MnOx-based catalysts possess excellent low-temperature NH3 selective catalytic reduction (NH3-SCR) activity, but the poor SO2/sulfate poisoning resistance and the narrow active-temperature window limit their application for NOx removal. Herein, TiO2 nanoparticles and sulfate were successively introduced into MnOx-based catalysts to modulate the NH3-SCR activity, and the active-temperature window (NO conversion above 80%, T80) was significantly broadened to 100-350 °C (SO42--TiO2@MnOx) compared to that of the pristine MnOx catalyst (ca. T80: 100-268 °C). Combined with advanced characterizations and control experiments, it was clearly shown that the poisonous effects of sulfate on the MnOx catalyst could be efficiently inhibited in the presence of TiO2 species due to the interaction between sulfate and TiO2 to form a solid superacid (SO42--TiO2) species as NH3 adsorption sites for the low-temperature process. Furthermore, such solid superacid (SO42--TiO2) species could weaken the redox ability to inhibit the excessive oxidation of NH3 and thus enhance the high-temperature activity significantly. This work not only puts forward the TiO2 predecoration strategy that converts sulfate to a promoter to broaden the active temperature window but also experimentally proves that the requirement of redox ability and acidity in the MnOx-based NH3-SCR catalyst was dependent on the reaction temperature range.
Keywords: MnOx-based catalysts; NH3-SCR reaction; TiO2 predecoration; solid superacid; sulfate.