Development of a Zeolite-Based (HC Trap Type) Cold-Start Catalyst (CSC) for the Future more Stringent Vehicle Tailpipe Emission Standards, Part III

<div class="section abstract"><div class="htmlview paragraph">This is a follow-up paper to the two previous reports [<span class="xref">1</span>, <span class="xref">2</span>] regarding the development of a zeolite-based, hydrocarbon (HC) trap-type cold-start catalyst (CSC) as a method to meet future vehicle tailpipe emission standards. In this paper, vehicle tests at a low ambient temperature of -7°C have been performed and the CSC has been shown to further decrease the tailpipe cold start non-methane hydrocarbon (NMHC) emissions by 59% when compared to a standard 23°C WLTC test. This work has proven that the increased presence of condensed water at low ambient temperatures within the exhaust system does not affect the ability to provide a NMHC reduction, in fact the lower ambient temperature enables an increase in the reduction capability due to the ability to retain and then release the stored NMHC in a more controlled manner. Additionally, the impact of the zeolite loading level was investigated and the high zeolite loading within a CSC did improve the cold-start NMHC but the benefits did become saturated as the total zeolite used was further increased. Furthermore, tests with aged CSC parts, that were purposely chosen to be aged at temperature (800°C) above those expected for the target vehicle application, have also been proven to retain the significant amount of the NMHC cold start emissions reduction for the order of 48% to 92% when compared with a baseline fresh sample. The performance retention implies that a CSC can be positioned in several potential locations within a target vehicle aftertreatment system without undue concerns for thermal deterioration. The limitation still being a close-coupled location because the CSC maximum NMHC storage capability is hindered by high temperature and a zeolite coating decreases the TWC washcoat loading in the CSC, which cannot offer the conversion capability for the additional exhaust pollutants for NOx and CO when compared to a standard three-way catalyst (TWC). Furthermore, for repeatability, the CSC must be in a position that will attain sufficient exhaust gas temperature above 550°C for soot reduction [<span class="xref">2</span>, <span class="xref">3</span>], to be able to release all the cold start stored NMHC (clean up deposit), to ensure it is always able to store when the next engine cold start occurs. As an addition to this work, the CSC technology has been applied to a current US Tier3 Bin30 hybrid electric vehicle (HEV), and it has been possible to show a decrease in the vehicle NMHC tailpipe emissions to achieve below Tier 3 Bin 20, thus showing the possibility of an emission improvement with no changes other than the addition of the CSC hardware.</div></div>