Sulfur impact on NOx storage, oxygen storage and ammonia breakthrough during cyclic lean/rich operation of a commercial lean NO_x trap

Journal Article · Mon Jan 01 04:00:00 EST 2007 · Applied Catalysis B

DOI:https://doi.org/10.1016/j.apcatb.2007.07.025· OSTI ID:932042

Choi, Jae-Soon ^[1]; Partridge, Jr, William P ^[1]; Daw, C Stuart ^[1]

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1. ORNL

The objective of the present study was to develop an improved understanding of how sulfur affects the spatiotemporal distribution of reactions and temperature inside a monolithic lean NO{sub x} trap (LNT). These spatiotemporal distributions are believed to be major factors in LNT function, and thus, we expect that a better understanding of these phenomena can benefit the design and operation of commercial LNTs. In our study, we experimentally evaluated a commercial LNT monolith installed in a bench-flow reactor with simulated engine exhaust. The reactor feed gas composition was cycled to simulate fast lean/rich LNT operation at 325 C, and spatiotemporal species and temperature profiles were monitored along the LNT axis at different sulfur loadings. Reactor outlet NO{sub x}, NO, N{sub 2}O, and NH{sub 3} were also measured. Sulfur tended to accumulate in a plug-like fashion in the reactor and progressively inhibited NO{sub x} storage capacity along the axis. The NO{sub x} storage/reduction (NSR) reactions occurred over a relatively short portion of the reactor (NSR zone) under the conditions used in this study, and thus, net NO{sub x} conversion was only significantly reduced at high sulfur loading. Oxygen storage capacity (OSC) was poisoned by sulfur also in a progressive manner but to a lesser extent than the NO{sub x} storage capacity. Global selectivity for N{sub 2}O remained low at all sulfur loadings, but NH{sub 3} selectivity increased significantly with sulfur loading. We conjecture that NH{sub 3} breakthrough increased because of decreasing oxidation of NH{sub 3}, slipping from the NSR zone, by downstream stored oxygen. The NSR and oxygen storage/reduction (OSR) generated distinctive exotherms during the rich phase and at the rich/lean transition. Exotherm locations shifted downstream with sulfur accumulation in a manner that was consistent with the progressive poisoning of NSR and OSR sites.

• Research Organization: Oak Ridge National Laboratory (ORNL); Fuels, Engines and Emissions Research Center
• Sponsoring Organization: EE USDOE - Office of Energy Efficiency and Renewable Energy (EE)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 932042
• Journal Information: Applied Catalysis B, Journal Name: Applied Catalysis B Journal Issue: 1-2 Vol. 77
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
AIR POLLUTION CONTROL
CATALYTIC EFFECTS
DESIGN
EXHAUST GASES
NITROGEN OXIDES
OPERATION
PERFORMANCE
POISONING
POLLUTION CONTROL EQUIPMENT
SULFUR