Abstract: A series of Cr-Mn mixed-oxide catalysts comprising a novel CrMn_1.5O₄ crystal phase were prepared by the coprecipitation method and applied to low-temperature selective catalytic reduction (SCR) of NO_x with NH₃ in the presence of O₂. The experimental results showed that the NO_x conversion increased with the increase of Cr content and peaked at the Cr(0.4)-MnO_x catalyst with the molar ratio of Cr/(Mn+Cr) = 0.4, which yielded nearly 90% NO_x conversion at 140 ^oC with a high space velocity of 30 000 h^-1. The characterization of N₂ adsorption, X-ray diffraction, and X-ray photoelectron spectroscopy indicated that the addition of Cr generated the novel CrMn_1.5O₄ crystal phase and adjusted the surface electronic properties, leading to the enrichment of higher oxidation states Mn⁴⁺ and Mn³⁺ on the surface. This promotes the oxidation of NO and is helpful for the adsorption of NH₃, so that the catalyst exhibits higher low-temperature SCR activity.

Key words: coprecipitation, nitrogen oxide, selective catalytic reduction, ammonia, low-temperature, chrome, manganese