EFFECT OF ENGINE-BASED THERMAL AGING ON SURFACE MORPHOLOGY AND PERFORMANCE OF LEAN NOX TRAPS

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

DOI:https://doi.org/10.1016/j.cattod.2007.02.027· OSTI ID:931684

Toops, Todd J ^[1]; Bunting, Bruce G ^[1]; Nguyen, Ke ^[2]; Gopinath, Ajit ^[1]

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1. ORNL
2. University of Tennessee, Knoxville (UTK)

A small single-cylinder diesel engine is used to thermally age model (Pt + Rh/Ba/{gamma}-Al{sub 2}O{sub 3}) lean NOx traps (LNTs) under lean/rich cycling at target temperatures of 600 C, 700 C, and 800 C. During an aging cycle, fuel is injected into the exhaust to achieve reproducible exotherms under lean and rich conditions with the average temperature approximating the target temperature. Aging is performed until the cycle-average NOx conversion measured at 400 C is approximately constant. Engine-based NOx conversion decreased by 42% after 60 cycles at 600 C, 36% after 76 cycles at 700 C and 57% after 46 cycles at 800 C. The catalyst samples were removed and characterized by XRD and using a microreactor that allowed controlled measurements of surface area, precious metal size, NOx storage, and reaction rates. Three aging mechanisms responsible for the deactivation of LNTs have been identified: (i) loss of dispersion of the precious metals, (ii) phase transitions in the washcoat materials, and (iii) loss of surface area of the storage component and support. These three mechanisms are accelerated when the aging temperature exceeds 850 C--the {gamma} to {delta} transition temperature of Al{sub 2}O{sub 3}. Normalization of rates of NO reacted at 400 C to total surface area demonstrates the biggest impact on performance stems from surface area losses rather than from precious metal sintering.

• 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: 931684
• Journal Information: Catalysis Today, Journal Name: Catalysis Today Journal Issue: 1-4 Vol. 123; ISSN 0920-5861; ISSN CATTEA
• Country of Publication: United States
• Language: English

Related Subjects

33 ADVANCED PROPULSION SYSTEMS
AGING
CATALYSTS
DEACTIVATION
DIESEL ENGINES
MORPHOLOGY
PERFORMANCE
REACTION KINETICS
SINTERING
STORAGE
SURFACE AREA
TRANSITION TEMPERATURE
X-RAY DIFFRACTION