Isotope exchange kinetics under conditions of diffusion hindrance

Kinetic behaviour of the isotopic exchange reaction H2 + D2 reversible 2HD is studied under conditions of internal diffusion hindrances. In the case where the number of molecules of the H2-D2 mixture is many times as great as the amount of surface centres Hsub(s) and Dsub(s) containing hydrogen (homoexchange), kinetic behaviour is described by an equation being similar to the equation which is valid for fast diffusion. In contrast to this, kinetics of exchange of H2 and D2 molecules of the gas phase with surface Hsub(s) and Dsub(s) centres (heteroexchange) is substantially different under conditions of diffusion hindrances and fast diffusion. For the case of slow diffusion the rate of homoexchange can be 10-100 times as great as the rate of heteroexchange. Analysis of literature data on kinetics of oxygen isotopic exchange is given