Novel Effective Catalyst for Elemental Mercury Removal from Coal-Fired Flue Gas and the Mechanism Investigation.

Mercury pollution from coal-fired power plants has drawn attention worldwide. To achieve efficient catalytic oxidation of Hg(0) at both high and low temperatures, we prepared and tested novel IrO2 modified Ce-Zr solid solution catalysts under various conditions. It was found that the IrO2/Ce0.6Zr0.4O2 catalyst, which was prepared using the polyvinylpyrrolidone-assisted sol-gel method, displayed significantly higher catalytic activity for Hg(0) oxidation. The mechanism of Hg(0) removal over IrO2/Ce0.6Zr0.4O2 was studied using various methods, and the Hg(0) oxidation reaction was found to follow two possible pathways. For the new chemisorption-regeneration mechanism proposed in this study, the adsorbed Hg(0) was first oxidized with surface chemisorbed oxygen species to form HgO; the HgO could desorb from the surface of catalysts by itself or react with adsorbed HCl to be release in the form of gaseous HgCl2. O2 is indispensable for the chemisorption process, and the doping of IrO2 could facilitate the chemisorption process. In addition, the Deacon reaction mechanism was also feasible for Hg(0) oxidation: this reaction would involve first oxidizing the adsorbed HCl to active Cl species, after which the Hg(0) could react with Cl to form HgCl2. Additionally, doping IrO2 could significantly improve the Cl yield process. In summary, the novel IrO2 modified catalyst displayed excellent catalytic activity for elemental mercury oxidation, and the proposed reaction mechanisms were determined reasonably.

Mechanism of the selective catalytic oxidation of slip ammonia over Ru-modified Ce-Zr complexes determined by in situ diffuse reflectance infrared Fourier transform spectroscopy.

The slip ammonia from selective catalytic reduction (SCR) of NOx in coal-fired flue gas can result in deterioration of the utilities or even the environmental issues. To achieve selective catalytic oxidation (SCO) of slip ammonia, Ru-modified Ce-Zr solid solution catalysts were prepared and evaluated under various conditions. It was found that the Ru/Ce(0.6)Zr(0.4)O2(polyvinylpyrrolidone (PVP)) catalyst displayed significant catalytic activity and the slip ammonia was almost completely removed with the coexistence of NOx and SO2. Interestingly, the effect of SO2 on NH3 oxidation was bifacial, and the N2 selectivity of the resulting products was as high as 100% in the presence of SO2 and NH3. The mechanism of the SCO of NH3 over Ru/Ce(0.6)Zr(0.4)O2(PVP) was studied using various techniques, and the results showed that NH3 oxidation follows an internal SCR (iSCR) mechanism. The adsorbed ammonia was first activated and reacted with lattice oxygen atoms to form an -HNO intermediate. Then, the -HNO mainly reacted with atomic oxygen from O2 to form NO. Meanwhile, the formed NO interacted with -NH2 to N2 with N2O as the byproduct, but the presence of SO2 can effectively inhibit the production of N2O.

Novel regenerable sorbent based on Zr-Mn binary metal oxides for flue gas mercury retention and recovery.

To capture and recover mercury from coal-fired flue gas, a series of novel regenerable sorbents based on Zr-Mn binary metal oxides were prepared and employed at a relatively low temperature. PXRD, TEM, TPR, XPS, and N2-adsorption methods were employed to characterize the sorbents. The Hg(0) adsorption performance of the sorbents was tested, and the effects of the main operation parameters and the gas components on the adsorption were investigated. Zr significantly improved the sorbent's mercury capacity, which was nearly 5mg/g for Zr0.5Mn0.5Oy. Furthermore, the spent sorbent could be regenerated by heating to 350°C, and the highly concentrated elemental mercury released could be facilely recycled. Therefore, a much greener process for mercury capture and recovery could be anticipated based on this regenerable sorbent.

Significance of RuO2 modified SCR catalyst for elemental mercury oxidation in coal-fired flue gas.

Catalytic conversion of elemental mercury (Hg(0)) to its oxidized form has been considered as an effective way to enhance mercury removal from coal-fired power plants. In order to make good use of the existing selective catalytic reduction of NO(x) (SCR) catalysts as a cobenefit of Hg(0) conversion at lower level HCl in flue gas, various catalysts supported on titanium dioxide (TiO(2)) and commercial SCR catalysts were investigated at various cases. Among the tested catalysts, ruthenium oxides (RuO(2)) not only showed rather high catalytic activity on Hg(0) oxidation by itself, but also appeared to be well cooperative with the commercial SCR catalyst for Hg(0) conversion. In addition, the modified SCR catalyst with RuO(2) displayed an excellent tolerance to SO(2) and ammonia without any distinct negative effects on NO(x) reduction and SO(2) conversion. The demanded HCl concentration for Hg(0) oxidation can be reduced dramatically, and Hg(0) oxidation efficiency over RuO(2) doped SCR catalyst was over 90% even at about 5 ppm HCl in the simulated gases. Ru modified SCR catalyst shows a promising prospect for the cobenefit of mercury emission control.