超薄氧化物包裹对铂催化剂在丙三醇氢解反应中的催化性能调控

发布时间：2017-12-28 18:09

本文关键词：超薄氧化物包裹对铂催化剂在丙三醇氢解反应中的催化性能调控　出处：《中国科学技术大学》2017年硕士论文　论文类型：学位论文

【摘要】：同时含有金属和酸性位点的双功能催化剂已广泛用于石油加氢裂解和可再生生物质转化。这两种位点之间的距离对双功能协同作用起着至关重要的作用,进而对催化剂的催化活性与选择性有重大影响。近年来,由生物质转化生产生物燃料和化学品得到了广泛的关注。相比于石油裂解工艺,金属-酸性位点临近效应在生物质转化反应中鲜有报道。甘油是来自生物柴油生产过程中的廉价副产物(约总产量的10%)。通过选择性氢解将其转化为具有高附加价值的化学品如1,2-丙二醇和1,3-丙二醇是提高其附加值的主要途径。甘油氢解包含脱水与加氢两个过程,分别发生于酸性位点与金属位点上。根据文献报道,Lewis酸位点倾向于进攻甘油端位的羟基,而生成中间产物丙酮醇,而Br(?)nsted酸则更易进攻甘油中间位的羟基产生3-羟基丙醛;随后两者进一步加氢分别生成1,2-丙二醇和1,3-丙二醇。负载型金属催化剂广泛应用于甘油氢解反应中,在金属催化剂中添加酸性助剂能显著提高催化剂的活性。大量研究表明,无论是将酸性物种添加到金属颗粒表面或者是载体上甚至是简单的物理混合,均能有效提升催化剂的催化性能。然而据我们所知,金属-酸性位点之间的临近效应还未在甘油氢解反应中报道过。因此,我们选择负载型Pt催化剂应用于甘油氢解作为平台反应,通过ALD技术沉积酸性多孔的氧化铝薄膜包裹Pt催化剂来研究金属-酸性位点临近效应对Pt催化剂在甘油氢解反应中的作用与影响。在本课题中,我们运用原子层沉积技术(ALD),凭借其原子层面上精确控制的技术优势,我们在Pt纳米颗粒催化剂的表面精确沉积氧化物包裹层,研究形成的金属-氧化物界面、金属-酸性双功能活性位的临近效应对Pt催化剂在丙三醇氢解反应中的活性以及选择性的调控。主要的研究成果如下:(1)我们通过湿化学浸渍法合成了负载型Pt/Al203催化剂,随后使用ALD技术在Pt纳米颗粒表面生长氧化铝多孔薄膜,利用氧化铝的Lewis酸性以及其与Pt金属的临近效应,来提高该催化剂的双功能协同效应从而提高了丙三醇氢解反应的活性和对1,2-丙二醇的选择性。我们研究发现30个周期的氧化铝包裹后催化剂具有最高的活性与选择性,在高分辨透射电镜(HRTEM)下能观测到包裹层厚度为3.6 nm。通过对丙酮醇中间产物加氢反应的对比实验,我们发现,氧化铝酸性和Pt加氢位点临近效应在催化性能提高中,起着重要的作用。另外,通过降低Pt颗粒的粒径,同样有助于1,2丙二醇选择性的提高。因此,我们初步认为多孔氧化铝包裹把Pt颗粒表面分割成小的Pt聚集体,是提高1,2丙二醇选择性的主要原因。(2)此外,我们通过ALD技术,在商用Pt/C催化剂上进一步生长了不同周期的FeOx,发现微量的FeOx能显著提高催化剂的活性。我们发现沉积三个周期的FeOx在Pt/C催化剂上具有最高的活性,相同时间内丙三醇氢解反应的转化率是Pt/C催化剂的三倍以上。
[Abstract]:The dual functional catalysts, which contain both metal and acid sites, have been widely used in petroleum hydrocracking and renewable biomass conversion. The distance between the two loci plays an important role in the dual function synergy, which has a great influence on the catalytic activity and selectivity of the catalyst. In recent years, biomass conversion and production of biofuels and chemicals have been widely concerned. Compared with the petroleum cracking process, the metal acid site proximity effect is rarely reported in the biomass conversion reaction. Glycerol is a cheap by-product of biodiesel production (about 10% of the total production). The conversion of a selective hydrogen solution into a high added value chemical, such as 1,2- propanediol and 1,3- propanediol, is the main way to increase the added value. The hydrogenolysis of glycerol consists of two processes of dehydration and hydrogenation, which occur on acid sites and metal sites, respectively. According to reports, Lewis acid sites tend to attack the hydroxyl end of glycerol, and generate intermediate acetol and Br (?) nsted Acid is easier to attack the hydroxyl glycerol intermediate to produce 3- hydroxyl propylaldehyde; then two further hydrogenation respectively generate 1,2- propylene glycol and 1,3- propylene glycol. Supported metal catalysts are widely used in the hydrogenation of glycerol. The addition of acid additives in metal catalysts can significantly increase the activity of the catalyst. A large number of studies have shown that both the acidic species added to the surface of the metal particles, or even the simple physical mixing can effectively enhance the catalytic performance of the catalyst. However, as far as we know, the proximity effect between the metal acid sites has not been reported in the glycerol hydrogenolysis reaction. Therefore, we chose the supported Pt catalyst for glycerol hydrogenolysis as a platform reaction. The ALD porous alumina membrane was used to encapsulate Pt catalyst to study the effect of the metal acid site proximity effect on the Pt catalyst in glycerol hydrogenolysis. In this paper, we use the atomic layer deposition (ALD), with the advantage of accurate control of the atomic level, we in the precise surface deposition of oxide coating Pt nanometer particle catalyst, proximity formation of metal oxide interface, metal acid bifunctional active sites of Pt catalysts in the hydrogenation of glycerol the solution in the reaction activity and selectivity control. The main results are as follows: (1) by wet chemical impregnation method synthesized Pt/Al203 catalyst, then use the ALD technology in the growth surface of porous alumina film Pt nanoparticles, using Lewis and Pt as well as its acidic alumina metal proximity effect, synergistic effect to improve the dual functional catalyst to improve the glycerol hydrogen the solution reaction activity and selectivity of propylene glycol 1,2-. Our study found that the alumina coated with 30 cycles had the highest activity and selectivity. Under the high-resolution transmission electron microscope (HRTEM), the thickness of the coating layer was observed to be 3.6 nm. By comparing the hydrogenation of acetone alcohols intermediates, we found that the acidity of alumina and the proximity effect of Pt hydrogenation sites play an important role in improving the catalytic performance. In addition, by reducing the particle size of Pt particles, it also helps to improve the selectivity of 1,2 propanediol. Therefore, we preliminarily think that porous alumina parcels divide the surface of Pt particles into small Pt aggregates, which is the main reason for improving the selectivity of 1,2 propanediol. (2) in addition, we have further grown FeOx with different cycles on commercial Pt/C catalyst through ALD technology. It is found that trace FeOx can significantly improve the activity of the catalyst. We found that the FeOx with three cycles of deposition has the highest activity on Pt/C catalyst, and the conversion rate of glycerol hydrogenolysis is three times higher than that of Pt/C catalyst in the same time.
【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36

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