Ho-modified Mn-Ce/TiO2 for low-temperature SCR of NO with NH3: Evaluation and characterization

Low-temperature selective catalytic reduction (SCR) of NO with NH3 was tested over Ho-doped Mn–Ce/TiO2 catalysts prepared by the impregnation method. The obtained catalysts with different Ho doping ratios were characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), temperature-programmed reduction (H2-TPR), temperature-programmed desorption of NH3 (NH3-TPD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The catalytic activities were tested on a fixed bed. Their results indicated that the proper doping amount of Ho could effectively improve the low-temperature denitrification performance and the SO2 resistance of Mn–Ce/TiO2 catalyst. The catalyst with Ho/Ti of 0.1 presented excellent catalytic activity, with a conversion of more than 90% in the temperature window of 140–220 °C. The characterization results showed that the improved SCR activity of the Mn–Ce/TiO2 catalyst caused by Ho doping was due to the increase of the specific surface area, higher concentration of chemisorbed oxygen, higher surface Mn4+/Mn3+ ratio, and higher acidity. The SO2 resistance test showed that the deactivating influence of SO2 on the catalyst was irreversible. The XRD and XPS results showed that the main reason for the catalyst deactivation was sulfates that had formed on the catalyst surface and that Ho doping could inhibit the sulfation to some extent.