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In the development of HC traps (HCT) for reducing vehicle cold start hydrocarbon (HC)/nitrogen oxide (NOx) emissions, zeolite-based adsorbent materials were studied as key components for the capture and release of the main gasoline-type HC/NOx species in the vehicle exhaust gas. Typical zeolite materials capture and release certain HC and NOx species at low temperatures (<200°C), which is lower than the light-off temperature of a typical three-way catalyst (TWC) (≥250°C). Therefore, a zeolite alone is not effective in enhancing cold start HC/NOx emission control. We have found that a small amount of Pd (<0.5 wt%) dispersed in the zeolite (i.e., BEA) can significantly increase the conversion efficiency of certain HC/NOx species by increasing their release temperature. Pd was also found to modify the adsorption process from pure physisorption to chemisorption and may have played a role in the transformation of the adsorbed HCs to higher molecular weight species.

Selective Catalytic Reduction (SCR) catalysts have been designed to reduce NOx with the assistance of an ammonia-based reductant. Diesel Particulate Filters (DPF) have been designed to trap and eventually oxidize particulate matter (PM). Combining the SCR function within the wall of a high porosity particulate filter substrate has the potential to reduce the overall complexity of the aftertreatment system while maintaining the required NOx and PM performance. The concept, termed Selective Catalytic Reduction Filter (SCRF) was studied using a synthetic gas bench to determine the NOx conversion robustness from soot, coke, and hydrocarbon deposition. Soot deposition, coke derived from propylene exposure, and coke derived from diesel fuel exposure negatively affected the NOx conversion. The type of soot and/or coke responsible for the inhibited NOx conversion did not contribute to the SCRF backpressure.

A study was performed on a lean NOx trap in which the loading of a ceria-containing mixed oxide in the washcoat was varied. After a mild stabilization of the traps, the time required to purge the NOx trap generally increased with increasing amount of mixed oxide. The purge NOx release also increased with increasing mixed oxide level but was greatly diminished after thermal aging. The sulfur tolerance of the NOx trap improved as the mixed oxide content was increased from 0% to 37%. The sample with 0% mixed oxide was more difficult to desulfate than the other samples due to poor water-gas-shift capability. After thermal aging, the NOx reduction efficiency on a 60 second lean/5 second rich cycle was highest for the samples with 0% to 37% mixed oxide at evaluation temperatures of 400°C to 500°C.