Abstract
Maghemite (γ-Fe2O3) catalysts were prepared by two different methods, and their activities and selectivities for selective catalytic reduction of NO with NH3 were investigated. The methods of X-ray powder diffraction (XRD), Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), ammonia temperature-programmed desorption (NH3-TPD), transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDS), and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) were used to characterize the catalysts. The resulted demonstrated that the γ-Fe2O3 nanoparticles prepared by the facile method (γ-Fe2O3–FM) not only exhibited better NH3-SCR activity and selectivity than the catalyst prepared by the coprecipitation method but also showed improved SO2 tolerance. This superior NH3-SCR performance was credited to the existence of the larger surface area, better pore structure, a high concentration of lattice oxygen and surface-adsorbed oxygen, good reducibility, a lot of acid sites, lower activation energy, adsorption of the reactants, and the existence of unstable nitrates on the surface of the γ-Fe2O3–FM.
Highlights
Nitrogen oxides (NOx, x = 1, 2) are the main sources of global environmental concerns like acid rain, fine particle pollution, smog, and ozone depletion [1]
Surface lattice oxygen was credited with the reduction process of maghemite to magnetite (γ-Fe2 O3 → Fe3 O4 ) in the low-temperature peak, and the bulk lattice oxygen was responsible for the reduction of magnetite to metallic iron (Fe3 O4 → Fe) in the the reduction process of maghemite to magnetite (γ-Fe2O3 → Fe3O4) in the low-temperature peak, and
NH3 -selective catalytic reduction (SCR) performance for low temperatures. This result showed that under these conditions the active sites generated on the catalysts may have changed; the NO2 produced in large quantities at higher temperatures (300–350 ◦ C) did not play its part in the NH3 -SCR activity due to its deactivation mechanism
Summary
The demand for reducing fuel consumption and making the environment clean has increased with increased awareness in society about protecting the global environment Due to this persistent demand, NOx legislation for both point and mobile sources has become more and more strict [2]. In the recent era, a lot of focus is given to the removal of NOx by the researchers To meet these strict regulations for NOx abatement, selective catalytic reduction (SCR) of NOx with ammonia (NH3 ) has become the most efficient and widely used. Yang et al [5] substituted low-cost Fe2 O3 to replace WO3 in the V2 O5 /WO3 -TiO2 catalyst to improve the N2 selectivity of the catalyst He found that the support (Fe2 O3 -TiO2 ) mainly resulted in the acid sites in the catalysts, so the adsorbed NH3 was favored to be activated by Fe3+ rather than by V5+.
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