Preparation, Characterization and Low-Temperature NH3-SCR Activity of MnOx/SAPO-11 Catalysts

MnOx/SAPO-11 catalysts were prepared by impregnation, citric acid, and precipitation methods for low-temperature selective catalytic reduction (SCR) of NO with NH3. The results indicated that the MnOx/SAPO-11 catalyst with 20%(w) Mn loading prepared by the precipitation method showed the best SCR activity and N-2 selectivity. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), atomic absorption spectrometry (AAS), N-2 adsorption-desorption, X-ray photoelectron spectroscopy (XPS), H-2 temperature-programmed reduction (H-2-TPR), NH3 temperature-programmed desorption (NH3-TPD), NO/O-2 temperature-programmed desorption, and mass spectrometry (NO/O-2-TPD-MS) were used to analyze the structural properties and catalytic performance of the catalysts. The results indicated that different manganese oxides were formed on the surface of SAPO-11 by the three different preparation methods. MnOx loaded via the precipitation method existed as MnO2 phase and amorphous MnOx. The advantages of the catalyst prepared via this method were a large mesoporous and external surface area, the highest content of chemisorbed oxygen and Mn2+ as well as more favorable medium and strong acid sites. Thus, more NO2 was produced on the catalyst during low-temperature SCR, which was a primary goal. MnOx prepared by all three methods could be well-dispersed on the surface of SAPO-11. The dispersive action of SAPO-11 could affect the formation of MnOx which could affect the acidity of the catalysts. Thus, the temperature window was widened and N-2 selectivity was improved compared with pure MnOx, with SAPO-11 acting as an excellent carrier.