TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Catalysts: The catalysts capable of selectively oxidizing carbon monoxide and differing from each other in the application temperature comprises a first catalyst for selectively oxidizing carbon monoxide, the first catalyst including a carrier and Pt acting as an active metal and supported on the carrier, and a second catalyst for selectively oxidizing carbon monoxide, the second catalyst including a carrier and an active metal consisting of at least one kind or metal selected from Pd, Ru, Rh and Ir and supported on the carrier.The carrier of the first and second catalysts for selectively oxidizing carbon monoxide is selected from Y-type zeolite, mordenite, A-type zeolite, gamma-Al2O3, anatase and a crystalline silicate having the highest to the fifth highest peaks in the powder x-ray diffraction using CuKalpha ray in the lattice spacing of 3.65+/-0.1A, 3.75+/-0.1 A, 3.85+/-0.1A, 10.0+/-0.3A and 11.2+/-0.3A, respectively, and having the composition of formula (1) under a dehydrated state: (1+/-0.8)R2O.(aM2O3.bNO.cAl2O3).ySiO2 (1),R = alkali metal or H;M = element selected from VIII group elements, rare earth elements, Ti, V, Cr, Nb, Sb and Ga;N = element(s) selected from Mg, Ca, Sr and Ba;a = 0 or more;b = 0-20;a+c = 1;y = 11-3000.Each of the catalysts. capable of selectively oxidizing carbon monoxide and differing from each other in the application temperature. is formed of a catalyst including a carrier and an active metal consisting of at least one kind of metal selected from Pd, Ru, Rh and Ir supported on the carrier.Preferred Process: The temperature of the gaseous mixture is 50-280 degreesC when the gaseous mixture is introduced into the catalyst bed.The CO concentration of the gaseous mixture is not higher than 4 %. EXAMPLE - A first low temperature honeycomb catalyst of Pt and a second high temperature honeycomb catalyst of Ru. The inlet temperature of the first catalyst layer was 100 degreesC and the outlet temperature was 160 degreesC, and the CO concentration at outlet of catalyst layer was 1200 ppm, on the high temperature side, the outlet temperature was 190 degreesC and the CO concentration at outlet of catalyst layer was 13 ppm.