DFT Study On Preparation Of U(?) By Reduction Of U(?) By Hydrazine With Platinum

In the closed cycle reprocessing industry,the choice of reducing agent is very important for the separation of uranium and plutonium.The 1B process in which U???-hydrazine is a reducing agent is stable,which is the most ideal reducing agent at present.However,U???is unstable,and a separate preparation process is required for practical application.At present,heterogeneous catalytic reduction method is gradually becoming a mainstream process in the industrial process of preparing U???due to its stable conversion rate and no impurities.The preparation of U???by reducing U???with platinum catalyzed hydrazine has been studied extensively.Due to the fact that the actual reaction process is fast and the actual reaction environment is acidic,the capture of the transition state and the structure study are limited,so it is difficult to explore the specific mechanism of hydrazine catalytic decomposition from the experimental perspective.Based on the shortage of current experimental data,this paper conducts density functional?DFT?research on the preparation of U???reaction by reduction of U???by Pt catalyzed N₂H₄ from the perspective of quantum chemistry by means of simulation calculation.Gaussian09 program is used for all calculations in this paper,and Multiwfn program is used for wave function analysis.The functional used B3LYP,the U atom used the pseudo-potential set ECP60MWB,the Pt atom used the Los Alamos pseudo-potential set Lanl2TZ?f?,and the other atoms in the system used the 6-31g**basis set.SMD solvation model was used to simulate the solution environment.Transition state structure is obtained by simulation of preparation of U???reaction by reduction of U???by hydrazine with platinum.Based on further analysis of the transition state structure and wave function,the reaction mechanism of preparing U???from reduction of U???by hydrazine catalyzed by platinum is obtained as follows:The first step is the decomposition of hydrazine catalyzed by platinum to produce free radicals.N₂H₄ is adsorbed on Pt,and N-N bond breaking occurs under the catalytic action of Pt.Under the influence of acidic environment,N-N bond length increases,making N-N bond breaking more easily.At the same time,N-H bond break also occurs in N₂H₄,which can be divided into two cases under the influence of acidic conditions.If N₂H₄ is protonized,then N-H bond breaking is more likely to occur.If H is adsorbed on catalyst Pt,the charge property of Pt will change.It not only hinders N-H bond breaking and inhibits·H desorption from Pt,but also causes N-H bond breaking reverse reaction.In the case of N-N and N-H broken bonds,acid conditions can promote N-N bond breaking and hinder N-H bond breaking.The second step is the decomposition of hydrazine catalyzed by platinum to produce the reaction between free radicals and UO₂?H₂O?₅²⁺.It is speculated that there are two reaction paths.One is that the free radical and UO₂?H₂O?₅²⁺attach to the same catalyst Pt atom.Through the electron transfer capability of Pt,the free radical transfers the electron to the O atom on UO₂?H₂O?₅²⁺,thereby reducing U???.The other is that UO₂?H₂O?₅²⁺attaches to the catalyst Pt,and the free radical reacts directly with O atoms to reduce U???.