The kinetics of water desorption from porous glasses silica gel and porous aluminosilicates were followed through the TG and DTG methods.In all cases only one thermodesorption peak appeared. The kinetic parameters were determined by standard nonisothermal methods. The activation energy is constant and independent of the coverage degree and pore diameter in the system porous glass-water. The function E (0) were determined for the silica gel and porous aluminosilicates E = E 0 + a exp ( -bO). The parameters Eo, a and b depend on the SiO2/A1203 ratio and on the distribution of active centers on the surface.Desorption kinetics is most commonly presented by the equation:In which n is the reaction order, A the pre-exponential factor and E the activation energy. In the general case, kinetic parameters depend upon the degree of coverage [1].Such an equation can be applied to high-energy chemisorbed states and to lowenergy physisorbed states. Silicate and aluminosilicate are typical examples of systems on which there exist physisorbed and chemisorbed molecules at the same time [2]. It is known that surface hydroxyl groups act as primary centres in the physical adsorption of water [3][4][5]. Zettlemoyer [5] considers the hydroxy ! groups to be donors and water molecules to be acceptors of hydrogen-bonds. According to the results of Kiselev [6], an adsorptive complex is formed in which approximately two hydroxyl groups correspond to one molecule of water. Dehydroxylation (associative desorption) is preceded by the desorption of physically adsorbed water and, due to the considerable difference in bond energy, it can be expected that these processes take place as two independent consecutive stages. It is probable that John Wiley & Sons, Limited, Chichester AkadOmiai Kiad6, Budapest
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