Physicochemical Properties and NH₃-SCR Performance of Supported CeO₂–MnO_x Mixed Oxides Catalysts

CeO₂–MnO_x mixed oxides supported on different carriers (ZSM-5, TiO₂, and SAPO-34) were prepared by the sol-gel combustion method and evaluated for the selective catalytic reduction of NO with NH₃. The physicochemical properties of the samples were determined by using XRD, TEM, N₂ adsorption (BET method), H₂-TPR, and NH₃-TPD. The Ce–Mn/TiO₂ exhibited a higher NO conversion than Ce–Mn/ZSM-5 in the 100-200°C temperature range, but the NO conversion of Ce–Mn/ZSM-5 increases with reaction temperature (being the N₂ selectivity close to 100%) whereas, for Ce–Mn/TiO₂, the N₂ selectivity extremely decreases. The reducibility and surface acidity of samples seems to explain the catalytic performance. Thus, although the reducibility of Ce–Mn/ZSM-5 and Ce–Mn/TiO₂ was similar, the large number of surface acid sites of Ce–Mn/ZSM-5 could be a plausible reason for its excellent SCR activity. In fact, the superior SCR activity of Ce–Mn/ZSM-5 (94% NO conversion and 95% N₂ selectivity at 300°C) is related to the presence of well-dispersed Ce–Mn mixed oxide nanoparticles, high reducibility, and a large number of surface acid sites.