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

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