Abstract: 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 NO_x 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 Mn_0.2Zr_0.8O_1.8 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 NO_x conversion is over 90% in the temperature range of 240–424 ^oC, and it has good low-temperature activity and wide temperature window.

Key words: nitrogen oxides, selective catalytic reduction, monolithic catalyst, zirconium dioxide, manganese dioxide, cerium oxide, tungsten trioxide