Regenerable Sorbent with a High Capacity for Elemental Mercury Removal and Recycling from the Simulated Flue Gas at a Low Temperature

To remove and recycle elemental mercury from flue gas, a serial of Ce–Mn binary metal oxides was prepared and tested as the regenerable sorbents for mercury capture. Ce_0.5Mn_0.5O_<i>y</i> showed the best performance at 100 °C (about 5.6 mg g^–1 adsorption capacity), and Ce–Mn binary metal oxides could adsorb more elemental mercury than MnO_<i>y</i>. Furthermore, it was found that captured mercury can be released from the sorbent in the form of elemental mercury by heating to 350 °C. Meanwhile, the sorbent can be regenerated and repeatedly used. Powder X-ray diffractometer (PXRD), transmission electron microscopy (TEM), hydrogen temperature-programmed reduction (H₂-TPR), ammonia temperature-programmed desorption (NH₃-TPD), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption methods were employed to characterize the sorbents. A model based on mercury temperature-programmed desorption (Hg-TPD) data was built to calculate mercury desorption activation energy from the sorbent. Additionally, the impacts of the temperature and flue gas components on the adsorption capacity were investigated. NO had negligible impact on mercury adsorption, while the presence of SO₂ slightly inhibited the capability of sorbents for mercury capture. The results indicated that Ce–Mn binary metal oxides are a promising sorbent for the mercury removal and recycling from flue gas

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 Hg⁰ 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/Ce_0.6Zr_0.4O₂ catalyst, which was prepared using the polyvinylpyrrolidone-assisted sol–gel method, displayed significantly higher catalytic activity for Hg⁰ oxidation. The mechanism of Hg⁰ removal over IrO₂/Ce_0.6Zr_0.4O₂ was studied using various methods, and the Hg⁰ oxidation reaction was found to follow two possible pathways. For the new chemisorption–regeneration mechanism proposed in this study, the adsorbed Hg⁰ 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 Hg⁰ oxidation: this reaction would involve first oxidizing the adsorbed HCl to active Cl species, after which the Hg⁰ 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 NO_<i>x</i> 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_0.6Zr_0.4O₂(polyvinylpyrrolidone (PVP)) catalyst displayed significant catalytic activity and the slip ammonia was almost completely removed with the coexistence of NO_<i>x</i> 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_0.6Zr_0.4O₂(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