Ag_2~-催化CO氧化反应机理的理论研究

用密度泛函理论B3LYP方法详细研究了Ag_2~-催化CO氧化反应的机理.计算结果表明,O2分子在Ag_2~-和Au_2~-上吸附能相差不大,而CO分子在Ag_2~-上吸附要比在Ag_2~-上弱得多.Ag_2~-催化CO氧化反应共有四条反应途径.最可能反应通道为CO插入Ag2O_2~-中的Ag—O键形成中间体Ag—AgC(O—O)O]-,然后直接分解形成产物CO2和Ag2O-,或另一分子CO进攻中间体Ag—AgC(O—O)O]-形成两分子产物CO2和Ag_2~-.在动力学上最难进行的反应通道为经历碳酸根双银中间体,需要克服约0.24eV的能垒.Ag_2~-催化CO氧化反应活性要高于Au_2~-.

Theoretical Study on Mechanism of CO Oxidation Catalyzed by Ag_2~-

The mechanism of Ag_2~--catalyzed CO oxidation was investigated at the level of B3LYP theory.The computational results indicate that the absorption energy of O_2 on Ag_2~- is close tp that of O_2 on Au_2~-,while the absorption of CO on Ag_2~- is stronger than that of CO on Au_2~-,There are four reaction pathways for CO oxidation catalyzed by Ag_2~-.The most feasible pathway is the CO insertion into the Ag-O bond of Ag_2~- to produce an intermediate Ag-AgC(O-O)O]~-,and then the intermediate Ag-AgC(O-O)Q]~-decomposes into product CO_2 and Ag_2~-,or another CO molecule attacks Ag-AgC(O-O)O]~- to form two C0_2 molecules and Ag_2 anion.The most difficult pathway is the di-silver carbonate intermediate pathway,which needs to overcome a total energy barrier of about 0.24 eV.Since for gold,the carbonate-like intermediate pathway requires an activation barrier of 0.61 eV,silver proves to be a better catalyst than gold.