Hierarchical TS-1 synthesized via the dissolution-recrystallization process: Influence of ammonium salts

TS-1 was post-modified by ammonium salts or tetrapropylammonium hydroxide (TPAOH). During the ammonium salts modification, the crystals were eroded and extra-framework titanium species were formed. After the combined-modification, hierarchical TS-1 with secondary pore volume in the 0.22-0.28 cm3/g range was obtained via the intensified dissolution-recrystallization process, although more extra-framework titanium species were generated as five-/six-coordinated species. In cyclohexene oxidation with tert-butyl hydroperoxide (TBHP) as the oxidant, the activity of modified TS-1 decreased when anatase was formed only. However, it increased in the presence of five-/six-coordinated titanium. The secondary porosity further improved the catalytic performance and the activity of the combined-modified TS-1 samples increased remarkably by > 100%.