Selective Catalytic Oxidation Of Ammonia To Nitrogen Over Cu-based Catalysts

Ammonia as one of typical toxic and hazardous industrial gaseous pollutants shows very harmful effect on the human health and ecological environment. Therefore, the purification of ammonia has attracted widespread concern. At present, there are many technologies to eliminate ammonia, and Selective Catalytic Oxidation (NH3-SCO) is an effective method for NH3 removal.In this paper, the Cu based catalysts such as Cu/γ-Al2O3 and Cu/CeO2 were prepared by wet impregnation method, and the SCO activity measurements was performed in a fixed-bed quartz reactor. We systematically investigated the influences of the reaction temperature, copper loading, calcination temperature and precursor and analyzed the crystal structures, reducibility and dispersion of the catalysts using XRD,H2-TPR,ESR,UV-Vis,Raman,TPD and TEM techniques. The activity measurement over the Cu/CeO2/Al2O3 wire-mesh honeycomb was also investigated.(1) Copper loading obviously affected the copper species distribution of the Cu/CeO2 catalysts and its activity in NH3-SCO reaction. The load capacity of CeO2 was 1.2 mmol/100 m2 when the copper loading was lower than the capacity, and the copper species was highly dispersed on the surface of the catalysts with the form of Cu-Ce-O solid solution or dispersed CuO. The activity of the catalysts was enhanced with the increase of copper loading. When the copper loading was above the capacity, the crystalline CuO phase appeared, and the activity would not change with the increase of copper loading. Calcination temperature had little effect on the activity of the Cu/CeO2 catalysts, although with the increase of calcination temperature, the particle size of CeO2 was dereasing. Linking the surface structure to the catalyst activity, it was believed that highly dispersed Cu species was active in NH3-SCO, while crystalline CuO contributed little in NH3-SCO reaction.(2) Different precursors and calcination temperatures affected the Cu species distribution on the catalysts, thus influenced their activity in NH3-SCO reaction. It was found that a mixture of CuO phase and cupric spinel CUAl2O4 phase formed on the Cu/γ-Al2O3 catalysts. More CuO phase was observed on the catalyst using the cupric acetate as precursor, however the cupric sulfate was inclined to form cupric spinel CUAl2O4 phase. Calcination temperature at 600℃favored for the dispersion CuO phase on the support. Activity measurement suggested that the well-dispersed CuO phase formed on the support related to its high activity in the NH3-SCO reaction.(3) Cu/CeO2 catalyst and wire mesh honeycomb catalyst Cu/CeO2/Al2O3 showed excellent activity and stability in NH3-SCO reaction, the NH3 conversion stayed 99% at 260℃for 24h.