Synergistic effects between copper and tungsten on the structural and acidic properties of CuOx/WOx–ZrO2 catalyst

Abstract

Different amounts of tungsten oxide were introduced to zirconia to form WO_x–ZrO₂ solid solutions by a coprecipitation method, followed by impregnation with copper nitrate. The received catalysts were characterized by X-ray diffraction, Brunauer–Emmett–Teller surface area, X-ray photoelectron spectroscopy, Raman spectroscopy, diffuse reflectance UV-vis spectroscopy, H₂ temperature-programmed reduction and in situFTIR of NH₃ /NO+O₂ adsorption. Higher dispersions of CuO_x are obtained on the tungsten-containing catalysts due to the increased surface area of the support. Highly dispersed WO_x clusters in tetrahedral coordination are generated when tungsten exceeds its solubility in the solid solutions, and polymerized WO_x clusters are formed for further increasing the loading amount of tungsten. The formation of Cuⁿ⁺–O²⁻–Wⁿ⁺ bonds at the interface between CuO_x and WO_x clusters leads to an improved capacity to form nitrite and an enhanced Brønsted acidity, which enhance the activity of the catalyst for NH₃-SCR reaction.