Fe-substituted nanometric La0.9K0.1Co1−xFexO3−δ perovskite catalysts used for soot combustion, NOx storage and simultaneous catalytic removal of soot and NOx

A series of nanometric Fe-substituted La0.9K0.1Co1−xFexO3−δ (x = 0, 0.05, 0.1, 0.2, 0.3) perovskite catalysts were prepared by citric acid complexation, which show novel activity for diesel soot oxidation, NOx storage, and simultaneous NOx–soot removal. Their structures and physical–chemical properties were examined by XRD, BET, SEM, XPS and EXAFS techniques. In La0.9K0.1Co1−xFexO3−δ catalysts, the partial substitution of Co3+ by Fe3+ significantly enhances the catalytic activity towards soot oxidation or NOx storage and reduction. The catalyst La0.9K0.1Co0.9Fe0.1O3−δ shows the highest activity for simultaneous NOx–soot removal, over which the maximal soot oxidation rate is achieved at only 362 °C (Tm), the NOx storage capacity reaches 213 μmol g−1, and the percentage for NOx reduction by soot is 12.5%. Compared with the unsubstituted one (La0.9K0.1CoO3−δ), the activity enhancement of Fe-substituted samples results from the formation of high valence ion (Fe4+) at B-site, relative high content of surface lattice oxygen and the high concentration of NO2. Different from the widely accepted viewpoint that surface adsorbed oxygen species are responsible for soot combustion over perovskite catalysts, the surface lattice oxygen is identified as active oxygen species for soot combustion.