Search Results

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.

A principle mode of TWC deactivation is the agglomeration of Rh under high temperature lean conditions. This is particularly pronounced with aging cycles that incorporate a fuel shut-off, since the latter creates a severely oxidizing environment. We have attempted to stabilize Rh based on the fact that Rh3+, which is the dominant species under the above-mentioned conditions, is highly interactive, forming ternary oxides with a large number of base metal oxides (BMOs). Such compound formation can be expected to decrease the tendency to agglomerate. A potential pitfall, however, is the need for the BMO-Rh3+ complex to undergo reductive decomposition, releasing active Rh0, under stoichiometric/reducing conditions. Thus, the BMO-Rh3+ interaction must be intermediate in strength. Consistent with these expectations, an exploratory program showed that weakly basic BMOs were superior to strongly basic BMOs.

H2S emissions from a three-way catalyst are suppressed by incorporating copper or manganese oxide into a section downstream of the three-way catalyst.