Ordered mesoporous titanosilicates with better catalytically active titanium sites assembled from preformed titanosilicate precursors with zeolite building units in alkaline media

Abstract

Mesostructured titanosilicates have been successfully synthesized from the assembly of preformed titanosilicate precursors with CTAB surfactant micelle in both alkaline media (MTS-5) and strongly acidic media (MTS-8). The samples were characterized by powder X-ray diffraction (XRD), nitrogen isotherms, 29Si MAS NMR, IR, and UV–visible spectroscopy. These materials exhibit highly hydrothermal stability, as compared with Ti-MCM-41. Characterization results indicate that these mesostructured titanosilicates of MTS-5 and MTS-8 have TS-1-like titanium species, and that the mesoporous walls contain the primary and secondary building units similar to those in microporous crystal of TS-1 zeolite. In catalytic hydroxylation of 2,3,6-trimethylphenol, MTS-5 and MTS-8 show higher activities in comparison with microporous crystal of TS-1 and mesoporous material of Ti-MCM-41. More importantly, MTS-5 assembled from preformed titanosilicate precursors in alkaline media has higher silica condensation degree, compared with MTS-8 synthesized in strongly acidic media. After heating at 550 °C for 4 h, MTS-5 basically remains its catalytic activities in hydroxylation of phenol and 2,3,6-trimethylphenol, indicating its higher stability of Ti species for calcination. In contrast, calcined MTS-8 shows much lower conversion than as-synthesized MTS-8.