Facile synthesis of MnZryOx solid solutions for enhanced low-temperature selective catalytic reduction of NOx

The fabrication of manganese-based catalysts with excellent low-temperature activity and outstanding activity-temperature-window for selective catalytic reduction (SCR) of NO_x remains a formidable challenge in the field of flue gas denitrification. In this contribution, a series of MnZr_yO_x solid solution (MZOSS) catalysts with controllable Mn/Zr ratios were elaborately designed and synthesized by a sol–gel protocol, and their catalytic performances for NH₃-SCR of NO_x were investigated. It was confirmed by a series of characterization techniques that the present catalysts have the distinct characteristics of solid solution and that the tunable composition and synergistic interaction between Mn and Zr has a significant effect on the formation of oxygen vacancy concentration, active oxygen species amount, as well as surface acidity and redox properties of the MZOSS catalysts. Among them, MnZr₄O_x shows roust stability, excellent hydrocarbons resistance, superior simultaneous elimination of VOC and NO_x activity, and superior catalytic efficacy with above 90 % NO_x conversion across the temperature range of 107–265 °C, surpassing the majority of contemporary studies. Further investigation of the mechanism by in-situ DRIFTS spectra unveil that the appropriate Zr/Mn ratio is favorable to the generation of reactive nitrates, such as bidentate nitrate and ad-NO₂, which in turn accelerate the low-temperature SCR rate mainly through the L-H reaction mechanism, thereby greatly improving the NH₃-SCR performances of MZOSS catalysts. However, the higher Zr/Mn notably increases the surface acidity and inhibit the desorption of adsorbed NH₃/NH₄⁺ species, thereby seriously suppressing the low-temperature NH₃-SCR activities of corresponding MZOSS catalysts. Therefore, this work presents a facile strategy to prepare efficient low-temperature NH₃-SCR catalyst by regulating the composition of MZOSS.