Study on the synthesis, structure and catalytic performance of Bi-MSU-4 silicas molecular sieves

A kind of mesoporous silica molecular sieves Bi-MSU-4 were synthesized successfully using nonionic ethoxylated sorbitan esters (Tween-x, x = 20,-40,-60, or-80) as structure directors respectively and TEOS as silicate source at room temperature. Structures of the synthesized molecular sieves were characterized by X-ray diffraction (XRD), FT-IR, UV-vis, N2 absorption/desorption and SEM methods. The influence of factors such as templates, mineralizer and Si/Bi molar ratios on Bi-MSU-4 mesoporous structure and styrene catalytic oxidation were examined. The results indicated that Bi-MSU-4 exhibited mesoporous structures and bismuth entered the framework already. The pore size and pore volume of samples increased with the augment of the hydrophobic chain length of templates, which led to the rise of catalytic performance. In addition mineralizing structured framework and expelled it from hydrophilic PEO shell. With the increasing of Si/Bi molar ratio catalytic performance increased first and then decreased. T-XBi-MSU-4 were superior in styrene oxidation reaction and the conversion of styrene was 55.0% and the yield of benzaldehyde was 41.5% especially for T-60Bi-MSU-4.