无水乙醇中β-O-4型木素模型物在铯取代的多氧金属盐上的降解:酸性和氧化还原性的影响（英文）

发布时间：2018-05-05 09:41

本文选题：木素模型物 + β-O-醚键　；参考：《催化学报》2017年07期

【摘要】：随着化石能源的日益减少,从木质生物质获得能源、燃料和化学品变得至关重要.木素是木质生物质的第二大主要组分,但是目前远未得到充分利用.随着对木素结构的充分认识和相关催化科学技术的发展,由木素制得大宗燃料或精细化学品,特别是芳香类化合物显示出越来越具有技术和经济可行性.由于木质素大分子中复杂的C O和C C连接,先研究模型物的断裂机理并同时考虑从木素模型物小分子迁移到木质素大分子的问题,然后设计出合适的催化材料并开发出可行的工艺过程,这条技术路线看起来更具有可行性.近年来,几种均相或非均相多氧金属盐(Polyoxometalates(POMs),或称杂多酸)用于降解木素或者木素模型物,但是β-O-4醚键断裂的氢解还是酸解机理及其竞争合作作用尚不清晰.我们在几种多氧金属盐(POMs)的催化下研究了β-O-4模型物2-phenoxyacetophenone(2-PAP)在以无水乙醇作为供氢溶剂体系下的催化断裂机理和行为.结果表明,随着无水乙醇溶剂处理温度的提高,溶剂的供氢能力增强.酸性催化剂的加入提高了溶剂供氢能力.原因是催化剂的酸性改变了乙醇自氧化还原反应的平衡,使平衡向生成乙醛并释放出活性氢的方向进行.我们还发现,Cs-PMo的氧化还原性,对促进活性氢的释放起更大的作用.2-PAP反应底物的加入消耗了活性氢,从而促使乙醇自氧化还原平衡向右移动.在酸性催化剂的作用下,2-PAP的转化裂解可以按照氢转移机制或酸催化的氧摀离子机制进行.大部分转化反应按照哪个机制进行,取决于所采用体系的供氢能力和酸强度/数量的竞争关系,大部分反应将屈从于占竞争优势的机制.在强供氢及转移能力占优势,而酸强较低酸量较少时,反应主要按氢转移机制进行.在酸强很强且数量较多,反应将主要按酸催化氧摀离子机制进行.Cs-PMo这个拥有酸性和强氧化还原性的双功能催化剂的使用,既促进了活性氢的释放,又增强了活性氢的还原能力及转移能力,因而导致了在极高转化率(99%)的下极佳的选择性(98.6%苯酚和91.1%苯乙酮).这些发现将对理解木质素中醚键的断裂结果和机理提供启示,为设计开发出木质素选择性地催化裂解为芳香小分子的可行的工业过程打下初步理论基础.
[Abstract]:With the decrease of fossil energy, it is very important to get energy from wood biomass. Lignin is the second major component of woody biomass, but it is far from being fully utilized. With the full understanding of lignin structure and the development of related catalytic science and technology, the preparation of bulk fuels or fine chemicals from lignin, especially aromatic compounds, shows more and more technical and economic feasibility. Because of the complex C / O and C / C junctions in lignin macromolecules, the fracture mechanism of the model compounds is studied and the problem of migration from small molecules of lignin model compounds to lignin macromolecules is considered at the same time. Then a suitable catalytic material is designed and a feasible process is developed, which seems to be more feasible. In recent years, several homogeneous or heterogeneous polyoxometalates have been used to degrade lignin or lignin models. However, the mechanism of hydrogenolysis or acidolysis of 尾 -O-4 ether bond and its competitive cooperation are not clear. The catalytic fracture mechanism and behavior of 尾 -O-4 model compound 2-phenoxyacetophenoneophenone 2-PAPs in anhydrous ethanol as hydrogen donor solvent were studied under the catalysis of several polyoxometalates (POMs). The results showed that the hydrogen donor capacity of the solvent increased with the increase of the temperature of ethanol solvent treatment. The addition of acid catalyst improved the hydrogen supply ability of solvent. The reason is that the acidity of the catalyst changes the equilibrium of the self-redox reaction of ethanol, which leads to the formation of acetaldehyde and the release of active hydrogen. We also found that the redox property of Cs-PMo plays a more important role in promoting the release of active hydrogen. The addition of substrates of 2-PAP consumes active hydrogen, thus promoting the self-redox equilibrium of ethanol to move to the right. The conversion and cleavage of 2-PAP under the action of acid catalyst can be carried out according to the mechanism of hydrogen transfer or the mechanism of acid catalyzed oxygen masking. The mechanism in which most of the conversion reactions take place depends on the hydrogen supply capacity of the system and the competitive relationship of acid strength / quantity. Most of the reactions will be subservient to the competitive advantage mechanism. In the case of strong hydrogen supply and transfer ability, the reaction was mainly carried out according to the mechanism of hydrogen transfer when the acid content was relatively low. When the acidity is very strong and the quantity is large, the reaction will be carried out mainly according to the mechanism of acid catalyzing oxygen covering ion. Cs-PMo, a bifunctional catalyst with acid and strong redox property, will promote the release of active hydrogen. The reduction ability and transfer ability of active hydrogen were also enhanced, which resulted in excellent selectivity of 98.6% phenol and 91.1% acetophenone at the very high conversion rate of 99%. These findings will provide enlightenment for understanding the fracture results and mechanism of ether bonds in lignin and lay a preliminary theoretical foundation for the design and development of a feasible industrial process for the selective catalytic decomposition of lignin to aromatic small molecules.
【作者单位】：复旦大学化学系能原材料协同创新中心先进材料实验室上海分子催化与创新材料重点实验室;广西科学院国家非粮生物质能源工程技术研究中心非粮生物质酶解国家重点实验室广西生物质工程技术研究中心广西生物质产业化工程院广西生物炼制重点实验室;复旦大学化学系;
【基金】：supported by the National Key Basic Research Program of China(973 program,2013CB934101) National Natural Science Foundation of China(21433002,21573046) China Postdoctoral Science Foundation(2016M601492) International Science and Technology Cooperation Projects of Guangxi(15104001-5)~~
【分类号】：O636.2

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