Lanthanum supported catalysts for the simultaneous removal of soot and nitrogen oxides: effect of Rhodium

BÁRBARA S. SÁNCHEZ,; EDUARDO E. MIRÓ; CARLOS A. QUERINI

San Francisco, California, Estados Unidos

Congreso; 21st North American Meeting; 2009

The main contaminants present in diesel exhaust gases are soot particles and nitrogen oxides. The combination of traps and catalysts appears as the most suitable after treatment to remove soot particles [1]; while NOx adsorbers are a developing technology for the elimination of nitrogen oxides in diesel engines (oxigen excess conditions) [2].   We have previously shown that La2O3 is capable of adsorbing NOx [3]; and that K/La2O3  catalyst is very active for soot oxidation [4]. In this work, different lanthanum supported catalysts were evaluated for the simultaneous removal of diesel contaminants, using rhodium in catalyst formulation to enhance NOx adsorption and decomposition. It was shown that lanthanum supported catalysts, which have good NOx adsorbing capacities, are able to burn soot at temperatures between 300 and 350 ºC in a nitrogen stream, using as oxidant the nitrates adsorbed onto the catalysts surface.  The presence of  potassium in the catalyst formulation is required to oxidize significant amounts of carbonaceous materials. On the other hand, the remarkable ability of rhodium to decompose adsorbed nitrates does not favour the soot combustion process. However, this is very important for NOx trap design, and it is expected that rhodium could have an effect in the reduction of NOx released from the catalyst surface to N2.