Kinetics and Mechanisms of hydrogenation of DMO Li Siming 2012.7.15
Mechanisms of ester hydrogenation M. Mokhtar et al. Only Cu0 acts as the active sites in ester hydrogenation E.K. Poels et al. Cu0 dissociatively adsorbs H2, Cu+ stabilizes the methoxy and the acyl species A.Y. Yinet.al. Cu+ may function as electrophilic or Lewis acid sites to polarize the C=O bond via the electron lone pair on oxygen. M. A. Kohleret al. The kinetics of the reaction were well described by a L-H model in which dissociatively adsorbed dimethyl succinate reacts with adsorbed molecular hydrogen. M. Mokhtar, C. Ohlinger, J. H. Schlander, T. Turek, Chemical Engineering & Technology 2001, 24, 423-426. E. K. Poels, D. S. Brands, Applied Catalysis A: General 2000, 191, 83-96. A. Yin, X. Guo, W.-L. Dai, K. Fan, The Journal of Physical Chemistry C 2009, 113, 11003-11013. M. A. Kohler, M. S. Wainwright, D. L. Trimm, N. W. Cant, Ind. Eng. Chem. Res. 1987, 26, 652-656.
J. A. Dumesic1 et al . The rate of reduction of n-alkyl acetates is determined by the dissociative adsorption of these molecules and by the surface hydrogenation of surface acyl species Dumesic1 et al .. Journal of Catalysis 2000. 193 16–28 .
B. Ju et al. The dissociative adsorption of Buthylbutyrate would be involved in the elementary steps for the hydrogenolysis reaction. The rate-determining step involves dissociative adsorption of butyl butyrate. I. B. Ju, W. Jeon, M.-J. Park, Y.-W. Suh, D. J. Suh, C.-H. Lee, Applied Catalysis A: General 2010, 387, 100-106.
Mechanisms of hydrogenation S. Sitthisa et al. molecular adsorption of furfural (FAL糠醛 ), furfuryl alcohol (FOL糠醇), and 2-methyl furan (MF) Dissociative adsorption of hydrogen Surface reaction is the rate-determining step. Crotonaldehyde(巴豆醛) adsorbed on Cu+ sites with hydrogen spilled over from Cu0 sites. Hydrogenation of an intermediate species as the rate-determining step . A. Dandekar et al. S. Sitthisa, T. Sooknoi, Y. Ma, P. B. Balbuena, D. E. Resasco, Journal of Catalysis 2011, 277, 1-13. A. Dandekar, R. T. K. Baker, M. A. Vannice, Journal of Catalysis 1999, 183, 131-154.
Mechanisms of DMO hydrogenation DMO dissociatively adsorb on the catalyst via cleavage of C–O bond The reaction mainly proceeds along Route (2), only small amounts of (B) will react along Route (1) Dissociative adsorption is slower than hydrogenation. MG will dissociatively adsorb on the active site of the catalyst. S. G. Hui, B. Zhang, S. H. Zhang, W. Li, J. Nat. Gas Chem. 2012, 21, 753-758.
DMO MG EG Ethanol ① dissociative adsorption ester/ H2 adsorption ② molecular adsorption ① ester adsorption control step ② H2 adsorption ③ Surface reaction Model of DMO hydrogenation Hydrogenation of DMO is a consecutive reaction. It involves: Assumptions: • The mechanism of DMO to MG is similar to that of MG to EG. • The activation energy of adsorption and desorption is independent of coverage rate (Langmuir homogeneous adsorption) 3. The control step is surface reaction, adsorption of reactants.
Previous work Figure 1. The correlation of Yields of EG with surface Cu0/(Cu0+Cu+) At first, the catalyst has only one active site, Cu0— H2 is activated, the reactant is adsorbed through the hydroxyl group and cleaved. Cu0 activates H2 , Cu+ species adsorbs DMO.
解离的甲氧基吸附在最优化的13个铜原子上 -ΔE (DFT)=130 kJ/mol -ΔE (DFT)=166 kJ/mol 通过红外研究和微量量热法得到的 吸附热可以得出甲醇/乙醇是解离吸 附在铜原子表面的。
实验值 [kJ/mol] 90-140 80-120 在相同过实验条件下，乙 氧基比甲氧基更易脱氢。 铜表面的甲氧基物种通常 与吸附的氢反应生成甲醇 并脱附，乙氧基物种趋于 脱氢生成乙醛。
通过红外研究和微量量热法得到的 吸附热可以得出乙酸乙酯/乙酸甲酯/ 乙酸是解离吸附在铜原子表面的。 活化能降低
MF FOL FAL • 假设： • FAL, FOL,MF——分子吸附 • 氢气——解离吸附 • 吸附与覆盖度无关 • 表面反应控制
-ΔH =11.9 kcal/mol Van’t Hoff 方程
Van’t Hoff 方程 吸附热： FAL：12.3 kcal/mol FOL： 6.9 kcal/mol Arrhenius方程： FAL FOL E1=11.8 kcal/mol 与DFT模拟 结果一致 FOL MF E2=12.4kcal/mol
环式吸附 不稳定 羰基吸附 垂直吸附 更强
Work plan 1. Choose conformable condition to make sure the catalyst have high activity 2. Finish the work about elimination of External/ Internal Diffusion effects 3. Measure the intrinsic reaction rate and select the most possible model.