a 大连理工大学 石油与化学工程学院 精细化工国家重点实验室 盘锦 124221;
b 辽宁科技大学 化学工程学院 鞍山 114051
Dehydrogenation Mechanism of Ethanol on Co(111) Surface: A First-principles Study
Fu Wenwenaa, Li Yanb, Liang Changhaia
a State Key Laboratory of Fine Chemicals, School of Petroleum and Chemical Engineering, Dalian University of Technology, Panjin 124221;
b School of Chemical Engineering, University of Science and Technology Liaoning, Anshan 114051
The detailed reaction mechanism of ethanol dehydrogenation on Co(111) surface was studied using the density functional theory (DFT) and slab periodic model. The structures and energies of the species involved in the reaction adsorbed on different adsorption sites (top, fcc, hcp and bridge sites) of the surface were calculated and compared. The calculated results show that ethanol adsorbs weakly on the Co(111) surface. CH3CH2O, CH and C prefer hcp sites with adsorption energies of -2.72 eV, -6.85 eV, and -6.92 eV, respectively. CH3CHO adsorbs weakly at the bridge-η1(O)-η1(Cα) site with adsorption energy of -0.47 eV. CH3CO and CH2 adsorb stably on Co(111) surface through their unsaturated C atoms with binding energies of -2.31 eV and -3.90 eV, respectively. CH3 and CH4 prefer to locate at top sites through the C atom with adsorption energies of -1.95 eV and -0.12 eV, respectively. CO and H are bind stably at fcc sites with binding energies of -1.62 eV and -2.77 eV, respectively. Due to the complexity of the decomposition of ethanol, the scissions of O-H, C-H, C-O and C-C bonds of CH3CH2OH were examined. The results show that ethanol decomposition on Co(111) surface starts with the scission of the O-H bond, and the dehydrogenation reaction of ethanol on Co(111) surface can be described as three reaction pathways: Path I is the gradual dehydrogenation of CH3CH2OH via intermediate CH3CHO, which ultimately produces CH4 and CO; Path II is the reaction of CH3CH2O and CH3CHO which were generated by dehydrogenation of ethanol, to form CH4 and CO2 via CH3COOH intermediate; Path III is the process of CH3CH2O reacts with CH3CO to generate CH3COOC2H5. On the basis of our computational results, Path I (CH3CH2OH → CH3CH2O → CH3CHO → CH3CO → CH3+CO → CH2 → CH → CH4+CO+C+H) is more favorable than Paths II and III and the dehydrogenation of CH3CH2O to CH3CHO is the rate-determining step with a reaction energy barrier of 1.61 eV.