Soot capture and combustion for perovskite La–Mn–O based catalysts coated on honeycomb ceramic in practical diesel exhaust

Nanosized perovskite oxides of LaMnO3, La0.8K0.2MnO3 and La0.8K0.2Co0.5Mn0.5O3 with grain sizes about 16–28 nm were prepared by the citrate–gel process and their coatings with thickness about 30 μm and a coherent interface between the coating and the honeycomb ceramic were obtained by the sol–gel assisted dip-coating technique. The powders and coatings were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. The specific surface area was measured by the Brunauere–Emmette–Teller method. The catalytic performance was evaluated by thermo-gravimetric analysis under model conditions and by the smoke opacity measurement for the practical exhaust gas emissions at 200–400 °C, respectively. The results show that all three perovskite oxide catalysts have a capture effect of soot and a catalytic activity for soot combustion. The capture effect is mainly related to the porous structural characteristic of the catalyst and the catalytic performance for soot combustion is largely affected by the chemical composition, grain size, specific surface area and pore structure, which are related to the ions substitution and calcination temperature. Among these three catalysts, La0.8K0.2MnO3 shows the best comprehensive catalytic performance and the La0.8K0.2MnO3 coated honeycomb ceramic will be a promising device for diesel exhaust gas emissions.