The present invention provides a method of removing harmful gases from an
automobile exhaust. The method of the invention comprises contacting a
thermally stable NO.sub.x trap composition with a first exhaust gas
mixture at a temperature of at least 200.degree. C. The first exhaust gas
mixture includes exhaust gases from an internal combustion engine
operating in a fuel-lean condition. After, NO.sub.x has been absorbed
onto the NO.sub.x absorber material, the NO.sub.x trap composition is
then contacted with a second exhaust gas composition. In this step, the
second exhaust gas mixture includes exhaust gases from an internal
combustion engine operating in a fuel-rich condition. The present
invention also provides the NO.sub.x trap composition used in the method.
The NO.sub.x trap of the invention includes a precious metal, a NO.sub.x
absorber material, an oxide that inhibits the decrease in NO.sub.x
storing ability of the NO.sub.x trap composition, and a support material.