The catalytic performances of bismuth-molybdenum binary oxides for the selective oxidation of hydrogen sulfide to elemental sulfur were studied in a fixed-bed glass reactor in the temperature range 200-280 degrees C. A synergistic phenomenon in catalytic activity was observed for the bismuth molybdate catalysts. Under identical reaction conditions, the hydrogen sulfide conversions of the binary oxide catalysts were superior to those of the corresponding single oxide catalysts. The most active bismuth/molybdenum composition for the binary oxide catalysts was found to be 2:3 atomic ratio, which suggests that the compound Bi2Mo3O12 formed in the binary oxides is much more active than the corresponding single oxide catalysts for the selective oxidation of hydrogen sulfide. The reaction rates of hydrogen sulfide oxidation over the catalysts were found to exhibit first-order dependence on the hydrogen sulfide concentration.