Catalytic systems based on Ce, Zr, K for soot oxidation

Systems based on Ce-Zr are used in catalytic converters for their oxygen storage ability. Recently, their application for soot abatement is under investigation. In this paper, preliminary results of the performance of Ce-Zr systems with the addition of K are reported by varying potassium content and calcination temperature. The powder catalysts were prepared by a variant of the citrates route developed at University of L’Aquila. Characterization of the catalysts after calcination was performed by different techniques: profile fitting of the XRD data, estimation of surface composition by XPS, evaluation of catalytic performance by temperature programmed oxidation tests of the soot-catalyst mixture and of redox properties by carbothermic reduction and subsequent oxidation in a high resolution thermobalance. The characterization by XRD showed that the system maintains the crystallographic structure Fm-3m and that the potassium is segregated on the grain boundaries. The catalytic activity results showed that the systems are particularly active even after 10 hours of calcination at 900° C in fluidized bed. This temperature is high enough to get reasonably stable systems for practical applications. Moreover, the soot oxidation rate has a maximum at 368°C in the sample with the best performance, therefore in the range of temperatures of diesel engine exhaust gases. The XPS data showed the presence of Ce, Zr, K and also of significant amount of Cl. Other formulations were prepared by adding small amounts of the different potassium halides.