(244f) Influence of Pt Dispersion On Oxidation of NO By Lean NOx Trap Catalysts: A Comparison

Wentworth, T., Chalmers University of Technology
Stagg-Williams, S. M., University of Kansas
Depcik, C. D., University of Kansas

Recently the implementation of lean burn diesel engines for automotive use has been increasing in popularity due to their increased fuel efficiency.  These engines generate higher NOx concentrations and higher oxygen concentrations than traditional stoicheometric engines.  Stringent EPA regulations on the emissions of lean operating diesel engines has necessitated a major research emphasis in the area of NOx reduction due to the ineffectiveness of traditional three way catalysts to convert NOx under these exhaust conditions.  The addition of cerium to the traditional noble metal - alkali earth metal alumina supports formulation has been shown to increase the reduction of stored NOx during rich phase operation[1].  A fundamental understanding of the deviation of the oxidation step as the catalyst degrades is critical to the effective implementation of LNT catalysts as exhaust after treatment devices.

This paper presents the NO oxidation light off curves for traditional LNT and novel cerium supported catalyst formulations with varying platinum particle dispersion, in the range of 100-450°C.  Lean NOx trap (LNT) catalysts have been produced by incipient wetness impregnation of gamma alumina, to yield the desired weight percentage loading.  The catalysts examined and corresponding wt. % loadings are as follows: Pt/Ba/Al, Pt/Ba/Ce/Al catalysts with weight ratio loadings of 1/20/100 and 1/20/5/100 respectively.  Catalyst degradation has been estimated by varying calcinations temperature to change platinum particle size and dispersion.  Pt particle size and dispersion have been estimated through CO chemisorption and verified by TEM.  The catalyst has also been characterized by XRD and EDAX.  NO and total NOx concentrations have been measured through Chemiluminescence detection. 

1.            Infantes-Molina, A., et al., Characterization and reactivity of Ce-promoted PtBa lean NOx trap catalysts. Catalysis Today, 2012. 197(1): p. 178-189.