A reinforced study on the synthesis of microporous titanosilicate ETS-10

Abstract

This work was aimed at unifying the synthesis recipe, identifying the most appropriate titanium precursor, and elucidating the formation mechanism of microporous titanosilicate ETS-10. To achieve these aims, the effects of titanium sources that had been and have not been studied in the literature, fluoride ions, pH of synthesis gel, contents of water, Na + and K + ions in the synthesis gels, SiO 2/TiO 2 molar ratios, and synthesis time and temperature on the crystallization of ETS-10 were systematically examined. It was observed that nano-sized Degussa titanium dioxide (commercially known as P25) is the best titanium source, with which highly pure ETS-10 can be synthesized from an optimized synthesis system of 3.4Na 2O–1.5K 2O–TiO 2– xSiO 2– yH 2O (where x = 4.5–5.5 and y = 150–180) at pH 10.4 without the presence of seeds or organic template. It was noted that the presence of K + ions in the synthesis gels favors the formation of pure ETS-10, most probably due to the structure-directing role of K + ions. It was identified that F − ions is not essential to the crystallization of ETS-10. Instead, the presence of F − ions has an adverse effect, resulting in the formation of quartz impurity. The crystallization kinetics of ETS-10 in the optimized synthesis system was investigated at 180, 200, 230 and 250 °C. A modified Avrami–Erofeev equation was fitted to the experimental data. The apparent activation energy of crystallization was calculated to be 89 kJ/mol.