金属纳米簇催化剂催化性能调控的理论研究

发布时间：2018-03-21 11:21

本文选题：金属纳米簇　切入点：催化性能　出处：《北京化工大学》2017年博士论文　论文类型：学位论文

【摘要】：金属纳米簇催化剂凭借其独特的表面效应、体积效应和量子尺寸效应,展现了纳米催化材料优异的催化性能,广泛应用于化工领域中的低温催化一氧化碳(CO)氧化、燃料电池反应、低温水煤气转换反应和氮氧化物(NOx)催化分解等,被称为第四代催化剂。形貌、尺寸、组成和原子排序都可以对金属纳米簇的催化性能进行调控,使金属合金纳米簇的构效关系及反应机理变得更加复杂。除此之外,载体对催化剂催化性能的影响也是不容忽视的。本论文以质子交换膜燃料电池(proton exchange membrane fuel cell, PEMFC)的氧还原反应(oxygen reduction reaction,ORR)活性和抗CO中毒特性为出发点,利用密度泛函理论(density functional theory, DFT)计算方法,研究了在PEMFC中,形貌、载体、组成和原子排序对金属纳米簇催化剂催化性能的影响和调控。主要研究的内容和创新点如下:1、形貌对金属纳米簇催化剂催化性能的调控。用密度泛函理论计算方法研究了形貌结构对金属纳米簇催化剂的催化性能的调控。首先根据金属纳米簇剩余能的大小,确定了具有不同形貌结构的金属纳米簇催化剂的相对稳定性;然后根据反应物在金属纳米簇上的吸附能以及反应能垒的大小确定了具有不同形貌结构金属纳米簇催化剂的催化性能。主要研究了形貌对纯Pt金属纳米簇和AuPd双金属纳米簇的催化性能调控。(1)采用第一性原理的密度泛函理论计算方法,研究了形貌对Pt13团簇ORR催化活性和抗CO中毒特性的调控。首先,计算了四种低对称Pt13团簇(Pt13-1和Pt13-4是Cs对称,Pt13-2和Pt13-3是C2v对称)和一种具有正二十面体(ICO)结构的高对称的Pt13-5 (Ih对称)团簇的剩余能,根据剩余能的大小确定了不同形貌结构的Pt13团簇的相对稳定性。接着,研究CO,O2,O和OH在这五种不同形貌结构的t13催化剂上的吸附能以及O2分子的解离能垒和不同反应机理下CO分子氧化的反应能垒。计算结果表明,Pt13-1和Pt13-2具有适宜(居中)的O和OH吸附能,、较低的O2分子解离能,所以,这两个团簇具有较高的ORR催化活性。在包含O2解离过程的LH反应机理下,Pt13-1和Pt13-2两个形貌结构的Pt13团簇催化CO氧化反应的能垒也是最低的(0.2 eV)。综合考虑,具有低对称形貌的Pt13-1和Pt13-2这两种Pt13团簇拥有最好的ORR催化活性和抗CO中毒特性。(2)通过密度泛函理论计算方法,研究了具有正二十面体(ICO)和截角八面体(TO)两种不同形貌结构的Au13, Au12Pd1,Pd12Au1和Pd13组成的四种AuPd双金属纳米簇。剩余能的结果表明,对于富Pd的Pd13和Pd12Au1团簇而言,ICO形貌结构是相对稳定的结构,而对于富Au的Au12Pd1和Au13团簇而言,TO形貌结构的是相对稳定的结构。O2吸附在具有ICO形貌结构的Au13和Au12Pd1团簇上时,团簇会由ICO结构转变成TO结构。2、载体对金属纳米簇催化剂催化性能的调控。通过密度泛函理论对载体和催化剂的电子态密度(DOS)进行分析,得到载体和催化剂之间存在电荷的转移,也正是因为这种载体-催化剂体系内的电荷转移,使得载体可以调控金属纳米簇催化剂的催化性能。本论文主要研究了有无石墨烯负载的AuPd金属纳米团簇和MgO(100)负载的AuPt金属纳米簇催化剂催化CO氧化的催化性能。(1)首先,通过计算Au13, Au12Pd1, Pd12Au1和Pd13这四种不同组成的裸露的AuPd双金属纳米簇催化CO氧化的反应能垒,得出Au12Pd1是最优的CO氧化催化剂,反应能垒是0.17 eV。然后,将Au12Pd1负载在单空位缺陷的石墨烯上,计算Au12Pd1金属纳米簇催化剂的稳定性和催化CO氧化的活性。和裸露的Au12Pd1双金属纳米簇催化剂进行对比,结果表明,缺陷石墨烯负载的Au12Pd1催化剂虽然没有提高催化CO氧化的活性(反应能垒为0.41eV),但是提高了催化剂的稳定性。借助DOS分析的结果,可以说明石墨烯载体与Au12Pd1催化剂之间的电荷转移是催化剂稳定性提高的根本原因。(2)计算了 MgO(100)负载的亚纳米的PtxAu3-x金属纳米簇催化剂上CO 通过 Langmuir-Hinshelwood (LH), trimolecular Langmuir-Hinshe-lwood(3LH)和Eley-Rideal(ER)三种不同反应机理反应时的反应能垒。结果表明,不同反应机理下,PtxAu3-x/MgO金属纳米簇催化CO氧化的反应活性高低的排序是不同,但综合考虑这三种机理,Pt2Au1/MgO是最优的CO氧化催化剂。电荷分析的结果表明,Pt2Au1/MgO具有高催化活性的根本原因是MgO载体与Pt2Au1团簇间的电荷转移的数量最为显著。3、组成和原子序对金属纳米簇催化剂催化性能的调控。借助密度泛函理论,我们计算了不同组成下PdCu金属纳米簇的ORR反应的活性以及抗CO中毒的特性。计算中,我们用O2分子的解离能以及O, OH和OOH三种含氧中间物的吸附能来评价PdCu双金属纳米簇对ORR反应的催化活性,用CO氧化反应的反应能垒来评价PdCu双金属纳米簇的抗CO中毒特性。无论是ORR反应还是CO氧化反应,O2分子的激活都是反应进行的关键,比例为50:50的Pd27Cu28团簇对O2分子的吸附是最弱的,即最容易被激活。所以,在本论文的研究体系中,Pd27Cu28金属纳米簇同时具有最高的ORR催化活性和最强的抗CO中毒特性。同时,我们研究了单一 Ni原子或者Co原子的化学序对Pt基双金属/三金属纳米簇催化剂催化性能的调控。对于具有ICO结构的Pt基金属合金纳米簇,单一 Ni或者Co原子有中心位置(core),次表层位置(subsurface),和两种不同的表面位置(T1和T2)四种不同的占据位置。CO氧化反应的反应能垒表明,单一 Ni或者Co原子占据催化剂的中心位置时,催化剂具有最高的催化活性,这与完美对称的核壳结构催化剂的高稳定性是密不可分的。单一 Ni或者Co原子占据次表面次之,占据表面时,催化剂具有最低的催化活性,这与不同原子序下金属纳米簇的稳定性是正相关的,催化剂越稳定,催化剂的活性越高。
[Abstract]:Metal nanocluster catalyst with its unique surface effect, volume effect and quantum size effect, show excellent catalytic properties of nano catalytic materials, catalytic carbon monoxide is widely used in chemical industry in the field of fuel cell (CO) oxidation reaction, low-temperature water gas conversion reaction and catalytic decomposition of nitrogen oxide (NOx), called as the fourth generation catalyst. The morphology, size, composition and atomic arrangement can be on the catalytic performance of metal nanoclusters of regulation, make the structure-activity relationship and reaction mechanism of metal alloy nanoclusters have become more complex. In addition, effect of support on catalytic performance can not be ignored. This paper based on proton exchange membrane fuel the battery (proton exchange membrane fuel cell, PEMFC) of the oxygen reduction reaction (oxygen reduction reaction, ORR CO) activity and anti poisoning characteristics as the starting point, using density functional theory (D Ensity functional theory, DFT) calculation method, based on PEMFC, morphology, carrier, composition and atomic arrangement effect on catalytic performance of metal nanocluster catalyst and control. The main research content and innovation are as follows: 1. The morphology control on the catalytic performance of metal nanocluster catalyst. The catalytic performance of regulation of morphology the metal nanocluster catalyst by density functional theory calculation method. According to the residual energy and the size of metal nanoclusters, determined the relative stability of metal nano cluster catalysts with different morphologies; then according to the reactant adsorption on the metal nanoclusters on energy and reaction energy barrier is determined by the size of the catalytic performance of structure different morphologies of metal nanocluster catalyst. The main study on catalytic performance regulation of pure Pt metal nanoclusters and AuPd bimetallic nanoclusters morphology (1) by the first. The calculation method of density functional theory principle, study the morphology control of Pt13 clusters ORR catalytic activity and resistance to CO poisoning characteristics. Firstly, four kinds of low symmetry Pt13 clusters were calculated (Pt13-1 and Pt13-4 is Pt13-2 and Pt13-3 is Cs symmetry, C2v symmetry) and a positive twenty surface (ICO) structure the high symmetry Pt13-5 (Ih symmetry) clusters according to the residual energy and residual energy, the size of the relative stability of Pt13 clusters with different morphologies were determined. Then, the research of CO, O2, O and OH adsorption dissociation in these five kinds of different structures on the T13 catalyst and O2 molecules can the reaction of CO oxidation and molecular reaction mechanism under different barrier barrier. The calculation results show that Pt13-1 and Pt13-2 have proper (centered) O and OH O2, the molecular dissociation adsorption energy, low energy, so the catalytic activity of ORR of the two clusters is higher. In the solution containing O2 from LH reaction mechanism in the process of Next, Pt13 clusters of CO oxidation catalyzed by Pt13-1 and Pt13-2 two the morphology and structure of the energy barrier is the lowest (0.2 eV). Considering the low symmetry morphology of Pt13-1 and Pt13-2 of the two Pt13 clusters of ORR has the best catalytic activity and anti poisoning characteristics. CO (2) by density functional the theoretical calculation method, the study has twenty surface body (ICO) and truncated eight surface (TO) of two different structures of Au13, Au12Pd1, Pd12Au1 and AuPd four Pd13 consisting of two metal nanoclusters. The remaining energy results show that for the Pd13 and Pd12Au1 clusters Pd rich, ICO morphology structure is relatively stable, while for Au12Pd1 and Au13 clusters of Au rich in terms of the structure and morphology of TO.O2 structure is relatively stable in the adsorption of Au13 and Au12Pd1 clusters with ICO structure on the morphology, clusters by ICO structure into TO structure of.2, carrier of metal nanoclusters catalyst The performance of control. Through the density of states of the density functional theory of the carrier and catalyst (DOS) analysis, obtained the charge transfer between the carrier and the catalyst, it is because of the charge carrier catalyst system in the transfer, the carrier can control metal catalytic performance of nano cluster catalyst was studied in this paper. There is no graphene supported AuPd metal nanoclusters and MgO (100) catalyzed CO AuPt metal nanocluster catalyst oxidation load. (1) first of all, through the calculation of Au13, Au12Pd1, Pd12Au1 and Pd13 of the four kinds of bare AuPd bimetallic cluster catalyst for CO oxidation reaction energy barrier that is, the Au12Pd1 CO catalysts for the oxidation of the optimal reaction barrier is 0.17 eV. and the Au12Pd1 load in the graphene single vacancy defects on the stability and catalytic oxidation of CO Au12Pd1 metal nano cluster catalyst The activity of comparison, and bare Au12Pd1 bimetallic cluster catalyst. The results showed that Au12Pd1 catalyst supported on graphene defects although not improve the catalytic activity of CO oxidation (reaction energy barrier of 0.41eV), but the stability of catalyst was improved. The results of DOS analysis, can explain the charge between graphene and Au12Pd1 carrier the catalyst transfer is the basic reason for the stability of the catalyst increased. (2) MgO (100) calculated load of sub nanometer PtxAu3-x metal nanocluster catalyst on CO by Langmuir-Hinshelwood (LH), trimolecular Langmuir-Hinshe-lwood (3LH) and Eley-Rideal (ER) three different reaction mechanism of the reaction barrier. The results show that different the reaction mechanism, reaction activity level of PtxAu3-x/MgO metal nanocluster catalytic CO oxidation sequencing is different, but considering the three kinds of mechanism, Pt2Au1/MgO is the best C O oxidation catalyst charge. Analysis results show that the main reason for the Pt2Au1/MgO with high catalytic activity is the most significant.3 is the number of Pt2Au1 clusters and MgO charge carrier transfer between the atomic composition and regulation on the catalytic performance of metal nanocluster catalyst. Using the density functional theory, we calculated the ORR reaction of PdCu metal nanoclusters the different component activity and characteristics of resistance to CO poisoning. In the calculation, we use O2 and O to the molecular dissociation, adsorption of OH and OOH three kinds of oxygen intermediates to evaluate the catalytic activity of PdCu bimetallic clusters on the ORR reaction, CO anti poisoning characteristics of CO oxidation reaction energy barrier to evaluate the PdCu bimetallic cluster. Either ORR or CO oxidation reaction, the activation of O2 molecules is the key of reaction, adsorption ratio of Pd27Cu28 cluster 50:50 of O2 molecule is the weakest, which is most likely to be stimulated Live. So, in the study system of this thesis, CO anti poisoning characteristics of Pd27Cu28 metal nanoclusters also has the highest catalytic activity of ORR and the strongest. At the same time, we studied the regulation of Pt based bimetallic nanoclusters / catalytic metal catalyst three can chemical order single Ni atom or Co atom for Pt. Base metal alloy nanoparticles with ICO structure, a single Ni or Co atom Center (core), surface position (subsurface), and two different surface sites (T1 and T2) of four different.CO occupy the position of the reaction barrier that single Ni or Co atoms occupy the center the position of catalyst, the catalyst has high catalytic activity, high stability of the core-shell structure catalyst and the perfect symmetry is inseparable. Single Ni or Co atoms occupy the second surface, occupy the surface, with the lowest catalytic catalyst The activity of the catalyst is positively related to the stability of the metal nanoclusters under different atomic sequence. The more stable the catalyst, the higher the activity of the catalyst.

【学位授予单位】：北京化工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.36

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