Effect of Ce/Zr molar ratio on the performance of Cu–Cex–Zr1 − x/TiO2 catalyst for selective catalytic reduction of NOx with NH3 in diesel exhaust

Copper–cerium–zirconium catalysts loaded on TiO2 prepared by a wet impregnation method were investigated for NH3-selective catalytic reduction of NOx, aiming to study the effects of the Ce/Zr molar ratio on the performance of Cu–Ce–Zr/TiO2 catalysts. The Cu–Ce0.25–Zr0.75/TiO2 sample exhibited nearly 100% NOx conversion over a wide temperature range (165–450 °C), which is strikingly superior to that of Cu/TiO2 (210–389 °C) within the range of exhaust temperatures of diesel engines. The factors that govern the activity enhancement were extensively investigated by using a series of characterization techniques, namely X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction by hydrogen (H2-TPR). The results showed that the addition of zirconium and/or cerium refined the copper dispersion, prevented copper crystallization and partially incorporated the copper ions into the zirconia (ceira) lattice, which led to enhance the redox abilities of Cu–Ce–Zr/TiO2 catalysts.