Improved N 2 Selectivity of MnO x Catalysts for NO x Reduction by Engineering Bridged Mn 3+ Sites.

Mn-based catalysts are promising for selective catalytic reduction (SCR) of NO _x with NH ₃ at low temperatures due to their excellent redox capacity. However, the N ₂ 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 _x as the support (Mn/ZrTi-A) with both excellent low-temperature NO _x conversion and N ₂ selectivity. It is found that the amorphous structure of ZrTiO _x modulates the metal-support interaction for anchoring the highly dispersed active MnO _x species and constructs a uniquely bridged Mn ³⁺ bonded with the support through oxygen linked to Ti ⁴⁺ and Zr ⁴⁺ , respectively, which regulates the optimal oxidizability of the MnO _x species. As a result, Mn/ZrTi-A is not conducive to the formation of ammonium nitrate that readily decomposes to N ₂ O, thus further increasing N ₂ selectivity. This work investigates the role of an amorphous support in promoting the N ₂ selectivity of a manganese-based catalyst and sheds light on the design of efficient low-temperature deNO _x catalysts.