Hydrothermal Stability of CeO-WO-ZrO Mixed Oxides for Selective Catalytic Reduction of NOx by NH.

CeO-WO-ZrO mixed oxides were prepared by the homogeneous precipitation method for the selective catalytic reduction of NOx with NH (NH-SCR). The effects of hydrothermal aging on the catalytic performances of CeO-WO-ZrO were investigated. The results showed that CeO-WO-ZrO catalyst exhibited excellent NH-SCR activity for removal of NOx and hydrothermal stability. After hydrothermal aging at 850 °C for 16 h, the optimum CeO-WO-ZrO catalyst could still realize 80% NOx conversion at 300-500 °C even under a high gas hourly space velocity of 250 000 h. The structural properties, redox ability, surface species, and acidity of fresh and hydrothermally aged CeO-WO-ZrO catalysts were characterized by N-physisorption, XRD, Raman, H-TPR, XPS, NH-TPD, and in situ DRIFTS. The characterization results showed that decreases of 89% of the surface area and 71% of the NH storage capacity as well as new phase formation occurred for the CeO-WO-ZrO sample after hydrothermal aging at 850 °C for 16 h. The activity of hydrothermally aged CeO-WO-ZrO was mainly attributed to the retention of redox-acid sites and their interaction due to the formation of Ce-Zr solid solutions and CeWO.