Thermal analysis of cation-exchanged zeolites before and after their amorphization by ball milling

Zeolite X, synthetic mordenite and zeolite A in which a part of the original sodium ions has been exchanged by other cations (Li+, K+, Cs+) were investigated by means of simultaneous thermal analysis, before and after mechanochemical amorphization by ball milling. In all the examined cases, the initial rate of dehydration of amorphized sample was higher than the initial rate of dehydration of the original (crystalline) Samples, and the temperature at which the rate of dehydration is largest was lower in the case of the amorphized samples than in the case of the crystalline samples. The influence of cations on the rate of dehydration and on the critical temperature of dehydration of amorphized samples was different from the influence of cations on the rate of dehydration and on the critical temperature of dehydration of the original (crystalline) samples. Analysis of the experimental data led to the conclusion that the rate of dehydration of crystalline samples is controlled by the diffusion of desorbed water through the channel/void system of the zeolite structure and that the rate of dehydration of the amorphized samples is controlled by the cation-water interactions. The observed differences are explained by the difference in the pore system between the original (crystalline) and amorphized samples.