TY - JOUR
T1 - Evaluation of Sol-Gel Processed BaO·nAl2O3 Materials as NOx Traps
AU - Narula, Chaitanya K.
AU - Nakouzi, Sabine R.
AU - Wu, Ruowen
AU - Goralski, Christian T.
AU - Allard, Lawrence F.
PY - 2001/3
Y1 - 2001/3
N2 - 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 work well, but cannot sustain their NOx trapping efficiency after repeated exposure to high temperatures during regeneration. In search of thermally stable materials, a series of sol-gel processed BaO·nAl2O3 (n = 1, 4, 6) materials including BaO·6Al2O3 molecular sieves were synthesized and evaluated as NOx traps using simulated exhaust at a 25,000 h-1 space velocity. Changes in structure and surface properties occurring on thermal treatment of sol-gel processed BaO·nAl2O3 materials significantly affect the NOx trapping efficiency of these materials. Among these materials, sol-gel processed and precious metal impregnated BaO· 6Al2O3 powder offers the optimum combination of thermal stability and NOx trapping efficiency. We deposited this powder on a honeycomb substrate, impregnated it with 2% Pt and 0.4% Rh, and re evaluated it. The NOx trapping efficiency ofthis catalyst is 95% (cf. 75% for the powder) at 310°C. Our data on Pt/BaO·6Al2O3 also suggest that the optimum lean cycle length for this class of NOx traps is 1 min. The efficiency of NOx traps decreases rapidly and falls in 10-20% range with an alternating 5 min lean cycle and 1 min rich cycle.
AB - 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 work well, but cannot sustain their NOx trapping efficiency after repeated exposure to high temperatures during regeneration. In search of thermally stable materials, a series of sol-gel processed BaO·nAl2O3 (n = 1, 4, 6) materials including BaO·6Al2O3 molecular sieves were synthesized and evaluated as NOx traps using simulated exhaust at a 25,000 h-1 space velocity. Changes in structure and surface properties occurring on thermal treatment of sol-gel processed BaO·nAl2O3 materials significantly affect the NOx trapping efficiency of these materials. Among these materials, sol-gel processed and precious metal impregnated BaO· 6Al2O3 powder offers the optimum combination of thermal stability and NOx trapping efficiency. We deposited this powder on a honeycomb substrate, impregnated it with 2% Pt and 0.4% Rh, and re evaluated it. The NOx trapping efficiency ofthis catalyst is 95% (cf. 75% for the powder) at 310°C. Our data on Pt/BaO·6Al2O3 also suggest that the optimum lean cycle length for this class of NOx traps is 1 min. The efficiency of NOx traps decreases rapidly and falls in 10-20% range with an alternating 5 min lean cycle and 1 min rich cycle.
UR - http://www.scopus.com/inward/record.url?scp=0035265688&partnerID=8YFLogxK
U2 - 10.1002/aic.690470320
DO - 10.1002/aic.690470320
M3 - Review article
AN - SCOPUS:0035265688
SN - 0001-1541
VL - 47
SP - 744
EP - 753
JO - AIChE Journal
JF - AIChE Journal
IS - 3
ER -