化学气相沉积法合成Fe_2O_3/SiO_2及其苯酚羟基化性能

Phenol hydroxylation to dihydroxyhenzene over Fe_2O_3/SiO_2 catalysts synthesized by chemical vapor deposition

分别以二茂铁和二氧化硅为前驱体和载体,通过"一步法"化学气相沉积(CVD)来合成Fe2O3/SiO2催化剂.在二茂铁升华温度为110℃、载体400℃,N2作为载气,反应气氛为空气,真空度为0.08 MPa的条件下合成出了不同担载量的Fe2O3/SiO2催化剂.同时,以Fe(NO3)3·9H2O为前驱体通过等体积浸渍法制备相同担载量的Fe2O3/SiO2催化剂作为参比催化剂,并用于苯酚羟基化反应以评价其催化活性.通过BET、AAS、HR-TEM、FTIR、XRD、H2-TPR等手段对催化剂的理化性质进行了表征,以双氧水为氧化剂进行了苯酚羟基化反应.结果表明,通过化学气相沉积合成了高分散的SiO2担载的、高分散的α-Fe2O3纳米颗粒催化剂,活性物种α-Fe2O3纳米颗粒和载体SiO2间存在强相互作用.在反应时间为1h,反应温度40℃,苯酚与双氧水的摩尔比为1:1,催化剂质量为0.05g的反应条件下,CVD法制备的0.2mmol·g-1的Fe2O3/SiO2催化剂具有最高的反应活性,苯酚转化率为39.16%,邻苯二酚与对苯二酚的选择性分别为59.18%和35.11%.具有相同负载量、浸渍法制备的催化剂没有检测到苯酚的转化.

Fe2O3/SiO2 catalysts were synthesized by＂one-step＂Chemical Vapor Deposition（CVD）with ferrocene and fumed silica（A380）as substrate and precursor,respectively.The optimized synthesis conditions include a precursor sublimation temperature of 110 ℃,a substrate temperature of 400 ℃,a vacuum degree of 0.08 MPa and using nitrogen as carrier gas and air as reaction gas.The reference catalysts were prepared by incipient wetness impregnation with the same nominal loading as the ones synthesized by CVD.The physical and chemical properties of the catalysts were characterized by low-temperature nitrogen adsorption,Atomic Absorption Spectroscopy（AAS）,High-Resolution Transmission Electron Microscopy（HRTEM）,Fourier Transform Infrared spectroscopy（FT-IR）,X-ray Diffraction（XRD）and H2 Temperature Programmed Reduction（H2-TPR）,and the catalytic performances of the synthesized samples were tested by phenol hydroxylation to dihydroxyhenzene in the presence of H2O2 as oxidants.The result shows that the highly-dispersedα-Fe2O3 nano-particle catalysts are successfully supported over the surface of fumed silica（A380）with a uniform diameter around 4nm,and the strong interaction between the Fe2O3 nano-particles and the support silica was confirmed by the FT-IR analysis.It was found thatthe Fe2O3/SiO2 catalysts synthesized by CVD with a nominal loading of 0.2mmol·g-1 exhibited a conversion of 39.16%,and a selectivity to catechol（CAT）of 59.18%,a selectivity to hydroquinone（HQ）of 35.11%.Its counterpart prepared by impregnation was found no activity for phenol hydroxylation in the same reaction conditions.