高分散纳米银催化剂一锅高效催化生物质基甘油和苯胺合成3-甲基吲哚

One-Pot Efficient Synthesis of 3-Methylindole from Biomass-Derived Glycerol with Aniline by Highly Dispersible Nanosilver Catalyst

将ZnO改性的高分散纳米银催化剂(Ag/SiO_2-ZnO)成功地用于生物质基甘油与苯胺一锅高效合成3-甲基吲哚的反应中。通过X射线衍射(XRD)、透射电子显微镜(TEM)、氢气程序升温还原(H_2-TPR)、氨气和二氧化碳程序升温脱附(NH_3-TPD或CO_2-TPD)、热重(TG)分析和电感耦合等离子体(ICP)发射光谱技术手段研究了银基催化剂的结构和性能。结果表明,向Ag/SiO_2-ZnO催化剂加入ZnO助剂能增强银与载体之间的相互作用,使银粒子可以牢固地锚定在SiO_2-ZnO载体上,不仅提高了银的分散度,而且有效抑制了反应过程中银纳米粒子的聚集或烧结。此外,ZnO还能显著增加银基催化剂的酸性位点及碱性位点,这对甘油氢解生成1,2-丙二醇非常有利,明显促进了3-甲基吲哚的合成。反应16 h,3-甲基吲哚收率高达64%,催化剂重复使用4次,收率仅降低4%。另外,提出了甘油和苯胺在Ag/SiO_2-ZnO催化剂上合成3-甲基吲哚的机理,其中1,2-丙二醇是制备3-甲基吲哚的中间体。

A highly dispersible nanosilver catalyst of ZnO modified Ag/SiO2 was successfully applied to the one-pot efficient synthesis of 3-methylindole from aniline and biomass-derived glycerol for the first time. The catalyst exhibited an excellent catalytic performance. The investigations of Ag-based catalysts via X-ray diffraction( XRD), transmission electron microscopy( TEM), temperature programmed reduction of H2( H2-TPR),temperature programmed desorption( TPD) of NH3 or CO2,thermogravimetric( TG) analysis and inductively coupled plasma( ICP) emission spectroscopy indicate that ZnO can enhance the interaction between silver and the support and make Ag particles be firmly anchored on the support of SiO2-ZnO. As a result,not only the dispersion of silver is increased obviously,but also the aggregation or sintering of silver nanoparticles is inhibited effectively. In addition,ZnO can also increase the acid and base sites of the Ag-based catalyst significantly,which is very beneficial to the hydrogenolysis of glycerol to 1,2-propanediol and promoted the synthesis of 3-methylindole greatly. The yield of 3-methylindole is up to 64% at the reaction time of 16 h and is only decreased by 4% after Ag/SiO2-ZnO is reused four times. Furthermore,the synthesis mechanism of3-methylindole from glycerol and aniline over Ag/SiO2-ZnO catalyst was proposed,in which 1,2-propanediol is the intermediate to produce 3-methylindole.