Mn-Cu Binary Metal Oxides with Molecular-Scale Homogeneity for Hg0 Removal from Coal-Fired Flue Gas

Binary oxides of MnOx and CuO, prepared by coprecipitation (CuMnxOy-C) and redox-precipitation (CuMnxOy-R) methods, were employed for removing Hg-0 from coal-fired flue gas. The catalysts were characterized systematically by N-2 physisorption, X-ray diffraction, scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The Hg-0 removal performances under various operating conditions were studied, and the resistance to SO2 was investigated particularly. The results show that the redox-precipitation method is effective to form homogenously dispersed Cu and Mn binary oxides. Compared with MnOx, the Hg-0 removal capacities of CuMnxOy-C and CuMnxOy-R were significantly improved. Particularly, CuMnxOy-R exhibited excellent Hg-0 removal performance in the temperature ranging from 50 to 200 degrees C. The larger surface area, higher valance of the Mn form, and abundance of surface chemisorbed oxygen (O-beta) were responsible for the excellent Hg(0 )removal performance. SO2 led to the formation of MnSO4 over MnOx, hence inhibiting the Hg-0 removal capacity. However, the resistance to SO2 over CuMnxOy was significantly improved because CuO reacted with SO2 preferentially and the active sites (i.e., MnOx) were protected from SO2 poisoning. Since CuO was homogeneously distributed on the CuMnxOy-R, a higher resistance to SO2 was obtained compared with that on CuMnxOy-C. The excellent Hg-0 removal performance of CuMnxOy-R in the presence of SO2 demonstrates great potential for practical applications.