Kinetics of the Vanadium-catalysed Oxidation

Independently of the work on the chemical composition of sulphuric acid catalysts, attempts to develop kinetic equations to describe the rate of reaction both for mechanistic analysis and reactor design purposes have been numerous. There is much evidence to suggest that in common with its catalytically oxidative behaviour in other environments, valency states of vanadium of V and V are involved. Mars and Maessen in 1964 developed a rate expression based on a simple two-step redox mechanism  

Aramata, and R. Furvichi, Nippon Kagaku Kaishi, 1972, 226. 

Proceedings of the 3rd International Congress on Catalysis , North-Holland, Amsterdam, 1965, Vol. 1, Discussion, p. 280. 

It was argued that the second step, the reoxidation of tetravalent vanadium, was rate controlling and that the fall in activation energy from 43 kcal rnole at low temperatures (450 °C) to 19 kcal rnole above 500 °C was attributable to the displacement to the left of the exothermic fast reversible first step. This analysis gives an equation of the form 

Weijchert and Urbanek ° have considered 34 such expressions. Most of these indicate an inverse dependence on SO 3 partial pressure with a range of positive dependences on the oxygen and sulphur dioxide partial pressures ranging between 0 to 1.0. 

---