Autocatalytic Kinetics and Mechanism of the Reduction of Crystalline Cobalt Molybdate in hydrogen

Abstract

Reduction of α-CoMoO₄ in hydrogen results in the formation of Co₂Mo₃O₈ and Co₂MoO₄. Its kinetics as measured in a vacuum microbalance and in a X-ray high temperature camera is first order with respect to hydrogen and follows sigmoidal curves. These are well described by the equation of an autocatalytic reaction in a shrinking sphere model dx/dt = k₁ /(l+k₂x). p(H₂) . S. (1-x)^3/2with activation energy 28.2 kcal/mole. The autocatalytic effect is due to traces of metallic cobalt forming in the course of reaction and activating hydrogen, the reduction then proceeding through a spillover effect.