Toward development of single-atom ceramic catalysts for selective catalytic reduction of NO with NH3

Highlights: • One-pot defect-induced synthesis of single-atom ceramic catalysts. • Single-atom catalysts are formed by highly dispersed metal aluminates in γ-Al₂O₃. • Insertion of transition metals into γ-Al₂O₃ boosts their dispersion and stability. • Selective reduction of NO with NH₃ is achieved on catalysts with Mn, Fe, and Cu. • Insertion of Fe species in γ-Al₂O₃ gives stable catalysts impeding N₂O formation. Insertion of transition metal species into crystalline alumina at low temperatures is proposed to achieve the dispersion of these species at atomic level paired with exceptional textural properties. Precisely, MeAl₂O₄/γ-Al₂O₃ (Me = Mn, Fe, Co, Ni, and/or Cu) nanostructured ceramic catalysts were fabricated with ultra large mesopores (16−30 nm), and high specific surface area (180−290 m² g⁻¹) and pore volume (1.1-1.6 cm³ g⁻¹). These ceramics were applied as efficient catalysts for the selective catalytic reduction (SCR) of NO with NH₃, and their selectivity was discussed in terms of N₂O formation, an undesirable byproduct. The catalysts containing Fe, Cu, or Mn showed the highest activities, however, within different temperature ranges. Further tuning of the catalytic activity and selectivity was achieved by creating ceramic catalysts with mixed compositions, e.g., CuFe and MnFe. Upon insertion of the transition metal species into crystalline structure of alumina to maximize atom efficiency, the N₂O formation profile did not change significantly for all metal aluminates except MnAl₂O₄, indicating that these catalysts are suitable for SCR and selectively promote the reduction of NO.