Abstract: The promotional effect of cerium oxide on the catalytic properties of Ce-Mn-Ti-O composite oxide catalysts prepared by the sol-gel method was studied using NH₃-temperature programmed desorption (NH₃-TPD), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H₂-temperature programmed reduction (H₂-TPR), and BET surface area measurements combined with microreactor tests of NO selective catalytic reduction (SCR). The results showed that the addition of a cerium oxide component remarkably increased the low-temperature SCR activity of Mn-Ti-O composite oxide catalyst. When the cerium content was increased, NO conversion increased significantly and reached a maximum around Ce/Mn molar ratio of 0.08. Further increases in the cerium content resulted in a decrease in NO conversion over the catalyst. The experimental results indicated that the addition of a cerium oxide component does not influence the surface acidity of Mn-Ti-O composite oxide catalyst, but increases the surface concentration of catalytically active Mn species, the relative content of Mn⁴⁺, and the reducibility of Mn species, leading to an increase in the SCR activity of Ce-Mn-Ti-O composite oxide catalysts. When the Ce/Mn molar ratio was greater than 0.08, the formation of amorphous multilayer Ce-O-Mn species composed of Ce and Mn species may reduce the Mn/Ti molar ratio and the reducibility of Mn species, leading to a decrease in the SCR activity of Ce-Mn-Ti-O composite oxide catalysts.

Key words: Cerium oxide, Manganese oxide, Titania, Nitric oxide, Selective catalytic reduction