Surface lattice oxygen activation via Zr⁴⁺ cations substituting on A²⁺ sites of MnCr₂O₄ forming Zr_xMn_1−xCr₂O₄ catalysts for enhanced NH₃-SCR performance

Zr⁴⁺ cations were incorporated into the lattice of MnCr₂O₄ spinels, forming a series of novel ternary Zr_xMn_1−xCr₂O₄ (x = 0, 0.05, 0.1 and 0.2) catalysts. The as-prepared Zr-doped catalysts all exhibited enhanced performance selective catalytic reduction of NO_x by NH₃ than undoped MnCr₂O₄ catalyst. Among all the prepared catalysts, the Zr_0.05Mn_0.95Cr₂O₄ exhibited the best catalytic performance, with good stability in the presence of H₂O, the lowest T₅₀ and T₉₀ (149 °C and 201 °C, respectively) and the broadest T₈₀ operation window (183–354 °C) under a gas hourly space velocity (GHSV) of 112,000 h⁻¹. The characterization results revealed that Zr⁴⁺ cations were successfully incorporated, and the resultant lattice deformation changed the physical and chemical properties of the catalysts remarkably. The introduction of zirconium produced higher levels of beneficial Mn³⁺, Mn⁴⁺ and Cr⁵⁺ species and increased the acidity and redox ability, and electrons transfer effects might be established between Mn, Cr and Zr cations. Moreover, surface lattice oxygen species are activated by Zr doping, and play an important role in NH₃-selective catalytic reduction (NH₃-SCR). The promoted electrons transfer effects and surface lattice oxygen activation are further substantiated by density functional theory (DFT) results.