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Li XB, Wu QY, Wang CZ, Lan JH, Zhang M, Chai ZF, Shi WQ. Unveiling the Reduction Mechanism of Pu(IV) by Acetaldoxime. J Phys Chem A 2023; 127:7479-7486. [PMID: 37668451 DOI: 10.1021/acs.jpca.3c03830] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/06/2023]
Abstract
The separation of plutonium (Pu) from spent nuclear fuel was achieved by effectively adjusting the oxidation state of Pu from +IV to +III in the plutonium uranium reduction extraction (PUREX) process. Acetaldoxime (CH3CHNOH) as a free salt reductant can rapidly reduce Pu(IV), but the reduction mechanism remains indistinct. Herein, we explore the reduction mechanism of two Pu(IV) ions by one CH3CHNOH molecule, where the second Pu(IV) reduction is the rate-determining step with the energy barrier of 19.24 kcal mol-1, which is in line with the experimental activation energy (20.95 ± 2.34 kcal mol-1). Additionally, the results of structure and spin density analyses demonstrate that the first and second Pu(IV) reduction is attributed to hydrogen atom transfer and hydroxyl ligand transfer, respectively. Analysis of localized molecular orbitals unveils that the reduction process is accompanied by the breaking of the Pu-OOH bond and the formation of the OOH-H and C-OOH bonds. The reaction energies confirm that the reduction of Pu(IV) by acetaldoxime is both thermodynamically and kinetically accessible. In this work, we elucidate the reduction mechanism of Pu(IV) with CH3CHNOH, which provides a theoretical understanding of the rapid reduction of Pu(IV).
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Affiliation(s)
- Xiao-Bo Li
- Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, College of Nuclear Science and Technology, Harbin Engineering University, Harbin, Heilongjiang 150001, China
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
| | - Qun-Yan Wu
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
| | - Cong-Zhi Wang
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
| | - Jian-Hui Lan
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
| | - Meng Zhang
- Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, College of Nuclear Science and Technology, Harbin Engineering University, Harbin, Heilongjiang 150001, China
| | - Zhi-Fang Chai
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
| | - Wei-Qun Shi
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
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Li XB, Wu QY, Wang CZ, Lan JH, Zhang M, Gibson JK, Chai ZF, Shi WQ. Reduction of Np(VI) with hydrazinopropionitrile via water-mediated proton transfer. Phys Chem Chem Phys 2022; 24:17782-17791. [PMID: 35848639 DOI: 10.1039/d2cp01730j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Effectively adjusting and controlling the valence state of neptunium (Np) is essential in its separation during spent fuel reprocessing. Hydrazine and its derivatives as free-salts can selectively reduce Np(VI) to Np(V). Reduction mechanisms of Np(VI) with hydrazine and four derivatives have been explored using multiple theoretical methods in our previous works. Herein, we examine the reduction mechanism of Np(VI) with hydrazinopropionitrile (NCCH2N2H3) which exhibits faster kinetics than most other hydrazine derivatives probably due to its σ-π hyperconjugation effect. Free radical ion pathways I, II and III involving the three types of hydrazine H atoms were found that correspond to the experimentally established mechanism of reduction of two Np(VI) via initial oxidation to [NCCH2N2H3]+˙, followed by conversion to NCCH2N2H (+2H3O+) and ultimately to CH3CN + N2. Potential energy profiles suggest that the second redox stage is rate-determining for all three pathways. Pathway I with water-mediated proton transfer is energetically preferred for hydrazinopropionitrile. Analyses using the approaches of localized molecular orbitals (LMOs), quantum theory of atoms in molecules (QTAIM), and intrinsic reaction coordinate (IRC) elucidate the bonding evolution for the structures on the reaction pathways. The results of the spin density reveal that the reduction of the first Np(VI) ion is the outer-sphere electron transfer, while that of the second Np(VI) ion is the hydrogen transfer. This work offers new insights into the nature of reduction of Np(VI) by hydrazinopropionitrile via water-mediated proton transfer, and provides a basis for designing free-salt reductants for Np separations.
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Affiliation(s)
- Xiao-Bo Li
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China. .,Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, College of Nuclear Science and Technology, Harbin Engineering University, Harbin, Heilongjiang, 150001, China
| | - Qun-Yan Wu
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China.
| | - Cong-Zhi Wang
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China.
| | - Jian-Hui Lan
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China.
| | - Meng Zhang
- Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, College of Nuclear Science and Technology, Harbin Engineering University, Harbin, Heilongjiang, 150001, China
| | - John K Gibson
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA
| | - Zhi-Fang Chai
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China.
| | - Wei-Qun Shi
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China.
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Cheng ZP, Li XB, Wu QY, Chai ZF, Shi WQ. Theoretical insights into the reduction mechanism of neptunyl nitrate by hydrazine derivatives. RADIOCHIM ACTA 2022. [DOI: 10.1515/ract-2021-1120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
In the advanced spent fuel cycle, the control and adjustment of neptunium valence state is greatly important for the highly efficient separation of neptunium. Hydrazine and its derivatives as salt-free reagents can selectively reduce Np(VI) to Np(V), but their reduction mechanisms are still unclear. We explored the reduction of [NpVIO2(H2O)2(NO3)2] by N2H4 and its two derivatives HOC2H4N2H3 and CHON2H3 using scalar relativistic density functional theory. The thermodynamic energy of the reactions [NpVIO2(H2O)2(NO3)2] with three reductants are sensitive to the substitution group, HOC2H4N2H3 enhances thermodynamic ability of the reaction and CHON2H3 shows contrary result. Both HOC2H4N2H3 and CHON2H3 have lower energy barrier compared to N2H4 based on the potential energy profiles (PEPs), which probably attributes to the intramolecular hydrogen bond of hydrazine derivatives. The nature of these redox reactions is that the hydrogen atom of reductants is gradually transferred to the axis oxygen atom of neptunyl, which accompanies the N–H bond dissociation and Oax–H bond formation. The reduction of Np(VI) with HOC2H4N2H3 is the most favorable reaction based on the thermodynamic and kinetic results. This work provides theoretical perspective into the reduction of Np(VI) to Np(V), which is beneficial to the development of more effective free-salt reductants for the separation of neptunium from uranium and plutonium in spent fuel reprocessing.
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Affiliation(s)
- Zhong-Ping Cheng
- State Key Laboratory of Nuclear Resources and Environment, East China University of Technology , Nanchang , Jiangxi , 330013 , China
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences , Beijing , 100049 , China
| | - Xiao-Bo Li
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences , Beijing , 100049 , China
| | - Qun-Yan Wu
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences , Beijing , 100049 , China
| | - Zhi-Fang Chai
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences , Beijing , 100049 , China
- Engineering Laboratory of Advanced Energy Materials, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences , Ningbo , Zhejiang , 315201 , China
| | - Wei-Qun Shi
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences , Beijing , 100049 , China
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Li XB, Wu QY, Wang CZ, Lan JH, Zhang M, Chai ZF, Shi WQ. Theoretical Insights into the Reduction Mechanism of Np(VI) with Phenylhydrazine. J Phys Chem A 2021; 125:6180-6188. [PMID: 34235933 DOI: 10.1021/acs.jpca.1c04198] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Effectively adjusting and controlling the valence state of neptunium from the spent fuel reprocessing process is essential to separating neptunium. Hydrazine and its derivatives as free-salt reductants have been experimentally demonstrated to effectively reduce Np(VI) to Np(V). We have theoretically investigated the reduction mechanisms of Np(VI) with hydrazine and three derivatives (HOC2H4N2H3, CH3N2H3, and CHON2H3) in previous works. Herein, we further explored the reduction reaction of Np(VI) with phenylhydrazine (C6H5N2H3) including the free radical ion mechanism and the free radical mechanism. Potential energy profiles (PEPs) indicate that the rate-determining step of both mechanisms is the first stage. Moreover, for the free radical ion mechanism, phenylhydrazine possesses better reduction ability to Np(VI) compared to HOC2H4N2H3, CH3N2H3, and CHON2H3, which falls completely in line with the experimental results. Additionally, the analyses of the quantum theory of atoms in molecules (QTAIM), natural bond orbitals (NBOs), electron localization function (ELF), and localized molecular orbitals (LMOs) have been put forward to elucidate the bonding evolution for the structures of the reaction pathways. This work offers insights into the reduction mechanism of Np(VI) with phenylhydrazine from the theory point of view and contributes to design more high-efficiency reductants for the separation of U/Np and Np/Pu in spent fuel reprocessing.
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Affiliation(s)
- Xiao-Bo Li
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China.,Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, College of Nuclear Science and Technology, Harbin Engineering University, Harbin, Heilongjiang 150001, China
| | - Qun-Yan Wu
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
| | - Cong-Zhi Wang
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
| | - Jian-Hui Lan
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
| | - Meng Zhang
- Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, College of Nuclear Science and Technology, Harbin Engineering University, Harbin, Heilongjiang 150001, China
| | - Zhi-Fang Chai
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China.,Engineering Laboratory of Advanced Energy Materials, Ningbo Institute of Industrial Technology, Chinese Academy of Sciences, Ningbo, Zhejiang 315201, China
| | - Wei-Qun Shi
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
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