Preparation of highly active manganese oxides supported on functionalized MWNTs for low temperature NOx reduction with NH3

Abstract

Manganese oxide catalysts (MnOx) supported on functionalized multi-walled carbon nanotubes (FMWNTs) for low temperature selective catalytic reduction (LTSCR) of nitrogen oxides (NOx) with NH3 in the presence of excess O2 were prepared by the incipient wetness impregnation method. These catalysts were characterized by N2 adsorption, Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and H2-temperature programmed reduction (H2-TPR) methods. The effects of reaction temperature, MnOx loading, calcination temperature and calcination time were investigated. The presence of surface nitrate species under moderate calcination conditions may play a favorable role in the LTSCR of NOx with NH3. Under the reaction conditions of 200°C, 1bar, NO=NH3=900ppm, O2=5vol%, GHSV=30,000h−1 and 12wt% MnOx, NOx conversion and N2 selectivity were 97% and 99.5%, respectively. The SCR activity was reduced in the presence of 100ppm SO2 and 2.5vol% H2O from 97% to 92% within 6h at 200°C, however such an effect was shown to be reversible by exposing the catalyst to a helium flow for 2h at 350°C due to thermal decomposition of ammonium sulphate salts.