Preparation of highly active manganese oxides supported on functionalized MWNTs for low temperature NO_χ reduction with NH_3

摘要

Manganese oxide catalysts (MnO_χ) supported on functionalized multi-walled carbon nanotubes (FMWNTs) for low temperature selective catalytic reduction (LTSCR) of nitrogen oxides (NO_χ) with NH3 in the presence of excess O_2 were prepared by the incipient wetness impregnation method. These catalysts were characterized by N_2 adsorption, Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and H_2-temperature programmed reduction (H_2-TPR) methods. The effects of reaction temperature, MnO_χ 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 NO_χ with NH_3. Under the reaction conditions of 200 ℃, 1 bar, NO - NH_3 - 900 ppm, O_2-5vol%, GHSV- 30,000 h~(-1) and 12wt% MnO_χ, NO_χ conversion and N_2 selectivity were 97% and 99.5%, respectively. The SCR activity was reduced in the presence of 100 ppm SO_2 and 2.5 vol% H_2O from 97% to 92% within 6 h at 200 ℃, however such an effect was shown to be reversible by exposing the catalyst to a helium flow for 2 h at 350 ℃ due to thermal decomposition of ammonium sulphate salts.