K/CeO2 catalysts supported on cordierite monoliths: Diesel soot combustion study

The combination of filters and oxidation catalysts is one of the most effective after-treatment techniques to eliminate soot particles from the exhaust gases of diesel engines. The activity of powder K/CeO2 catalysts has been extensively reported in the literature but few studies refer to K/CeO2 supported on monoliths. This work presents a study of K/CeO2 catalysts supported on cordierite for the reaction of diesel soot combustion. The catalysts were prepared by sequential impregnation of the monolith with ceria and different potassium precursors. The activity was studied by temperature-programmed oxidation (TPO) in the soot combustion with loose contact. No deactivation was observed after six cycles of combustion-soot charge. The activity depends on the potassium precursor used, decreasing in the order KNO3 > K2CO3 > KOH. The structural effects caused by the different precursors of potassium determine the material activity. The X-ray diffraction characterization does not indicate a crystalline structure change before and after reaction. The optical microscopy and scanning electron microscope determined a redistribution of the crystals in the monolith by heating or by the soot combustion reaction. A weight loss during the reaction was ascribed to the degradation of the catalytic monolith. The non-deactivation of the samples during the reaction allowed us to discard the volatilization of the active species in the temperature range of 20-600 degrees C, in which the tests were performed. On the other hand, the ageing treatments at 800 degrees C led to the deactivation of K/CeO2 catalysts due to a partial loss of potassium loading. (C) 2011 Elsevier B.V. All rights reserved.