Promotional effects of Nb on selective catalytic reduction of NO with NH₃ over Fe_x-Nb₀._5-x-Ce_0.5 (x = 0.45, 0.4, 0.35) oxides catalysts

Citric acid method was employed to prepare a series of Nb-promoted Fe_x-Nb₀._5-x-Ce_0.5 (x = 0.45, 0.4, 0.35) oxides for selective catalytic reduction with NH₃ (NH₃-SCR) of NO process. The structure, redox ability and reactivity of NH₃ and absorbed NO species on the catalysts were explored by using various characterization techniques such as X-ray diffraction (XRD), temperature program reduction with H₂ (H₂-TPR), temperature program desorption of NH₃ (NH₃-TPD), temperature program desorption of NO (NO-TPD), X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). It was found that the Nb promoted Fe_x-Nb₀._5-x-Ce_0.5 (x = 0.45, 0.4, 0.35) oxides catalysts showed outstanding NH₃-SCR of NO activity, excellent N₂ selectivity and remarkable SO₂/H₂O resistance, meanwhile, Fe_0.4-Nb_0.1-Ce_0.5 exhibited above 90% NO conversion in the range of 180–400 °C, together with near 100% N₂ selectivity. The characterization results point out that the excellent catalytic performance of Fe_0.4-Nb_0.1-Ce_0.5 can be ascribed to the strong interaction among Nb, Fe and Ce oxides. The strong interaction not only increases the BET surface area and redox ability of the catalyst, but also significantly improves the acid amount leading to the enhancement of the adsorption and activation of NH₃, which is advantage of the reactivity of adsorbed nitrate together with the adsorbed NH₃ species.