Role of CuO in improving NH₃ and SO₂ capture on nanoporous Fe₂O₃ sorbents

In this work, mixed Fe/Cu oxides as sorbents for SO₂ and NH₃ removal were investigated. Nanoporous iron oxide mixed with 10, 20 and 30 at.% CuO were prepared by thermal decomposition of the corresponding oxalates at 250 °C for 5 h in air. The mixed Fe/Cu oxalates were obtained from the co-precipitation of iron/copper sulfate and ammonium oxalate during ultrasonication. The physical properties of the oxalate precursors and the resulting mixed Fe/Cu oxides were characterized with SEM, TGA-DSC, FTIR, powder XRD and Mössbauer spectroscopy. The porosity was studied by N₂ adsorption-desorption isotherms and small angle X-ray scattering. Evenly dispersed CuO hindered the crystallization of Fe₂O₃, which significantly increased the specific BET surface area from 211 m²/g for Fe₂O₃ to 354 m²/g for Fe_0.8Cu_0.2O_x. As a result, SO₂ and NH₃ adsorption on Fe_0.8Cu_0.2O_x were enhanced by about 70% compared to Fe₂O₃. Compared to Fe₂O₃-impregnated activated carbons, nanoporous Fe_0.8Cu_0.2O_x could capture five times more SO₂ per unit weight, which will be attractive for applications in respirators with lower weight and smaller size.