糠醛在Pt(111)表面的吸附和脱碳反应

采用广义梯度近似的密度泛函理论并结合平板模型的方法, 优化了糠醛分子在Pt(111)面的吸附模型,并探究了糠醛脱碳反应形成呋喃的机理. 结果表明: 吸附后糠醛分子环上的C―H(O)键及支链―CHO相对于金属表面倾斜上翘, 分子平面被扭曲, 易于呋喃的形成; 同时, 糠醛分子向Pt表面转移电子0.765e, 环中的大π键与Pt(111)表面的d轨道发生较强的相互作用, 使得糠醛的芳香性被破坏, 环上的碳原子呈现准sp³杂化. 此外, 对糠醛脱碳反应中的各反应步骤进行过渡态搜索, 通过比较各步骤的活化能, 得出糠醛更易先失去支链上的H形成酰基中间体(C₄H₃O)CO, 中间体继续脱碳加氢形成产物呋喃. 该过程的控速步骤为(C₄H₃O)CO^*+^*→C₄H₃O^*+CO^* (^*为吸附位),活化能为127.65 kJ·mol^-1.

Adsorption and Decarbonylation Reaction of Furfural on Pt(111) Surface

The reaction mechanismof furan formation during decarbonylation of furfural on the Pt(111) plane was investigated by density functional theory generalized gradient approximation calculations with the slab model. The adsorption energy of furfural was calculated to determine preferred adsorption sites on the Pt(111) plane. The revealed possible mechanisms for the decarbonylation of furfural on the Pt(111) plane were studied. The results showed that a furfural molecule loses 0.765 electrons after adsorption on the Pt(111) surface. The d orbitals of the metal surface interact strongly with the π bonds of the furfural ring. This reduced the aromaticity of the furfural ring and the Catoms showed characteristics consistent with sp³ hybridization. The molecular plane of the adsorbate was distorted, and corresponding changes of bond lengths were found. The C―H(O) bonds and―CHO of furfural tilted away from the Pt surface. The calculations showthat furan was a possible product of the decarbonylation reaction. We then searched the transition states (TSs) and reaction potential energy surfaces with the linear and quadratic synchronous transit (LST/QST) complete search. By comparing energy barriers, we obtained the optimal path, which involved furfural forming an acyl intermediate by loss of the Hatom from the branched chain rather than direct decarburization. Furan was then formed by decarburization and hydrogenation of the acyl intermediate. The calculated barrier for the rate-determining step(C₄H₃O)CO^*+^*→C₄H₃O^*+ CO^* (^* is adsorption site) is 127.65 kJ·mol^-1.