Converting Poisonous Sulfate Species to an Active Promoter on TiO 2 Predecorated MnO x Catalysts for the NH 3 -SCR Reaction.

MnO x -based catalysts possess excellent low-temperature NH 3 selective catalytic reduction (NH 3 -SCR) activity, but the poor SO 2 /sulfate poisoning resistance and the narrow active-temperature window limit their application for NO x removal. Herein, TiO 2 nanoparticles and sulfate were successively introduced into MnO x -based catalysts to modulate the NH 3 -SCR activity, and the active-temperature window (NO conversion above 80%, T 80 ) was significantly broadened to 100-350 °C (SO 4 2- -TiO 2 @MnO x ) compared to that of the pristine MnO x catalyst (ca. T 80 : 100-268 °C). Combined with advanced characterizations and control experiments, it was clearly shown that the poisonous effects of sulfate on the MnO x catalyst could be efficiently inhibited in the presence of TiO 2 species due to the interaction between sulfate and TiO 2 to form a solid superacid (SO 4 2- -TiO 2 ) species as NH 3 adsorption sites for the low-temperature process. Furthermore, such solid superacid (SO 4 2- -TiO 2 ) species could weaken the redox ability to inhibit the excessive oxidation of NH 3 and thus enhance the high-temperature activity significantly. This work not only puts forward the TiO 2 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 MnO x -based NH 3 -SCR catalyst was dependent on the reaction temperature range.