Evaluation of sol-gel processed BaO center dot nAl(2)O(3) material as NOx traps

Among various strategies to treat NOx, trapping is considered an economical , consumer transparent approach for gasoline engines. The conventional NOx traps are based on alkaline-earth metal impregnated alumina. These traps wo rk well, but cannot sustain their NOx trapping efficiency after repeated ex posure to high temperatures during regeneration. In search of thermally sta ble materials, a series of sol-gel processed BaO . nAl(2)O(3) (n=1,4,6) mat erials including BaO . 6Al(2)O(3) molecular sieves were synthesized and eva luated as NOx traps using simulated exhaust at a 25,000 h(-1) space velocit y. Changes in structure and surface properties occurring on thermal treatme nt of sol-gel processed BaO . nAl(2)O(3) materials significantly affect the NO, trapping efficiency of these materials. Among these materials, sol-gel processed and precious metal impregnated BaO . 6Al(2)O(3) powder offers th e optimum combination of thermal stability and NO, trapping efficiency. We deposited this powder on a honeycomb substrate, impregnated it with 2% Pt a nd 0.4% Rh, and reevaluated it. The NO, trapping efficiency of this catalys t is 95% (cf: 75% for the powder) at 310 degreesC. Our data on Pt/BaO . 6Al (2)O(3) also suggest that the optimum lean cycle length for this class of N Ox traps is I min. The efficiency of NOx traps decreases rapidly and falls in 10-20% range with an alternating 5 min ban cycle and I min rich cycle.