Activity and hydrothermal stability of CeO2-ZrO2-WO3 for the selective catalytic reduction of NOx with NH3

A series of CeO2-ZrO2-WO3 (CZW) catalysts prepared by a hydrothermal synthesis method showed excellent catalytic activity for selective catalytic reduction (SCR) of NO with NH3 over a wide temperature of 150-550 degrees C. The effect of hydrothermal treatment of CZW catalysts on SCR activity was investigated in the presence of 10% H2O. The fresh catalyst showed above 90% NOx conversion at 201-459 degrees C, which is applicable to diesel exhaust NOx purification (200-440 degrees C). The SCR activity results indicated that hydrothermal aging decreased the SCR activity of CZW at low temperatures (below 300 degrees C), while the activity was notably enhanced at high temperature (above 450 degrees C). The aged CZW catalyst (hydrothermal aging at 700 degrees C for 8 hr) showed almost 80% NOx conversion at 229-550 degrees C, while the V2O5-WO3/TiO2 catalyst presented above 80% NOx conversion at 308-370 degrees C. The effect of structural changes, acidity, and redox properties of CZW on the SCR activity was investigated. The results indicated that the excellent hydrothermal stability of CZW was mainly due to the CeO2-ZrO2 solid solution, amorphous WO3 phase and optimal acidity. In addition, the formation of WO3 clusters increased in size as the hydrothermal aging temperature increased, resulting in the collapse of structure, which could further affect the acidity and redox properties. (C) 2015 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.