硅源对Bi-MSU-4结构及催化性能的影响

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

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。

Mesoporous silica Bi-MSU-4 molecular sieves were synthesized with nonionic ethoxylated sorbitan esters （Twcen-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 suhs 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.