Au/Ti-MCM-41(H)催化丙烯气相直接环氧化

采用纳米组装法制备了一系列不同Ti含量的具有微孔-介孔复合结构(hybrid)的钛硅分子筛Ti-MCM-41(H)载体,继而用沉积-沉淀法制得纳米金催化剂.通过粉末X射线衍射(XRD)、氮气等温吸附-脱附、傅里叶变换红外(FT-IR)光谱、紫外-可见漫反射(DRUV-Vis)光谱、透射电镜(TEM)及等离子体原子发射光谱法(ICP-AES)对催化剂进行了表征,并考察了纳米金催化剂在氢气/氧气共存条件下丙烯气相直接氧化制环氧丙烷反应中的催化性能.结果表明:合成的微孔-介孔复合结构的钛硅分子筛Ti-MCM-41(H)具有典型的MCM-41结构,Ti(IV)以高分散的形式存在于分子筛的骨架结构中.在常压、423K反应温度下,以Ti/Si摩尔比为1%的Ti-MCM-41(H)为载体制备纳米金催化剂表现出了最佳的催化性能,反应30min,丙烯的转化率达5.4%,环氧丙烷的选择性为74.2%,环氧丙烷的生成速率为73.1g·h-1·kg-1;反应330min后,丙烯的转化率为4.9%,环氧丙烷的选择性为67.3%.

Direct Gas-Phase Epoxidation of Propylene over Au/Ti-MCM-41(H) Catalysts

Microporous-mesoporous hybrid Ti-MCM-41(H) was successfully synthesized by the nano-cluster assembling method. Gold nano-particles were prepared by the deposition-precipitation method. The samples were characterized by powder X-ray diffraction (XRD), nitrogen isothermal adsorption-desorption, Fourier transforminfrared (FT-IR) spectroscopy, diffuse reflectance UV-Vis (DR UV-Vis) spectroscopy, transmission electron microscopy (TEM) and inductively coupled plasma emission spectrometry (ICP-AES). The catalytic performance of the gold nano-particles was evaluated by the direct gas phase epoxidation of propylene using hydrogen and oxygen. Results revealed that the Ti-MCM-41(H) had a typical mesoporous MCM-41 structure. The results also suggested that isolated Ti(IV) was introduced into the siliceous framework of the support material. Superior catalytic performance was obtained with the gold catalyst supported on Ti-MCM-41(H) in which the Ti/Si molar ratio was 1%. Propylene conversion reached 5.4% at the initial 30 min with 74.2% propylene oxide (PO) selectivity and produced rate 73.1 g·h-1·kg-1. The conversion and PO selectivity were 4.9%and 67.3%after running 330 min on streamat 423 K.