Ag表面乙醇选择性催化氧化的密度泛函理论研究

Density functional study of selective oxidation of ethanol over silver catalysts

采用密度泛函理论计算对Ag(111)和Ag(211)表面乙醇催化氧化过程进行了系统性研究。研究发现原子氧物种是常温下乙醇氧化的关键中间体。在表面原子氧物种辅助下,乙醇O—H键和α-C—H键依次断裂,生成乙氧基中间体和乙醛产物(活化能(Ea)<38.0kJ/mol)。乙醛随后与表面原子氧和羟基氧物种作用,导致CCOO(在Ag(111)表面发生CCOO→C+CO2)和CH2COO(在Ag(211)表面发生CH2COO→CH2+CO2)中间体C—C键断裂生成CO2,该过程是速率控制步骤(Ea>95.5kJ/mol)。计算结果表明乙醇在Ag表面催化氧化过程为结构敏感反应,降低表面缺陷位数量可提高产物中乙醛选择性。

A systematic study on the catalytic oxidation of Ag(111) and Ag(211) on the surface of Ag(111) was carried out by density functional theory.It was found that atomic O* is necessary to initiate the reaction at the ambient conditions.The O-H bond in the ethanol is activated with the help of adsorbed atomic O* to form ethoxy, which then further transfers hydrogen in α-C-H to adsorbed O* forming the acetaldehyde (Ea<38 kJ/mol),which, in turn,reacts with atomic O*/OH* to form final product CO2.To generate CO2,C-C bond breaking (CCOO→C+ CO2 on Ag(111) and CH2COO→CH2+ CO2 on Ag(211)) exhibits the highest barriers (Ea>95.5 kJ/mol),which indicated it is the rate-determining step.The results indicate that the catalytic oxidation of ethanol on silver surfaces is structural sensitive.Selectivity towards value-added products like acetaldehyde would be improved by reducing the density of defected sites.