Mercury/oxygen reaction mechanism over CuFeO catalyst.

CuFeO is regarded as a promising candidate of catalyst for Hg oxidation in industrial flue gas. However, the microcosmic reaction mechanism governing mercury oxidation on CuFeO remains elusive. Herein, experiments and quantum chemistry calculations were conducted for understanding the chemical reaction mechanism of oxygen-assisted mercury oxidation on CuFeO. CuFeO shows the optimal catalytic activity towards mercury oxidation at 150 ºC. The reactivity difference of different lattice oxygen species is associated with its atomic coordination environment. The lattice oxygen coordinating with two octahedral Cu atoms and a tetrahedral Fe atom shows higher catalytic activity towards mercury oxidation than other lattice oxygen atoms. The inverse spinel structure of CuFeO is favorable for O activation due to the Jahn-Teller effect, thereby promoting mercury oxidation. O molecule preferably adsorbs on iron active site and dissociates into active oxygen species. Hg oxidation is a three-step reaction process: Hg adsorption, Hg(ads) → HgO(ads), and HgO desorption. The energy barrier of mercury oxidation by chemisorbed oxygen is lower than that of mercury oxidation by lattice oxygen. The chemisorbed oxygen preserves higher reactivity towards mercury oxidation than lattice oxygen. Hg(ads) → HgO(ads) is the rate-determining step of mercury oxidation by chemisorbed oxygen because of the higher energy barrier of 116.94 kJ/mol. This work could provide the theoretical guidance for the diversified structure design of highly-efficient catalysts used for elemental mercury oxidation.