ON THE UNUSUALLY HIGH APPARENT ACTIVATION-ENERGY OF CHEMICAL CONVERSION UNDER SINGLE-FILE CONDITIONS

The temperature behaviour of transport-reaction systems undergoing sin gle-file diffusion (the particles are not able to change their order) is investigated systematically The influence of exchange limitations a t the margins, of attraction between the particles, and of a small pos sibility that adjacent particles exchange their positions are consider ed. The investigation is based on an isoline diagram which proves to b e a very useful tool applicable to any transport-reaction system. If t he channels are crowded, if the intrinsic reaction rate is large enoug h so that the total conversion is transport-controlled and if the acti vation energies of the elementary processes of the transport fulfil ce rtain relations (e.g., if passages of neighbouring particles are possi ble with an activation energy higher than the intrinsic activation ene rgy of the conversion), then the apparent activation energy of the con version in the single-file system can exceed the intrinsic activation energy. Such a behaviour is impossible for systems undergoing normal d iffusion but was found experimentally for some single-file zeolites in the literature. (C) 1998 Academic Press.