Simultaneous oxidation of Hg0 and NH3-SCR of NO by nanophase Ce x Zr y Mn z O2 at low temperature: the interaction and mechanism

Simultaneous oxidation of Hg⁰ and NH₃-SCR of NO by catalyst is one of the key methods for co-purification of coal-fired flue gas. Till now, the interaction between the oxidation of Hg⁰ and NH₃-SCR of NO and its mechanism have not clarified. In this study, a series of nanophase Ce ₓ Zr y Mn z O₂ was prepared for the simultaneous oxidation of Hg⁰ and NH₃-SCR of NO at low temperature. The catalysts were characterized using surface area analysis, X-ray diffraction, temperature-programmed techniques, and several types of microscopy and spectroscopy. The experimental results indicated that the Ce₀.₄₇Zr₀.₂₂Mn₀.₃₁O₂ exhibited superior Hg⁰ removal efficiency (> 99%) and NO conversion efficiency (> 90%) even at 150 °C, and it also exhibited a good durability in the presence of SO₂ and H₂O. The excellent performance of Ce₀.₄₇Zr₀.₂₂Mn₀.₃₁O₂ on co-purifying Hg⁰ and NO was due to the stronger synergistic effects of Ce-Zr-Mn in Ce₀.₄₇Zr₀.₂₂Mn₀.₃₁O₂ than that of the others, which was illustrated by the characterization results of XPS, XRD, and FT-IR. Moreover, it was found that the NO conversion of Ce₀.₄₇Zr₀.₂₂Mn₀.₃₁O₂ could be slightly influenced by Hg⁰ and was decreased about 4% to the max, while that of Hg⁰ could rarely be affected by the selected catalytic reduction process of NO. It might be due to the co-purification mechanism of NO and Hg⁰. The mechanism of the simultaneous oxidation of Hg⁰ and NH₃-SCR of NO was mainly due to the synergetic effect on the mobility of surface oxygen and the activation of lattice oxygen of Ce₀.₄₇Zr₀.₂₂Mn₀.₃₁O₂. The effect of the oxidation of Hg⁰ on the NH₃-SCR of NO was mainly due to the absorbed Hg⁰/Hg²⁺ on the surface of Ce₀.₄₇Zr₀.₂₂Mn₀.₃₁O₂, which attenuated the formation of NH₃₍ₐd₎, −NH₂₍ₐd₎, and NH₄⁺ on its acid sites. Similarly, the NH₃-SCR of NO process could hardly influence the oxidation of Hg⁰ when NO and Hg⁰ were co-purified.