Denitrification performance and mechanism of NH3-SCR rare earth tailings catalyst modified by Ce combined with Mn

Abstract

CeMn-rare earth tailings catalysts with wide temperature window and high denitrification were prepared by hydrothermal method. The results show that the optimum ratio of Ce/Mn is 1:1, and the NO_x conversion can reach 90% at the range of 100–300 °C. The introduction of Mn improves the dispersion of CeCO₃F on the catalyst surface, exposing more active adsorption sites. In addition, the interaction of MnO_x with Ce and Fe in the rare earth tailings promotes redox, which facilitates the oxidation of NO to NO₂. Meanwhile Mn also increases the abundance and stability of NO adsorption species and Lewis acid sites, forming important intermediates such as Mn⁴⁺-ONO₂, NH₄NO₃ and NH₂NO. But the strong oxidizing ability of Mn and the reaction between monodentate nitrate and adsorbed NH₃ results in N₂ selectivity decrease rapidly. Catalysts follow both E-R and L–H mechanism in the NH₃-SCR reaction. Moreover, the excellent redox performance and Lewis acid sites improve the NH₃-SCR catalytic activity together.