ESR法研究Pt催化N_2H_4分解机制  

Mechanism of Pt-catalyzed N_2H_4 Decomposition by ESR Method

作　　者：郝帅 李斌[2] 周贤明[2] 刘利生[2] 张晓腾 蒋冬梅[3] 夏良树[1] 

机构地区：[1]南华大学核科学技术学院,湖南衡阳421001 [2]中国原子能科学研究院放射化学研究所,北京102413 [3]南华大学创新创业学院,湖南衡阳421001

出　　处：《原子能科学技术》2018年第2期247-254,共8页Atomic Energy Science and Technology

基　　金：国家自然科学基金资助项目(11575078)

摘　　要：采用电子自旋共振谱(ESR)法,研究了酸性条件下·NH_2的转化,HClO_4体系下反应时间对溶液中自由基产生的影响、pH值对N_2H_4断键的影响以及HNO_3中N是否对溶液中的·NH_2有贡献,确定了Pt催化N_2H_4分解的反应机理。结果表明:在酸性条件下·NH_2被DMPO捕捉时反应式为·NH_3^++HO—H+DMPO=NH_4^++DMPO(·OH),硝酸在Pt催化N_2H_4体系中不会发生断键产生·NH_2,所产生的·NH_2是由N_2H_4断键形成的;在HClO_4体系中,随着Pt催化N_2H_4反应时间的延长,N_2H_4中N—N断键的趋势逐渐减小,N—H断键的趋势逐渐增大;随pH值的增大,N_2H_4中N—N断键的速率先快速减小,pH>3后缓慢增大;Pt催化N_2H_4分解反应中N—N断键和N—H断键两种方式共存,但N—N断键占优;反应体系中N_2H_4与H^+浓度之比决定了N—N断键生成·NH_2的速率,而·NH_2与H^+的浓度又决定了·NH_2转化成产物的速率,这两方面共同决定了N_2H_4分解的速率。Electron spin resonance(ESR)method was used in researching the conversion of·NH_2 under acidic conditions,the effect of reaction time on the free radical production in HClO_4 system,the effect of pH on the broken bond of N_2H_4,and whether N in HNO_3 impacts on the production of·NH_2.The reaction mechanism of N_2H_4 catalyzed by Pt was determined.The results show that the reaction of·NH_2 captured by DMPO under acidic conditions is·NH_3^++HO—H+DMPO=NH_4^++DMPO(·OH).In Pt-catalyzed N_2H_4 the HNO_3 doesn't break bond,and the·NH_2 is only from N_2H_4.In the HClO_4 system,as the reaction proceeds,the trend of N—N bond-breaking in N_2H_4 decreases gradually and the trend of N—H bond-breaking increases gradually.With the increase of pH,the rate of N—N bond-breaking in N_2H_4 decreases rapidly and then increases slowly after pH>3,N—N bond-breaking and N—H bond-breaking coexist in Pt-catalyzed N_2H_4 decomposition process,but the N—N bond-breaking is dominant.In the reaction system,the concentration ratio of H^+ to N_2H_4^+ determines the formation rate of·NH_2 from N—N bond breaking,the concentrations of·NH_2 and H^+ also determine the rate of·NH_2 converted to the products,and the two aspects determine the rate of N_2H_4 decomposition together.

关 键 词：ESR 肼 自由基 断键 铂黑 分解机理 

分 类 号：O643.12[理学—物理化学]