本文選題：密度泛函理論 + 表面催化�。� 參考：《南京師范大學(xué)》2017年博士論文

【摘要】：催化劑表面的吸附和反應(yīng)研究無論在催化科學(xué)領(lǐng)域還是工業(yè)應(yīng)用及環(huán)境保護(hù)方面都有極其重要的意義,也是當(dāng)前研究的熱門課題之一。固體催化劑的不同晶面由于其原子排列、電子結(jié)構(gòu)等特性不同,使得所具有的性質(zhì)也不同。這些性質(zhì)主要包括對吸附質(zhì)的吸附性、穩(wěn)定性,對化學(xué)鍵的選擇性以及對化學(xué)反應(yīng)的催化活性等。因此,從原子水平上研究催化劑不同晶面的特性十分重要,不僅有助于更好的理解催化劑表面上的化學(xué)反應(yīng),更有利于調(diào)控催化劑的性能。目前從電子結(jié)構(gòu)入手從分子尺度上控制物質(zhì)性能的方法不僅僅被用于催化劑領(lǐng)域,而是成為整個化學(xué)、物理和材料科學(xué)領(lǐng)域的一個共同的思路。本學(xué)位論文以甲醇的脫氫反應(yīng)作為研究反應(yīng)體系,使用密度泛函理論方法(DFT)研究了其在Pt-Ni合金表面的反應(yīng)過程,構(gòu)建反應(yīng)勢能面以及反應(yīng)網(wǎng)絡(luò)力求從微觀層面深入解釋反應(yīng)機理,在已有實驗研究的基礎(chǔ)上,通過將實驗現(xiàn)象和理論計算的結(jié)果加以比較分析,從而確定控制反應(yīng)進(jìn)行的關(guān)鍵步驟及影響因素,為設(shè)計更好的催化劑提供理論指導(dǎo)。通過DFT計算并結(jié)合周期性平板模型,進(jìn)行了結(jié)構(gòu)優(yōu)化、過渡態(tài)搜索及反應(yīng)勢能面構(gòu)建;采用態(tài)密度、功函數(shù)變化、Bader電荷分析等手段實現(xiàn)了對吸附構(gòu)型及各基元反應(yīng)過程的電子結(jié)構(gòu)分析;進(jìn)一步探討了反應(yīng)微觀動力學(xué)分析對反應(yīng)選擇性的決定因素。本論文的主要內(nèi)容及結(jié)果如下:1.研究了 CH3OH在Pt3Ni催化劑的(111)、(100)和(110)表面上的吸附行為。利用DFT方法以及范德華校正(vdW)優(yōu)化了 CH3OH在Pt3Ni催化劑的(111)、(100)和(110)面上吸附的結(jié)構(gòu)并且計算了相應(yīng)的吸附能,分析結(jié)果表明CH3OH在Pt3Ni催化劑上的吸附強度遵循(110) (111) (100)順序。同時從結(jié)構(gòu)中Ni的d帶中心相對于費米能級的移動、態(tài)密度、Bader電荷分析、功函變化以及CH3OH對不同表面的極化作用等方面討論了 CH3OH吸附行為的機理。結(jié)果發(fā)現(xiàn)在吸附過程中Ni原子或者周圍含Ni原子多的位點有利于CH3OH的吸附,即配體效應(yīng)明顯。同時極化作用也對吸附有一定的影響。本章結(jié)果為適用于非均相催化的納米結(jié)構(gòu)催化劑表面的合理設(shè)計和構(gòu)建提供理論指導(dǎo)。2.研究了 Pt3Ni(111)上的甲醇分解反應(yīng)機理。利用DFT方法以及范德華校正優(yōu)化了 CH3OH及其在Pt3Ni(111)上分解的中間體的結(jié)構(gòu)、吸附穩(wěn)定性和最佳吸附位點,發(fā)現(xiàn)由于Pt3Ni(111)表面上的Pt和Ni原子分別帶有少量的負(fù)電荷和正電荷,大多數(shù)中間體(如自由基中間體和具有孤對電子的物質(zhì))易于吸附在Ni位點周圍。根據(jù)相關(guān)過渡態(tài)的空間位阻效應(yīng)和電子結(jié)構(gòu)以及Bronsted-Evans-Polanyi (BEP)關(guān)系討論了通過O-H, C-H和C-O鍵的初始斷裂的可能途徑,研究發(fā)現(xiàn),CH30H分解最初優(yōu)先發(fā)生O-H鍵斷裂而不是C-H和C-O鍵斷裂。結(jié)合分解途徑中基元反應(yīng)步驟的熱化學(xué)信息和反應(yīng)能壘最終得到反應(yīng)最佳路徑。計算這些中間體吸附狀態(tài)的振動頻率,并利用簡諧過渡態(tài)理論計算每個可能基元步驟的反應(yīng)速率常數(shù)。構(gòu)造勢能面(PES),確定反應(yīng)速控步,獲得反應(yīng)最佳途徑是CH3OH → CH30 → CH20 → CHO →CO,其中O-H鍵的斷裂是速控步。通過本工作與其他系統(tǒng)的結(jié)果比較時發(fā)現(xiàn)在DMFCs中Pt3Ni(111)可以有效地促進(jìn)甲醇分解和減輕CO中毒問題。CH3OH及其分解中間體在Pt3Ni(111)吸附行為主要受配體效應(yīng)影響,其脫氫過程主要受幾何效應(yīng)影響。本章結(jié)果將為更好的理解直接甲醇燃料電池(DMFC)中的PtNi陽極特性以及提高DMFC性能提供了理論指導(dǎo)。3.研究了 Pt3Ni(100)上的甲醇分解反應(yīng)。利用DFT方法以及范德華校正(vdW)優(yōu)化了 CH3OH及其在Pt3Ni(100)上分解的中間體的結(jié)構(gòu)、吸附穩(wěn)定性和最佳吸附位點,研究發(fā)現(xiàn),與Pt3Ni(111)表面類似,在Pt3Ni(100)上大多數(shù)中間體(如自由基中間體和具有孤對電子的物質(zhì))易于吸附在Ni位點周圍,其中Pt和Ni均對脫氫反應(yīng)起協(xié)同催化作用。根據(jù)相關(guān)過渡態(tài)的空間位阻效應(yīng)和電子結(jié)構(gòu)以及BEP關(guān)系討論了發(fā)生O-H, C-H和C-O鍵初始斷裂的可能途徑,結(jié)果發(fā)現(xiàn)CH3OH分解起始發(fā)生O-H斷裂在熱力學(xué)和動力學(xué)上最有利,C-H鍵斷裂的活化能比O-H鍵斷裂稍低,在常溫下也可能發(fā)生,因此我們認(rèn)為在Pt3Ni(100)表面上O-H斷裂與C-H鍵斷裂存在競爭機制。C-O鍵斷裂在常溫下最難發(fā)生。反應(yīng)最佳途徑是CH3OH → CH30 → CH20→CHO → CO,其中CHO中C-H鍵的斷裂是速控步,與Pt3Ni(111)面上的速控步不同。此結(jié)果將為更好的理解PtNi合金的(100)面對合金總的催化性能的貢獻(xiàn)以及提高DMFC性能提供了理論指導(dǎo)。
[Abstract]:The study of adsorption and reaction on the surface of the catalyst is of great significance in both the field of catalytic science, industrial application and environmental protection. It is also one of the hot topics in current research. The properties of different crystalline surfaces of solid catalysts are different because of their atomic arrangement and electronic structure. These properties are also different. It mainly includes adsorbability, stability, selectivity to chemical bonds and catalytic activity for chemical reactions. Therefore, it is very important to study the characteristics of different crystalline surfaces from the atomic level, which is not only helpful to better understand the chemical reaction on the surface of the catalyst, but also to control the performance of the catalyst. The method of controlling material performance from the molecular scale is not only used in the field of catalyst, but also a common thought in the field of chemistry, physics and materials science. This dissertation uses methanol dehydrogenation as the reaction system, and uses the density functional theory method (DFT) to study its Pt-Ni alloy table. In the reaction process, the reaction potential energy surface and the reaction network are constructed to explain the reaction mechanism deeply from the microscopic level. On the basis of the existing experimental research, the key steps and the influencing factors of the control reaction are determined by comparing the results of the experimental and theoretical calculations, so as to provide a better catalyst for the design of the catalyst. The structure optimization, the transition state search and the reaction potential surface construction are carried out by DFT calculation and the periodic plate model. The electronic structure analysis of the adsorption configuration and the reaction process of each basic element is realized by means of state density, work function change and Bader charge analysis, and the reaction microdynamics analysis is further discussed. The main determinants of this paper are as follows. The main contents and results of this paper are as follows: 1. the adsorption behavior of CH3OH on the surface of (111), (100) and (110) of Pt3Ni catalyst was studied. The structure of CH3OH adsorbed on Pt3Ni catalyst (111), (100) and (110) was optimized by DFT method and Fan Dehua correction (vdW), and the corresponding adsorption energy was calculated. The analysis results show that the adsorption strength of CH3OH on the Pt3Ni catalyst follows (110) (111) (100) order, and the mechanism of CH3OH adsorption behavior is discussed from the movement of the d band center of Ni relative to the Fermi level, the density of state, the charge analysis of Bader, the change of the work function and the polarization of CH3OH on different surfaces. In the process, the Ni atom or the surrounding loci containing Ni atoms are beneficial to the adsorption of CH3OH, that is, the ligand effect is obvious. Meanwhile, the polarization effect also has a certain influence on the adsorption. This chapter provides a theoretical guidance for the rational design and construction of the surface of the nano structured catalyst for heterogeneous catalysis..2. has studied the methanol fraction on Pt3Ni (111). The reaction mechanism is solved by using the DFT method and the Fan Dehua correction to optimize the structure of CH3OH and its intermediates on Pt3Ni (111), the adsorption stability and the best adsorption site. It is found that the Pt and Ni atoms on the Pt3Ni (111) surface have a small amount of negative charge and positive charge respectively, and most intermediates (such as free radical intermediates and soliton pairs). The matter of electrons is easy to adsorb around the Ni site. According to the spatial steric effect of the associated transition state and the electron structure and the relationship between the Bronsted-Evans-Polanyi (BEP) relationship, the possible pathways through the initial fracture of the O-H, C-H and C-O bonds are discussed. It is found that the first priority of the CH30H decomposition is the fracture of the O-H bond instead of the C-H and C-O bond breakages. The thermo chemical information and the reaction energy barrier of the radical reaction step in the solution are finally obtained the best path of the reaction. The vibration frequency of the adsorption state of these intermediates is calculated and the reaction rate constant of each possible basic element is calculated by the simple harmonic transition state theory. The potential energy surface (PES) is constructed and the reaction speed control step is determined. The best way to obtain the reaction is CH3O H, CH30, CH20, CHO to CO, the fracture of the O-H bond is a speed control step. By comparing the results of this work with the results of other systems, it is found that Pt3Ni (111) in DMFCs can effectively promote methanol decomposition and reduce CO poisoning..CH3OH and its decomposition intermediate in Pt3Ni (111) adsorption is mainly influenced by ligand effect, and its dehydrogenation process is main. The results of this chapter will provide a theoretical guide for better understanding of the PtNi anode properties in direct methanol fuel cell (DMFC) and the improvement of DMFC performance..3. studies the methanol decomposition reaction on Pt3Ni (100). The DFT method and Fan Dehua correction (vdW) are used to optimize the intermediates of CH3OH and its decomposition on Pt3Ni (100). The structure, adsorption stability and the best adsorption site have been found to be similar to the Pt3Ni (111) surface. Most of the intermediates on Pt3Ni (100) (such as free radical intermediates and substances with isolated electrons) are easy to adsorb around the Ni site, and both Pt and Ni have synergistic catalytic action on dehydrogenation. The spatial steric effect of the related transition states The possible way to break the initial fracture of O-H, C-H and C-O bonds is discussed with the electronic structure and the BEP relationship. It is found that the initiation of O-H fracture at the beginning of CH3OH decomposition is most favorable in thermodynamics and kinetics. The activation energy of the C-H bond fracture is slightly lower than that of the O-H bond and may occur at the normal temperature. Therefore, we think the O-H fracture and C- on the Pt3Ni (100) surface are on the C-. The H bond fracture is the most difficult for the.C-O bond fracture at normal temperature. The best way to react is CH3OH to CH30, CH20 to CHO and CO, in which the fracture of the C-H bond in CHO is the speed control step, which is different from the speed control step on the Pt3Ni (111) surface. The result will be a better understanding of the contribution of the (100) to the overall catalytic performance of the PtNi alloy and the extraction of the overall catalytic properties of the PtNi alloy. High DMFC performance provides theoretical guidance.

【學(xué)位授予單位】：南京師范大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：O643.36

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本文編號：1889542