Sulfation of K-based Lean NOx Trap while Cycling Between Lean and Rich Conditions: I. Microreactor Study

Journal Article · Tue Jan 01 04:00:00 EST 2008 · Catalysis Today

DOI:https://doi.org/10.1016/j.cattod.2008.02.007· OSTI ID:931018

Toops, Todd J ^[1]; Pihl, Josh A ^[1]

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1. ORNL

Exposure of Pt/K/Al{sub 2}O{sub 3} to 15 ppm SO{sub 2} reduces the NOx activity at 200, 300, and 400 C at significantly different rates--1.5, 8.5, and 18.0 {micro}mol NOx/(h g{sub cat}), respectively. During the initial sulfation, NOx conversion is directly linked to lean phase storage capacity, and sulfation does not impact the reduction kinetics since the amount of unconverted NOx was constant or decreased with increasing sulfation time. A portion of sulfur stored at 200 C desorbs upon mild heating to 400 C while cycling between lean and rich conditions. This apparently is a result of sulfur being released from Al{sub 2}O{sub 3}; however, performance is not significantly recovered as much of the sulfur is re-adsorbed on the K-phase. This is apparent from analysis of the NOx storage and release profiles. Additional analysis of these profiles suggests that SO{sub 2} initially adsorbs near Pt before interacting with other sites further away from Pt at 300 C. At 400 C, it appears that SO{sub 2} either preferentially adsorbs near Pt and then quickly diffuses along the surface to other less proximal sites, or it directly adsorbs on sites further away from Pt. De-sulfurization up to 800 C using a temperature programmed reduction (TPR) procedure and rich conditions with both CO{sub 2} and H{sub 2}O restored 73=94% of the LNT performance at 300 and 400 C. However, the recovered performance measured at 200 C was only 34-49% of the original NOx reduction activity. H{sub 2}S and SO{sub 2} were the primary de-sulfurization products with H{sub 2}S having a maximum release between 690 and 755 C, while SO{sub 2} had a peak release between 770 and 785 C. The sulfation temperature does not have a significant impact on the recovered performance, the de-sulfurization products or the sulfur release temperature.

• 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: 931018
• Journal Information: Catalysis Today, Journal Name: Catalysis Today Journal Issue: 1-2 Vol. 136; ISSN 0920-5861; ISSN CATTEA
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
AIR POLLUTION ABATEMENT
ALUMINIUM OXIDES
CATALYSTS
CHEMICAL REACTION KINETICS
DESULFURIZATION
NITROGEN OXIDES
PERFORMANCE
PLATINUM
POTASSIUM
SULFATION
SULFUR DIOXIDE