Promotional effect of rare earths and transition metals in the combustion of diesel soot over CeO2 and CeO2-ZrO2

The soot combustion behavior and the textural and structural characteristics of CeO2 and a series of ceria-modified materials have been studied. It is shown that ceria doped with transition metals (Zr and Fe) and rare earth elements (La, Pr, Sm, Tb) results in more active catalysts with enhanced textural properties. ZrO2 enhances the thermal stability and the oxygen storage capacity of pure ceria, resulting in better performance in soot oxidation. Remarkably, cerium-zirconium solid solution doped with rare earth does not achieve lower temperature of combustion, providing performances comparable to CeO2 and CeO2-ZrO2. Cerium doped with Fe2O3 presents the better results as far as fresh samples are taken into account, but suffers from a net loss of activity after calcination. TGA experiments under N2 atmosphere have confirmed the key role of oxygen storage capacity in soot oxidation.