Preparation And Performance Of Supported LaCoO₃Perovskite Catalysts Used For The Catalytic Combustion Of Soot

Currently diesel engines have been widely employed in vehicles, however, thesoot particulates produced from the diesel combustion are serious pollutants to theenvironment and human health, therefore, many countries have formulatedincreasingly stringent standards to limit the release of soot emission. Now the mosteffective way for soot removal is the catalytic combustion, and the key technique isthe exploration of advanced catalysts. Due to the high thermal stability, high oxidationperformance and low price, perovskite catalysts have widely applied to the catalyticoxidation of soot. Nevertheless, perovskite catalysts often exhibit small specificsurface area, which limits the further improvement of its activity. In this study, wetried to prepare supported perovskite catalysts, and investigated their performance insoot oxidation reaction. Meanwhile, the effects of different supports and perovskiteloading on the activity were also studied.Firstly, we prepared several kinds of supported perovskite catalysts using ceriumoxide, zirconium oxide, aluminum oxide and cerium-zirconium solid solution assupports. The results of XRD and FT-IR prove that supported perovskite has beensuccessfully synthesized on the supports except the Al2O3, on which LaAlO3phasewas formed. The activity results show that the supported perovskite catalysts havehigher activity for soot combustion than bulk perovskite catalyst; but the sampleLaCoO3/Al2O3is much less active for soot oxidation than other supported catalysts.The BET, H2-TPR, SEM, Soot-TPR characterization results show that the activity ofthe catalysts is related to their specific surface area, redox properties and theinteraction between perovskite and supports. In comparison, the cerium-zirconiumsolid solution is the best support.Secondly, the ratio of cerium/zirconium in the cerium-zirconium solid solution isoptimized. The activity tests show that the Ce0.8Zr0.2O2solid solution has the largestspecific surface area and its supported sample has the best activity for sootcombustion. The presence of zirconium can effectively restrain the sintering of thesupports, making the cerium-zirconium solid solution has larger specific surface areathan the single cerium oxide.Finally, the loading of LaCoO3on the Ce0.8Zr0.2O2support is optimized based upon the catalytic activity. The activity tests show that the sample with5wt%LaCoO3exhibits the best activity for soot combustion. Although the sample with2wt%LaCoO3has larger surface area, it has less amount of active phase LaCoO3; thusit shows lower activity as compared with the sample with5wt%LaCoO3. For thesample with the LaCoO3loading larger than10wt%, the LaCoO3phase canaccumulate and form larger particles, decreasing the activity of the catalysts.