镁基复合氧化物催化烯烃环氧化反应

Epoxidation of Olefins Catalyzed by Magnesium-Based Mixed Oxides with Hydrogen Peroxide

制备了一系列镁基复合氧化物MgM-n样品(M=Sn,Al,Ti,La,Ce,Zr;n为Mg/M原子比),用X射线衍射、N2吸附-脱附、CO2程序升温脱附、紫外可见漫反射光谱和电子自旋共振等手段表征了它们的结构和表面性质,并考察了其以过氧化氢为氧化剂催化烯烃环氧化反应性能.结果表明,MgM-n样品表面碱量和催化性能与其中M的种类及含量密切相关.MgSn-4样品的表面碱量比MgAl-4低,虽两者在催化苯乙烯环氧化反应中,苯乙烯转化率和环氧化物选择性均为95%左右,过氧化氢利用率大于80%,但在循环使用过程中MgSn-4的催化性能更为稳定,并在不同结构烯烃的环氧化反应中表现出优良的催化性能.这除与MgSn-4表面碱强度适当有关外,还与其中存在高分散的Sn4+物种及其结构特性有关.

A series of Mg-based mixed oxides MgM-n （M = Sn,Al,Ti,La,Ce,Zr; n = Mg/M atomic ratio） were prepared. The physicochemical properties of these mixed oxides were characterized by X-ray diffraction,N2-adsorption/desorption,CO2 temperature-programmed desorption,ultraviolet and visible diffuse reflectance spectroscopy,and electron spin resonance. The catalytic activity of MgM-n for the epoxidation of olefins was investigated with H2O2 as an oxidant. The results indicated that the catalytic performance and basicity of MgM-n mixed oxides were correlated to the type and doping amount of M species. The MgAl-4 and MgSn-4 samples showed a conversion and epoxide selectivity as high as 95% along with over 80% H2O2 efficiency for the epoxidation of styrene. However,MgSn-4 possessed lower surface basicity and more stable performance during consecutive reuse in comparison with MgAl-4. Moreover,MgSn-4 could catalyze the epoxidation of olefins of different structure with excellent performance. With the characteristic studies,it was presumed that such a superior performance of MgSn-4 could essentially be ascribed to the highly dispersed Sn4＋ species and its unique structure as well as the proper ba-sicity.