Uncontrolled automobile emissions contain a variety of potentially harmful chemicals. Exhaust gases typically include hydrocarbons (HCs), carbon monoxide (CO), and nitrogen oxides (NOX). In urban areas, the environmental accumulation of such pollutants can threaten public health. Consequently, over the past several decades, the world's industrialized nations have formulated motor vehicle emission regulations. In response to these government mandates, automakers developed the catalytic converter. These devices facilitate the degradation of harmful compounds. Of all the different converters, the three-way catalytic converter has generally proven to be both durable and effective. Nonetheless, increasingly stringent environmental regulations have spurred continuing research into converter technologies. New devices currently being considered for the control of automotive emissions include such things as heated catalytic converters and hydrocarbon adsorbers.
About the mid-1960s, the state of California enacted automotive emission controls which eventually led to the development of the catalytic converter ("Catalysts," 1989, pp. 69-75). As the United States' emissions standards became more stringent, it became necessary for new cars to have the devices installed as part of their exhaust system. Catalytic converters have been widely used in the United States since 1974 (1975 model year vehicles). The early converters typically consisted of an "inlet plenum, a narrow louvered catalyst bed, and an exhaust plenum" (Taylor, 1987, pp. 97-115). Exhaust gases flowed in at the top of the converter through the decreasing inlet plenum (see illustration). They then passed through the catalyst bed and exited through a lower increasing outlet plenum. The general purpose of this design was to create exhaust flow uniformity, reduce flow restriction, and minimize the potential for catalyst movement. In addition, the first catalytic co...