Insights into the heterogeneous Hg0 oxidation mechanism by H2O2 over Fe3O4 (0 0 1) surface using periodic DFT method

Abstract

The gaseous oxidation process for Hg0 oxidation is regarded as an efficient and low-cost option for mercury control in solid fuel combustion devices. The heterogeneous Hg0 oxidation by gaseous H2O2 over Fe3O4 (0 0 1) surface was calculated using periodic density functional theory (DFT) method to gain a fundamental understanding of Hg0 oxidation mechanism on H2O2/Fe3O4 (0 0 1) surface. The results showed that on the Fe3O4 (0 0 1) surface, the Fetet site (A layer) is more active than the Feoct site (B layer). H2O2 can easily undergo dissociation process to form two OH radicals, which have highly active in Hg0 oxidation over the A layer. The Mulliken charge population analysis showed that a large amount of electron transfer occurred from Hg0 to the produced OH. The calculated reaction energy barriers suggested that the interaction between OH and Hg0 is exothermic and Hg0 oxidation processes by OH produced from H2O2 are thermodynamically and kinetically favorable. In addition, Hg0 oxidation processes on the H2O2/Fe3O4 (0 0 1) surface may simultaneously undergo through three different pathways. The possible Hg-OH product will easily desorbs from the surface, whereas the Hg(OH)2 is stable on the surface and belongs to chemisorption. The detailed mechanism for the oxidation reaction over Fe3O4 makes it an attractive method for Hg control from flue gases.