Effect of samarium on the N2 selectivity of SmxMn0.3-xTi catalysts during selective catalytic reduction of NOx with NH3

This work aims to study the improvement effect of Sm on Mn-based catalysts for selective catalytic reduction (SCR) of NO with NH3. A series of SmxMn0.3-xTi catalysts (x = 0, 0.1, 0.15, 0.2, and 0.3) were prepared by co-precipitation. Activity tests indicated that the Sm0.15Mn0.15Ti catalyst showed superior performances, with a NO conversion of 100% and N-2 selectivity above 87% at 180-300 degrees C. The characterizations showed that Sm doping suppressed the crystallization of TiO2 and Mn2O3 phases and increased the specific surface area and acidity. In particular, the surface area increased from 152.2 m(2)center dot g(-1) for Mn0.3Ti to 241.7 m(2)degrees g(-1) for Sm0.15Mn0.15Ti. These effects contributed to the high catalytic activity. The X-ray photoelectron spectroscopy (XPS) results indicated that the relative atomic ratios of Sm3+/Sm and O-beta/O of Sm0.15Mn0.15Ti were 76.77at% and 44.11at%, respectively. The presence of Sm contributed to an increase in surface-absorbed oxygen (O-beta) and a decrease in Mn4+ surface concentration, which improved the catalytic activity. In the results of hydrogen temperature-programmed reduction (H-2-TPR), the presence of Sm induced a higher reduction temperature and lower H-2 consumption (0.3 mmol center dot g(-1)) for the Sm0.15Mn0.15Ti catalyst compared to the Mn0.3Ti catalyst. The decrease in Mn4+ weakened the redox property of the catalysts and increased the N-2 selectivity by suppressing N2O formation from NH3 oxidation and the nonselective catalytic reduction reaction. The in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) revealed that NH3-SCR of NO over the Sm0.15Mn0.15Ti catalyst mainly followed the Eley-Rideal mechanism. Sm doping increased surface-absorbed oxygen and weakened the redox property to improve the NO conversion and N-2 selectivity of the Sm0.15Mn0.15Ti catalyst.