Effect of lean/rich high temperature aging on NO oxidation and NO sub(x) storage/release of a fully formulated lean NO sub(x) trap

• Published in: Applied catalysis. B, Environmental Environmental, 2011-01, Vol.101 (3-4), p.486-494
• Main Authors: Ottinger, Nathan A, Toops, Todd J, Nguyen, Ke, Bunting, Bruce G, Howe, Jane
• Format: Article
• Language: English
• Subjects: Aluminum oxide; Dispersions; Drift; Nitrates; Oxidation; Platinum; Reduction; Storage capacity; Surface chemistry
• ISSN: 0926-3373
• DOI: 10.1016/j.apcatb.2010.10.020

Commercial-intent lean NO sub(x) traps (LNTs) containing Pt, Pd, Rh, Ba, Ce, Zr, and other proprietary additives were thermally aged at 750, 880, 930, and 1070 degree C using lean/rich cycling and then investigated for effects of aging on NO sub(x) storage capacity, NO oxidation, NO sub(x) reduction, and materials properties. Additionally, DRIFTS analysis was used to determine the effects of high temperature aging on surface chemistry and NO sub(x) storage. As platinum group metal (PGM) dispersion decreases with aging, the NO turnover frequency (TOF) for NO oxidation at 200, 300, and 400 degree C is shown to increase. The fraction of stored NO sub(x) that is successfully reduced also increases with aging, and it is suggested that this is accounted for by a slower release of more stable NO sub(x) species resulting from thermal aging. NO sub(x) storage and NO sub(x) release experiments performed with DRIFTS at 200, 300, and 400 degree C indicate that a substantial amount of NO sub(x) is stored on Al sub(2)O sub(3) as nitrates at 200 and 300 degree C before aging. However, almost no nitrates are seen on alumina after aging at 900 and 1000 degree C, resulting in a significant reduction in NO sub(x) storage capacity. This is most likely due to a 45% reduction in total surface area and a high temperature redispersion of Ba over remaining alumina sites. No evidence of BaAl sub(2)O sub(4) was observed with XRD.