Study on NH₃-SCR of Cerium-based Substances in Rare Earth Concentrates from Bayan Obo

In this paper, CePO₄ and CeCO₃F were prepared by hydrothermal synthesis based on the ratio of bastnaesite to monazite in the process mineralogy of Baiyun Ebo rare earth concentrate. A comparison of the two treatments, ball milling and ball milling sulphation, revealed that the denitrification efficiency of the catalysts treated with ball milling sulphation increased by 20 percentage points, compared to those treated without sulphation, with denitrification efficiencies of up to 80%. The surface properties, redox properties and catalytic mechanism of the samples before and after the sulphation treatment were analyzed, by using XRD, NH₃-TPD, H₂-TPR, XPS and in situ IR characterization. The results showed that the CeF₃ diffraction peaks in the XRD patterns disappeared in the sulphated samples, NH₃-TPD showed that the adsorption capacity of NH₃ on the surface of the samples was enhanced, and the introduction of sulphuric acid provided a large number of acidic sites on the catalyst surface, among which the Lewis acidic sites might be more favorable for the promotion of SCR reaction. The acidification of sulphuric acid greatly increases the redox capacity of the catalyst, and the interconversion between Ceⁿ⁺ was enhanced. XPS showed a significant increase in the amount of adsorbed oxygen on the surface of the sample. The presence of -NO₂, an important intermediate in the L-H mechanism, was also detected by IR analysis. reactant species during the L-H mechanism reaction were monodentate nitrate, bridged nitrate and NH₄⁺ species produced by NH₃ adsorption on the Brønsted acidic site of the catalyst surface.