Performance and mechanism of low-temperature NH3-SCR denitrification over Mn/CePO4-SiO2 catalysts

Abstract

Preparation of low-temperature NH3-SCR catalysts by Si and Mn modification and Si and Mn co-modification of CePO4 catalysts using mixed roasting and hydrothermal methods. XRD,BET,SEM and other characterisation tools were used to investigate the effect of Si and Mn modification on the catalyst structure. A series of different Si and Mn loadings and changes in catalyst denitrification performance, sulfur and water resistance after co-modification with Si and Mn were tested using NH3-TPD, H2-TPR and XPS, and the reaction pathways were investigated and the reaction mechanism of the catalysts was explored by FTIR detection in situ. The results show that CePO4-SiO2 catalyst at 250℃∼400℃, denitrification rate of about 90%; The optimum temperature for denitrification activity of the Mn/CePO4 catalyst was reduced, with a denitrification rate of 82% at 150℃; Mn/CePO4-SiO2 catalyst denitrification activity with significantly lower temperature and wider range. The denitrification rates of the catalysts were greater than 90% at 50℃∼300℃, with an optimum denitrification rate of 95 % at 150℃. The N2 selectivity of the catalyst is greater than 95 % in the low temperature range (below 200℃), good resistance to sulfur and water. The CePO4, SiO2 diffraction peaks on the surface of the sample decreased under the combined effect of Si and Mn. More acid sites appeared on the surface of the catalyst with elevated ratios of Ce3+ and adsorbed oxygen Oα, which promoted the catalyst's oxygen migration and conversion ability. After Si modification, the proportion of Mn4+ was significantly increased, which promoted the redox cycling of the catalyst in the low-temperature section. In situ IR results show that the catalyst follows both the Eley-Rideal mechanism and the Langmuir-Hinshelwood mechanism at 150℃. A variety of nitrate species produced by NO adsorption of the Si and Mn co-modified samples reacted rapidly with NH4+ species adsorbed at the Brønsted acid sites, which favoured the NH3-SCR reaction on the catalyst surface and improved the low-temperature denitrification efficiency.