【作者】 杨博；

【导师】 庞先勇；

【作者基本信息】 太原理工大学 ， 高分子化学与物理， 2014， 硕士

【摘要】 本文在第一性原理量子力学计算基础上,应用VASP软件包,在广义梯度近似(GGA) PAW-91密度泛函理论(DFT)水平上,结合平板模型,研究了乙二醇在纯Pt和Pt-Ni、Pt-Au等双金属合金不同晶面及同一晶面不同形貌表面上的吸附及分解反应机理,为之后的研究提供理论参考,具体结论如下：1)Pt(111)上：第一步乙二醇分子吸附在表面,O-H键解离得到了HOCH2CH2O中间体,活化能为0.64eV；第二步C-H键断裂得到HOCH2CHO中间体,活化能为0.27eV；第三步C-H解离得到了HOCH2CO中间体,此过程的活化能为0.32eV；.第四步是O-H断裂,生成了OCH2CO中间体(活化能0.51eV)；第五步是C-H断裂得到了OCHCO中间体,反应活化能为0.07eV,是一个瞬时完成的反应,此时C-C键发生断裂,活化能为0.49eV生成了CO和HCO。可以看出在Pt(111)上乙二醇完全分解的控速步骤为：C2H6O2→HOCH2CH2O+H。2)Pt(100)上：第一步也是从活化能为0.37eV的O-H解离开始,但从次级脱氢开始,反应路径与Pt(111)上不同,Pt(100)上第二步即次级脱氢后得到了OCH2CH2O中间体,此过程的活化能为0.41eV,第三步C-H解离,得到OCHCH2O,活化能为0.29eV；第四步继续C-H断裂得到OCCH2O中间体,活化能大小为0.24eV。第五步OCCH2O中间体发生C-C断裂得到了CO和H2CO(甲醛),此反应的活化能为0.31eV。其控速步骤为：HOCH2CH2O→OCH2CH2O+H。3)Pt(211)：第一步乙二醇分子吸附在表面,O-H解离,活化能为0.28eV得到HOCH2CH2O中间体；之后第二步还是O-H解离,反应活化能为0.46eV,生成OCH2CH2O;第三步OCH2CH2O中间体发生C-H断裂反应,生成OCHCH2O中间体,此反应活化能为0.43eV；第四步又是C-H解离,反应活化能为0.22eV,得到了OCHCHO中间体；第五步OCHCHO中的C-C断裂,活化能为0.79eV。至此,乙二醇中的C-C在Pt(211)断裂。控速步骤为：OCHCHO→HCO+HCO。4) Pt(111)-double-step:第一步O-H解离,得到HOCH2CH2O,活化能为0.49eV；第二步依然是O-H断裂,活化能为0.52eV生成OCH2CH2O中间体；第三步OCH2CH2O继续解离,C-H断裂,反应活化能为0.54eV,产生OCHCH2O中问体；第四步继续C-H断裂得到OCCH2O中间体,该反应的活化能为0.26eV；第五步OCCH2O此时发生C-C解离,活化能大小为0.40eV得到了CO和甲醛(H2CO)。乙二醇在Pt(111)-double-step上的分解路径与Pt(100)相同。其控速步骤为：OCH2CH2O→OCHCH2O+H。5) Ni/Pt(111):第一步反应为O-H断裂,活化能0.36eV,得到HOCH2CH2O中间体。之后HOCH2CH2O发生O-H解离得到OCH2CH2O中间体,活化能大小为0.25eV。6) Pt-Ni-Pt(111)：第一步同样为O-H解离,活化能为0.93eV。HOCH2CH2O中间体发生C-H断裂(与Pt(111)上相同)得到HOCH2CHO,活化能0.48eV。7) Pt/Au(111)：第一步O-H断裂,得到HOCH2CH2O中间体,活化能为0.49eV。第二步HOCH2CH2O中间体O-H断裂,活化能为0.45eV,得到OCH2CH2O中间体。8) Pt-Au-Pt(111):第一步O-H解离,得到HOCH2CH2O中间体,活化能为0.52eV。之后C-H解离,得到HOCH2CHO中间体,活化能为0.38eV。更多还原

【Abstract】 In this thesis, the reaction mechanism that adsorption and decomposition of ethylene glycol on different plane surface of pure Pt, Pt-Ni and Pt-Au bimetallic alloy has been studied by the first principle quantum mechanism calculations at the level of generalized gradient approximation (GGA) of density functional theory (DFT) with slab model. the specific conclusions are as follows:1) Pt (111):firstly, the molecule of ethylene glycol adsorbed on the surface, O-H bond dissociation, the activation energy is0.64eV obtained HOCH2CH2O intermediate, then C-H bond cleavage formed HOCH2CHO intermediate, the activation energy is0.27eV. C-H been continued HOCH2CO intermediate dissociation activation energy of this process is0.32eV. Followed by O-H fracture OCH2CO intermediate was generated (activation energy of0.51eV). Followed by C-H fracture, intermediates OCHCO was formed, the reaction activation energy was only0.07eV, indicated that this reaction is almost instantaneous finish. C-C bond rupture occurred at this time and then generated CO and HCO, the activation energy is0.49eV. As can be seen in the Pt(111) on the complete decomposition of ethylene glycol speed control steps:C2H6O2→HOCH2CH2O+H. 2) Pt(100):The first step to start from O-H dissociation, the activation energy is0.37eV, but the beginning of secondary dehydrogenation different with Pt(111) on the reaction path, Pt (100) to get the last stage dehydrogenation the OCH2CH2O intermediates, the activation energy for this process is0.41eV, followed by dissociation of C-H get OCHCH2O, activation energy of0.29eV. C-H fracture continues to get OCCH2O intermediate, the activation energy is0.24eV. C-C rupture on OCCH2O intermediates occurred CO and H2CO (formaldehyde), the activation energy for this reaction is0.31eV. Its speed control steps:HOCH2CH2O→OCH2CH2O+H.3) Pt (211):glycol molecules adsorbed on the surface, O-H dissociation, the activation energy is0.28eV get HOCH2CH2O intermediates. Then O-H dissociation, the activation energy of0.46eV, generates OCH2CH2O. OCH2CH2O intermediate C-H cleavage occurs, resulting OCHCH2O intermediates, reaction activation energy of0.43eV. Came to the C-H dissociation, the activation energy of0.22eV, has been formed OCHCHO intermediates.Finally, the C-C rupture, the activation energy is0.79eV. Speed control steps:OCHCHO→HCO+HCO.4) Pt (111)-double-step:O-H First dissociation get HOCH2CH2O, activation energy of0.49eV, O-H remains after fracture, the activation energy is0.52eV to continue to generate an intermediate OCH2CH2O, C-H breaking activation energy of0.54eV, generation OCHCH2O intermediates obtained OCCH2O fracture continues intermediate C-H activation energy of the reaction is0.26eV. C-C dissociation occurs at this time, the size of the activation energy is0.40eV was formed CO and formaldehyde (H2CO). The decomposition path is same with Pt(100). Its speed control steps:OCH2CH2O→OCHCH2O+H.5) Ni/Pt (111):The first reaction step is O-H breaking activation energy0.36eV, to get the intermediate HOCH2CH2O. O-H dissociation occurs after HOCH2CH2O get OCH2CH2O intermediate size of the activation energy0.25eV.6) Pt-Ni-Pt (111):The same first step is O-H dissociation activation energy of0.93eV. HOCH2CH2O intermediate C-H rupture occurred (and Pt (111) on the same) to get HOCH2CHO, the activation energy is0.48eV.7) Pt/Au (111):OH rupture to get intermediate HOCH2CH2O, activation energy is0.49eV. HOCH2CH2O intermediate O-H fracture, the activation energy is0.45eV, formed OCH2CH2O intermediates.8) Pt-Au-Pt (111):Firstly, the dissociation of O-H to be intermediate HOCH2CH2O activation energy is0.52eV. After the C-H dissociation, get HOCH2CHO intermediates, activation energy is0.38eV.9) The first step of decomposition on all selective surface are O-H broken, there are different paths from after the start of the second step, the intermediate portion to generate HOCH2CHO part to generate OCH2CH2O intermediate. By comparison, the more active Ni/Pt(111) and Pt/Au(111), the secondary dehydrogenation intermediate OCH2CH2O easily obtained. In pure Pt surface with different morphologies, such as Pt (100), Pt(211), Pt(111)-double-step, the same get OCH2CH2O intermediates, which shows the structure of the sensitivity of ethylene glycol.更多还原