READSORPTION AND DIFFUSION-LIMITED TPD OF WATER FROM ZEOLITE LINDE 4A

Coupled effects due to diffusion and readsorption of desorbed species on temperature-programmed desorption (TPD) data have been analyzed and compared with experimental curves during TPD of water from zeolite Li nde 4A. The effects of different heating rates and carrier-gas flow ar e considered explicitly. A simple model is presented which allows stra ightforward extraction of kinetic parameters from the experimental dat a, even in the presence of effects due to readsorption and diffusion. In this system, it is found that an extensive readsorption of gas occu rs within the zeolite pellet and the local adsorbate coverage is gover ned by equilibrium adsorption. We found that neglecting the effects of diffusion can cause activation energy falsifications of the order of 10%. When readsorption and diffusion are not taken into account, calcu lated pre-exponential factors are very small and convey no direct phys ical meaning. (C) 1998 Elsevier Science B.V.