emission control, automotive catalysis may turn out to be a short boom. Automotive catalysis is still in its infancy, with tremendous potential for improvement. The innovations of catalytic scientists and engineers in the future will determine whether catalysis is the long term solution to automotive emissions. 

With the exception of ruthenium and chromium, all the materials mentioned for automotive catalysts are lower than lead in toxicity (74). The danger to human use is minimal, except during manufacturing and installation of the catalysts where safety precautions can be adequately controlled. 

Which metals are used in the automotive catalyst and what reactions do they catalyze ... 

Three-way automotive catalysts based on palladium, rather than the more expensive metals platinum and rhodium, have long been desired. However, Pd is more sensitive than R to poisoning by lead (Pb) compounds [1-4], Consequently, widespread commercial use of Pd-based automotive three-way catalysts (TWC) was delayed in the U.S. until the early 1990s, by which time residual Pb concentrations in unleaded gasoline had decreased to negligible levels. The past five years have witnessed... 

Shelef, M. and McCabe, R. W. (2000) Twenty-five years after introduction of automotive catalysts what next Catal. Today, 62, 35. 

Uenishi, M., Tanigushi, M., Tanaka, H. et al. (2005) Redox behavior of palladium at start-up in the perovskite-type LaFePdO automotive catalysts showing a self-regenerative function, Appl. Catal. B 57, 267. 

Three-way catalysts are used in most 1981 gasoline-fueled automobiles to lower the levels of NO, CO, and hydrocarbons in engine exhaust. These catalysts normally operate under dynamic conditions catalyst temperature increases rapidly after the engine starts (during catalyst "warmup"), and exhaust flowrate and composition fluctuate under most modes of operation. The warmup of automotive catalysts is reasonably well understood (1). The operation of three-way catalysts in the dynamic exhaust environment after warmup is complex and less well understood. 

During the last three years, thirty patents have been published describing the use of rare earths in exhaust gas purification. In the event that all automotive catalysts in the USA were to contain 1% rare earth oxide, the market volume would be approximately 100 tons/year. It is probable that where Ce02 is used, the level will be between 1% and 10% in the catalyst. 

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