Selective Catalytic Reduction of NO with NH_3 on Modified ZrO_2-MnO_2 Monolithic Catalysts

A ZrO2-MnO2 catalyst was prepared by the co-precipitation method,and modified with CeO2,MoO3,and WO3 by impregnation. The catalytic activity of the monolithic catalysts for selective catalytic reduction of NOx with NH3(NH3-SCR) was studied. All the catalysts were characterized by low temperature nitrogen adsorption-desorption,X-ray diffraction,X-ray photoelectron spectroscopy,and NH3/NO-temperature-programmed desorption. The results show that the phase of the catalysts is Mn0.2Zr0.8O1.8 solid solution,and CeO2 and WO3 are well dispersed in catalysts. When adding MoO3 or WO3 into the catalyst,some medium-strength acid sites and the strongly adsorbed NO species that are beneficial to the elevated temperature catalytic activity increase. Mn and Ce exist as Mn4+ and Ce4+. The low temperature SCR activity is improved by the modification with CeO2,but the temperature window of the reaction is relatively narrow. When MoO3 or WO3 is introduced into CeO2/ZrO2-MnO2,the catalyst exhibits better catalytic performance and wider temperature window. The light-off temperature of WO3/CeO2/ZrO2-MnO2 is 176 oC,and the NOx conversion is over 90% in the temperature range of 240–424 oC,and it has good low-temperature activity and wide temperature window.