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

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.

Preparation of mesoporous ZnAl2O4 nanoflakes by ion exchange from a Na-dawsonite parent material in the presence of an ionic liquid

Herein, mesoporous ZnAl₂O₄ spinel nanoflakes were prepared by an ion-exchange method from a Na-dawsonite parent material in the presence of an ionic liquid, 1-butyl-2,3-dimethylimidazolium chloride ([bdmim][Cl]), followed by calcination at 700 °C for 2 h. The as-obtained products were characterized by several techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). The ZnAl₂O₄ nanoflakes with the thickness of ∼20 nm were composed of numerous nanoparticles, which resulted in a high specific surface area of 245 m² g⁻¹. The formation mechanism of the ZnAl₂O₄ nanoflakes was comprehensively investigated, and the results showed that a 2D growth process of the Zn₆Al₂(OH)₁₆(CO₃)·4H₂O crystallites with the assistance of [bdmim][Cl] was the key for the induction of ZnAl₂O₄ nanoflakes. Moreover, mesopores were formed between adjacent nanoparticles due to the release of CO₂ and H₂O molecules from Zn₆Al₂(OH)₁₆(CO₃)·4H₂O during the calcination process.

Herein, mesoporous ZnAl₂O₄ spinel nanoflakes were prepared by an ion-exchange method from a Na-dawsonite parent material in the presence of an ionic liquid, 1-butyl-2,3-dimethylimidazolium chloride ([bdmim][Cl]), followed by calcination at 700 °C for 2 h.