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A study was performed to assess the effects of the catalyst volume and the ceria content in the washcoat on the aged emission performance of underfloor catalytic converters containing platinum and rhodium. Catalyst volumes of 1.4 L and 2.8 L were evaluated, while the ceria level was varied from 0 to 60% of the weight of the washcoat. The concentration of noble metals (g/L) was the same for both catalyst volumes, so the larger volume also contained more noble metal. Catalyst performance was evaluated on an air/fuel ratio sweep test, at steady-state conditions on an engine, and on the FTP test. In light of the new catalyst monitoring requirements for OBD II, each catalyst was also evaluated at steady-state conditions using a dual oxygen sensor technique in order to produce an O2 sensor index. The evaluations were performed at several intermediate stages as the catalysts were aged on engines using high temperature durability schedules intended to simulate high mileage conditions.

Copper-based catalytic converters can offer significant HC and CO conversion at stoichiometry when close-coupled to the engine. The higher temperatures that result from close-coupling are needed to prevent sulfur poisoning of the catalyst as well as to increase the catalytic activity. However the ability of copper catalysts to convert NOx is very small at stoichiometry. This report summarizes the progress made in improving the NOx conversion and 3-way performance of copper-based catalysts. An A/F algorithm involving slightly rich operation was developed which significantly increased the NOx conversion of an aged copper catalyst while still utilizing a standard stoichiometric oxygen sensor. The addition of periodic A/F maneuvers further increased the NOx conversion, presumably by manipulating the copper into an oxidation state most active for NOx reduction. Air was injected ahead of a second copper catalyst.

A theory of diesel exhaust catalysis using an oxidation flow-through type catalyst to reduce particulate emissions is explained. The effects of converter design, catalyst support materials, and the use of noble metals for light and heavy duty applications are discussed. Experiments were performed to determine, 1) the sulfur storage and release characteristics of alumina and silica catalyst support materials and 2) the ability of platinum and palladium to oxidize SO2 to sulfate particulate. Light duty FTP and heavy duty transient results are also presented.