Cold-Start Emission Reduction Potential and Limitations of Commercial Passive Hydrocarbon Adsorbers

Abstract

Effective control of hydrocarbon (HC) emissions during cold start is critical to meeting more stringent future emission standards, and the passive HC adsorber is one possible technology to improve cold-start HC emission control. HC adsorbers for gasoline applications typically contain zeolite materials for HC storage and a noble metal-based three-way catalyst (TWC) for oxidation of stored HCs, both of which are susceptible to hydrothermal aging. In the present study, state-of-the-art HC adsorbers from two catalyst suppliers were evaluated for their cold-start HC emission reduction potential. After aging at 800 °C, the HC adsorbers tested provided reasonably high conversion efficiencies for aromatics and a moderate level of conversion for olefins but were not able to control paraffins to a significant degree. This resulted in a total HC conversion efficiency of 40–50% over the best HC adsorber for the simulated feed stream used in this study. The overall adsorber performance can be improved somewhat by increasing the noble metal loading or the O2 concentration in the feed stream and was found to be sensitive to adsorber volume (space velocity). After aging at 900 °C, however, none of the HC adsorbers tested was able to convert more than 10% of the HC in the feed.