The reactivity of Zhundong chars is remarkably affected by the high sodium content of their parent Zhundong coal. The functional mechanism of inorganic sodium (NaCl) on the structure and reactivity of Zhundong chars was investigated in this study. Chars were prepared in a single-bed reactor under different pyrolysis temperatures and durations. Preliminary experimental results showed that inorganic sodium has a dual effect on the char yield of pyrolyzed Zhundong coal: inorganic sodium can decrease char yield at high pyrolysis temperatures of ≥600 °C but increase char yield at the low pyrolysis temperature of 400 °C. Nitrogen adsorption technique and scanning electron microscopy were utilized to identify the effects of inorganic sodium on the physical structure of Zhundong chars. The results showed that inorganic sodium affects pore structure detrimentally, inhibits the growth of char vesicles, and enables the formation of smooth char surfaces. Fourier transform infrared spectroscopy and Raman spectroscopy were used to identify the effect of inorganic sodium on the chemical structure of Zhundong chars and to investigate the homogeneous and heterogeneous NaCl–char interactions that occur during pyrolysis. The results showed that homogeneous and heterogeneous NaCl–char interactions both can affect the char’s chemical structure. Homogeneous NaCl(s)–char interactions accelerate the decomposition of O-containing functional groups and the formation of new Na-containing carboxylic groups. Heterogeneous NaCl(g)–char interactions accelerate the decomposition of functional groups and increase the ratio of small aromatic ring systems to large aromatic ring systems in the char. Thermogravimetric analysis revealed that inorganic sodium has a catalytic effect on the combustion reactivity of Zhundong chars. Finally, the catalytic mechanism of inorganic sodium on the reactivity of Zhundong chars was proposed.

•Ag@AgCl/Ag2CO3 hybrids were used to remove gas-phase Hg0 under fluorescent light.•Simultaneous removal of Hg0 and SO2 was carried out in a wet scrubbing reactor.•Hg0 was mainly removed by photo-induced holes (h+) under fluorescent light.•The possible reaction mechanism for enhanced Hg0 removal was elucidated.Photocatalytic oxidation removal of elemental mercury (Hg0) by Ag@AgCl/Ag2CO3 hybrids was carried out in a wet scrubbing reactor under fluorescent light. The photocatalysts synthesized via a modified coprecipitation method were characterized by using SEM-EDS, HRTEM, N2 adsorption-desorption, XRD, XPS, DRS, and ESR. Effects of operational parameters on Hg0 removal, including AgCl content, fluorescent light (FSL) irradiation, pH value, reaction temperature, and flue gas components (O2, SO2 and NO) were studied in detail. Furthermore, simultaneous removal of Hg0 and SO2 was investigated and the possible mechanism of highly enhanced Hg0 removal efficiency was proposed. The results showed that AgCl amount, fluorescent light irradiation, reaction temperature, SO2 and NO had notable impact on Hg0 removal efficiency. Simultaneous removal efficiencies of 98% for SO2 and 80% for Hg0 were obtained by coupling Ag@AgCl(0.3)/Ag2CO3 with Ca(OH)2 under FSL. The trapping studies of reactive radicals exhibited that holes (h+) were one of the main reactive species for Hg0 removal.Download high-res image (184KB)Download full-size image

A series of magnetically separable AgI–BiOI/CoFe2O4 hybrid composites were successfully synthesized via a solvothermal and subsequent coprecipitation method. The microstructure and magnetism of the materials were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), photocurrent test, electron spin resonance (ESR) and vibrating sample magnetometer (VSM). The photocatalytic performance of AgI–BiOI/CoFe2O4 composites on Hg0 removal from simulated flue gas was carefully designed and evaluated under fluorescent light (FSL) irradiation. The results showed that AgI–BiOI/CoFe2O4 composites displayed superior photocatalytic activities because of the synergistic effects between AgI, BiOI, and CoFe2O4 under FSL irradiation. The optimal weight ratio between AgI and the total weight of AgI–BiOI/CoFe2O4 photocatalyst was 0.3. The presence of a small amount of SO2 had a dramatic inhibition on Hg0 removal, while the inhibitory effect of NO on Hg0 removal could only be observed at a higher NO concentration. The trapping experiments indicated that photoinduced holes (h+) and superoxide radicals (˙O2−) were the primary active substances in the AgI–BiOI/CoFe2O4 photocatalytic oxidation system. According to the experimental and characterization results, one plausible mechanism for enhanced Hg0 removal performance over AgI–BiOI/CoFe2O4 composites was proposed.

•Fe–Mn–Ce/γ-Al2O3 catalyst showed high SCR activity at low temperature.•Adding Fe strengthened the surface acidity of Brønsted and Lewis acid sites.•NO and NH3 could be adsorbed on the catalyst in different forms.•The SCR reaction route mainly followed the Eley–Rideal mechanism.Fe–Mn–Ce/γ-Al2O3 granular catalyst was synthesized using the sol-gel method and then developed in the low temperature selective catalytic reduction (SCR) of NO with NH3. It achieved outstanding SCR activity at low temperature and also showed excellent space velocity tolerance and favorable SO2 and H2O resistance. The addition of Fe obviously increased the surface area and pore volume of the catalyst, and it also strengthened the surface acidity of Brønsted and Lewis acid sites, which was beneficial with the increase of SCR activity. The TPD and DRIFT results showed that the number of Lewis acid sites on the catalyst was much more than Brønsted sites, which could facilitate the formation of coordinated NH3 and –NH2 species. NO could be adsorbed in the form of unstable nitrates, which could then react with the adsorbed NH3 species directly. The most possible reaction pathway was proposed as that NH3 was firstly adsorbed on the catalyst after the competitive adsorption, and then the formed coordinated NH3 and –NH2 species reacted with the gas phase NO and generated N2 and H2O. That is, the SCR reaction route mainly followed the Eley–Rideal mechanism.

CuO−CeO2−MnOx/γ-Al2O3 granular catalysts were synthesized by the sol−gel method. Performance of the CuO−CeO2−MnOx/γ-Al2O3 catalyst was explored in a fixed bed adsorption system. The optimum temperature range for NO reduction over the CuO−CeO2−MnOx/γ-Al2O3 catalyst was 200−450 °C. The catalysts maintained nearly 100% NO conversion effectivity at 350 °C. Comprehensive tests were carried out to study the behavior of NH3 and NO over the catalyst in the presence of oxygen. The NH3 oxidation experiments showed that both NO and N2O were produced gradually with the temperature raising. The catalysts in this experiment had a relatively stronger oxidation property on NH3, which improved the activity at low temperature. The over-oxidation of NH3 at high temperature is the main reason causing the decrease of NO conversion. The NO oxidation experiments revealed that NO was oxidized to NO2 over the catalysts. The NH3 and NO desorption experiments proved that NH3 and NO were adsorbed on CuO−CeO2−MnOx/γ-Al2O3 catalysts. NH3/O2 and NO/O2 adsorption processes on the catalyst and the transient response of NH3 and NO were investigated by in situ diffuse reflectance infrared transform spectroscopy (DRIFTS) to study the mechanism. It was found that the selective catalytic reduction (SCR) reaction on the CuO−CeO2−MnOx/γ-Al2O3 catalyst accorded not only the Eley−Rideal mechanism but also the Langmuir−Hinshelwood hypothesis. The adsorbed NO may contribute to the high activity of the catalyst.

•A novel technique of Hg0 removal by BiOX (X = Cl, Br, I) under fluorescent light was proposed.•BiOBr and BiOI exhibited much higher Hg0 removal performance.•Superoxide radical (O2−) and holes (h+) played key roles in Hg0 removal in the BiOBr system.•I2 might be an important species for higher Hg0 removal in the BiOI system.BiOX (X = Cl, Br, I) photocatalysts were synthesized by a simple coprecipitation method and were characterized by SEM, TEM, HRTEM, XRD, TG, DRS, PL, and ESR techniques. The photocatalytic activity of Hg0 removal and the effects SO2 and NO were investigated under fluorescent light. The Hg0 removal performance was in the sequence of BiOI > BiOBr > BiOCl. Compared with BiOBr, BiOI showed much excellent SO2 resistance on Hg0 removal. In the BiOBr reaction system, h+ and O2− could play key roles in Hg0 removal, while for BiOI photocatalytic system, I2 might be an important species for higher Hg0 removal.Download full-size image

The efficiency of the CuO–MnO2–Fe2O3/γ-Al2O3 (CMFA) catalysts on mercury oxidation and the effects of individual flue gas (O2, HCl, NO, SO2) were investigated in our previous study. To elucidate the mercury oxidation mechanism, a thermal desorption (TD) method was applied in this study to analyze the characteristics of the mercury species formed on the CMFA catalysts. A series of pure mercury compounds mixed with fresh CMFA were first studied as the controls. Then, the TD method was employed to identify the Hg species formed on used CMFA catalysts pretreated under different operation conditions. The formation of HgO, HgCl2, Hg(NO3)2 and HgSO4 during the oxidation process was confirmed and the reaction pathway proposed. The mercury species present were mainly HgCl2 after CMFA catalysts were used to oxidize Hg0 under simulated flue gas conditions. HgO and HgSO4 were found to exist in very low concentrations. This has shown that the TD method is an efficient technique for mercury speciation on the catalyst surface.