Effect of crystallization temperature on the synthesis of ETS-4 and ETS-10 titanosilicates

Abstract

The effect of temperature on the crystallization and purity of (Na,K)-ETS-4 and (Na,K)-ETS-10 from gels with an optimized composition was examined. Microporous titano silicates (Na,K)-ETS-4 and (Na,K)-ETS-10 were obtained by hydrothermal synthesis from gels of molar composition 5x.Na2O: 3KF: TiO2: 6.4x.HCl: 7.45SiO2: 197.5 H2O where x = 2.0 for ETS-4 and x = 1.0 for ETS-10 in absence of seeds and organic template agents. The kinetics of crystallization at 160, 180 and 200 °C, respectively, by comparing gel crystallinity (%) at different times, the induction times and the apparent activation energies for nucleation and crystallization were studied. The induction time (linked to the formation of the first nuclei) suggests that the nucleation is more difficult in the case of ETS-10 and the crystal growth rates are similar at higher temperatures (>180 °C). The apparent activation energies are smaller for the (Na,K)-ETS-4 (a stable structure) crystallization than of (Na,K)-ETS-10 (a metastable structure). The characterization of these microporous materials was carried out by XRD, SEM and TGA-DSC techniques.