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Since the signing of the Minamata Convention in 2013, attempts have been primarily focused on reducing the emission of elemental mercury (Hg0) from coal-fired power plants (CFPPs). The most cost-effective measure for controlling the emission of mercury involves oxidizing Hg0 to mercury oxides, which are then removed using wet flue gas desulfurization (WFGD). Thus, novel photocatalysts with the best properties of photocatalytic ability and thermal stability need to be developed urgently. In this study, titanium dioxide (TiO2)-based photocatalysts were synthesized through the modification of three metal oxides: CuO, CeO2, and Bi2O3. All the photocatalysts were further characterized using X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence, and ultraviolet-visible spectrometry. The photocatalytic oxidation efficiencies of Hg0 were evaluated under an atmosphere of N2 + Hg0 at 100–200 °C. The photocatalytic reactions were simulated by kinetic modeling using the Langmuir–Hinshelwood (L–H) mechanism. The results showed that Bi2O3/TiO2 exhibited the best thermal stability, with the best oxidation efficiency at 200 °C and almost the same performance at 100 °C. L–H kinetic modeling indicated that photocatalytic oxidation reactions for the tested photocatalysts were predominantly physical adsorption. Additionally, the activation energy (Ea), taking into account Arrhenius Law, decreased dramatically after modification with metal oxides. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu(II)O/TiO 2 as photothermal catalysts with were explored to remove Hg. • 5%Cu(II)O/TiO 2 has the greatest Hg0 oxidation performance. • NO and SO 2 could chemisorb on the surface of catalysts. • The influence of SO 2 and NO in the Hg0 oxidation reaction was clarified by DFT. This study aimed to apply sol–gel synthesized Cu(II)O doped TiO 2 to enhance the oxidation of gaseous elemental mercury (Hg0) in the flue gases containing NO and SO 2 at the temperatures of 120-180℃ under the irradiation of near-ultraviolet (near-UV). The influences of SO 2 and NO on the oxidation efficiency of Hg0 were investigated by in-situ diffuse reflection infrared spectroscopy (DRIFT) and density functional theory (DFT). Experimental results showed that an optimal 5 %Cu(II)O/TiO 2 had the oxidation efficiencies of Hg0 from 40 to 100 % at 120-180℃. The oxidation efficiencies of Hg0 were 85 and 70 % at 120℃, and 40 and 5 % at 180 °C, in the presence of solely SO 2 and NO, respectively. Surface characterization showed that Cu(II)O was evenly dispersed over the surface of TiO 2 catalysts. NO could inhibit the oxidation of Hg0 since it consumed the chemisorbed oxygen (O α) and compete with Hg0 at the surface active sites. In contrast, SO 2 could promote the oxidation efficiency of Hg0 due to the formation of HgSO 4 on the surface of Cu(II)O/TiO 2 catalysts. In the exposure of NO/SO 2 , NO and SO 2 can be adsorbed on the catalyst surface reacting with ̇OH. The photothermal oxidation reactivity of Hg0 was inhibited due to the competitive adsorption between NO/SO 2 and Hg0. The Langmuir-Hinshelwood (L-H) kinetic model successfully simulated the oxidation rate of Hg0. Moreover, DFT was further applied to estimate the binding energies of different gas molecules confirming the competence for active sites on the surface of Cu(II)O/TiO 2 between NO/SO 2 and Hg0. [ABSTRACT FROM AUTHOR]

In this study, the photo-oxidation and kinetics of elemental mercury (Hg0) with self-prepared TiO 2 and CeO 2 /TiO 2 at 100–200 ℃ were explored. The surface properties of the photocatalysts were characterized before conducting the Hg0 photo-oxidation experiments. Both field emission scanning electron microscopy and high-resolution transmission electron microscopy showed that the grain size of TiO 2 {101} was smaller than TiO 2 {001}. XPS spectral showed that cerium (Ce) valence shifting between CeO 2 and Ce 2 O 3 generated strong oxidant O 2 -. Chemisorbed oxygen (O α) was found to be more active than lattice oxygen (O β). Doping CeO 2 to anatase-TiO 2 effectively enhanced the photo-oxidation of Hg0. Higher Hg0 photo-oxidation efficiency and better thermal stability were observed in CeO 2 /TiO 2 {001} than CeO 2 /TiO 2 {101}. The photo-oxidation efficiency of Hg0 decreased with reaction temperature. In N 2 +Hg0+NO, low NO concentration (< 100 ppm) suppressed and high NO concentration (>300 ppm) enhanced the oxidation of Hg0. In N 2 +Hg0+SO 2 , SO 2 competed with Hg0 for active sites on the surface of photocatalysts and suppressed the photo-oxidation of Hg0 since sulfate and sulfite as reaction products were observed on the surface of photocatalysts. Both facets could not prevent from being poisoned, however, CeO 2 /TiO 2 {001} could decelerate sulfur poisoning. On simulation by LH kinetic model, the reaction rate constant increased and the equilibrium constant decreased with reaction temperature, indicating that the photo-oxidation of Hg0 was dominated by physical adsorption. [Display omitted] • TiO 2 {001} facet showed higher Hg0 oxidation efficiency than TiO 2 {101} facet. • Ce doped TiO 2 {001} had higher Hg0 oxidation activity and better thermal stability. • CeO 2 /TiO 2 {001} remained Hg0 oxidation efficiency and decelerate sulfur poisoning. • Temperature, (001) facet, and NO/SO 2 were crucial for Hg0 oxidation efficiency. • The photocatalytic oxidation of Hg0 was dominated by physical adsorption. [ABSTRACT FROM AUTHOR]