SO2 Deactivation Mechanism of MnOx/MWCNTs Catalyst for Low-Temperature Selective Catalytic Reduction of NOx by Ammonia

Manganese oxides supported on multi-walled carbon nanotubes (MnOx/MWCNTs) catalysts were prepared by pore volume impregnation using MWCNTs as the catalyst support which was pretreated by concentrated nitric acid and oxygen dielectric barrier discharge plasma. The catalysts were characterized by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction/desorption (TPR/TPD), and Fourier transform infrared (FTIR) spectroscopy. The effect of SO2 on the activity of the catalysts for low-temperature selective catalytic reduction (SCR) of NOx by ammonia and the SO2 poisoning mechanism were investigated. The results showed that SO2 had an obvious poisoning effect on the SCR activity of MnOx/MWCNTs at low temperature. The activity decreased more rapidly as reaction temperature and SO2 concentration increased. The observed deactivation was attributed to the sulfation of the active center atoms. Formation of ammonium sulfate on the catalyst surface and the inhibiting effect of SO2 on NO adsorption also resulted in the deactivation of the catalysts to some extent.