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 O-2. Various characterization methods such as N-2 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. (c) 2007 Elsevier B.V. All rights reserved.