A comparative theoretical study: Reaction mechanism of Hg0 and H2S/H2Se on α-Fe2O3 (001) surface

Selenium has emerged as a modifier of mercury sorbent in recent years following sulfur, and H2Se is expected to be helpful for mercury capture as H2S do. To explore the differences in the impact of H2S and H2Se on mercury control, the reaction mechanism of Hg and H2S/H2Se on the alpha-Fe2O3(001) surface was investigated by density functional calculations. The results show that the H2S and H2Se perform similar adsorption behaviors on alpha-Fe2O3 (001) surface, and they tend to undergo a complete dissociative adsorption, with H atoms bonding to surface O atoms, and S/Se atoms bonding to surface Fe atoms. Comparatively, the adsorption of H2Se is more favorable than H2S in both thermodynamics and kinetics. The active S/Se site, derived from the dissociative adsorption of H2S/H2Se, can stabilize Hg atoms firmly through the generation of HgS/HgSe with a negligible energy barrier. However, HgS and HgSe are unlikely to desorb from alpha-Fe2O3 (001) surface indicated by their high adsorption energy of above 320 kJ/mol. These findings not only elucidate the reaction mechanisms involved in the interaction between H2Se and mercury on the alpha-Fe2O3 (001) surface but also predict the superior performance of H2Se compared to H2S in enhancing mercury capture over sorbents.