采用三种氨基硅烷试剂(APTS:3-氨丙基三甲氧基硅烷,TPED:N-(2-氨乙基)-3-氨丙基三甲氧基硅烷,TPDT:3-[2-(2-氨基乙基氨基)乙基氨基]丙基-三甲氧基硅烷)对介孔SBA-15分子筛进行后嫁接表面功能化(分别记为APTS-SBA-15,TPED-SBA-15和TPDT-SBA-15),然后利用氨基与氯金酸之间的静电作用及化学还原法,将金纳米粒子引入分子筛的介孔孔道.采用N2物理吸附、X射线衍射(XRD)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)等手段对催化剂的结构和电子性质进行了系统表征;以巴豆醛液相加氢制巴豆醇反应比较了氨基硅烷的种类对催化性能的影响.结果表明,氨基硅烷的给电子能力是决定金催化剂上C=O键加氢选择性的主要因素,氨基硅烷的给电子能力越强,金活性位上的电子密度越高,则巴豆醇的选择性和收率就越高.
Three kinds of aminosilane (APTS: 3-aminopropyltrimethoxysilane, TPED: N-[3-(trimethoxysilyl)- propylethylene]diamine, TPDT: trimethoxysilyl propyl diethylenetriamine) functionalized mesoporous SBA- 15 molecular sieves (denoted APTS-SBA-15, TPED-SBA-15 and TPDT-SBA-15) were synthesized by post-grafting. Using the static interaction between the amino group and chloroauric acid followed by chemical reduction, the gold nanoparticles were immobilized into the channels of SBA-15. The Au/aminosilane-SBA-15 catalysts were systematically characterized by N2 physisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The liquid phase hydrogenation of crotonaldehyde to crotyl alcohol (CROL) was used to investigate the effect of aminosilanes on the catalytic performance of the Au/amine-SBA-15 catalysts. The results revealed that the electron-donating ability of the aminosilane determines the selectivity towards the hydrogenation of the C=O bond on the gold catalyst. A stronger aminosilane electron-donating ability results in higher electron density on the gold active sites, which leads to the higher selectivity and yield of CROL.