575 / 2019-01-18 22:04:20

Effect of Cerium on the Catalytic Performance of Mn-Fe/Al nanocatalyst for NO Oxidation and Fast SCR Reaction

NO oxidation; Fast SCR; NOx conversion; Cerium

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NOx (including NO and NO2) is the main air pollutant emitted from fossil fuel combustion, which can lead to acid rain, photochemical oxidation, ozone depletion and further impact of global warming. Various reaction mechanisms have been proposed and the characteristics of the main selective catalytic reduction (SCR) reactions and fast SCR reactions have also been systematically studied. The results show that the rate of fast SCR reactions is significantly higher than that of standard SCR reactions. Therefore, the pre-oxidation of NO before SCR process is conducive to accelerate the SCR reaction by artificially increasing the molar ratio of NO2:NO. Ce-Mn-Fe/Al nanocatalysts with different Ce doping amount were prepared in order to reveal the synergistic effect of Ce and Fe-Mn on catalytic oxidation of NO to NO2 and catalytic activity of fast selective catalytic reaction (SCR). The results showed that cerium-doped Mn-Fe/Al nanocatalyst could significantly improve the oxidation rate of NO to NO2. When Ce-Mn-Fe/Al nanocatalyst with the Ce:Fe:Mn = 1:2:16, the optimum catalytic activity was obtained. The conversion efficiency of NOx was more than 95.5% at 100-350 ℃, and the oxidation efficiency of NO reached 55.1% at 350 ℃. Scanning electron microscopy (SEM), X-ray diffraction (XRD), H2 temperature programmed reduction (TPR), NH3 temperature programmed desorption (TPD), NO-TPD and X-ray photoelectron spectroscopy (XPS) were used to characterize the results. It was found that the dispersion of active elements and the binding of iron and manganese elements were enhanced with the introduction of cerium. The crystallinity of metal oxides was reduced. Doping cerium increased Mn4+/Mnn+ and Fe3+/ Fen+, and increases the number of lattice oxygen and oxygen vacancies, thus increasing the oxidation rate of NO to NO2, and finally increasing the rate of rapid SCR reaction. However, excessive doping of cerium can lead to the crystallization of cerium. This study shows that Ce-Mn-Fe/Al sample, as a good nanocatalyst, has good prospects for NO pre-oxidation and fast SCR reaction.