Facile synthesis of CuSO4/TiO2 catalysts with superior activity and SO2 tolerance for NH3-SCR: physicochemical properties and reaction mechanism

Abstract

A series of CuSO₄/TiO₂ binary oxide catalysts with different CuSO₄ loadings (0–20 wt%) were prepared by a facile solid state impregnation protocol. The physicochemical properties of the catalysts and the NO reaction route were extensively characterized via N₂ adsorption/desorption, XRD, Raman, NH₃-TPD, NO-TPD, H₂-TPR, XPS, and in situ DRIFTS. The CuSO₄ content had significant influence on catalytic activity. High CuSO₄ loading favored the solid reaction between CuSO₄ and TiO₂, promoted the formation of sulfite and weak acid sites, and obviously increased the activity at temperatures below 340 °C. However, at a temperature higher than 340 °C, NH₃ oxidation increased with CuSO₄ loading and caused NO_x conversion to decrease when the CuSO₄ loading was higher than 10 wt%. Thus, the sample with 10 wt% CuSO₄ loading presented the broadest temperature window and it also showed an excellent resistant to SO₂ and H₂O. Both Brønsted and Lewis acid sites were formed on the catalyst. S–OH of sulfate and sulfite were the main reason for formation of Brønsted acid sites. NH₃-SCR reaction on CuSO₄/TiO₂ followed the Eley–Rideal mechanism: NH₃ first adsorbed on Brønsted and Lewis acid sites as NH₄⁺ and NH₃, then reacted with gaseous NO and O₂ to form N₂ and H₂O.