La–Li–Cr perovskite catalysts for diesel particulate combustion

Nano-structured bulk Li-substituted La–Cr perovskites (La0.8Cr0.9Li0.1O3, La0.8Cr0.8Li0.2O3, La0.8Cr0.7Li0.3O3) were prepared (by combustion synthesis), characterized (by XRD, AAS, BET, SEM, TEM, TPD/R, XPS analyses), tested (in a temperature-programmed combustion TPC microreactor and in a DSC analyzer) in comparison with the reference LaCrO3. The progressive increase in the Li content of the catalysts induces an increase in the catalytic activity owing to the enhancement of the amount of weakly chemisorbed oxygen O− species (even exceeding 1200 μmol/g), key players in the soot oxidation mechanism. However, beyond 20% Cr substitution with Li, part of this latter metal got segregated as LiCrO2. The best single-phase catalyst (La0.8Cr0.8Li0.2O3) was already active well below 350 °C. Catalytic traps were prepared by in situ combustion synthesis within cordierite (CORNING) and SiC (IBIDEN) wall-flow filters on the basis of the above catalysts and tested on real diesel exhaust gases in an engine bench, fully confirming the encouraging results obtained on powder catalysts.