Manganese oxide catalysts for NOx reduction with NH₃ at low temperatures

Manganese oxide catalysts prepared by a precipitation method with various precipitants were investigated for the low temperature selective catalytic reduction (SCR) of NOx with NH₃ in the presence of excess O₂. Various characterization methods such as N₂ adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA) and X-ray absorption near edge structure (XANES) were conducted to probe the physical and chemical properties of MnOx catalysts. The active MnOx catalysts, precipitated with sodium carbonate and calcined in air at moderate temperatures such as 523 K and 623 K, have the high surface area, the abundant Mn⁴⁺ species, and the high concentration of surface oxygen on the surface. The amorphous Mn₃O₄ and Mn₂O₃ were mainly present in this active catalyst. The carbonate species appeared to help adsorb NH₃ on the catalyst surface, which resulted in the high catalytic activity at low temperatures.