过渡金属元素作用下H_2O_2碱性分解动力学及机理

Decomposition Kinetics and Mechanism of Alkaline Hydrogen Peroxide with Transition Metals

通过调节体系pH值,并引入微量的过渡金属元素与OH-共同作用,研究了过氧化氢碱性分解动力学及反应机理.结果表明:碱性条件下过氧化氢的分解反应宏观表现为"准"一级反应,10.0≤pH≤11.6时,过氧化氢分解"准"一级反应动力学速率常数kobs随pH值的增加而增大,70℃下、pH=11.6时kobs达最大值0.0922min-1;pH>11.6时,kobs随pH值的增加而呈下降趋势.文中还考察了过渡金属胶体粒径随体系pH值及时间的变化,发现Mn2+和Fe3+形成的胶体颗粒的平均粒径分别随反应时间和pH值的增加而增大,指出过渡金属胶体催化分解和过氧化氢碱性电离是过氧化氢的碱性分解的原因所在.

Trace transition metals were introduced in the catalytic decomposition of alkali hydrogen peroxide at va-rious pH values,and the corresponding decomposition kinetics and mechanism were investigated.The results indicate that the decomposition of hydrogen peroxide follows the quasi-first-order law in alkaline conditions,that the quasi-first-order rate constant of the alkali decomposition,kobs,increases with the pH value when 10.0≤pH≤11.6 but decreases when pH11.6,and that kobs reaches the maximum 0.0922 min-1 at 70℃ and pH11.6.Moreover,the effects of pH value and reaction time on the size of transition-metal colloidal particles were also discussed,finding that the average sizes of Mn2＋ and Fe3＋ colloidal particles increase with the reaction time and the pH value,respectively.Thus,it is concluded that the decomposition of alkaline hydrogen peroxide is due to the catalytic decomposition of transition metal colloids and the alkaline ionization of hydrogen peroxide.