Effect of the calcination temperature of cerium–zirconium mixed oxides on the structure and catalytic performance of WO3/CeZrO2 monolithic catalyst for selective catalytic reduction of NOx with NH3
A series of WO3/CeZrO2 catalysts, prepared at different calcination temperatures (400, 500, 600 and 700 °C) of cerium–zirconium mixed oxides (CeZrO2) for the selective catalytic reduction of NOx with ammonia (NH3-SCR), were investigated via various characterizations, such as N2 physisorption, XRD, Raman, NH3-TPD, DRIFTS, XPS and H2-TPR. The catalytic performance of NH3-SCR was remarkably promoted by modestly increasing the calcination temperature of CeZrO2: WO3/CeZrO2-500 possessed the lowest light-off temperature (173 °C) and complete conversion temperature (205 °C), while W/CeZrO2-600 could achieve greater than 90% NOx conversion in a broad temperature range of 220–455 °C. The characterization results indicated that modest enhancement of the calcination temperature of CeZrO2 was beneficial to stabilizing the structure of the catalysts. The largest amount of Lewis acid sites, Ce3+ and surface active oxygen species, as well as strong redox properties of WO3/CeZrO2-500 should together contribute to its better low-temperature deNOx activity. Moreover, increasing the calcination temperature of cerium–zirconium mixed oxides resulted in the enhancement of Brønsted acid sites, which was responsible for the widened operation temperature window. Therefore, WO3/CeZrO2 serial catalysts with appropriate calcination treatment of CeZrO2 would be a good choice for the removal of NOx emitted from diesel engines.