单原子催化剂的可控合成及其催化性能研究

发布时间：2018-09-10 18:37

【摘要】：目前,日益严重的全球能源短缺和环境污染问题已经受到国际社会和各国政府的高度关注。作为最大的发展中国家,中国面临着前所未有的能源与环境双重考验。高效催化剂的发展是解决能源与环境问题的有效途径。但是,目前广泛使用的催化剂还有很大的改进空间。单原子催化剂作为一种新型催化剂,由于其特殊的电子结构和几何结构,在小分子活化转化、有机催化、电催化等系列重要催化反应中展现出优异的活性、选择性和稳定性。单原子催化剂的催化应用以及机理研究已经成为国际催化学界的研究热点和前沿。本论文旨在发展快速、便捷、大规模的单原子催化剂合成方法,将单原子催化的概念扩展到生物酶和传统催化剂改性领域,同时将单原子催化剂应用到具有重大经济效益的反应中,并从原子分子层面深入研究催化机理,凝练出控制催化性能的关键因素,指导开发高效、廉价的新型催化体系。本论文具体包括以下几个不同体系:1.将单原子催化的概念括展到生物酶催化体系,构造CaHP04/淀粉酶复合纳米生物催化体系。由于淀粉酶具有别构效应,Ca2+被认为是催化体系中的活性控制中心。总共三种形貌的CaHPO4/淀粉酶纳米生物催化体系被合成,包括纳米花、纳米片和平行六面体结构。催化测试显示淀粉酶的生物活性受到纳米结构形貌和别构效应的双重影响。2.成功构造了负载在CoO衬底材料上的Rh单原子催化剂材料(Rh1/CoO)。将Rh1/CoO应用于氢甲酰化反应,相对于Rh纳米团簇和颗粒催化剂,发现Rh1/CoO具有更高的催化活性和对直链产物的选择性。进一步的原位谱学和理论计算共同表明,在CO和H2氛围下,可以诱导Rh单原子的结构再构,从而增强Rh单原子对烯烃的吸附。通过Rh单原子特殊的构型和配位效应,可以有效选择性生成直链产物。3.成功构造了负载在VO_2衬底材料上的Rh单原子催化剂材料(Rh1/VO_2)。VO_2是一种特殊的金属-绝缘体相变材料。在氨硼烷水解反应中,Rh1/VO_2的表观活化能随着温度的改变而改变。进一步的研究表明,活化能的改变同Rh单原子的最高占据态紧密相关,而Rh单原子的最高占据态是由VO_2的物相所决定的。基于对氨硼烷水解反应机理的理解,我们进而设计并构造了非贵金属单原子催化剂,在氨硼烷水解反应中也展现出较高的活性。4.将单原子催化概念括展到非金属元素中心和传统催化剂改性,构造适用于CO_2加氢的高效Co4N纳米片催化剂。Co4N纳米片催化剂是通过Co纳米片在NH3氛围下高温氨化处理得到的。相对于Co纳米片,Co4N纳米片的催化性能有了一个量级以上的提升。后续的原位谱学表明,Co4NHx是催化过程中真正的活性物相,催化剂表面富含氨基基团。氨基基团中的H原子直接加氢到CO_2分子中形成HCOO*物种,特殊的反应路径使得Co4N对CO_2活化转化的温度大幅下降,从而极大提升催化活性。非金属元素N可以认为是这个催化剂体系中特殊的催化中心组成部分。
[Abstract]:As the largest developing country, China is facing an unprecedented dual test of energy and environment. The development of high-efficiency catalysts is an effective way to solve energy and environmental problems. However, it is now widely used. Monoatomic catalysts, as a new type of catalysts, exhibit excellent activity, selectivity and stability in a series of important catalytic reactions, such as small molecule activation and conversion, organic catalysis, electrocatalysis and so on, due to their special electronic and geometric structures. Mechanisms have become the focus and frontier of catalysis research in the world. This paper aims to develop a fast, convenient and large-scale synthesis method of monoatomic catalysts, which extends the concept of monoatomic catalysis to the fields of enzyme modification and traditional catalyst modification, and applies monoatomic catalysts to reactions with significant economic benefits. In this paper, several different catalytic systems have been developed: 1. The concept of mono-atom catalysis has been extended to bio-enzyme catalytic system to construct CaHP04/amylase composite nano-biocatalytic system. Ca2+ is considered to be the active control center in the catalytic system because of the allosteric effect of amylase. A total of three morphologies of CaHPO4/amylase nano-catalytic systems were synthesized, including nanoflowers, nanosheets and parallel hexahedral structures. Catalytic tests showed that the biological activity of amylase was influenced by the morphology and allosteric effect of nanostructures. Rh monoatomic catalyst materials supported on CoO substrates (Rh1/CoO) were successfully constructed. Rh1/CoO was applied to hydroformylation. Compared with Rh nanoclusters and granular catalysts, Rh1/CoO exhibited higher catalytic activity and selectivity for straight chain products. Further in situ spectroscopy and theoretical calculations showed that Rh1/CoO exhibited higher catalytic activity and selectivity for CO and H. Rh mono-atom can be induced to reconstruct the structure of Rh atom in the atmosphere of 2, which can enhance the adsorption of olefins by Rh mono-atom. The linear products can be selectively generated by the special configuration and coordination effect of Rh mono-atom. 3. Rh mono-atom catalyst material supported on VO_2 substrate material (Rh1/VO_2) has been successfully constructed. VO_2 is a special metal-absolute. The apparent activation energy of Rh_1/VO_2 varies with temperature in the hydrolysis of ammonia-borane. Further studies show that the change of activation energy is closely related to the highest occupied state of Rh atom, and the highest occupied state of Rh atom is determined by the phase of VO_2. Based on the mechanism of the hydrolysis of ammonia-borane We then designed and constructed non-noble metal mono-atom catalysts, which exhibited high activity in the hydrolysis of aminoborane. 4. The concept of mono-atom catalysis was extended to the center of non-metallic elements and modified by traditional catalysts to construct high-efficiency Co4N nanosheet catalysts for CO_2 hydrogenation. Co4N nanosheet catalysts were prepared via Co nanoparticles. Compared with Co nanosheets, the catalytic performance of Co_4N nanosheets has been improved by an order of magnitude. The subsequent in-situ spectroscopy showed that Co_4NHx was the real active phase in the catalytic process and the catalyst surface was rich in amino groups. H atoms in the amino groups were hydrogenated directly to CO_2 molecules to form HCO. O* species, the special reaction path makes the temperature of Co4N to CO_2 activation and conversion greatly decreased, thus greatly enhancing the catalytic activity. The non-metallic element N can be considered as a special component of the catalytic center in this catalyst system.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.36

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