特种氧化铝负载氧化钛作为异丙醇还原肉桂醛的高性能催化剂（英文）

发布时间：2018-05-24 00:33

本文选题：Meerwein-Ponndorf-Verley还原 + 肉桂醛　；参考：《催化学报》2017年08期

【摘要】：肉桂醇在香料、香精以及医药等诸多高端领域有着重要应用,常通过肉桂醛加氢法制备.由于热力学上肉桂醛中C=C C=O官能团的C=C双键加氢比C=O双键更有优势,因此不管是从学术角度还是工业生产角度来看,高选择性还原C=O基团都是一项极具挑战的任务.肉桂醛加氢反应的副产物苯丙醛以及苯丙醇的生成不仅导致肉桂醇收率降低,而且大大增加分离纯化成本,因此设计并制备出有利于C=O官能团高选择性氢化的高效催化剂具有重要意义.Meerwein-Ponndorf-Verley(MPV)反应以异丙醇为氢供体,是一种可选择加氢C=C C=O中C=O官能团的反应.目前用于MPV还原的催化剂(均相或多相)在实际应用中通常选择性不高,使得目标产物得率低且分离成本高.本文报道了负载于一种特殊氧化铝表面的氧化钛催化剂(记为TiO_x/γ-Al_2O_3-nt),其催化肉桂醛经MPV还原为肉桂醇的催化性能优异,表征结果发现该特殊氧化铝可导致表面氧化钛呈较高比例的低价钛物种高度分散状态,从而成为一种高效的肉桂醛MPV还原催化剂.TEM结果表明,这种特殊氧化铝和普通氧化铝在形貌上有很大差别,具有比较规整的一维纳米粒子形貌.综合XRD,TEM,Raman以及H/D同位素交换表征结果 ,可得到氧化钛高度分散在氧化铝表面的结论 .原位XPS结果表明,TiO_x/γ-Al_2O_3-nt催化剂表面具有较高浓度的Ti(III)物种,而以普通氧化铝为载体的催化剂TiO_x/γ-Al_2O_3-c在相同的还原条件下其表面Ti(III)物种浓度较低,这种差异的来源是具有规整形貌的一维纳米氧化铝提供了更加均匀的表面位点使得表面高度分散的氧化钛容易被还原为低价态.NH_3-TPD结果表明,TiO_x/γ-Al_2O_3-nt催化剂具有高的L酸酸量.肉桂醛MPV还原反应结果显示,表面负载氧化钛的特殊氧化铝(TiO_x/γ-Al_2O_3-nt)是一种非常高效的催化剂,具有很高的目标产物肉桂醇的选择性,几乎观察不到副产物的生成,多次套用实验结果也证实该催化剂具有良好的稳定性.该催化剂的高性能可归纳为以下两个方面的原因:一方面,L酸是MPV还原反应的活性中心,该催化剂具有高的L酸酸量,因此转化率高;另一方面,其表面较高浓度的Ti(III)物种可以使肉桂醛以垂直吸附模式(吸附终端为C=O)在催化剂表面吸附,这种吸附模式可以高选择性地还原为目标产物肉桂醇,因此同时具有很高的选择性.
[Abstract]:Cinnamol is widely used in many high-end fields, such as perfume, essence, medicine and so on. It is often prepared by cinnamaldehyde hydrogenation. Because the hydrogenation of C / C double bonds in cinnamaldehyde is more advantageous than that of C / O double bonds in cinnamic aldehyde, the highly selective reduction of Con O groups is a challenging task from both the academic and industrial point of view. The by-products of cinnamaldehyde hydrogenation, phenylpropanal and phenylpropanol, not only lead to the decrease of yield of cinnamol, but also increase the cost of separation and purification. Therefore, it is of great significance to design and prepare a highly selective hydrogenation catalyst for the hydrogenation of Con O functional groups. Meerwein-Ponndorf-Verley MPV) reaction with isopropanol as a hydrogen donor is a selective hydrogenation of Con O functional groups in C ~ (2 +) C ~ (2 +). At present, the catalyst (homogeneous or multiphase) used for MPV reduction is usually not selective in practical application, which results in low yield of target product and high separation cost. In this paper, a titanium oxide catalyst supported on a special alumina surface (TiO_x/ 纬 -Al _ 2O _ 3-ntr) is reported. It has excellent catalytic performance for the reduction of cinnamaldehyde to cinnamol by MPV. The characterization results show that this special alumina can lead to a high dispersion of titanium oxide in a high proportion of low valence titanium species, and thus become an efficient catalyst for MPV reduction of cinnamaldehyde. The morphology of this kind of special alumina is very different from that of ordinary alumina. It is concluded that titanium oxide is highly dispersed on the surface of alumina by synthesizing the Raman spectra and the H / D isotope exchange results. The results of in-situ XPS showed that TiTiIII species were higher on the surface of TiOstix / 纬 -Al2O3-nt catalyst, while the surface TiIII species concentration of the catalyst TiO_x/ 纬 -Al _ 2O _ 3-c was lower under the same reduction conditions, while that of TiO_x/ 纬 -Al _ 2O _ 3-c catalyst supported on ordinary alumina was lower than that on the surface of tio _ 2O _ 3-nt catalyst. The source of this difference is that the one-dimensional nano-alumina with regular morphology provides a more uniform surface site so that the highly dispersed titanium oxide on the surface is easily reduced to the low-valence state. NH3-TPD results show that the tio _ x / 纬 -Al _ 2O _ 3-nt catalyst has a high L acid content. The results of MPV reduction reaction of cinnamaldehyde showed that the special alumina tio _ x / 纬 -Al _ 2O _ 3-nt) with titanium oxide on the surface was a very efficient catalyst with high selectivity to the target product cinnamyl alcohol and the formation of by-products was almost impossible to be observed. The stability of the catalyst was also confirmed by repeated application of the catalyst. The reasons for the high performance of the catalyst can be summarized as follows: on the one hand, L acid is the active center of MPV reduction reaction, and the catalyst has a high L acid content, so the conversion rate is high, on the other hand, The higher concentration of TiOIII species on the surface of the catalyst can make cinnamaldehyde adsorbed on the catalyst surface in a vertical adsorption mode (the terminal of adsorption is Con O). This adsorption mode can be selectively reduced to the target product cinnamyl alcohol, so it has high selectivity at the same time.
【作者单位】：南京大学化学化工学院介观化学教育部重点实验室;
【基金】：supported by the National Natural Science Foundation of China (91434101) the National Key R&D Plan (2017YFB0702800)~~
【分类号】：O643.36;TQ243.4

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