Molecular Mechanistic Nature of Elemental Mercury Oxidation by Surface Oxygens over Co3O4 Catalyst

Co3O4 has been regarded as a potential active catalyst component for Hg0 oxidation from flue gas with low or no chlorine due to its excellent redox activity, high element abundance, and good thermal stability. The reaction mechanisms of Hg0 oxidation by different surface oxygens (chemisorbed oxygen and lattice oxygen) on the Co3O4 surface were investigated using density functional theory (DFT) calculations. It is found that Hg0 and HgO adsorptions on Co3O4(110) are controlled by the chemisorption mechanism. The surface Co3+ atom is determined as the major active adsorption site. O2 is chemisorbed on Co3O4(110) in perpendicular and parallel orientations with the adsorption energies of −1.00 and −1.20 eV, respectively. The parallelly adsorbed O2 can be activated after overcoming an energy barrier of 0.87 eV to produce active oxygen atoms. The reaction processes of Hg0 oxidation by surface oxygens undergo three steps: (1) Hg0 → Hg(ads), (2) Hg(ads) → HgO(ads), and (3) HgO desorption, in which the HgO formati...