Chapter 2: Interactions Between Surface Vanadate and Surface Sulfate Species on Metal Oxide Catalysts

J. P. DUNN, J-M JEHNG, D. S. KIM, L. E. BRIAND, H. G. STENGER AND I. E. WACHS

Oxidation of Sulfur Dioxide to Sulfur Trioxide Over Supported Vanadia Catalysts

UMI Dissertation Services, A. Bell & Howell Co.

Lugar: Ann Arbor, Michigan USA; Año: 1998; p. 39 - 59

The oxidation of SO2 to SO3 over supported vanadia catalysts occurs in many industrial processes, for example the manufacture of sulfuric acid, the selective catalytic reduction of NOx to NH3 and the regeneration of petroleum refinery cracking catalysts. The objective of this reserach is to establish the fundamental molecular structure-reactivity relationships and kinetics for SO2 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)3V5+=O species. At higher vanadia loadings, the isolated (M-O)3V5+=O species polimerize on the oxide support surface breaking two V-O-M bonds and forming two V-O-V bridging bonds. The turnover frequency for SO2 oxidation was very low at 400 oC due to the low adsorption of SO2 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, SO2 oxidation activity of the supported vanadia catalysts varied by an order of magnitude (Ce>Zr,Ti>Al). The basicity of the bridging V-O-M oxygen appears to be responsible for influencing the adsorption and oxidation of the acidic SO2 molecule.