CO与Pd_n(n=1-8)团簇的相互作用

Interaction of CO with Palladium Clusters Pd_n(n=1-8)

采用密度泛函理论对CO与钯团簇的相互作用进行了系统研究.结果表明,PdnCO(n=1-8)体系的最低能量结构是在Pdn(n=1-8)团簇最低能量结构或亚稳态结构的基础上吸附CO生长而成;CO的吸附以端位吸附为主,其吸附没有改变Pdn团簇的结构;CO分子在Pdn团簇表面发生的是非解离性吸附.与优化的CO键长(0.1166nm)相比,除了n=2,团簇PdnCO的C—O键长为0.1167-0.1168nm,吸附后C—O键长变化较小,CO分子被活化程度较小.电荷集居数分析表明,CO的吸附对Pdn团簇的影响比较小;二阶能量差分表明,n=4,6的团簇是相对稳定的团簇.

Adsorption of CO onto Pdo （n=1-8） dusters was systematically investigated using density functional theory. Results indicate that the lowest energy structures of PdnCO are still generated when CO is adsorbed onto Pdn clusters. We found that among the molecular adsorption states, a weakly bound state with end-on type geometry is the most energetically favorable. The lowest energy structures of Pdn clusters are not changed by adsorbing CO molecules. Chemisorption of CO onto Pdn cluster surfaces is a non-dissociative adsorption process. An increased theoretical CO bond length of 0.1167-0.1168 nm in PdnCO cluster （compared to 0.1166 nm in free CO molecule） indicates a small activation for the CO bond except for the case where n =2. Natural bond orbital analysis shows that the interaction between a Pd atom and a CO molecule is small. The second-order energy difference shows that Pd4CO and Pd6CO clusters have enhanced stabilities.