Co3O4, NiCo2O4 and LaCo2O4 catalysts were synthesized by the citric acid-ligated method. These catalysts containing Co-oxide active components can largely lower the temperature of soot combustion under tight contact conditions. Under the conditions of loose contact NiCo2O4 cannot promote soot combustion, but LaCo2O4 can effectively promote soot combustion because the nanometric perovskite-type catalyst LaCoO3 produced in the LaCo2O4 sample.