Study on denitration performance and mechanism of SCR of NO with NH3 of rare earth tailings catalyst modified by Ce for at low temperature

Abstract

The NH₃-SCR method is the most prevalent technology utilised for the removal of NOx. Among the numerous types of catalysts, minerals are composed of multiple metallic elements that produce natural synergistic catalytic effects when applied in the denitrification process. This phenomenon underscores the potential for their application in this field of research. In this study, rare earth tailings were modified using a hydrothermal method with Ce as the modifying agent. The impact of Ce-modified tailings catalysts on low-temperature denitrification performance and physicochemical properties was examined through a series of analytical techniques, including XRD, BET, SEM–EDS, XPS, NH₃-TPD, H₂-TPR, XPS, and in situ DRIFTS analyses. The findings indicated that the denitrification efficiency and N₂ selectivity of 7.5% Ce/rare earth tailings were 83% and 90%, respectively. The reaction temperature window was expanded from 250 °C to 425 °C. A mesoporous surface structure with highly dispersed active components, namely cerium and iron, was obtained. Concurrently, the combined effect of Ce and Fe resulted in an increase in oxygen vacancies, acidic sites, and acid activity strength within the catalyst. The denitrification reaction is governed by both the E-R and L–H mechanisms. The catalyst surface exhibits both Brønsted and Lewis acidic sites, with Brønsted acidic sites being more conducive to denitrification. The SCR reaction is predominantly influenced by NH⁴⁺ species adsorbed on Brønsted acidic sites, resulting in the formation of NH₃. Two active centres of Ce⁴⁺ and Fe³⁺ in the rare earth tailings, and NO as gaseous adsorbed NO₂, monodentate nitrate, and small amounts of bridged nitrate and bidentate nitrate participate in the SCR reaction.