a process is disclosed for the conversion of carbon monoxide in sour synthesis gas mixtures in the presence of a catalyst which is active in the presence of sulfur compounds . the catalyst comprises known sulfactive metal oxides or sulfides supported on a shaped carrier . the catalytically active oxides or sulfides are doubly promoted with an alkali metal compound and an oxide or sulfide of manganese . the two promoters combined in proper ratio provide a synergistic effect on the activity of the catalyst which is enhanced beyond that of the singly promoted catalyst . the catalysts are active at relatively low temperatures of less than 500 ° f ., even in the presence of sulfur compounds . the equilibrium for the conversion of steam and carbon monoxide to hydrogen and co 2 is favored at lower temperatures .