Promoting the effects of CuSO4 on N2 selectivity in selective catalytic oxidation of ammonia over Pt/TiO2 catalysts

Abstract

Selective catalytic oxidation of NH₃ (NH₃-SCO) is a promising method to reduce NH₃ pollution. The Pt-based catalysts exhibited excellent activity in the NH₃-SCO reaction under low temperatures. However, it was easy for the NH₃ to be oxidized to N₂O and NO_x (NO and NO₂) over the Pt-based catalyst, causing a low N₂ selectivity. The CuSO₄, which could supply both Brønsted and Lewis acid sites on the catalyst, was used to promote N₂ selectivity. The N₂ adsorption–desorption, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), inductively coupled plasma mass spectrometry (ICP-MS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), NH₃-temperature programmed desorption (NH₃-TPD), H₂-temperature programmed reduction (H₂-TPR) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were used to characterize the catalyst. The addition of CuSO₄ could suppress the formation of N₂O and NO_x, thus the highest N₂ selectivity on the catalyst increased from 21.2% to 78.1%. An imide mechanism was the main reaction mechanism on the Pt/TiO₂ catalyst. After adding CuSO₄, the NH₃-SCO reaction over the CuSO₄-Pt/TiO₂ catalyst mainly followed an i-SCR mechanism where NH₃ was oxidized to N₂O and NO_x, and then the newly formed N₂O and NO_x were reacted with NH₃/NH₄⁺ adsorbed on the Lewis and Brønsted acid sites via an NH₃-SCR reaction over the catalyst, and finally N₂ was formed. The acid sites performed an important role in the formation of N₂ and this work should provide an effective method to promote N₂ selectivity in a NH₃-SCO reaction.