The enhancement effect of Nb over CeSi2 catalyst for the low-temperature NH3-SCR performance

Tuning the acid site on the surface of the catalyst tends towards facilitating the selective reduction of NOx by NH3 (NH3-SCR). In this study, a set of catalysts for the Nb/CeSi2 with different loadings of niobium were synthesized and evaluated in terms of NH3-SCR over a broad temperature range. The results indicated that a catalyst for 20Nb/CeSi2 exhibited the best low-temperature NH3-SCR performance while maintaining excellent SO2/H2O resistance. These catalysts were also characterized by BET, XRD, Raman, NH3-TPD, and H2-TPR to further explore the correlations between catalyst structure and performance after adding niobium. For the Nb/CeSi2 catalysts, the surface structure was blocked by niobium species, resulting in varying degrees of reduction in the specific surface areas. Also, the total acidity decreased with the declines of the specific surface areas while the acidity per unit was enhanced, which facilitates the occurrence of the SCR reaction. Furthermore, in situ DRIFTS results indicated that SCR reaction could occur following the Eley-Rideal (E-R) mechanism and Langmuir-Hinshelwood (L-H) mechanism simultaneously over 20Nb/CeSi2 catalyst, which could be attributed to the interaction between niobium and ceria in favor of the activation of inert surface nitrate, considered the primary factor for the improvement of the catalyst performance at low-temperature.