Influence of ignition atmosphere on the structural properties of magnetic iron oxides synthesized via solution combustion and the NH3-SCR activity of W/Fe2O3 catalyst

• Published in: Applied catalysis. A, General General, 2020-07, Vol.602, p.117726, Article 117726
• Main Authors: Li, Cheng-xu, Xiong, Zhi-bo, He, Jun-fei, Qu, Xiao-ke, Li, Zhen-zhuang, Ning, Xing, Lu, Wei, Wu, Shui-mu, Tan, Lu-zhi
• Format: Article
• Language: English
• Subjects: Ammonia; Annealing; Catalysts; Combustion; Crystal structure; Crystallites; De-nitrogen; Doping; High temperature; Hydrogen peroxide; Ignition atmosphere; Iron oxides; Low temperature; Low temperature resistance; Magnetic iron oxide; Magnetic properties; Porosity; Selective catalytic reduction; Sintering (powder metallurgy); Solution combustion; Surface area; Tungsten; Tungsten doping
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2020.117726

[Display omitted] •Two kinds of magnetic iron oxides are synthesized via solution combustion at the presence or absence of air, respectively.•The influence of ignition atmosphere on the structural properties of magnetic iron oxides is investigated.•The promotional effect of tungsten doping on the NH3-SCR activity of magnetic iron oxides is studied.•The influence of tungsten doping on the physical and chemical properties of magnetic iron oxides is characterized. Two kinds of magnetic iron oxides (Fe2O3-PO and Fe2O3-AO) are synthesized via the solution combustion coupled with the chemical oxidization of hydrogen peroxide. The magnetic carbon-containing Fe2O3-AO obtained at the absence of air presents the main γ-Fe2O3 crystal with smaller crystallite size and larger BET surface area, but not the aggregated and sintered α-Fe2O3 crystal of Fe2O3-PO. The doping of tungsten has no effect on the growth of α-Fe2O3 in Fe2O3-PO during the annealing process at 400 °C. However, the doping of tungsten effectively restrains the irreversible transformation of γ-Fe2O3 into α-Fe2O3 crystal and enhances the anti-collapse of the pore structure of Fe2O3-AO under the same annealing process at 400 °C by inducing a stronger interaction between tungsten species and γ-Fe2O3 crystal. In addition, the doping of tungsten improves the ratio of surface adsorbed oxygen, the Fe2+/(Fe2++Fe3+) ratio and the surface acidity of Fe2O3-PO-400 and Fe2O3-AO-400. Therefore, the doping of tungsten promotes the catalytic performance of Fe2O3-PO-400, especially its high-temperature activity, but exhibits a better promotional effect on the low-temperature activity of Fe2O3-AO-400. Magnetic 5W/Fe2O3-AO-400 shows the highest BET surface area, the largest Fe2+/(Fe2++Fe3+) ratio, the strongest surface acidity and the appropriate redox ability compared with the other tested catalysts, thus exhibits the highest low-temperature NH3-SCR activity and better resistance to SO2 and H2O than 5W/Fe2O3-PO-400. The formation of low crystallinity and high dispersive γ-Fe2O3 is an important reason on the good catalytic performance of magnetic 5W/Fe2O3-AO-400, which is also confirmed by the influence of annealing temperature. Furthermore, the results of steady-state kinetic experiments demonstrate that the 5W/Fe2O3-AO-400 catalyst mainly follows the Eley-Rideal mechanism.