Kinetics and Mechanisms of hydrogenation of DMO

Li Siming2012.7.15

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. Yin et.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. Kohler et 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.

Mechanisms of ester hydrogenation

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 butylbutyrate.

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.

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.

S. Sitthisa et al. molecular adsorption of furfural (FAL 糠醛 ), furfuryl

alcohol (FOL 糠醇 ), and 2-methyl furan (MF) Dissociative adsorption of hydrogenSurface 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.

Mechanisms of hydrogenation

Mechanisms of DMO hydrogenation

S. G. Hui, B. Zhang, S. H. Zhang, W. Li, J. Nat. Gas Chem. 2012, 21, 753-758.

DMO dissociatively adsorb on the catalyst via cleavage of C–O bondThe 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.

Model of DMO hydrogenation

Hydrogenation of DMO is a consecutive reaction. It involves:

DMO MG EG Ethanol

Assumptions:

1. The mechanism of DMO to MG is similar to that of MG to EG.

2. 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.

① ester adsorption

control step

② H2 adsorption

③ Surface reaction

① dissociative adsorption ester/ H2

adsorption

② molecular adsorption

At first, the catalyst has only one active site, Cu0— H2 is activated, the reactant is adsorbe

d through the hydroxyl group and cleaved.

Cu0 activates H2 , Cu+ species adsorbs DMO.

Figure 1. The correlation of Yields of EG with surface Cu0/(Cu0 +Cu+)

Previous work

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。

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。

实验值 [kJ/mol]90-14080-120

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

FAL FOL MF

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

L—H 模型：

-ΔH =11.9 kcal/mol Van’t Hoff 方程

Arrhenius 方程：FAL FOL E1=11.8 kcal/molFOL MF E2=12.4kcal/mol

与 DFT 模拟 结果一致

吸附热： FAL ： 12.3 kcal/mol FOL ： 6.9 kcal/mol

Van’t Hoff 方程

Adsorption of furfural on Cu(1 1 1)

环式吸附不稳定

垂直吸附

更强

羰基吸附

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.