Development of a High Performance Catalyzed Hydrocarbon Trap Using Ag-Zeolite 2004-01-1275
A high performance catalyzed hydrocarbon (HC) trap, consisting of a Ag-impregnated zeolite and a three-way catalyst (TWC), was developed to achieve the stringent exhaust regulations such as SULEV. To improve the HC retention ability and durability of Ag-zeolite, the effects of wash-coat loading, HCs species, space velocities (SV) etc. on HC desorption profiles upon heating-up were examined in detail. In the present study, a simulated durability test using a cyclic lean-stoichiometric aging, was developed and applied for durability evaluation. An ultraviolet visible near-infrared spectrophotometer (UV-Vis) showed that specific chemical species of Ag were responsible for the delay of HC desorption. After the cyclic aging, the retention effect of Ag was only seen with aromatic compounds. It was revealed that the HC retention effect on aromatic compounds was maintained at high SV values, which was confirmed by actual vehicle tests. To improve the emission performance for cold HCs and durability, various types of catalyzed HC traps consisting of Ag-zeolite and tri-metal TWCs, were prepared and evaluated after the simulated durability test. From these results, an optimized combination of HC trap and TWC was developed. A vehicle test was performed using a newly developed catalyzed HC trap aged with a bench engine. The developed catalyzed HC trap showed relatively good emission performance for cold HCs after bench engine aging for 100 hours at 700°C.