Theoretical Studies of the Dehydrogenation of Ethanol and Water-Gas Shift Reaction Mechanisms on a 2Ru/γ-Al2O3(110) Surface
| Autor: | Cheng-Hao Liao, 廖正豪 |
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| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 97 We applied periodic density-functional theory (DFT) to investigate the mechanism of ethanol dehydrogenation and water gas shift (WGS) reaction on a 2Ru/Al2O3 (110) surface. A structure with ethanol adsorbed with its O atom attached to the Al atom and βC terminal near by the Ru atom is calculated to exhibit the most stable adsorbed structure, which we name the βC path. The sequence of bond scission is βC–H → C-O that eventually forms CH2CH2(a) + OH(a) + H(a) on the surface, with respect to the barriers：0.109 → 1.159 eV. Another structure adsorbed via the O atom attached to the Al atom and αC terminal near by the Ru atom that exhibits the second stable adsorbed structure, which we name the αC-Ru path. The sequence of bond scission is αC-H → O-H → αC-H → C-C → βC-H, and eventually forms CH2(a) + CO(a) + 4H(a) on the surface, with respect to the barriers： 0.234 → 0.992 → 0.349 → 0.899 → 0.223 eV. These calculated results indicate that the DFT calculation corresponds with the experiment. There are two mainly mechanisms in water-gas-shift reaction:(1) carboxyl mechanism; (2) redox mechanism. Before water gas shift reaction we calculate the site with greatest adsorption energy of one CO and H2O molecule on the surface. After the H2O molecule dissociate into H(a) + OH(a), the reaction is blocked by a huge barrier over 2 eV to proceed the WGS reaction of next step. Then we put three H2O molecules on the Al atoms of the first layer on the surface, trying to discuss the water-gas-shift reaction. Based on DFT calculations, it is found that the water gas shift reaction prefers the redox mechanism on a 2Ru/γ-Al2O3(110) surface. It starts with the path: OH(a) → H(a) + O(a), which has a 1.219 eV barrier. And then form carbon dioxide: CO(a) + O(a) → CO2(a) with a barrier of 1.497 eV. The barriers of carboxyl mechanism are higher than that of the redox mechanism, and its local minimum is also less stable. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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