Sm-modified Mn-Ce oxides supported on cordierite as monolithic catalyst for the low-temperature reduction of nitrogen oxides

Nitrogen oxides (NO_x) are typical atmospheric pollutants that harm the environment and human body, and selective catalytic reduction (SCR) with NH₃ is one of the most effective technologies to deal with NO_x emissions at present. In this work, a monolithic catalyst, Sm-modified Mn-Ce composite oxides (Sm-MnCe) supported on cordierite (CC), is prepared by impregnation for the first time, and their denitration (de-NO_x) performance in NH₃-SCR reaction is evaluated in detail. The results show that 0.1Sm-MnCe/CC (Sm/Mn mole ratio is 0.1) has the best de-NO_x efficiency with above 80 % NO_x conversion from 60° to 270°C, and the high NO_x conversion can be maintained within 15 h in the presence of 100 ppm SO₂. It is found that appropriate introduction of Sm increases the specific surface area and acid sites, improves the redox environment, elevates the content of Mn⁴⁺ on the catalyst surface, which are conducive to the improvement of catalytic activity. In addition, the interaction between active components (Sm, Mn and Ce) also plays a positive role for the excellent de-NO_x activity. It is revealed by in-situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) that the NH₃-SCR reaction over the 0.1Sm-MnCe/CC catalyst follows Eley-Rideal (E-R) and Langmuir-Hinshel (L-H) mechanisms. This work provides ideas for the preparation and modification of monolithic catalysts, which is conducive to promoting the practical industrial application of low-temperature SCR de-NO_x technology.