The report gives results of a study of the oxidation of SO2 over a commercial vanadium pentoxide catalyst, using an all-glass, essentially gradientless reactor at 470-480C and at concentrations up to several percent of SO2. A theoretical development was derived for the use of isotopic tracers to study the kinetics and mechanism of complex catalytic reactions. Relationships developed on the basis of steady state conditions are combined with principles of thermodynamics and transition state theory. Data were obtained using radioactive sulfur 35 and the stable isotope oxygen 18 as tracers. The employment of two tracers simultaneously and the employment of more than one level of marking while still maintaining a fixed overall reaction velocity were often advantageous. Oxygen chemisorption was found to be the most important mechanistic step in SO2 oxidation. However, as equilibrium is approached, desorption of SO3 also assumes considerable importance. These findings led to the formulation of an improved rate equation, especially accurate near equilibrium for SO2 conversion. The use of sulfur 35 in developing improved catalysts is also suggested.

Grant number R801321 (formerly grant no. AP-00714-04), program element no. 1A2013. "August 1973." "EPA/650-2-73-020." Project officer: D.K. Oestreich.