H2O and SO2 deactivation mechanism of MnOx/MWCNTs for low-temperature SCR of NOx with NH3

• Investigate the poisoning effects of H2O and SO2 on MnOx/MWCNTs catalyst.
• Deactivation mechanism is proposed.
• Using Raman spectroscopy and in situ FT-IR measurements.
• H2O competitively adsorbs with NH3 on Lewis acid sites.
• SO2 increases the strength of Brønsted acidity by the accumulation of ammonium sulfates.

The effect of H2O and SO2 on the catalytic activity of manganese oxides supported on multi-walled carbon nanotubes (MnOx/MWCNTs) for low-temperature selective catalytic reduction (SCR) of NOx with NH3 was studied. Also, N2 adsorption, transient response experiments, X-ray powder diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and in situ FT-IR spectroscopy were performed to investigate the deactivation mechanism of MnOx/MWCNTs catalyst in the presence of H2O or SO2. Experimental results showed that H2O had a reversible negative effect on the catalytic activity of the catalyst. When the temperature was higher than 270 °C, the effect of H2O could be negligible. The competitive adsorption of H2O and NH3 on the Lewis acid sites contributed to the deactivation of the catalyst. The integrity increase of MWCNTs in the presence of H2O might be another reason for the deactivation of the catalyst. However, SO2 led to the irreversible deactivation of the catalyst. The higher the reaction temperature, the more dramatically the catalystic activity decreased. The sulfation of the active center atoms was the main poisoning route. Also, formation of ammonium sulfates on the catalyst surface and the competitive adsorption between SO2 and NO were responsible for the partial deactivation of the catalyst to some extent.

The inhibiting effect of H2O on MnOx/MWCNTs catalytic activity is reversible which is due to the competitive adsorption of H2O and Lewis NH3. The integrity increase of MWCNTs in the presence of H2O may be another reason for the deactivation of the catalyst. While SO2 leads to the catalyst permanent deactivation by the sulfation of active center atoms. Also, deposition of ammonium sulfates and competitive adsorption with NO contribute to the deactivation to some extent.Figure optionsDownload high-quality image (199 K)Download as PowerPoint slide