Method for catalytic conversion of carbon monoxide in a hydrogen-containing gas mixture with improved cold start behavior

A method for catalytic conversion of carbon monoxide with water to form carbon dioxide and hydrogen in a gas mixture that contains hydrogen and other oxidizable components comprising passing the gas mixture over a shift catalyst that is at an operating temperature for carbon monoxide conversion, wherein the shift catalyst comprises at least one of the noble metals selected from the group consisting of platinum, palladium, rhodium, ruthenium, iridium, osmium and gold on an oxide support material selected from the group consisting of aluminum oxide, silicon dioxide, titanium dioxide, rare earth oxides, mixed oxides thereof and zeolites and wherein oxygen is added to the gas mixture in order to bring the catalyst to its operating temperature for carbon monoxide conversion rapidly after a cold start, or to keep it at said temperature during operation, by catalytic combustion of a variable proportion of the oxidizable components of the gas mixture.