Evaluation of Sol-Gel Processed BaO·nAl2O3 Materials as NOx Traps

Chaitanya K. Narula, Sabine R. Nakouzi, Ruowen Wu, Christian T. Goralski, Lawrence F. Allard

Research output: Contribution to journalReview articlepeer-review

11 Scopus citations

Abstract

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.

Original languageEnglish
Pages (from-to)744-753
Number of pages10
JournalAIChE Journal
Volume47
Issue number3
DOIs
StatePublished - Mar 2001

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