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A series of La1–xCexMnO3+δ (x = 0, 0.05, 0.1, 0.2, and 0.3) perovskites and Mn–Ce mixed oxides were prepared. Their physico-chemical properties were systematically characterized and the NO oxidation activities of the catalysts were investigated. The La0.9Ce0.1MnO3+δ has the best activity among all of the catalysts, with a maximum NO conversion of 85% at 300 °C. The characterization results indicate that the doping of Ce improves the properties of the perovskites in terms of the specific surface area, the average valence state of Mn ions, the number of reactive oxygen species and the NOx desorption behaviors. The Mn–Ce mixed oxide calcined at 500 °C shows a similar NO oxidation activity with La0.9Ce0.1MnO3+δ. However, the activity of the mixed oxide obtained at 750 °C decreases a lot, which results from the loss of active sites and active oxygen species.

Increasingly stringent regulations in many countries require effective reduction and control of NOx emissions. To meet these limits, various methods have been exploited, among which the selective catalytic reduction of NOx using ammonia as the reductant (NH3-SCR) is the most favored technology. High catalytic activity, N2 selectivity and resistance to deactivation by sulfur, alkaline metals and hydrothermal conditions are the optimal properties of a successful SCR catalyst. Rare earth oxides, particularly CeO2, have been increasingly used to improve the catalytic activity and resistance to deactivation of deNOx catalysts, both modifying traditional vanadium catalysts, and also developing novel catalysts, especially for low temperature applications. This review summarized the open literature concerning recent research and development progresses in the application of rare earths for NH3-SCR of NOx. Additionally, the roles of rare earths in enhancing the performance of NH3-SCR catalyst were reviewed.

Various acidic components (MOx: phosphate, sulfate, tungstate and niobate) were loaded on Ce0.75Zr0.25O2 powders by an impregnation method. The as-prepared catalysts were hydrothermally treated at 760 °C for 48 h in air containing 10 vol.% H2O to obtain the aged catalysts. The catalysts were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, H2 programmed-reduction, NH3 adsorption and deNOx activity measurements. The results showed that, among the catalysts investigated, the phosphated Ce0.75Zr0.25O2 catalyst showed the highest hydrothermal stability. The remained high acidity of the phosphated catalyst with moderate redox property helped to maintain the excellent NH3-SCR activity of hydrothermally aged catalyst. Cerium tungstate led to the poor redox property of the tungstated catalyst although the acidity of catalyst was still high. The decomposition of sulfates at temperatures higher than 600 °C restrained the usage of sulfated catalysts in high temperature conditions. The overall dehydration of niobate to niobium oxides led to the low acidity of hydrothermally aged Nb2O5-Ce0.75Zr0.25O2 catalyst.

MnO x -TiO 2 , CeO 2 -MnO x -TiO 2 and V 2 O 5 -MnO x -TiO 2 catalysts for low-temperature NH 3 -SCR were prepared by sol-gel method. The results showed that both cerium and vanadium prevented the transformation of anatase TiO 2 to the rutile phase. The addition of vanadium oxide induced the segregation of crystalline Mn 2 O 3 , which contributed little to low-temperature SCR and ammonia oxidation, from the MnO x -TiO 2 solid solutions. However, the selectivity of the V-containing catalyst was almost 100% due to the decreased ammonia consumption and enhanced adsorption capacity of ammonia on Bronsted acid sites at relatively high temperatures. The electron-donating effect of cerium reduced the Mn 4+ /Mn 3+ ratio to some extent, resulting in a decreased activity for ammonia oxidation. This, in combination with the enhanced ammonia adsorption capacity by Ce n + as additional Lewis acid sites, endowed the Ce-doped catalyst a higher N 2 selectivity than MnO x -TiO 2 despite the slightly elevated light-off temperature for NO conversion.

Nickel and sulfate co-modified CeO2-ZrO2 catalysts were prepared by sol-gel method. The catalysts were characterized by XRD, FTIR, XPS, NH3 chemisorption and NH3-SCR activity tests. The results showed that the enhanced acidity of CeO2-ZrO2 catalysts by nickel and sulfate co-modification was responsible for the broadened temperature window and improved the selectivity to N2 in NH3-SCR deNOx. The introduction of nickel to CeO2-ZrO2 solid solutions resulted in more Ce3+ on surface of catalyst, leading to an increased Lewis acidity of catalyst. Higher Lewis acidity of catalyst facilitated ammonia activation at low temperature ( 300 °C) activity and selectivity of catalysts arose from the introduction of Bronsted acid sites (less oxidative than Lewis acid sites) by sulfate modification.

CeO 2 and CuO x -CeO 2 supported potassium catalysts were synthesized by wetness impregnation method. The catalysts were characterized by BET, NO-TPO, NO x -TPD and soot-TPO measurements. By the decoration of potassium and copper, the maximum soot combustion temperature of the ceria-based catalyst decreased to 338 and 379 °C in the presence and absence of NO under a loose contact mode, respectively. The pronouncedly enhanced NO oxidation ability by copper introduction and NO x storage capacity by potassium modification were especially important in the NO x -assisted soot oxidation reaction with the K/CuCe catalyst.