Fe2O3/γ-Al2O3 and NiO/γ-Al2O3 catalysts for the selective catalytic oxidation of ammonia

Abstract

Ammonia, a significant atmospheric pollutant, requires effective emission control due to its inherent toxicity and the generation of secondary pollutants like particulate matter. This control can be achieved through various methods, including catalytic processes. Therefore, our study focuses on evaluating the potential of catalysts based on iron oxide and nickel oxide supported on γ–Al₂O₃ for the selective catalytic oxidation of NH₃ to N₂ (NH₃-SCO). The γ–Al₂O₃ was obtained by thermal decomposition of aluminum hydroxide, and 5 or 10 wt% of Fe or Ni was added through wetness incipient impregnation. XRD diffractograms confirmed the formation of the γ–Al₂O₃ phase. XRD, H₂-TPR, and UV–vis DRS data showed the presence of Fe₂O₃, NiO, and NiAl₂O₄ in the catalysts. Introducing metal oxides onto the support led to a drop in the specific area, pore size, pore volume, and NH₃ desorption, which was higher for the catalysts containing Fe. The catalysts were active in NH₃-SCO, and the insertion of Fe or Ni was essential because it promoted a significant increase in the NH₃ conversion (∼75 % Fe and ∼55 % Ni), compared to pure support (∼8 %), mainly from 400 °C. However, doubling the metal content has not resulted in a considerable increase in NH₃ conversion. The N₂ selectivity was higher for the catalysts containing Ni (∼85 %) from 400 °C compared to catalysts containing Fe (∼76 %). Such behavior was due to the larger surface area of the Ni-containing catalysts. Despite that, the 5Fe/γ–Al₂O₃ catalyst emerged as the most effective option for NH₃-SCO applications, combining higher NH₃ conversion and good N₂ selectivity.