The mechanism of the CO oxidation promoted by a neutral Ag(55) cluster was investigated extensively, using density functional theory calculations. The CO oxidation process catalyzed by anionic and cationic Ag(55) clusters was also studied, to clarify the effects of the charge state. The Eley-Rideal (ER) and Langmuir-Hinshelwood (LH) mechanisms were discussed in detail. Six reaction pathways were found for the Ag(55)-mediated CO oxidation. It was found that the ER mechanism competed with the LH mechanism. The rate-limiting step of the CO oxidation was the reaction of CO with the Ag(55)O species. All of the anionic, neutral, and cationic Ag(55) clusters were able to promote CO oxidation at low temperatures. The present results enrich our understanding of the catalytic oxidation of CO by nano-sized Ag-based catalysts.
There are several approaches to evaluation of an electron-transfer (ET) matrix element. Among them, Koopmans' theory is a relatively simple one and can be used for large molecules. However, a limitation of this method is the application to some cases of a small donor-acceptor distance. In such cases, Koopmans' theory has been found to behave badly. The reasons of the failure are discussed in the present work. Investigation shows that the two orbitals included must be properly selected in evaluating the ET matrix element. It has been concluded that the sum of two relevant orbitals should be localized on the donor (acceptor), but the difference between them should be localized on the acceptor (donor). Different types of ET systems have been selected to show how to correctly employ Koopmans' theory to small donor-acceptor distance cases. According to our work, one can find what is the reason leading to the failure of Koopmans' theory, and it is suggested that such failures can be avoided by tracing the energy change of the frontier molecular orbitals against the donor-acceptor distance.
The rates of the electron self-exchange between uranyl(VI) and uranyl(V) complexes in solution have been investigated in detail with quantum chemical methods. The calculations have shown that the bond length of UOOyl is elongated by 0.1 Å when the extra electron is localized on the sites. The diabatic potential surfaces are obtained. The inner reorganization energies are 212.6 and 226.8 kJ mol Ϫ1 for hydroxide and fluoride bridge systems, respectively. The solvent reorganization energies are 28.12 and 31.60 kJ mol Ϫ1 for hydroxide and fluoride bridge systems, respectively. The nuclear frequency factors are 3.17 ϫ 10 13 and 3.12 ϫ 10 13 s Ϫ1 for hydroxide and fluoride bridge systems, respectively. The electronic coupling matrix elements are 1.89 and 4.06 kJ mol Ϫ1 for hydroxide and fluoride bridge systems, respectively. The electron-transfer rates of our calculations are 12.95 and 0.819 M Ϫ1 s Ϫ1 for hydroxide and fluoride bridge systems, respectively.
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