Cu/SiO_2结构及其催化苯酚羟基化反应性能的研究

以不同结构的SiO_2为载体,采用传统浸渍法,合成3种负载型的Cu/SiO_2.使用X射线衍射(XRD)、 N_2的等温吸-脱附、紫外漫反射光谱(DR UV-vis)、 X射线电子能谱(XPS)、等离子原子发射光谱(ICP)和H_2的程序升温还原(H_2-TPR)方法对样品进行表征.考察了以H_2O_2为氧化剂,样品对苯酚直接羟基化合成苯二酚的催化性能.结果表明:具有介孔和MFI结构的二氧化硅(MS-1),稳定性强,有利于引入Cu物种在其孔内扩散及分布,形成更多的高分散CuO.一定反应条件下, Cu/MS-1催化活性最高,苯二酚的收率和选择性分别高达38.91%和81.5%. Cu/MS-1催化剂重复使用10次后,苯二酚的收率为37.64%,而Cu含量仅从2.5%变为2.1%,具有较强稳定性;高分散CuO是目标反应的主要活性物种.

Study on the Structure of Cu/SiO2 and Their Catalytic Performance in the Reaction of Phenol Hydroxylation

Three kinds of Cu/SiO₂ were prepared by the impregnation method using the synthesized and purchased SiO₂ with different structures as the support. The samples were characterized by X-ray diffraction (XRD), N₂ isothermal absorption-desorption, ultraviolet-visible diffuse reflectance spectra, X-ray photoelectron spectroscopy, inductively coupled plasma atomic emission spectrometry and H₂ temperature programmed reduction. The catalystic activity of the samples in the phenol hydroxylation to dihydroxybenzenes using H₂O₂ was investigated. The results showed that good stability of MS-1 possessing MFI topology and mesoporous structure were advantageous to diffuse copper species from surface to pore and further formed more highly dispersed copper species. The Cu/MS-1 catalysts gave a desired dihydroxybenzenes yield (38.91%) with excellent selectivity (81.5%). The dihydroxybenzenes yield reached up to 37.64% and copper loading of the Cu/MS-1 dropped slightly from 2.5% to 2.1% after use ten runs. The results demonstrated good reusability of Cu/MS-1, and the highly dispersed CuO in samples was main active species of the selective oxidation of phenol with H₂O₂ produces catechol, hydroqinone and benzoquinone. We believed that MS-1 prepared in this study was a promising metial-supported and was widely used to catalytic field, particularly for those employing in macromolecular liquid reaction.