Selective oxidation of H_2S to elemental sulfur over chromium oxide catalysts

摘要

CrO_x and CrO_x supported on CiO_2 have been found to be active for the selective oxidation of hydrogen sulfide to elemental sulfur. The catalysts show maximum sulfur yield at a stoichiometric ratio of O_2/H_2S, 0.5. Amorphous Cr_2O_3 exhibits higher yield of sulfur and has stronger resistance against water than supported Cr/SiO_2, especially at low temperatures. At high temperatures above 300 deg C, the sulfur yield over the supported catalyst becomes similar to amorphous Cr_2O_3 because the Claus reaction occurring on the silica support removes SO_2 to increase the sulfur yield. Active sites are the amorphous monochromate species that can be detected as a strong temperature programmed reduction (TPR) peak at 470 deg C. Catalytic activity can be correlated with the amount of labile lattice oxygen and the strength of Cr-O bonding. The reaction proceeds via the redox mechanism with participation of lattice oxygen.