Engineering yolk–shell MnFe@CeOx@TiOx nanocages as a highly efficient catalyst for selective catalytic reduction of NO with NH3 at low temperatures

Abstract

To broaden the reaction temperature range and improve the H₂O-resistance of manganese-based catalysts, yolk–shell structured MnFe@CeO_x@TiO_x nanocages were prepared. The CeO₂ shell could effectively increase the oxygen vacancy defect sites, and the TiO₂ shell could remarkably improve the surface acid sites. Combining the advantages of the two shells could effectively solve the above questions. The catalytic efficiency of the yolk–shell MnFe@CeO_x@TiO_x-40 nanocages could reach above 90% in the range of 120–240 °C, and the water resistance could reach 90% at 240 °C. On the one hand, the construction of double shells could significantly increase the proportion of active species (Mn⁴⁺, Fe³⁺, Ce³⁺ and O_ads) and the interface effect between the shell layers could effectively enhance the interaction between metal oxides. On the other hand, the construction of double shells could achieve an appropriate balance between the redox capacity of the catalyst and surface acidity. Simultaneously, in situ DRIFT spectroscopy indicated that the yolk–shell MnFe@CeO_x@TiO_x-40 nanocages mainly followed the L–H mechanism during the NH₃-SCR reaction. Finally, this double-shell structure strategy provided a new idea for constructing a Mn-based catalyst with a wide temperature window and better low-temperature water resistance.