Pore size-tunable titanosilicates post-synthesized from germanosilicate by structural reorganization and H₂TiF₆-assisted isomorphous substitution

Titanosilicates with large porosities are highly desirable for the selective liquid-phase epoxidation of alkenes in particular requiring open reaction spaces. Structural collapse and healing took place readily in one-pot when calcined and as-synthesized UTL-type germanosilicates both were subject to severe acid treatment, benefiting from the structural instability and modifiability of Ge-rich double four ring (D4R) units. Several structural derivatives with continuously tunable pore sizes were obtained by precisely controlling the acid treatment process. Isomorphous incorporation of Ti active centers and structural reorganization were then simultaneously realized via solid-liquid phase treatment using aqueous hexafluorotitanic acid (H₂TiF₆) solution, giving rise to three titanosilicates of Ti-ECNU-14 (OKO), Ti-ECNU-15 and Ti-UTL with different pore sizes varying form medium pores (10-ring) to extra-large pores (14-ring). The obtained titanosilicates with high content of tertrahedrally coordinated Ti ions in framework performed unique catalytic performance in the epoxidation of cyclic alkenes using hydrogen peroxide or anhydrous tert-butyl hydroperoxide as an oxidant.