Soot Combustion over Lanthanum Cobaltites and Related Oxides for Diesel Exhaust Treatment

摘要

This paper reports a comparative study of a series of La_(1-x)(M)_xCoO_3 (M = Ce and Sr) perovskites and the related M'O_x (M' = La, Co, Ce, and Sr) sample oxides. These catalysts were characterized by N_2 adsorption. X-ray diffraction (XRD), temperature-programmed desorption (TPD) of oxygen, temperature-programmed reduction (TPR) by hydrogen, and temperature-programmed combustion (TPC) of soot. In the presence of perovskite-type catalysts, the soot oxidation was promoted, showing a shift of CO_2 peaks toward lower temperature compared to the non-catalytic process. In addition, the catalytic activity ofthese perovskites was found to follow the trend La_(0.8)Ce_(0.2)CoO_3 > La_(0.9)Ce_(0.1)CoO_3 > La_(0.9)Sr_(0.1)CoO_3 > La_(0.8)Sr_(0.2)CoO_3 ≈ LaCoO_3. A mechanism was proposed with an attack of soot by surface oxygen species, which migrate from the perovskite surface. The generation of CO (or carbonyl groups) as an intermediate and the possible formation of carbonate species over the most basic compounds are also discussed.