Improved N₂ Selectivity of MnO_<i>x</i> Catalysts for NO_<i>x</i> Reduction by Engineering Bridged Mn³⁺ Sites

Abstract

Mn-based catalysts are promising for selective catalytic reduction (SCR) of NO_<i>x</i> with NH₃ at low temperatures due to their excellent redox capacity. However, the N₂ selectivity of Mn-based catalysts is an urgent problem for practical application owing to excessive oxidizability. To solve this issue, we report a Mn-based catalyst using amorphous ZrTiO_<i>x</i> as the support (Mn/ZrTi-A) with both excellent low-temperature NO_<i>x</i> conversion and N₂ selectivity. It is found that the amorphous structure of ZrTiO_<i>x</i> modulates the metal-support interaction for anchoring the highly dispersed active MnO_<i>x</i> species and constructs a uniquely bridged Mn³⁺ bonded with the support through oxygen linked to Ti⁴⁺ and Zr⁴⁺, respectively, which regulates the optimal oxidizability of the MnO_<i>x</i> species. As a result, Mn/ZrTi-A is not conducive to the formation of ammonium nitrate that readily decomposes to N₂O, thus further increasing N₂ selectivity. This work investigates the role of an amorphous support in promoting the N₂ selectivity of a manganese-based catalyst and sheds light on the design of efficient low-temperature deNO_<i>x</i> catalysts.