Au(111)面上肉桂醛的选择性加氢机理

采用密度泛函理论并结合周期性平板模型的方法,优化了肉桂醛在Au(111)面上的吸附模型,并详细探讨了肉桂醛在Au(111)面上选择性加氢的反应机理(C=O,C=C以及1,4共轭加成机理).计算结果表明,肉桂醛以C=O和C=C协同吸附于Au(111)面上时,吸附构型最稳定.此时,不同吸附模式的吸附能平均在140.0kJ?mol-1.通过搜索不同机理下每个基元反应的过渡态,得出肉桂醛在Au(111)面上最可能的选择性加氢产物为苯丙醛,且其按照1,4共轭加成机理间接得到苯丙醛比C=C直接加氢机理具有更低的活化能.具体反应过程为:肉桂醛C=O的O优先加H形成烯丙基型中间体,继而该中间体中与苯环相连的C原子继续加H形成烯醇(ENOL),最终烯醇异构成苯丙醛.其中ENOL的生成过程所需的活化能最高,是反应的控速步骤.

Selective Hydrogenation Mechanism of Cinnamaldehyde on Au(111) Surface

The adsorption behavior and selective hydrogenation reaction mechanisms (C=O addition, C=C addition, and 1,4-conjugate addition) of cinnamaldehyde on an Au(111) surface were investigated by density functional theory combined with a periodic slab model. The adsorption energies of various adsorption models were obtained to determine the preferred adsorption configuration. The calculated results indicate that the most stable adsorption configuration involved the C=O and C=C double bond adsorbed on the Au(111) surface, with an average adsorption energy of 140.0 kJ·mol^-1. The transition states of each elementary reaction for all possible reaction mechanisms were also located. Comparison of the activation energy barriers revealed hydrocinnamaldehyde (HCAL) to be the most likely selective hydrogenation product of cinnamaldehyde on an Au(111) surface. In addition, the 1,4- conjugate addition mechanism, which generates 3-phenyl-1-propen-1-ol (ENOL) that readily tautomerizes to HCAL, required less activation energy than did the C=C direct addition mechanism. The dominant reaction pathway involved an O atom of cinnamaldehyde preferentially hydrogenating to generate a more stable allyl intermediate. Another H atom then added to a C atom directly connected to the phenyl ring of the allyl intermediate to yield ENOL. Finally, ENOL tautomerized to HCAL. Throughout the process, the generation of ENOL is the rate-determining step, for which the highest activation energy barrier was required.