Lu Pei,Yue Huifang,Xing Yi,Wei Jianjun,Zeng Zheng,Li Rui,Wu Wanrong
In this study, series of Ce x Zr y Mn z O 2 /r-Al 2 O 3 catalysts were prepared by impregnation method and explored to co-purification of NO x and Hg 0 at low temperature. The physical and chemical properties of the catalysts were investigated by XRD, BET, FTIR, NH 3 -TPD, H 2 -TPR, and XPS. The experimental results showed that 10% Ce 0.2 Zr 0.3 Mn 0.5 O 2 /r-Al 2 O 3 yielded higher conversion on co-purification of NO x and Hg 0 than the other prepared catalysts at low temperature, especially at 200–300 °C. 91% and 97% convert rate of NO x and Hg 0 were obtained, respectively, when 10% Ce 0.2 Zr 0.3 Mn 0.5 O 2 /r-Al 2 O 3 catalyst was used at 250 °C. Moreover, the presence of H 2 O slightly decreased the removal of NO x and Hg 0 owing to the competitive adsorption of H 2 O and Hg 0 . When SO 2 was added, the removal of Hg 0 first increased slightly and then presented a decrease due to the generation of SO 3 and (NH 4 ) 2 SO 4 . The results of NH 3 -TPD indicated that the strong acid of 10% Ce 0.2 Zr 0.3 Mn 0.5 O 2 /r-Al 2 O 3 improved its high-temperature activity. XPS and H 2 -TPR results showed there were high-valence Mn and Ce species in 10% Ce 0.2 Zr 0.3 Mn 0.5 O 2 /r-Al 2 O 3 , which could effectively promote the removal of NO x and Hg 0 . Therefore, the mechanisms of Hg 0 and NO x removal were proposed as Hg (ad) + [O] → HgO (ad), and 2NH 3 /NH 4 + (ad) + NO 2 (ad) + NO (g) → 2 N 2 + 3H 2 O/2H + , respectively.
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To optimize the simultaneous removal of NO x and Hg 0 , a series of Cu a Ce b Zr c O 3 /γ-Al 2 O 3 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), NH 3 -temperature-programmed desorption (NH 3 -TPD), H 2 -temperature-programmed reduction (H 2 -TPR), in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFT), and Fourier transform infrared spectroscopy (FT-IR). The results showed that 15% Cu 1.4 Ce 0.55 Zr 0.25 O 3 /γ-Al 2 O 3 resulted in the highest conversion efficiency for the simultaneous removal of NO x (93%) and Hg 0 (85%) at low temperatures (200 to 300 °C). Meanwhile, 15% Cu 1.4 Ce 0.55 Zr 0.25 O 3 /γ-Al 2 O 3 showed good stability and resistance to SO 2 and H 2 O, 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% Cu 1.4 Ce 0.55 Zr 0.25 O 3 /γ-Al 2 O 3 promoted the removal of NO x and Hg 0 . The synergistic effect between CuO and CeO 2 in 15% Cu 1.4 Ce 0.55 Zr 0.25 O 3 /γ-Al 2 O 3 can increase the mobility of chemically adsorbed oxygen and activates lattice oxygen, leading to an excellent performance. The DRIFT results showed that NH 3 , NH 4 + , nitrate, and nitrite participated in the selective catalytic reduction (SCR) reaction. On the basis of our experimental results, Hg 0 and NO x removal mechanisms were proposed as Hg (ad) + O* → HgO (ad) and 2NH 3 /NH 4 + (ad) + NO 2 /NO 3 − (ad) + NO→2N 2 + 3H 2 O/2H + , respectively.
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