ESR法研究Pt催化N2H4分解机制

采用电子自旋共振谱（ESR）法，研究了酸性条件下?NH₂的转化，HClO₄体系下反应时间对溶液中自由基产生的影响、pH值对N₂H₄断键的影响以及HNO₃中N是否对溶液中的?NH₂有贡献，确定了Pt催化N₂H₄分解的反应机理。结果表明：在酸性条件下?NH₂被DMPO捕捉时反应式为?NH⁺₃+HO-H+DMPO=NH⁺₄+DMPO(?OH)，硝酸在Pt催化N₂H₄体系中不会发生断键产生?NH₂，所产生的?NH₂是由N₂H₄断键形成的；在HClO₄体系中，随着Pt催化N₂H₄反应时间的延长，N₂H₄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，N₂H₄中N-N断键的速率先快速减小，pH>3后缓慢增大；Pt催化N₂H₄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N₂H₄与H^＋浓度之比决定了N-N断键生成?NH₂的速率，而?NH₂与H^＋的浓度又决定了?NH₂转化成产物的速率，这两方面共同决定了N₂H₄分解的速率。

Mechanism of Pt-catalyzedN2H4 Decomposition by ESR Method

Electron spin resonance (ESR) method was used in researching the conversion of ?NH₂ under acidic conditions, the effect of reaction time on the free radical production in HClO₄ system, the effect of pH on the broken bond of N₂H₄, and whether N in HNO₃ impacts on the production of ?NH₂. The reaction mechanism of N₂H₄ catalyzed by Pt was determined. The results show that the reaction of ?NH₂ captured by DMPO under acidic conditions is ?NH⁺₃+HO-H+DMPO=NH⁺₄+DMPO(?OH). In Pt-catalyzed N₂H₄ the HNO₃ doesn’t break bond, and the ?NH₂ is only from N₂H₄. In the HClO₄ system, as the reaction proceeds, the trend of N-N bond-breaking in N₂H₄ 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 N₂H₄ decreases rapidly and then increases slowly after pH>3, N-N bond-breaking and N-H bond-breaking coexist in Pt-catalyzed N₂H₄ decomposition process, but the N-N bond-breaking is dominant. In the reaction system, the concentration ratio of H⁺ to N₂H⁺₄ determines the formation rate of ?NH₂ from N-N bond breaking, the concentrations of ?NH₂ and H^＋ also determine the rate of ?NH₂ converted to the products, and the two aspects determine the rate of N₂H₄ decomposition together.