Tetrapropylammonium Hydroxide Treatment of Aged Dry Gel to Make Hierarchical TS-1 Zeolites for Catalysis

This work presents the development and systematic study of a method to prepare hierarchical titanium silicalite-1 (TS-1) zeolites with high tetra-coordinated framework Ti species content. The new method involves (i) the synthesis of the aged dry gel by treating the zeolite precursor at 90 °C for 24 h; and (ii) the synthesis of hierarchical TS-1 by treating the aged dry gel using tetrapropylammonium hydroxide (TPAOH) solution under hydrothermal conditions. Systematic studies were conducted to understand the effect of the synthesis conditions (including the TPAOH concentration, liquid-to-solid ratio, and treatment time) on the physiochemical properties of the resulting TS-1 zeolites, and the results showed that the condition of a TPAOH concentration of 0.1 M, liquid-to-solid ratio of 1.0, and treatment time of 9 h was ideal to enable the synthesis of hierarchical TS-1 with a Si/Ti ratio of 44. Importantly, the aged dry gel was beneficial to the quick crystallization of zeolite and assembly of nanosized TS-1 crystals with a hierarchical structure (S_ext = 315 m² g^-1 and V_meso = 0.70 cm³ g^-1, respectively) and high framework Ti Species content, making the accessible active sites ready for promoting oxidation catalysis.