Insight into the reaction mechanism of NH3-SCR and chlorobenzene oxidation over Mn-based spinel catalysts

Abstract

To evaluate potential of Mn-based spinel catalysts for multi-pollutant removal applications, a series of Mn-based spinel catalysts were developed and tested for NH₃ selective catalytic reduction (NH₃-SCR) reaction and chlorobenzene catalytic oxidation. It was found that the CrMn₂O₄ spinel catalysts showed the best NH₃-SCR activity and chlorobenzene catalytic removal activity among these Mn-based spinel catalysts. A NO removal efficiency above 90 % was achieved in the range of 163–283 °C with an apparent activation energy of 32.26 kJ/mol, whereas 90 % of chlorobenzene removal was achieved at nearly 300 °C with an apparent activation energy of 61.41 kJ/mol. CrMn₂O₄ exhibits the good performance for simultaneous removal of NO and chlorobenzene in the temperature range of 305–315 °C. Stability tests indicates that 6 vol% water inhibits the NH3-SCR reaction, but promoted the chlorobenzene oxidation and CO₂ yield. Its porous and fluffy structure provides a large specific surface area of 29.32 m²/g and facilitates the adsorption of reactants. The DFT calculations were used to investigate the valence effect of different A-site metal ions on elemental Mn and the adsorption of reactant molecules on the surface. The results indicate that Mn atoms exhibit a variety of oxidation states and are strongly electrophilic in CrMn₂O₄ spinel. DFT and in situ DRIFTS were combined to reveal the reaction mechanisms of NH₃-SCR and chlorobenzene oxidation. This study lays the foundation for the application of high-performance Mn-based spinel catalysts in multi-pollution abatement.