不同硅铈比Ce-MCM-41介孔分子筛酸性及结构表征

摘要

Ce-MCM-41 mesoporous molecular sieve with different silicon to cerium ratio(Si/Ce) was synthesized by hydrothermal method.The surface acidity,mesoporous structure,and chemical state of cerium were characterized by X-ray diffraction(XRD),NH3 temperature programmed desorption(NH3-TPD),pyridine adsorption infrared spectrum(PY-IR),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS) and N2 adsorption-desorption.The results indicated that when Si/Ce molar ratio drops from 150 to 30,the Ce-MCM-41 mesoporous molecular sieve exhibited the typical hexagonal mesoporous structure with both Lewis and Bronsted acid sites on the catalyst surface; when Si/Ce molar ratio declined further to 10,the ordered structure of the molecular sieve was partially diminished with mainly Bronsted acid on the catalyst surface.The Ce element introduced to the molecular sieve was in the form of Ce3+ and Ce4+valence state with predominantly the positive quadrivalence.%采用水热法合成了不同硅铈比的Ce-MCM-41介孔分子筛,并采用X射线衍射(XRD)、NH3程序升温脱附(NH3-TPD)、吡啶吸附红外光谱(PY-IR)、透射电镜(TEM)、X射线光电子能谱(XPS)和N2吸附-脱附等手段对Ce-MCM-41介孔分子筛的介孔结构、表面酸性、铈元素的含量和化学态进行表征.结果表明:当Si与Ce的物质的量之比(n(Si/Ce)由100减小至30时,Ce-MCM-41介孔分子筛仍具有典型的六方介孔结构特征,样品表面都存在B酸和L酸中心;当n(Si/Ce)为10时,样品结构有序性下降,B酸含量最多,分子筛中引入的金属Ce元素以Ce3+和Ce4+共存于催化剂中,但主要以Ce4+为主.