ESR法研究pH值对Pt催化N_2H_4断键的影响机制
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摘要
为明确酸性条件下Pt催化N_2H_4还原U(Ⅵ)制备U(Ⅳ)的反应历程和反应机理,有针对性地提高其反应速率、优化工艺流程,本文采用电子自旋共振(ESR)法实验研究·NH_2转化为·OH的机理及0.25 mol/L和0.5 mol/L N_2H_4浓度条件下不同酸度的高氯酸体系中Pt催化N_2H_4分解过程中产生的自由基,确定反应过程中pH值对N_2H_4断键的影响机制。结果表明,在高氯酸介质中,Pt催化N_2H_4分解反应体系中检测到的·OH是由N_2H_4分解产生的·NH_2转化而来;该反应体系中酸度会对N_2H_4分解产生影响,在酸度逐渐降低的过程中Pt催化N_2H_4分解的反应速率表现为先增大后减小的趋势,其中在pH=1～2之间时Pt催化N_2H_4分解反应最为迅速。
In order to determine the reaction process and reaction mechanism of U(Ⅳ) produced by hydrazine reducting U(Ⅵ) with platinum as catalyst in the nitric acid environment, improve the reaction rate, and optimize the process flow, the effect of pH value on hydrazine bond breaking with Pt as catalyst was studied. The electron-spin resonance(ESR) method was used to study the mechanism of conversion of ·NH_2 to ·OH, and analyze the free radicals generated during the decomposition of hydrazine catalyzed by Pt in perchloric acid systems with different acidity for 0.25 mol/L and 0.5 mol/L hydrazine solutions respectively to determine mechanism for pH affecting hydrazine bond breaking. The results show that in the perchloric acid environment, the ·OH detected in the Pt-catalyzed hydrazine decomposition reaction system is converted from ·NH_2 produced by the decomposition of hydrazine. The acidity of the reaction system will affect the decomposition of hydrazine. During the process of decreasing acidity, the reaction rate of Pt-catalyzed hydrazine decomposition reaction will increase first and then decrease, and the decomposition reaction is the fastest between pH=1-2.
In order to determine the reaction process and reaction mechanism of U(Ⅳ) produced by hydrazine reducting U(Ⅵ) with platinum as catalyst in the nitric acid environment, improve the reaction rate, and optimize the process flow, the effect of pH value on hydrazine bond breaking with Pt as catalyst was studied. The electron-spin resonance(ESR) method was used to study the mechanism of conversion of ·NH_2 to ·OH, and analyze the free radicals generated during the decomposition of hydrazine catalyzed by Pt in perchloric acid systems with different acidity for 0.25 mol/L and 0.5 mol/L hydrazine solutions respectively to determine mechanism for pH affecting hydrazine bond breaking. The results show that in the perchloric acid environment, the ·OH detected in the Pt-catalyzed hydrazine decomposition reaction system is converted from ·NH_2 produced by the decomposition of hydrazine. The acidity of the reaction system will affect the decomposition of hydrazine. During the process of decreasing acidity, the reaction rate of Pt-catalyzed hydrazine decomposition reaction will increase first and then decrease, and the decomposition reaction is the fastest between pH=1-2.
引文
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[19] TAKAYANAGI T,KIMIYA H,OHYAMA T.Formation of artifactual DMPO-OH spin adduct in acid solutions containing nitrite ions[J].Free Radic Res,2017,51(7):739-748.
[20] áLVAREZ-BARCIA S,RUSS M S,MEISNER J,et al.Atom tunnelling in the reaction NH+3+H2→NH+4+H and its astrochemical relevance[J].Faraday Discussions,2016,195:69-80.
[21] van der REST G,MOURGUES P,NEDEV H,et al.A prototype for catalyzed amide bond cleavage:Production of the [NH3,H2O]·+ dimer from ionized formamide and its carbene isomer[J].Journal of the American Chemical Society,2002,124(19):5 561-5 569.
[22] ZHANG H,WATANABE T,OKUMURA M,et al.Catalytically highly active top gold atom on palladium nanocluster[J].Nature Materials,2012,11(1):49-52.
[23] ZHANG H,OKUMURA M,TOSHIMA N.Stable dispersions of PVP-protected Au/Pt/Ag trimetallic nanoparticles as highly active colloidal catalysts for aerobic glucose oxidation[J].Journal of Physical Chemistry C,2011,115(30):14 883-14 891.
[2] BOLTOEVA M Y,TREFILOVA A V,ANAN’EV A V.Catalytic reduction of U(Ⅵ) with hydrazine on palladium catalysts in acid solutions[J].Radiochimica Acta,2008,50(1):34-40.
[3] BOLTOEVA M Y,SHILOV V P,ANAN’EV A V.Reactivity of platinum nanoaggregates in catalytic reduction of U(Ⅵ) with hydrazine in acid solutions[J].Radiochimica Acta,2007,49(6):603-606.
[4] BOLTOEVA M Y,TREFILOVA A V,ANAN’EV A V.Catalytic reduction of U(Ⅵ) with hydrazine on palladium catalysts in acid solutions[J].Radiochemistry,2008,50(1):38-45.
[5] BOLTOEVA M Y,SHILOV V P,ANAN’EV A V.Catalytic reduction of U(Ⅵ) with formic acid in acid solutions on palladium catalysts[J].Radiochimica Acta,2008,50(1):46-51.
[6] 李斌,何辉,张秋月,等.高氯酸体系中肼为还原剂催化还原U(Ⅵ)的反应动力学[J].核化学与放射化学,2012,34(4):213-217.LI Bin,HE Hui,ZHANG Qiuyue,et al.Catalytic reaction kinetics of U(Ⅵ) with hydrazine on platinum black in perchloric acid media[J].Journal of Nuclear and Radiochemistry,2012,34(4):213-217(in Chinese).
[7] 郝帅,李斌,周贤明,等.ESR法研究Pt催化N2H4分解机制[J].原子能科学技术,2018,52(2):247-254.HAO Shuai,LI Bin,ZHOU Xianming,et al.Mechanism of Pt-catalyzed N2H4 decomposition by ESR method[J].Atomic Energy Science and Technology,2018,52(2):247-254(in Chinese).
[8] 张晓腾,李斌,周贤明,等.Pt催化N2H4还原U(Ⅵ)制备U(Ⅳ)过程中N2H4断键机制研究[J].原子能科学技术,2018,52(2):240-246.ZHANG Xiaoteng,LI Bin,ZHOU Xianming,et al.Study on bond breaking mechanism for process of U(Ⅳ) produced by N2H4 reducing U(Ⅵ) with platinum as catalyst[J].Atomic Energy Science and Technology,2018,52(2):240-246(in Chinese).
[9] WANG J,ZHANG X B,WANG Z L,et al.Rhodium-nickel nanoparticles grown on graphene as highly efficient catalyst for complete decomposition of hydrous hydrazine at room temperature for chemical hydrogen storage[J].Energy & Environmental Science,2012,5(5):6 885-6 888.
[10] YAMADA K,YASUDA K,FUJIWARA N,et al.Potential application of anion-exchange membrane for hydrazine fuel cell electrolyte[J].Electrochemistry Communications,2003,5(10):892-896.
[11] YIN W X,LI Z P,ZHU J K,et al.Effects of NaOH addition on performance of the direct hydrazine fuel cell[J].Journal of Power Sources,2008,182(2):520-523.
[12] 周贤玉.核燃料后处理工程[M].哈尔滨:哈尔滨工程大学出版社,2009.
[13] ERTL G,GIOVANELLI T.Katalytischer zerfall von hydrazin an GaAs-oberfl?chen[J].Zeitschrift für Physikalische Chemie,1971,75(34):137-154.
[14] ERTL G,TORNAU J.Katalytischer zerfall von hydrazin an palladium[J].Zeitschrift für Physikalische Chemie,1974,93(1-6):109-118.
[15] FALCONER J L,SCHWARZ J A.Temperature-programmed desorption and reaction applications tosupported catalysts[J].Catalysis Reviews,1983,25(2):141-227.
[16] 杨海军,蒋敏,李勇.pH值对氨水中氨基自由基影响的ESR研究[C]//第十七届全国波谱学学术会议论文摘要集.咸宁:中国物理学会波谱学专业委员会,2012.
[17] MADDEN K P,TANIGUCHI H.The role of the DMPO-hydrated electron spin adduct in DMPO-·OH spin trapping[J].Free Radical Biology & Medicine,2001,30(12):1 374-1 380.
[18] AND H T,MADDEN K P.An in situ radiolysis time-resolved ESR study of the kinetics of spin trapping by 5,5-dimethyl-1-pyrroline-N-oxide[J].Journal of the American Chemical Society,1999,121(50):11 875-11 879.
[19] TAKAYANAGI T,KIMIYA H,OHYAMA T.Formation of artifactual DMPO-OH spin adduct in acid solutions containing nitrite ions[J].Free Radic Res,2017,51(7):739-748.
[20] áLVAREZ-BARCIA S,RUSS M S,MEISNER J,et al.Atom tunnelling in the reaction NH+3+H2→NH+4+H and its astrochemical relevance[J].Faraday Discussions,2016,195:69-80.
[21] van der REST G,MOURGUES P,NEDEV H,et al.A prototype for catalyzed amide bond cleavage:Production of the [NH3,H2O]·+ dimer from ionized formamide and its carbene isomer[J].Journal of the American Chemical Society,2002,124(19):5 561-5 569.
[22] ZHANG H,WATANABE T,OKUMURA M,et al.Catalytically highly active top gold atom on palladium nanocluster[J].Nature Materials,2012,11(1):49-52.
[23] ZHANG H,OKUMURA M,TOSHIMA N.Stable dispersions of PVP-protected Au/Pt/Ag trimetallic nanoparticles as highly active colloidal catalysts for aerobic glucose oxidation[J].Journal of Physical Chemistry C,2011,115(30):14 883-14 891.
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