Fe_3O_4协同H_2O_2气相高级氧化单质汞的机理

Mechanism of Hg removal by gaseous advanced oxidation process with Fe_3O_4 and H_2O_2

利用密度泛函理论分别研究了H_2O_2分子在Fe_3O_4(111)、(110)和(001)表面分解特性,并对单质汞在H_2O_2/Fe_3O_4体系的反应特性进行了研究。对比不同构型的结合能、Mulliken电荷转移和分态密度分析,详细讨论了H_2O_2分解产生羟基的规律以及Hg0的氧化态中间产物成键特性。结果表明:H_2O_2分子在Fe_3O_4(111)、(001)A和(110)A表面更容易分解产生羟基;不同表面产生的羟基对Hg0具有不同的氧化活性;Hg^0在表面羟基的作用下可有效通过电荷转移实现氧化。对比分析了三种表面汞氧化态中间产物的脱附路径,HO—Hg—OH和Hg—OH的表面脱附是主要的反应路径。

The decomposition properties of H2O2 molecule over Fe3O4（111）,（110）, and（001） surfaces were systematically investigated by using density functional theory（DFT） calculations. Hg adsorption and oxidation mechanisms over H2O2/Fe3O4 system were studied. Binding energies, optimized geometries, Mulliken population, and molecular orbital analysis of partial density of states（PDOS） between Hg and H2O2/Fe3O4 surfaces were proposed. The most favored configurations of H2O2 decomposition, which was associated with the generation mechanism of OH groups, as well as the intermediates of Hg species were discussed. The results showed that OH radicals were more likely produced on Fe3O4（111）,（001） A, and（110） A surfaces. The oxidative activity of OH produced on different surfaces varies a lot. In addition, Mulliken charge population revealed Hg0 oxidation when the systems were in equilibrium because a large number of electrons transferred from Hg0 to the surface hydroxyl. The calculated binding energies suggested that the process of HO—Hg—OH and Hg—OH generation were exothermic on Fe3O4 surface with H2O2. The desorption analysis showed that HO—Hg—OH and Hg—OH intermediates had a lower desorption energy when they detached from the surface.