鈀催化燃料脫氫氧化反應(yīng)機(jī)理研究
發(fā)布時(shí)間：2018-10-17 17:57
【摘要】：催化反應(yīng)機(jī)理是世界上一個(gè)非常重要的研究課題,特別是金屬表面的固/液交匯處的反應(yīng)更是研究的熱門領(lǐng)域。這個(gè)研究課題在燃料電池等方向上有著廣泛的運(yùn)用。本論文從理論出發(fā),運(yùn)用從頭算理論研究了甲酸和甲醇在催化劑表面覆蓋不同介質(zhì)情況下的氧化反應(yīng)機(jī)理,這個(gè)研究方向在燃料電池的運(yùn)用上有著巨大的潛力。本工作運(yùn)用密度泛函理論廣義梯度近似(DFT-GGA)計(jì)算了金屬/水表面體系,通過研究不同有機(jī)物在催化劑表面反應(yīng)的活化能,研究了不同反應(yīng)路徑的可行性。具體研究?jī)?nèi)容如下:(1)本文運(yùn)用vasp計(jì)算軟件包,建立了詳細(xì)的水分子在金屬表面的吸附模型以研究對(duì)甲酸催化分解反應(yīng)的影響,優(yōu)化了反應(yīng)過程中的反應(yīng)物、中間體、過渡態(tài)以及產(chǎn)物的構(gòu)型。具體研究了甲酸存在于H2O/Pd(111)體系中的吸附能以及不同的反應(yīng)通道。本文在相同基組的水平上對(duì)反應(yīng)的反應(yīng)物和產(chǎn)物進(jìn)行了優(yōu)化,計(jì)算了在3層Pd原子表面下甲酸的吸附能,確定了各個(gè)反應(yīng)體系的過渡態(tài)和中間體。得出了以下結(jié)論:研究結(jié)果發(fā)現(xiàn)氫鍵對(duì)甲酸在H2O/Pd(111)體系的吸附構(gòu)型有很大影響,,H2O分子和甲酸中的O和H原子形成氫鍵相互作用改變了甲酸在Pd表面的穩(wěn)定吸附形態(tài)。通過對(duì)甲酸催化裂解反應(yīng)過程過渡態(tài)的搜索,結(jié)果表明在水溶液和Pd金屬界面上甲酸C-OH鍵很難解離,只有C-H鍵解離這一條可行的反應(yīng)路徑,這個(gè)反應(yīng)路徑是甲酸生成CO2的決定性步奏。(2)本文運(yùn)用DFT方法第一次計(jì)算了質(zhì)子和質(zhì)子、甲酸根共同存在的情況下甲酸在H2O/Pd(111)體系中的反應(yīng)過程。研究表明,在質(zhì)子存在的情況下,C-OH鍵解離和C-H鍵解離都變成了結(jié)構(gòu)敏感反應(yīng),C-OH鍵解離所需的能壘相較于質(zhì)子不存在時(shí)降低了1.6eV,C-OH鍵解離后C-H鍵中的H吸附到Pd的表面,反應(yīng)最終生成CO和H2O;在甲酸根和質(zhì)子共同存在的情況下C-OH鍵的解離更加容易,C-H鍵解離所需的活化能卻升高了,通過電荷密度分析甲酸單獨(dú)存在和質(zhì)子、甲酸根存在的情況,發(fā)現(xiàn)甲酸根的電子云影響了甲酸的電荷密度使C-OH鍵裂解。由此說明CO和CO2的生成形成了競(jìng)爭(zhēng)關(guān)系。(3)本文研究了甲醇在Pd金屬表面的催化反應(yīng)機(jī)理,以及可能的裂解反應(yīng)步驟,計(jì)算了相關(guān)反應(yīng)的反應(yīng)物、過渡態(tài)、中間體以及產(chǎn)物,探索了甲醇在中性條件和堿性條件下在Pd金屬表面裂解的反應(yīng)通道。研究表明:甲醇吸附在Pd的表面上時(shí)容易被羥基負(fù)離子進(jìn)攻得到甲二醇離子OCH2OH-,OCH2OH-→OCH2O2-→HCOO-和OCH2OH-→HCOOH→HCOO-兩種反應(yīng)通道都是可行的,在反應(yīng)過程中他們的能壘都非常低。我們對(duì)HCOO-離子的脫氫過程進(jìn)行了研究,結(jié)果表明甲醛能通過這個(gè)反應(yīng)通道變成CO:H2CO→CHO→CO。甲醇在堿性環(huán)境下Pd電極表面生成CO和HCOO-的反應(yīng)機(jī)理是合理的。
[Abstract]:Catalytic reaction mechanism is a very important research topic in the world, especially the reaction of solid / liquid interface on metal surface is a hot field. This research topic has been widely used in fuel cell and so on. In this paper, the mechanism of oxidation of formic acid and methanol in different media was studied by ab initio theory. This research direction has great potential in the application of fuel cells. In this paper, the generalized gradient approximation (DFT-GGA) of density functional theory is used to calculate the metal / water surface system. The feasibility of different reaction paths is studied by studying the activation energy of different organic compounds on the surface of the catalyst. The specific research contents are as follows: (1) in this paper, a detailed adsorption model of water molecules on metal surface was established by using vasp software package to study the effect on the catalytic decomposition of formic acid, and the reactants and intermediates in the reaction process were optimized. Transition state and the configuration of the product. The adsorption energy and different reaction channels of formic acid in H2O/Pd (111) system were studied. In this paper, the reactants and products of the reaction were optimized at the same base group level. The adsorption energy of formic acid on the surface of three layers of Pd atoms was calculated, and the transition states and intermediates of each reaction system were determined. The results show that hydrogen bond has a great influence on the adsorption configuration of formic acid in H2O/Pd (111) system. The hydrogen bond interaction between H 2O molecule and O and H atoms in formic acid changes the stable adsorption of formic acid on Pd surface. By searching the transition states in the catalytic cracking of formic acid, the results show that the formic acid C-OH bond is difficult to dissociate at the interface between aqueous solution and Pd metal, and only C-H bond dissociates this feasible reaction path. This reaction path is the decisive step in the formation of CO2 from formic acid. (2) the reaction process of formic acid in H2O/Pd (111) system in the presence of proton, proton and formate is calculated for the first time by using DFT method. The results show that in the presence of proton, both C-OH bond dissociation and C-H bond dissociation become structure-sensitive reactions, and the energy barrier required for C-OH bond dissociation decreases the H adsorption of C-H bond to the surface of Pd after the dissociation of 1.6eV C-OH bond compared with the absence of proton. In the presence of formate and proton, the dissociation of C-OH bond is easier, but the activation energy required for C-H bond dissociation is increased, and the existence of formic acid alone and protons is analyzed by charge density analysis. It was found that the electron cloud of formic acid affected the charge density of formic acid and the C-OH bond was cracked. It is concluded that the formation of CO and CO2 forms a competitive relationship. (3) the catalytic reaction mechanism of methanol on the surface of Pd and the possible pyrolysis steps are studied. The reactants, transition states, intermediates and products of the related reactions are calculated. The reaction channels of methanol cracking on the surface of Pd metal under neutral and alkaline conditions were investigated. The results show that methanol adsorbed on the surface of Pd is easy to be attacked by hydroxyl anion to get OCH2OH-,OCH2OH- OCH2O2- HCOO- and OCH2OH- HCOOH HCOO-, both of which are feasible, and their energy barriers are very low during the reaction. We have studied the dehydrogenation process of HCOO- ion. The results show that formaldehyde can be transformed into CO:H2CO CHO CO. through this reaction channel. The reaction mechanism of methanol to form CO and HCOO- on the surface of Pd electrode in alkaline environment is reasonable.
【學(xué)位授予單位】：武漢理工大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類號(hào)】：O643.31;TM911.4
本文編號(hào)：2277493
[Abstract]:Catalytic reaction mechanism is a very important research topic in the world, especially the reaction of solid / liquid interface on metal surface is a hot field. This research topic has been widely used in fuel cell and so on. In this paper, the mechanism of oxidation of formic acid and methanol in different media was studied by ab initio theory. This research direction has great potential in the application of fuel cells. In this paper, the generalized gradient approximation (DFT-GGA) of density functional theory is used to calculate the metal / water surface system. The feasibility of different reaction paths is studied by studying the activation energy of different organic compounds on the surface of the catalyst. The specific research contents are as follows: (1) in this paper, a detailed adsorption model of water molecules on metal surface was established by using vasp software package to study the effect on the catalytic decomposition of formic acid, and the reactants and intermediates in the reaction process were optimized. Transition state and the configuration of the product. The adsorption energy and different reaction channels of formic acid in H2O/Pd (111) system were studied. In this paper, the reactants and products of the reaction were optimized at the same base group level. The adsorption energy of formic acid on the surface of three layers of Pd atoms was calculated, and the transition states and intermediates of each reaction system were determined. The results show that hydrogen bond has a great influence on the adsorption configuration of formic acid in H2O/Pd (111) system. The hydrogen bond interaction between H 2O molecule and O and H atoms in formic acid changes the stable adsorption of formic acid on Pd surface. By searching the transition states in the catalytic cracking of formic acid, the results show that the formic acid C-OH bond is difficult to dissociate at the interface between aqueous solution and Pd metal, and only C-H bond dissociates this feasible reaction path. This reaction path is the decisive step in the formation of CO2 from formic acid. (2) the reaction process of formic acid in H2O/Pd (111) system in the presence of proton, proton and formate is calculated for the first time by using DFT method. The results show that in the presence of proton, both C-OH bond dissociation and C-H bond dissociation become structure-sensitive reactions, and the energy barrier required for C-OH bond dissociation decreases the H adsorption of C-H bond to the surface of Pd after the dissociation of 1.6eV C-OH bond compared with the absence of proton. In the presence of formate and proton, the dissociation of C-OH bond is easier, but the activation energy required for C-H bond dissociation is increased, and the existence of formic acid alone and protons is analyzed by charge density analysis. It was found that the electron cloud of formic acid affected the charge density of formic acid and the C-OH bond was cracked. It is concluded that the formation of CO and CO2 forms a competitive relationship. (3) the catalytic reaction mechanism of methanol on the surface of Pd and the possible pyrolysis steps are studied. The reactants, transition states, intermediates and products of the related reactions are calculated. The reaction channels of methanol cracking on the surface of Pd metal under neutral and alkaline conditions were investigated. The results show that methanol adsorbed on the surface of Pd is easy to be attacked by hydroxyl anion to get OCH2OH-,OCH2OH- OCH2O2- HCOO- and OCH2OH- HCOOH HCOO-, both of which are feasible, and their energy barriers are very low during the reaction. We have studied the dehydrogenation process of HCOO- ion. The results show that formaldehyde can be transformed into CO:H2CO CHO CO. through this reaction channel. The reaction mechanism of methanol to form CO and HCOO- on the surface of Pd electrode in alkaline environment is reasonable.
【學(xué)位授予單位】：武漢理工大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類號(hào)】：O643.31;TM911.4
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