Au(111)面上噻吩加氢脱硫反应机理的理论研究

采用密度泛函理论方法研究了噻吩在Au(111)面上的吸附模式, 并探讨了其在Au(111)面上可能的加氢脱硫反应机理, 对不同机理下各个基元反应的过渡态进行了筛选, 得到了各个步骤的能量变化及所需活化能.计算结果表明, 噻吩在Au(111)面上以S端倾斜吸附在Top位时最稳定.直接脱硫机理表明, 其所需活化能较低, 升高温度有利于提高脱硫反应产率, 但脱硫产物较难控制; 间接脱硫机理表明, 脱硫反应最可能按照加氢异构方式进行, 降低温度有利于脱硫反应产率的提高.随着反应的进行, 噻吩环中的C—S键键长逐渐增大, 键能逐渐减小, 有利于C—S键断裂, 具体步骤为:(1) C₄H₄S+H₂α,α-C₄H₆S; (2) α,α-C₄H₆S+H₂C₄H₈S; (3) C₄H₈S+H₂C₄H₁₀+S, 其中S原子的脱去步骤所需活化能最高, 为反应的限速步骤.

Theoretical Studies on Reaction Mechanism of Hydrodesulfurization of Thiophene Catalyzed by Au(111) Plane

The adsorption of thiophene molecule at Au(111) and its mechanism of hydrodesulfurization were elucidated by desity functional theory(DFT) method. All the pertinent species of different mechanisms have been gathered to obtain their preferred adsorption sites. The activation energy and reaction energy of each steps in different mechanisms also have been calculated. The results show that the adsorption at the Top site is most stable when the thiophene plane tilt to the Au(111) surface with S atom. The direct hydrodesulfurization mechanism has a low energy of activation and high temperature is helpful for the hydrodesulfurization reaction, but it is difficult to control the products. The mechanism of indirect hydrodesulfurization is best fit for the hydroisomerization process. The reaction heat of hydrodesulfurization is negative, so reducing the temperature is helpful for the reaction. During the process, the bond length of C—S in thiophene increases gradually when the bond energy of C—S decreases. All of these changes are helpful to the cleavage of C—S. The most feasible reaction pathway is (1) C₄H₄S+H₂α,α-C₄H₆S, (2) α,α-C₄H₆S+H₂C₄H₈S, (3) C₄H₈S+H₂C₄H₁₀+S. Among different steps, the removal of S is the rate-determining step.