Importance

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Abstract

A catalyst composition has an upstream stage and a downstream stage, the upstream stage containing a catalytic material which is different from the catalytic material contained on the downstream stage and is characterized by having a low ignition temperature, e.g., 350.degree. C. to less than 400.degree. C. for the substantially simultaneous conversion of HC, CO and NO.sub.x pollutants contained in, e.g., the exhaust of an automobile engine operating at a substantially stoichiometric air-to-fuel weight ratio. The downstream catalytic material is characterized by having a higher conversion efficiency for substantially simultaneous conversion of HC, CO and NO.sub.x than the upstream catalytic material at elevated operation temperatures which may be, for example, from about 400.degree. to 800.degree. C. The method of the invention includes passing a gaseous exhaust stream containing HC, CO and NO.sub.x pollutants sequentially through first the upstream and then through the downstream catalytic materials.

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First Claim