Poisoning mechanism of alkali metal on Cu–Fe2O3 catalyst for selective catalytic reduction of NOx with NH3

Abstract

The poisoning mechanism of Na on Cu–Fe2O3 solid solution catalyst was studied by a series of characterization methods, such as X-ray diffraction (XRD), temperature-programmed reduction by hydrogen (H2-TPR), X-ray photoelectron spectroscopy (XPS), Temperature-programmed desorption (TPD) and in-situ Diffuse Reflectance Infrared Fourier Transform spectroscopy (in-situ DRIFT). The characterization results manifest that one part of Na ions can enter into the crystal lattice of Fe2O3, and replace the original Cu2+ in the crystal lattice of Fe2O3. The replacement results in the electrophilicity of Fe3+ species, thereby restraining the generation and adsorption of NO2, nitrate and nitrite species and reducing Lewis acid sites. In addition, the displaced Cu2+ ions form CuO species and lead to excessive oxidation of NH3 to NOx. In addition, Na2O covers the adsorption sites for NH3, NO2, nitrate and nitrite species. According to in-situ DRIFTS results, the reaction still proceeds through both “fast SCR” and Langmuir-Hinshelwood (L-H) reaction mechanism after sodium poisoning, but the reaction rate reduces obviously. This work reveals the influence and poisoning mechanism of alkali metal on the solid solution catalyst, establishes an alkali metal poisoning model, and offers a new way to develop low-temperature SCR catalysts with high alkali resistance.