Studies on the redox properties of chromite perovskite catalysts for soot combustion

This paper deals with the preparation (by combustion synthesis), the characterization (by XRD, AAS, BET, SEM, TEM, TPD/R, and XPS analyses), the catalytic activity testing (in a temperature-programmed combustion microreactor and in a DSC analyzer), and the assessment of the reaction mechanism of a series of nanostructured soot combustion catalysts based on La-Cr substoichiometric or alkali-metal-substituted perovskites (La0.9CrO3, La0.8CrO3, La0.9Na0.1CrO3, La0.9K0.1CrO3, La0.9Rb0.1CrO3, La0.8Cr0.9Li0.1O3), whose performance is compared with that of the standard LaCrO3. Some conclusions are drawn concerning the role of each single constituting element on the activity of the most promising catalyst, La0.8Cr0.9Li0.1O3, which is already active well below 400 °C. The role of weakly chemisorbed O− surface species in particular is pointed out as crucial for the soot combustion process. This indicates the way for the development of new, more active catalysts, possibly capable of delivering amounts of these oxygen species even higher than those obtained (about 700 μmol / g) for the most active Li-substituted lanthanum chromite catalyst developed.