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.