Effect of ZrO2 Crystal Structures on the Catalytic Performance of MnOx-CeO2/ZrO2 for Selective Reduction of NO with NH3 at Low Temperature

Abstract

A series of manganese oxide and cerium oxide catalysts supported on monoclinic zirconia (m-ZrO2), tetragonal zirconia (t-ZrO2) and cubic zirconia (c-ZrO2) were prepared by a wet-impregnation method. The catalytic performance and SO2 tolerance for the selective reduction (SCR) of NOx with NH3 were investigated. Measurements were carried out in a fixed-bed reactor. The results suggested that both SCR activity (NO conversion on the catalysts) and SO2 tolerance of the prepared catalysts decreased in the following order: 5 wt.% MnOx-CeO2/c-ZrO2(5c) > 5 wt.% MnOx-CeO2/t-ZrO2(5t) > 5 wt.% MnOx-CeO2/m-ZrO2(5m) Surface properties are discussed by using XRD, BET, SEM, XPS, TPR, TPD and TG-DTA, FT-IR. 5 wt.% MnOx-CeO2/c-ZrO2 catalyst exhibited the best redox property and the highest adsorption capacity for NH3 while 5 wt.% MnOx-CeO2/m-ZrO2 and 5 wt.% MnOx-CeO2/t-ZrO2 catalysts exhibited relatively poor performance. Also, there existed the largest density of acid sites and highest strength of acidity when c-ZrO2 was used as carrier. The deterioration of active component and deposition of NH4HSO4, (NH4)(2)SO4 or metallic sulfites were identified as the main causes of SO2 poisoning.