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

Xinxiang Pan,Huan Du,Yu Gao,Guangpeng Zhai,Zhitao Han

doi:10.1007/s11356-021-17006-3

Abstract

Pr-modified MnOx catalyst was synthesized through a facile co-precipitation process, and the results showed that MnPrOx catalyst exhibited much better selective catalytic reduction (SCR) activity and SO2 resistance performance than pristine MnOx catalyst. The addition of Pr in MnOx catalyst led to a complete NO conversion efficiency in 120-220°C. Moreover, Pr-modified MnOx catalyst exhibited a superior resistance to H2O and SO2 compared with MnOx catalyst. After exposing to SO2 and H2O for 4h, the NO conversion efficiency of MnPrOx catalyst could remain to 87.6%. The characterization techniques of XRD, BET, hydrogen-temperature programmed reduction (H2-TPR), ammonia-temperatureprogrammed desorption (NH3-TPD), XPS, TG and in situ diffuse reflectance infrared spectroscopy (DRIFTS) were adopted to further explore the promoting effect of Pr doping in MnOx catalyst on SO2 resistance performance. The results showed that MnPrOx catalyst had larger specific surface area, stronger reducibility, and more L acid sites compared with MnOx catalyst. The relative percentage of Mn4+/Mnn+ on the MnPrOx-S catalyst surface was also much higher than those of MnOx catalyst. Importantly, when SO2 exists in feed gas, PrOx species in MnPrOx catalyst would preferentially react with SO2, thus protecting the Mn active sites. In addition, the introduction of Pr might promote the reaction between SO2 and NH3 rather than between SO2 and Mn active sites, which was also conductive to protect the Mn active sites to a great extent. Since the presence of SO2 in feed gas had little effect on NH3 adsorption on the MnPrOx catalyst surface, and the inhibiting effect of SO2 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 MnOx catalyst, while SCR reactions through the Langmuir-Hinshelwood (L-H) mechanism were suppressed slightly.

Highlights

Nitrogen oxides (NOx) emitted from high-temperature combustion processes in diesel engines, power stations and industrial heaters are important atmospheric pollutants, which can lead to several environmental problems, for example, acid rain, ozone depletion, photochemical smog and greenhouse effects (Du et al 2020; Wang et al 2019; Zhu et al 2020; Kim et al 2020)
The results indicated that, in the presence of SO2 in feed gas, it seemed that PrOx rather than Manganese oxides (MnOx) were apt to react with SO2, which was favorable to protect Mn active sites on the catalyst surface to some extent
The characterization analysis results demonstrated that PrOx rather than MnOx were apt to react with SO2, which was favorable to protect Mn active sites on the catalyst surface to some extent, and Pr modification promoted the formation of (NH4)2SO4 or NH4HSO4 on the catalyst surface

Summary

Introduction

Nitrogen oxides (NOx) emitted from high-temperature combustion processes in diesel engines, power stations and industrial heaters are important atmospheric pollutants, which can lead to several environmental problems, for example, acid rain, ozone depletion, photochemical smog and greenhouse effects (Du et al 2020; Wang et al 2019; Zhu et al 2020; Kim et al 2020). For some plants with lower temperature flue gas, flue gas should be reheated by spare heater unit to meet the working temperature of commercial Vbased catalysts. Such heating process would cost more energy for industrial application. It is of great significance to develop non-toxic low-temperature SCR catalysts at desired working temperatures. MnOx catalysts have attracted increasing attention due to their low-temperature catalytic activities and low cost (Yang et al 2020; Xie et al 2020; Lee et al 2019; Zhang et al 2019; Liu et al 2020). MnOx catalysts still suffer from some challenging problems, such as narrow operation window, low N2 selectivity, and poor resistance to H2O and SO2, which restricts their commercial application. The poor SO2 and H2O tolerance of MnOx catalysts pose the greatest challenge for practical applications (Khan et al 2020; Kang et al 2020)

Results

Discussion

Conclusion