A basic comprehensive study on synergetic effects among the metal oxides in CeO2-WO3/TiO2 NH3-SCR catalyst

Abstract

• The impregnated CeW/Ti-I exhibits over 80% NO x conversion at 200–550 °C for NH 3 -SCR. • Substitution of Ce 4+ /Ti 4+ by W 6+ at the interface depends on dispersion of metal oxides. • Formation of solid solutions produces more lattice defects and M O M’ bridges. • Ce 3+ and oxygen vacancies facilitate the low-temperature activity via fast SCR route. • Unsaturated cations and Ce(Ti) O W bonds serve as Lewis and Brønsted acid sites. Two Ce-W-Ti mixed oxide catalysts were prepared by wet impregnation (CeW/Ti-I) and mechanical mixing (Ce/W/Ti-M) methods. CeW/Ti-I catalyst exhibits over 80% NO x conversion and nearly 100% N 2 selectivity at 200–550 °C. The superior catalytic performance is associated with the high dispersion of active CeO 2 and acidic WO 3 on TiO 2 and the synergistic effects among different components. The X-ray Diffraction, Raman spectroscopy, Nitrogen physisorption, X-ray photoelectron spectroscopy, H 2 temperature-programmed reduction, temperature-programmed desorption of ammonia and infrared spectroscopy were performed. It is found that the formation of solid solutions, as well as the high specific surface area, would increase the amounts of Ce 3+ , oxygen vacancies and acid sites in the catalyst. These broaden the operating temperature window of NH 3 -SCR reaction and enhance the N 2 selectivity by facilitating “fast SCR” reaction at low temperatures and inhibiting the unselective oxidation of NH 3 at high temperatures.