Catalytic oxidation of formaldehyde, carbon monoxide, and methanol over cordierite-supported manganese-cerium-aluminum mixed oxides was investigated in a laboratory reactor. The activities of base metal oxides (BMO) comprising 27% MnO2, 21% CeO2, and 52% Al2O3 supported on cordierite monoliths calcined at 1,000 ℃ for 3 h in air dropped very rapidly due to the migration of mobile silicon dioxide (SiO2) from the cordierite to the base metal oxides to react with or physically block the active catalysts. To immobilize migrating SiO2, barrier coats composed of alkali metal (Ba, Sr, Ca, Mg) oxides and alumina were applied to the cordierite prior to coating with active base metal oxides. The base metal oxides supported on cordierite monoliths pretreated with BaO-Al2O3 barrier coats and calcined at 1,000 ℃ for 3 h in air, initiated the oxidation of HCHO, CO, and CH3OH at 150, 220, and 170 ℃, respectively. These catalysts turned out to be more effective for the formaldehyde oxidation than 0.5% Pt/Al2O3 precious metal catalysts. Carbon monoxide and methanol oxidation conversions were comparable. The incorporation of small amount of palladium (0.147 wt%) to base metal oxides supported on cordierite monoliths pretreated with BaO-Al2O3 barrier coats, showed the superiority for HCHO, CO, and CH3OH oxidation to 0.5% Pt/Al2O3 precious metal catalysts. The temperatures of 50% conversion of formaldehyde, carbon monoxide and methanol were 70 ℃ lower over base metal oxides catalysts than over precious metal catalysts.