The effect of the support oxide. Pt precursor and reactant gas composition on the catalysis of soot oxidation was investigated using carbon black as a model soot and simulated exhaust gases. The Pt precursors used were Pt(NH3)(4)(OH)(2), H(2)PtCl(6)6H(2)O, Pt(NH3)(4)(NO3)(2), and Pt(NH3)(4)Cl-2. The support metal oxides used were SiO2, Al2O3, and ZrO2. Pt/SiO2 prepared from Pt(NH3)(4)(OH)(2) showed the highest carbon oxidation activity. It had much higher activity in the condition of N-2+O-2+H2O+NO+SO2 than without NO and SO2.