Mobile Engine Emission Control Catalysts

4 June 1994

Since the 1960s. the U. S. Government (and now many other countries) required automobile manufacturers control the emission of nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons produced by gasoline powered automobiles. Emissions regulations established for 1982 and later vehicles led to the development of the current three-way catalyst that simultaneously controls all three pollutants to the required levels. In the late 1980s, this was already a $500 million/year business in the U. S.*

Typical three way catalysts contain rhodium, platinum, and/or palladium metals with other additives that are all supported on an alumina support.# Generally, the supported catalyst is distributed onto a ceramic honeycomb that is then encased within a steel container mounted under the passenger compartment. Exhaust gases then diffuse into the pores and react with a catalyst and exit as non-pollutants. The catalyst reduces the pollutants within about 0.5 second and operates at about 1000°F. These durable systems operate efficiently for the life of the vehicle. Nevertheless, new changes to the regulations will demand further catalyst improvements. Improved catalysts are needed for controlling cold start emissions from lean fuel operated engines. Recently, B. J. Cooper summarized@ some of the technical challenges remaining in auto-emission control catalysis. Also, catalysts are needed for controlling emissions from diesel engines, especially with regard to soot control.

John N. Armor, PhD
Group Head
Catalysis Skill Center

* B. F. Greek, Chemical & Engineering News, (May 29, 1989) 29-56.
# K. C. Taylor, Chemtech, (September 1990) 551-555.
@ B. J. Cooper, Plat. Met. Rev. 38 (1994) 2-10.