An investigation on the promoting effect of Pr modification on SO2 resistance over MnOx catalysts for selective reduction of NO with NH3

Pr-modified MnO x catalyst was synthesized through a facile co-precipitation process, and the results showed that MnPrO x catalyst exhibited much better selective catalytic reduction (SCR) activity and SO 2 resistance performance than pristine MnO x catalyst. The addition of Pr in MnO x catalyst led to a complete NO conversion efficiency in 120–220 °C. Moreover, Pr-modified MnO x catalyst exhibited a superior resistance to H 2 O and SO 2 compared with MnO x catalyst. After exposing to SO 2 and H 2 O for 4 h, the NO conversion efficiency of MnPrO x catalyst could remain to 87.6%. The characterization techniques of XRD, BET, hydrogen-temperature programmed reduction (H 2 -TPR), ammonia-temperature programmed desorption (NH 3 -TPD), XPS, TG and in situ diffuse reflectance infrared spectroscopy (DRIFTS) were adopted to further explore the promoting effect of Pr doping in MnO x catalyst on SO 2 resistance performance. The results showed that MnPrO x catalyst had larger specific surface area, stronger reducibility, and more L acid sites compared with MnO x catalyst. The relative percentage of Mn 4+ /Mn n+ on the MnPrO x -S catalyst surface was also much higher than those of MnO x catalyst. Importantly, when SO 2 exists in feed gas, PrO x species in MnPrO x catalyst would preferentially react with SO 2 , thus protecting the Mn active sites. In addition, the introduction of Pr might promote the reaction between SO 2 and NH 3 rather than between SO 2 and Mn active sites, which was also conductive to protect the Mn active sites to a great extent. Since the presence of SO 2 in feed gas had little effect on NH 3 adsorption on the MnPrO x catalyst surface, and the inhibiting effect of SO 2 on NO adsorption was alleviated, SCR reactions could still proceed in a near-normal way through the Eley-Rideal (E-R) mechanism on Pr-modified MnO x catalyst, while SCR reactions through the Langmuir-Hinshelwood (L-H) mechanism were suppressed slightly.