Synthesis of titanosilicalite-1 using mixed templates and acid treated Ti-MWW catalysts for phenol hydroxylation

Abstract

Zeolite-structure typed titanosilicates namely Titanosilicalite-1 and Ti-MWW were able to be hydrothermally synthesized by rotating crystallization. TS-1 catalysts were able to be hydrothermally synthesized by rotating crystallization. TS-1 catalysts were synthesized using different types of template, i.e. pure TPAOH, pure TPABr, and mixture of both templates. The gel was crystallized at 170C for 4 days. The characterization results by XRD, SEM, UV spectrum, nitrogen adsorption of nanoparticle TS-1 prepared by using mixed templates are very close to that prepared by using pure TPAOH as template. The particle size of TS-1 becomes very large and the titanium mainly located in the extraframework position when pure TPABr was used as template. For Ti-MWW samples, the highes crystallinity was obtained by multistep crystallization at 130C for 1 day, 150C for 7 days. The locations of titanium are in both tetrahedral and octahedral sites before acid treatment. After acid treatment of Ti-MWW, only tetrahedral site of titanium was observed along with the slight change of lamellar structure. The catalytic activities were studied in phenol hydroxylation using H2O2as oxidant. Factors influencing on the catalysis, such as types of solvent, reaction time, and particle size of catalysts were investigated. TS-1 catalyst prepared by using mixed templates exhibits the highest catalytic activity. Both TS-1 and Ti-MWW has the most activity in water but inactive in methanol, acetone and acetonitrile. Ti-MWW catalysts exhibits much lower catalytic activity but extremely higher product selectivity to p-benzoquinone than Ts-1 catalysts