金催化CO氧化湿度增强效应的理论研究

Theoretical study of the moisture-enhanced catalysis of CO oxidation over Au nanoparticles

实验发现纳米金催化的CO氧化有良好的湿度增强效应,但有关机制仍不清楚.我们应用密度泛函理论研究了湿度增强效应的微观机制,以Au4团簇为例,研究了金催化CO氧化的微观机理,考察了H2O在反应中的角色和作用.计算结果表明,H2O与Au4团簇一样,在反应中扮演催化剂的角色,参与反应的进行、改变反应历程、降低反应能垒.催化循环包含4个基元步骤:O2+H2O→OOH+OH,CO+OOH→CO2+OH,CO+OH→COOH,和COOH+OH→CO2+H2O,其中自由基OOH和OH的形成是催化循环的速控步骤,其能垒为100.31kJ/mol,明显低于非水参与反应的能垒(161.41kJ/mol).目前的结果合理地解释了实验观测的CO催化氧化的湿度增强效应,给出了其微观反应机制.

While Au nanoparticles were found to exhibit the moisture-enhanced catalysis towards low-temperature CO oxidation,the debate concerning the mechanism has still not been resolved.This work studies the microcosmic mechanism of the moisture-enhanced catalysis using density function theory.The Au4 cluster was used as an example to determine the mechanism of CO oxidation and the role of H2O plays in the reaction.The result indicates that,like the Au4 cluster,H2O also functions as a catalyst which lowers the activation barrier by altering the pathway of the reaction.The catalytic cycle includes four elementary steps：O2＋H2O→OOH＋OH,CO＋OOH→CO2＋OH,CO＋OH→COOH,and COOH＋OH→ CO2＋H2O.Among them,the formation of the free radicals OOH and OH is the rate-determing step of the reaction,whose barrier is 100.31 kJ/mol and lower than that（161.41 kJ/mol） of the reaction where the water molecule does not participates.The present results rationally explain the moisture-enhanced catalysis observed by experiments and predicted the mechanism of the reaction at the molecular level.