Oxidation of sulfur dioxide to sulfur trioxide over supported vanadia catalysts

The oxidation of SO{dollar}sb2{dollar} to SO{dollar}sb3{dollar} over supported vanadia catalysts occurs in many industrial processes, for example, the manufacture of sulfuric acid, the selective catalytic reduction of NO{dollar}sb{lcub}rm x{rcub}{dollar} with NH{dollar}sb3{dollar} and the regeneration of petroleum refinery cracking catalysts. The objective of this research is to establish the fundamental molecular structure-reactivity relationships and kinetics for SO{dollar}sb2{dollar} oxidation over supported vanadia catalysts.; Raman spectroscopy was used to determine the coordination of surface species. At low vanadia loadings, vanadia preferentially exists on oxide support surfaces as isolated four-fold coordinated (M-O){dollar}sb3{dollar}V{dollar}sp{lcub}5+{rcub}{dollar} = O species. At higher vanadia loadings, the isolated (M-O){dollar}sb3{dollar}V{dollar}sp{lcub}5+{rcub}{dollar} = O species polymerize on the oxide support surface breaking two V-O-M bonds and forming two V-O-V bridging bonds.; The turnover frequency for SO{dollar}sb2{dollar} oxidation was very low, 10{dollar}sp{lcub}-4{rcub}{dollar} to 10{dollar}sp{lcub}-6{rcub}{dollar} sec{dollar}sp{lcub}-1{rcub}{dollar} at 400{dollar}spcirc{dollar}C, due to low adsorption of SO{dollar}sb2{dollar} onto surface vanadia species and was independent of vanadia coverage suggesting that only one vanadia site is required for the oxidation reaction. As the support was varied, SO{dollar}sb2{dollar} oxidation activity of the supported vanadia catalysts varied by an order of magnitude (Ce {dollar}>{dollar} Zr, Ti {dollar}>{dollar} Al). The basicity of the bridging V-O-M oxygen appears to be responsible for influencing the adsorption and oxidation of the acidic SO{dollar}sb2{dollar} molecule.; The turnover frequency for SO{dollar}sb2{dollar} oxidation over several binary catalysts followed the trend: V{dollar}sb2{dollar}O{dollar}sb5{dollar}/TiO{dollar}sb2 >{dollar} Fe{dollar}sb2{dollar}O{dollar}sb3{dollar}/TiO{dollar}sb2 >{dollar} Re{dollar}sb2{dollar}O{dollar}sb7{dollar}/TiO{dollar}sb2 sp{lcub}sim{rcub}{dollar} CrO{dollar}sb3{dollar}/TiO{dollar}sb2 sp{lcub}sim{rcub}{dollar} Nb{dollar}sb2{dollar}O{dollar}sb5{dollar}/TiO{dollar}sb2 >{dollar} MoO{dollar}sb3{dollar}/TiO{dollar}sb2 sp{lcub}sim{rcub}{dollar} WO{dollar}sb3{dollar}/TiO{dollar}sb2 > >{dollar} K{dollar}sb2{dollar}O/TiO{dollar}sb2.{dollar} The turnover frequencies of the binary catalysts are identical at low and high surface coverages indicating that the mechanism of SO{dollar}sb2{dollar} is not sensitive to the coordination of the surface metal oxide species. With the exception of K{dollar}sb2{dollar}O impregnated catalysts, a comparison of the activities of ternary catalysts (V{dollar}sb2{dollar}O{dollar}sb5{dollar}/M{dollar}sb{lcub}rm x{rcub}{dollar}O{dollar}sb{lcub}rm y{rcub}{dollar}/TiO{dollar}sb2{dollar}) with the corresponding binary catalysts (M{dollar}sb{lcub}rm x{rcub}{dollar}O{dollar}sb{lcub}rm y{rcub}{dollar}/TiO{dollar}sb2{dollar}) suggests that the surface vanadia and surface additive oxide redox sites act independently, without synergistic interactions, since the sum of the individual activities of the binary catalysts quantitatively correspond to the activity of the corresponding ternary catalyst.; Over the range of conditions studied, the rate of SO{dollar}sb2{dollar} oxidation is zero order in O{dollar}sb2{dollar}, first order in SO{dollar}sb2{dollar} and inhibited by SO{dollar}sb3.{dollar}...