Simultaneous removal of NOx and Hg0 from simulated flue gas over CuaCebZrcO3/r-Al2O3 catalysts at low temperatures: performance, characterization, and mechanism
2019
Yue, Huifang | Lu, Pei | Su, Wei | Xing, Yi | Li, Rui | Wang, Jiaqing
To optimize the simultaneous removal of NOₓ and Hg⁰, a series of CuₐCebZrcO₃/γ-Al₂O₃ catalysts prepared by the impregnation method were explored and their physical and chemical properties were analyzed by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, X-ray photoelectron spectroscopy (XPS), NH₃-temperature-programmed desorption (NH₃-TPD), H₂-temperature-programmed reduction (H₂-TPR), in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFT), and Fourier transform infrared spectroscopy (FT-IR). The results showed that 15% Cu₁.₄Ce₀.₅₅Zr₀.₂₅O₃/γ-Al₂O₃ resulted in the highest conversion efficiency for the simultaneous removal of NOₓ (93%) and Hg⁰ (85%) at low temperatures (200 to 300 °C). Meanwhile, 15% Cu₁.₄Ce₀.₅₅Zr₀.₂₅O₃/γ-Al₂O₃ showed good stability and resistance to SO₂ and H₂O, which is due to its low crystallinity, good textural performance, and strong redox ability. According to the TPD, TPR, and XPS results, the strong acidic character of 15% Cu₁.₄Ce₀.₅₅Zr₀.₂₅O₃/γ-Al₂O₃ promoted the removal of NOₓ and Hg⁰. The synergistic effect between CuO and CeO₂ in 15% Cu₁.₄Ce₀.₅₅Zr₀.₂₅O₃/γ-Al₂O₃ can increase the mobility of chemically adsorbed oxygen and activates lattice oxygen, leading to an excellent performance. The DRIFT results showed that NH₃, NH₄⁺, nitrate, and nitrite participated in the selective catalytic reduction (SCR) reaction. On the basis of our experimental results, Hg⁰ and NOₓ removal mechanisms were proposed as Hg (ad) + O* → HgO (ad) and 2NH₃/NH₄⁺ (ad) + NO₂/NO₃⁻ (ad) + NO→2N₂ + 3H₂O/2H⁺, respectively.
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