The Reaction Mechanism Of Ethylene Glycol Decomposition On Different Morphology Pt Surface And Bimetallic Surface

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:C2H6O2â†'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:HOCH2CH2Oâ†'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:OCHCHOâ†'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:OCH2CH2Oâ†'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.