Hydrogen sulfide oxidation on RE(RE = Sm, Y, La)–V–Sb catalysts: Effects of RE size and electronegativity

Three RE–V–Sb (RE was Sm, Y, and La) mixed-oxide catalysts were prepared for catalyzing the selective oxidation of hydrogen sulfide to sulfur. The multiphase RE–V–Sb catalysts were characterized by TPR, XRD, SEM and BET techniques. Synergistic phenomena in sulfur yield were observed with the solid-state reaction between REVO4 and α-Sb2O4 (antimony oxide/REVO4 weight ratio = 1/3), which was ascribed to the formation of SbVO4 species. Under identical reaction conditions, areal reaction rate decreased in the following order: Sm–V–Sb > La–V–Sb ∼ LaVO4 > Y–V–Sb > SmVO4 > YVO4. All RE–V–Sb catalysts exhibited 100% sulfur yield in a certain temperature range. The temperature window width for 100% sulfur yield decreased in the following order: La > Sm > Y, which was the same as the order of decreasing ionic radius (La > Sm > Y) and the order of increasing RE electronegativity (La < Sm < Y). The selectivity difference was explained in terms of active site isolation and product desorption effects. The rare earth cation size effect observed here for H2S oxidation to elemental sulfur was similar to the alkali cation size effect reported for the hydrocarbon oxidation.