Hydrothermal synthesis of aluminum-substituted titanosilicate, ETS-10

Abstract

One of ETS-10 variants, aluminum-substituted ETAS-10 was successfully synthesized with Al/Ti molar ratio of 0.1–0.4 using different titanium sources, titanium sulfate (Ti(SO₄)₂) and titanium oxysulfate (TiOSO₄). Through the compositional study, like ETS-10, the (Na + K)/Na molar ratio significantly affects the crystallinity and phase purity depending on titanium source. The 2³ factorial designs indicate that the high alkalinity mainly by Na⁺ content is very critical to the crystallization of pure ETAS-10 while the content of K⁺ cation should be carefully controlled. It suggests that the increase in K⁺ content with smaller hydrated radius than of Na⁺ makes the formation of ETAS-10 structure difficult. The optimum composition was chosen and applied to kinetic study. The activation energies for three different stages, nucleation, transition and crystallization were calculated using the modified Avrami–Erofeev equation. This result indicates that the nucleation and transition stage proceed at the similar rate, and then the crystallization stage proceeds with lower activation energy than those of previous two stages. In addition, the temperature dependency on the crystallization was quite significant, favoring high temperature.