nverters also employed ceramic catalyst supports. The following two basic support configurations were used: (1) a catalyst support consisting of alumina pellets; and (2) an alumina-coated ceramic monolith. These supports were then coated with catalyst. In 1975, United States Environmental Protection Agency regulations addressed only CO and HC emissions ("Catalytic converters", 1991, p. 29). Therefore, the early converters used either platinum or platinum/palladium mixtures ("Catalysts," 1989, pp. 69-75).
Over the years, however, the implementation of stricter emission requirements has resulted in the introduction of more complex emission control systems. Since 1981, for example, emission standards regulating nitrogen oxides have required additional emission controls. In addition to oxidation catalysts, current converters were also equipped with a reducing catalyst. The devices--which simultaneously convert CO, HCs, and NOXs over a single catalyst--employ a "three-way catalyst" (Taylor, 1987, pp. 97-115). As recently as 1991, three-way oxidation/reduction catalysts were installed on as many as 200 million automobiles in North America, Europe, and Asia ("Catalytic converters", 1991, p. 29). The catalyst's prime active ingredients are platinum, rhodium, and palladium. These precious metals are applied to a ceramic honeycomb with a large internal surface area, thus enabling them to trap and degrade exhaust pollutants (Ashley, 1994, pp. 81-82).
More recently, a new generation of catalytic converters has been developed for 1994 automobiles. Using a dense cordierite ceramic composition and thin-wall extrusion technology, Corning, Inc., has produced a thin-wall ceramic catalyst supp
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