The redox mechanism of NpVI with hydrazine: a DFT studyElectronic supplementary information (ESI) available: The structures and related bond length of all species in the Pathways I, II and III (Fig. S1, S2 and S4 respectively), Np-O bond length of [NpVIO2(H2O)5]2+ and [NpVO2(H2O)5]2+ (Table S1), the QTAIM parameters and ELF pictures of Pathways II and III (Tables S2 and S4, Fig. S3 and S5) as well as the WBIs and Mayer bond orders (Table S3) are provided. See DOI: 10.1039/c6ra13339h

• Main Authors: Cheng, Zhong-Ping, Wu, Qun-Yan, Liu, Yun-Hai, Lan, Jian-Hui, Wang, Cong-Zhi, Chai, Zhi-Fang, Shi, Wei-Qun
• Format: Article
• Language: English
• ISSN: 2046-2069
• DOI: 10.1039/c6ra13339h

Valence state control and adjustment of neptunium in spent fuel reprocessing is very important for improving the separation efficiency of U/Np and Np/Pu. Hydrazine and its derivatives have been experimentally demonstrated to be effective in the reduction of Np VI to Np V . In this work, hydrazine was used as a representative reductant and the reduction mechanisms of Np VI induced by hydrazine were investigated using density functional theory (DFT) calculations. Three reaction pathways were taken into account and characterized by gradually transferring a hydrogen atom from N 2 H 4 to the "yl"-oxygen of [Np VI O 2 (H 2 O) 5 ] 2+ followed by the valence state adjustment from Np VI to Np V . The calculated results of the potential energy profiles (PEPs) revealed that Pathway I should be the most likely to occur as the process of forming &z.rad;N 2 H 3 is considered to be the rate-determining step with the highest energy barrier of 32.02 kcal mol −1 , which is in favor of the experimental results. Pathway II hardly occurs and Pathway III probably occurs. The bonding evolution, along with the reaction pathways, was explored through natural bond orbitals (NBOs), quantum theory of atoms-in-molecules (QTAIM) and electron localization function (ELF) analyses. This work can shed light on the understanding of redox mechanisms of Np VI with N 2 H 4 and its derivatives and help further attempts to design more efficient reductants for the separation of U/Np and Np/Pu in spent nuclear fuel reprocessing in the near future. The probable reduction mechanisms of Np VI with N 2 H 4 are investigated by proposing three probable pathways based on the results of theoretical calculations.