Doping effect of Sm on the TiO2/CeSmOx catalyst in the NH3-SCR reaction: structure-activity relationship, reaction mechanism and SO2 tolerance

A series of environmentally benign TiO2/CeSmOx catalysts were prepared by combining coprecipitation and impregnation methods. The effect of doping Sm species into CeO2 for selective catalytic reduction of NO by NH3 (NH3-SCR) was investigated. The results of catalytic tests displayed that the catalyst with the optimal molar ratio (Ce : Sm = 20 : 1) exhibited the best deNO(x) performance. Moreover, the NH3-SCR efficiency of TiO2/CeSmOx (Ce : Sm = 20 : 1) was higher than that of TiO2/CeO2. The obtained samples were characterized by BET, XRD, Raman, HAADF-STEM, XPS, H-2-TPR, NH3-TPD and in situ DRIFTS techniques to investigate the effect of Sm doping on the physiochemical properties of the TiO2/CeSmOx catalyst. The XRD, Raman and HAADF-STEM results revealed that the Sm dopant had been incorporated into the CeO2 lattice successfully, and the Ti species were highly dispersed on the CeSmOx support. The H-2-TPR, NH3-TPD and in situ DRIFTS results suggested that the redox properties and surface acidity of the catalyst were adjusted to a good balance by the introduction of Sm species, which were beneficial to the enhancement of the catalytic activity at low temperatures (<300 degrees C). In addition, the NH3-SCR reaction followed the Langmuir-Hinshelwood mechanism on the TiO2/CeO2 catalyst surface in the whole temperature range. The introduction of Sm species changed the reaction pathway, and both the Eley-Rideal and Langmuir-Hinshelwood mechanisms existed when the temperature was higher than 250 degrees C. Furthermore, the addition of Sm to the TiO2/CeO2 catalyst improved the H2O and SO2 resistance ability of the catalyst due to suppression of the bulk sulfate formation.