Recent regulations on the air quality force automobiles to greatly reduce pollutants. Particulate matter smaller than 10 micrometers (PM10), largely produced by diesel engine, is more often responsible for this situation. Perovskite type mixed metal oxides ABO₃ are possible candidate as catalysts for the oxidation of the soot. The A-site is occupied by lanthanide metals (La, Sm, etc.) or alkaline earth metal (Sr, Ca, Ba, etc.), and the B-site is occupied by transition metal (Fe, Co, Cu, Cr, V, etc.).

In this study, perovskite type LaFeO₃ powders were synthesized by solution combustion method, and their activity to oxidize soot was examined. We used lanthanum nitrate, iron nitrate and citric acid as starting materials. The overall reactions are as follows:

Fe(NO₃)₃9H₂O+La(NO₃)₃6H2O+2(f-1/6)C₆H₈O₇+9(f-1)O₂->LaFeO₃+12(f-1/6)CO₂+(8f+41/3)H₂O

Here, f means the fuel/oxidizer ratio. LaFeO₃ powders were synthesized at various values of f, and properties and shapes of the particles were examined by XRD, SEM and TEM. The soot oxidation capability was studied by TG/DTA.