硅源对Bi-MSU-4结构及催化性能的影响

分别以正硅酸乙酯、硅溶胶、硅酸钠和硅胶H为硅源，聚氧乙烯失水山梨醇软脂酸单酯（Tween-40）为模板剂，硝酸铋为铋源，合成出一种含铋的介孔分子筛Bi-MSU-4。采用X射线衍射（XRD）、紫外-可见光谱（UV-vis）和扫描电镜（SEM）对样品进行表征。并将所合成的Bi-MSU-4用于苯乙烯选择性反应中考察其催化活性。结果表明，硅源对Bi-MSU-4的结构和催化性能产生较大的影响。以正硅酸乙酯、硅酸钠为硅源，由于其水解速率缓慢，有利于分子筛的合成，所制得的样品相对结晶度和催化活性度较高；硅溶胶水解－聚合速率过快不能与模板剂完全作用，所制得的样品规整性较差，结晶度和苯乙烯的转化率都有所下降；酸性条件下不利于硅胶H的水解，反应体系中仍有硅胶H微粒的存在，从而大大影响其产物的结晶度和催化性能。

Influence of silica source on the structure and catalytic activity of Bi-MSU-4 zeolites

Mesoporous silica Bi-MSU-4 molecular sieves were synthesized with nonionic ethoxylated sorbitan esters (Tween-40) as the structure directors, Bi(NO₃)₃·5H₂O as the bismuth source, and TEOS, Na₂SiO₃·9H₂O,Gel H and silica sol as silica sources, respectively. The structure and physical properties of the samples were investigated by XRD, UV vis and SEM. The catalytic activity of Bi-MSU-4 for oxidation of styrene to benzaldehyde using H₂O₂ as the oxidant in methanol medium was investigated. The sults showed that silicon resources had remarkable influence on the structure and catalytic properties of Bi-MSU-4. TEOS and Na₂SiO₃·9H₂O, hydrolyzed at lower speed, resulted in more regular framework and higher catalytic properties. Silica sol, with hydrolysis and polycondensation speed too fast to completely react with Tween-40, resulted in poor regularity of the structure and lower crystallinity and styrene conversion. Gel H did not hydrolyze completely under acidic condition and resulted in lower crystallinity and catalytic activity.