Lanthanum Cobaltite Catalysts for Diesel Soot Combustion

This paper deals with the preparation (by solution combustion synthesis), the characterization (by XRD, AAS, BET, FESEM, XPS and TPD/R analyses), the catalytic activity evaluation (in a temperature-programmed combustion microreactor), and the conception of a possible reaction mechanism of a series of nano-structured soot combustion catalysts based on La–Co substoichiometric or alkali metal-substituted perovskites (La0.9CoO3, La0.9Na0.1CoO3, La0.9K0.1CoO3, La0.9Rb0.1CoO3), whose performance has been compared with that of the standard LaCoO3. Significant catalytic activities have been measured in the 350–450 °C range, even after a specific thermal ageing protocol (at 850 °C for 16 h in the presence of water) or repeated combustion cycles (up to 9). The La0.9Rb0.1CoO3 catalyst has been found to allow the best compromise between satisfactory catalytic activity and stability. This catalyst has been then deposited on an SiC wall-flow trap, submitted to the same ageing treatment and then tested on a diesel engine bench (trap loading and regeneration inducing a temperature increase due to the catalytic combustion of the on purpose post-injected fuel). The presence of the catalyst in the wall-flow trap has enabled both a more complete regeneration and a significant reduction of the regeneration time compared to that of a non-catalytic trap, even after ageing, with a consequent potential saving of post-injected fuel.