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European car manufacturers have traditionally used Pt/Rh or Pd/Rh TWCs with PM loadings of 40-60 g/ft3. New regulations, however have stimulated interest in high Pd loadings (100 g/ft3 or more) in order to drastically reduce HC emissions. Pd is known to have good HC oxidation activity, high thermal stability and is relatively inexpensive. However, it suffers from excessive sensitivity to poisons and is usually associated with poor NOx conversion. A research program was initiated with the goal of capturing the benefits of high Pd concentrations while minimizing its disadvantages. It was found that trimetal formulations (Pt/Pd/Rh) could achieve high NOx conversions provided the loadings of the PMs were optimized based on a Box-Behnken design. Data showing the high thermal stability and low H2S emissions of these new “TriMax” catalysts will be presented. Their high performance has led to commercial acceptance by several European car manufacturers.

The revisions in the United States Clean Air Act of 1990 and recent regulatory actions taken by the California Air Resources Board and European Economic Community require the development of automobiles with much lower tailpipe emissions. A significant portion of the total pollutants emitted to the atmosphere by motor vehicles occurs immediately following the startup of the engine when the engine block and exhaust manifold are cold, and the catalytic converter has not yet reached high conversion efficiencies. An effective, energy efficient strategy for dealing with cold start hydrocarbon using carbon-free hydrocarbon traps and heat exchange related TWC catalyst beds has been successfully tested on a wide variety of current model vehicles. In each case U.S. FTP 75 total hydrocarbon emissions were reduced between 45 - 75% versus the vehicle's stock exhaust system.