La1-xKxCoO3 and LaCo1-yFeyO3 Perovskite Oxides: Preparation, Characterization, and Catalytic Performance in the Simultaneous Removal of NOx and Diesel Soot

Perovskite-type La1-xKxCoO3 and LaCo1-yFeyO3 catalysts were prepared and characterized by nitrogen sorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Catalytic activity for the simultaneous removal of NOx and soot was investigated using temperature-programmed reactions. For the La1-xKxCoO3 series, the introduction of K ions into the A-site caused the enhancement of Co valence state, which was beneficial to improving the catalytic activity. Excess K ions produced a Co3O4 phase adhering to the perovskite crystals, but the rhombohedral perovskite structure was well-maintained. In contrast, the B-site could be substituted by Fe ions with the doping ratio changing from null to 0.5, and no secondary phases were detected. With increasing K substitution, NOx conversion in the La1-xKxCoO3 series showed a declining trend after an initial ascent. The Co3O4 particles produced at high K content were responsible for this falling catalytic activity. For the LaCo1-yFeyO3 series, catalytic performances showed a monotonously decreasing trend as a function of Fe substitution. Among all of the perovskite oxides tested in this study, the La0.6K0.4CoO3 sample exhibited the highest catalytic activity for the simultaneous removal of NOx soot.