Copper-Lanthanum Catalysts for NOx and Soot Removal

The individual and simultaneous removal of NOx by Storage and Reduction with H-2 (H-2-NSR) and combustion of soot have been studied for La and CuLa catalysts. The NOx storage capacity of pure lanthanum oxide is improved either by copper addition or by using a colloidal crystal hard template for the synthesis of a macroporous structure. Although the NOx storage capacity of the CuLa macroporous material is around ten times lower regarding conventional PtBa catalysts, the kinetics of the H-2-NSR cycles are fast enough to allow high NOx removal (until 90 % removal). Lanthanum oxide catalyst prepared with uncontrolled structure has no activity for soot combustion, but the activity increases for a macroporous counterpart prepared using the colloidal crystal template because the macroporous structure improves the soot-catalyst contact and allows the nitrogen-oxygen surface groups yielded upon NOx chemisorption to oxidize soot. The soot combustion activity of lanthanum catalysts is also enhanced upon copper loading, because copper improves the NO2-assisted soot combustion mechanism and favors the chemisorption of NOx, enhancing soot oxidation by nitrogen-oxygen surface species. Finally, it is demonstrated that the simultaneous removal of NOx by H-2-NSR and soot combustion can be carried out with a CuLa catalyst at 450 degrees C. The simultaneous removal does not affect the combustion of soot and only has a small effect in NOx removal.