The Co-Ba-K catalysts supported on alumina ceramic substrates were prepared. All the catalysts were characterized by X-ray diffraction and thermogravimetry/differential scanning calorimetry. The catalytic activities were evaluated by a soot oxidation reaction using the temperature-programmed reaction system. The catalytic activities of Co3O4, Ba(NO3)(2), Co-Ba, and Co-Ba-K catalysts were studied and the effect of the contact mode on the soot onset ignition temperature and soot oxidation rate was also discussed. The soot onset ignition temperature is 373 degrees C for Co-Ba catalysts with molar ratios of 1:2, 1:1 and 2: 1, which is the same as that of pure Co3O4. The Co-Ba catalysts containing KNO3 can greatly lower the soot onset ignition temperature value. The catalytic activity of pure Co3O4 and Ba(NO3)(2) is affected by catalyst-soot contact intensity. The soot onset ignition temperature is not affected by contact intensity for the catalysts with proper Co-Ba-K ratios. The soot oxidation rate is greatly accelerated when the Co-Ba-K catalysts and soot are in the tight contact mode. (C) 2008 Elsevier B.V. All rights reserved.