The nanocrystalline, porous, perovskite La1-xKxFeO3 (x = 0-0.4) powders and La0.8K0.2FeO3-coated honeycomb ceramic device were prepared by the citrate-gel process and the citrate-gel assisted dip-coating method at a low calcination temperature of 600 degrees C for 6 h, respectively. All the perovskite powders can effectively catalyze the soot combustion and among them the La0.8K0.2FeO3 catalyst exhibits the highest catalytic activity for the soot combustion, with a lowest T-50 (350 degrees C) owing to a high specific surface area and large pore sizes. This optimized La0.8K0.2FeO3 catalyst is proved by the bench test for the practical exhaust gas emission and the La0.8K0.2FeO3-coated honeycomb ceramic device has a effective capture of particulate matter from the exhaust emission at a low temperature and starts to efficiently catalyze oxidization reactions of the particulate matter at the temperature around 245 degrees C (T-20), leads the smoke opacity near zero at the operational temperature of 400 degrees C.