Synthesis of Co/Ni-Doped mesoporous spinel ferrite microspheres for enhanced Low-Temperature SCR performance

Abstract

The iron-based catalysts commonly used in the selective catalytic reduction (SCR) process cannot meet the increasingly stringent low-temperature NOx emission targets. In this study, mesoporous microspherical MFe2O4 (M=Co, Ni) spinel ferrite catalysts were synthesized by hydrothermal method and applied to the SCR of ammonia (NH3-SCR) reaction. Compared to Fe3O4, both NiFe2O4 and CoFe2O4 catalysts showed higher SCR catalytic activity at low temperature. The NiFe2O4 catalyst achieved a NO conversion of 95.5 % at 240 °C, while CoFe2O4 exhibited a high NO conversion of 97.6 % at 180 °C and a N2 selectivity of 99.6 %. Various characterization experiments revealed that the introduction of Co and Ni resulted in the formation of a specific mesoporous microsphere morphology in CoFe2O4 and NiFe2O4 catalysts, along with the generation of a large number of oxygen vacancies and acidic sites on the surface. These features facilitate the sequential adsorption and activation of NH3 and NOx species, resulting in excellent catalytic activity at low temperatures. Detailed in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) measurements showed that on NiFe2O4 the reaction follows the Eley–Rideal (E–R) mechanism, whereas it proceeds through the Langmuir–Hinshelwood (L–H) and Eley–Rideal (E–R) mechanisms on the CoFe2O4 catalyst. This work provides a feasible strategy for enhancing the low-temperature SCR reaction over iron-based catalysts; moreover, the elucidation of the complete reaction mechanism offers a solid foundation for future improvements in denitrification catalysts.