Effect of Aging on the NOx Storage and Regeneration Characteristics of Fully Formulated Lean NOx Trap Catalysts

Journal Article · Sat Jan 01 04:00:00 EST 2011 · Applied Catalysis B

DOI:https://doi.org/10.1016/j.apcatb.2011.02.005· OSTI ID:1010998

Ji, Yaying ^[1]; Easterling, Vencon ^[1]; Graham, Uschi ^[1]; Fisk, Courtney ^[1]; Crocker, Mark ^[1]; Choi, Jae-Soon ^[2]

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1. University of Kentucky
2. ORNL

In order to elucidate the effect of washcoat composition on lean NO{sub x} trap (LNT) aging characteristics, fully formulated monolithic LNT catalysts containing varying amounts of Pt, Rh and BaO were subjected to accelerated aging on a bench reactor. Subsequent catalyst evaluation revealed that in all cases aging resulted in deterioration of the NO{sub x} conversion as a consequence of impaired NO{sub x} storage and NO{sub x} reduction functions, while increased selectivity to NH{sub 3} was observed in the temperature range 250--450 C. Elemental analysis, H{sub 2} chemisorption and TEM data revealed two main changes which account for the degradation in LNT performance. First, residual sulfur in the catalysts, associated with the Ba phase, decreased catalyst NO{sub x} storage capacity. Second, sintering of the precious metals in the washcoat occurred, resulting in decreased contact between the Pt and Ba, and hence in less efficient NO{sub x} spillover from Pt to Ba during NO{sub x} adsorption, as well as decreased rates of reductant spillover from Pt to Ba and reverse NO{sub x} spillover during catalyst regeneration. For the aged catalysts, halving the Pt loading from 100 to 50 g/ft{sup 3} was found to result in a significant decrease in overall NO{sub x} conversion, while for catalysts with the same 100 g/ft{sup 3} Pt loading, increasing the relative amount of Pt on the NO{sub x} storage components (BaO and La-stabilized CeO{sub 2}), as opposed to an Al{sub 2}O{sub 3} support material (where it was co-located with Rh), was found to be beneficial. The effect of Rh loading on aged catalyst performance was found to be marginal within the range studied (10--20 g/ft{sup 3}), as was the effect of BaO loading in the range 30--45 g/L.

• Research Organization: Oak Ridge National Laboratory (ORNL); Fuels, Engines and Emissions Research Center; National Transportation Research Center
• Sponsoring Organization: ORNL work for others; ME USDOE - Office of Management, Budget, and Evaluation
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1010998
• Journal Information: Applied Catalysis B, Journal Name: Applied Catalysis B Journal Issue: 3-4 Vol. 103; ISSN 0926-3373
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
54 ENVIRONMENTAL SCIENCES
AGING
AIR POLLUTION CONTROL
BARIUM OXIDES
CATALYSTS
KINETICS
NITROGEN OXIDES
PERFORMANCE TESTING
PLATINUM
REGENERATION
RHODIUM