Study On Ce Based Catalysts With Different Morphology For The Selective Catalytic Reduction Of NO_x By NH₃

In this paper,different morphology of CeO2 nanoparticles,including nano cube,nano octahedron,nano spindles,nanospheres,nanorods,nanosheets,nanowires,nanometer Rod and flower structure,were prepared by the hydrothermal method,For 5%W/CeO2 nanocatalyst prepared by impregnation method,the morphology of CeO2 was destroyed after doped W and the activity was low in NH3-SCR reaction.CeMnOx composite oxide catalyst prepared by hydrothermal method was not active for the NH3-SCR of NOx.In this work,CeOx@MnOx and CeOx@WOx core-shell catalysts were prepared using CeO2 cube as the core,and compared with the CeMnOx and CeWOx catalysts prepared by the conventional coprecipitation method.It was found that the ratios of Ce/Mn and Ce/W had little effect on the activity of the core-shell structure catalyst.Compared with the CeMnOx and CeWOx catalysts,The CeOx@MnOx catalyst had a wider operating temperature window.At 100-300℃,the conversion of NOx was above 90%.Even under high GHSV,the conversion of NOx is still relatively high.Morevoer,the resistance against water and SO2 was greatly improved.The NOx conversion and N2 selectivty Of the CeOx@WOx catalyst reached about 100%at 250-450 ℃.According to BET,XRD,XPS analysis,the strong interaction between Ce and Mn species or Ce and W species in CeOx@MnOx or CeOx@WOx catalysts could led to a much higher dispersion of Ce species,with a larger Ce3+/Ce4+ ratio and more oxygen vacancies,resulting in higher NO oxidation ability and thus better SCR activity at low temperatures.In addition,due to the increased capacity for adsorption of NH3 species on both Bronsted acid sites and Lewis acid sites.the NH3 unselective oxidation at high temperatures was also greatly inhibited,thus leading to higher SCR activity and N2 selectivity simultaneously.