Fe_(2)O_(3)上AsH_(3)催化氧化反应机理的理论研究

Theoretical study on the mechanism of the catalytic oxidation of AsH_(3)on Fe_(2)O_(3)

本文采用密度泛函理论方法研究了Fe_(2)O_(3)上AsH_(3)的催化氧化反应机理.该反应以Fe_(2)O_(3)中的两个Fe原子为不同的活性中心进行研究,每个活性中心均设计了3个步骤.AsH_(3)分子依次与3个O_(2)分子在催化剂上相互作用分别形成中间体H_(3)AsO_(2)、H_(3)AsO_(4)及最终产物H_(3)AsO_(6).研究发现,当氧化反应发生在1号铁原子(Fe1)附近,其速度控制步骤活化自由能垒为49.99 kcal/mol;当氧化反应发生在2号铁原子(Fe2)附近,其活化自由能垒为21.20 kcal/mol,与直接氧化(50.14 kcal/mol)相比大大降低.可见AsH_(3)在Fe_(2)O_(3)上的催化氧化反应更易发生在Fe2附近.

The mechanism of the catalytic oxidation of arsine hydrogen(AsH_(3))on Fe_(2)O_(3)was studied by density functional theory.The reactions with two Fe atoms in Fe_(2)O_(3)were used as different active centers,and each active center was designed with 3 steps.The AsH_(3)molecule interacted with three O_(2) molecules in sequence on the catalyst to form intermediates H_(3)AsO_(2),H_(3)AsO_(4),and the final product H_(3)AsO_(6).It is found that when the oxidation reaction occurs near the iron atom(Fe1),the activation free energy barrier for the rate control step is 49.99 kcal/mol,while when the oxidation reaction occurs near the iron atom(Fe2),the activation free energy barrier is 21.20 kcal/mol,which is geatly reduced compared with direct oxidation(50.14 kcal/mol).It can be seen that the catalytic oxidation reaction of AsH_(3)is more likely to occur near Fe2.