Desulfurization of gaseous fuels using activated carbons as catalysts for the selective oxidation of hydrogen sulfide

The removal of low concentrations of hydrogen sulfide (H2S) from hydrogen-rich gaseous fuels by selective catalytic oxidation, using activated carbon as the catalyst, was studied. The capacities of four activated carbons for reducing the H2S concentration down to the parts per billion (ppb) level were determined to be strongly related to their microstructures and impurities, even though their activity and selectivity were strongly dependent on the test conditions, such as reaction temperature, O-2:H2S ratio, space velocity, and length-to-diameter (L/D) ratio of the catalyst bed. Because the side reactions that form COS and SO2 are sometimes unavoidable under real fuel processing conditions, the complete and exclusive conversion of H2S to elemental sulfur (S) requires that activated carbon has catalytic activities not only for the oxidation of H2S, but also for the oxidation of COS and the reaction between H2S and SO2. Because one of the activated carbons (sample W-22) had such catalytic functions and a relatively large capacity of trapping sulfur in its micropores, this carbon showed a combination of excellent activity and selectivity on removing H2S from both hydrogen and simulated reformate streams at a reaction temperature of similar to 150 degrees C.