Unraveling Excellent Performance in NH3–SCR over Cr-Doped NiMn-LDO Catalysts: A Combined Experimental and Computational Study

A sequence of Cr-doped NiMnO_x layered double oxide catalysts was synthesized through coprecipitation and applied in selective catalytic reduction of NO with ammonia (NH₃–SCR). The catalytic performance for NO reduction was enhanced by tuning the Ni/Mn/Cr molar ratios of the Ni₁Mn₁Cr_x-LDO precursors (x = 1, 2, 3); notably, Ni₁Mn₁Cr₂-LDO achieved over 90% NO conversion and N₂ selectivity within the temperature range of 150–300 °C. Moreover, Ni₁Mn₁Cr₂-LDO demonstrated significant resistance to SO₂ and H₂O along with exceptional stability. From the results of the characterization of the physicochemical properties of the catalysts, the presence of Cr species in Ni₁Mn₁Cr_x-LDO may enhance the surface acidity and reducibility. Additionally, higher amounts of Mn⁴⁺, Ni³⁺, Cr³⁺, and surface-adsorbed oxygen species were detected on the Ni₁Mn₁Cr₂-LDO catalyst. Through in situ DRIFTS experiments, the promotion of the NH₃–SCR process on Ni₁Mn₁Cr₂-LDO was confirmed to involve a combination of Langmuir–Hinshelwood and Eley–Rideal mechanisms.