The interaction of low concentrations of sulfur dioxide with carbon monoxide proceeds efficiently on a bifunctional iron-alumina catalyst. The iron component in the pelletized, mixed catalyst was rapidly transformed to pyrrhotite, FeS, with an apparent decrease in activity. The catalyst effectiveness then remained steady for a prolonged period of time. The catalyst decay can be temporarily delayed by carbidizing its iron component. Carbonyl sulfide by-product begins to form when all the iron surface is sulfidized; hence it was absent in the effluent gas during the catalyst break-in period. Red bauxite and Surinam red mud showed promise as commercial catalysts for recovery of sulfur from sulfurous waste gases.