NOVELTY - Method of oxidizing carbon monoxide to carbon dioxide involves heating a gaseous mixture comprising carbon monoxide and/or oxygen with a catalyst mixture comprising palladium and/or manganese(II,III) oxide at 0-60 degrees C. The conversion rate of carbon monoxide to carbon dioxide is 40-100%.    USE - Method of oxidizing carbon monoxide to carbon dioxide. Uses include but are not limited to proton exchange membrane fuel cells, automotive applications, air cleaning systems, tunnels, parking areas, garages, submarines, respiratory protection systems, chemical plants, power generation plants, ammonia plants, and polymerization reaction of hydrocarbons.    ADVANTAGE - The method enables oxidation of carbon monoxide to carbon dioxide at low temperature with high conversion rate, using mesoporous support having high mechanical strength and excellent abrasion resistance. The mesoporous support can be economically manufactured by simple process. The poisoning of electrodes of proton exchange membrane fuel cells by carbon monoxide can be prevented.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) preparation of palladium/manganese(II,III) oxide catalyst, which involves contacting manganese(II,III) oxide with palladium compound to form a reaction mixture, contacting the reaction mixture with a reducing agent to form a precipitate, and isolating the precipitate;    (2) palladium/manganese(II,III) oxide catalyst, which comprises mesoporous palladium/manganese(II,III) oxide support and palladium nanoparticles(S) provided on at least one portion of the mesoporous support, where the content of palladium contained in the catalyst is 1-5 wt.%; and    (3) system for oxidizing carbon monoxide to carbon dioxide, which comprises a gas source configured to supply the gaseous mixture, and a reactor configured to contain a volume of catalyst. The reactor comprises an inlet configured to receive the gaseous mixture, such that the gaseous mixture passes through the volume of catalyst, and an outlet configured to allow gaseous mixture that has passed through the volume of catalyst to exit the reactor.