Investigation of the Promotional Effect of W Modification on Selective Catalytic Reduction Performance of Ce0.4ZrOx Catalysts

Various amounts of W were modified on Ce0.4ZrOx catalysts via a wet impregnation method. Among them, the W0.1/Ce0.4ZrOx catalyst with W/Zr molar ratio of 0.1 exhibited a much better catalytic activity and a good SO2 resistance. Its active temperature window corresponding to 80% NOx conversion was as wide as 210–450 °C. It could maintain a high NOx conversion efficiency (>96%) after treatment in 100 ppm SO2 atmosphere for 18 h. Characterization results indicated that the W element successfully entered the lattice of the Ce–Zr solid solution via partially replacing Zr atoms. This led to an electron redistribution on the surface of the W0.1/Ce0.4ZrOx catalyst, which was beneficial to form Ce3+ and oxygen vacancies, thus significantly improving the redox performance. In addition, WOx also significantly enhanced the surface acidity of the Ce0.4ZrOx catalyst, which was conducive to the adsorption of NH3. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results confirmed that nitrate species adsorbed on the surface of the W0.1/Ce0.4ZrOx catalyst could be activated by W, thus reacting with NH3 species efficiently. The reaction pathway over the W0.1/Ce0.4ZrOx catalyst followed both Eley–Rideal and Langmuir–Hinshelwood mechanisms at 300 °C. The enhancement effect of W modification on SO2 resistance of W0.1/Ce0.4ZrOx catalyst was mainly ascribed to the balance between the redox and acidic properties.