Extruded monolith MnOx-CeO2-TiO2 catalyst for NH3-SCR of low temperature flue gas from an industry boiler: Deactivation and recovery

Abstract

The selective catalytic reduction (SCR) of NOx with NH3 (NH3-SCR) technology has been widely applied for reducing NOx emissions from stationary and mobile sources. In this work, the extruded monolith MnOx-CeO2-TiO2 catalyst was installed in a cement kiln for NH3-SCR of NOx, where the flue gas temperature was 110–140 ℃. It is found that the monolith catalyst is severely deactivated after operating for about 200 h with almost no NOx conversion at 160 ℃ under GHSV of 50000 h−1, while the fresh monolith catalyst remains 60% NOx conversion. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of SO2 (SO2-TPD) and thermogravimetric-differential thermal analysis (TG-DTG) experiments reveal that both MnOx and CeO2 oxides in monolith are severely sulfated to manganese sulfate and cerium sulfate, and the external monolith walls are covered by massive ceria sulfate and little ammonium nitrate. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis demonstrates that the formation of nitrates at low temperatures is inhibited due to the occupation of active sites in MnOx-CeO2-TiO2 by sulfates, resulting in the decrease of low temperature activity. After washing with water, the activity of deactivated monolith catalyst can be partially recovered, together with significant loss of manganese and cerium from monolith.