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Highlights: [•] Mn, Co, Ni and Zn are doped into the structure of iron spinel oxides. [•] Surface acidity and redox properties are related to iron spinel structures. [•] Competition of NH3-CR and NH3-CO exists over metal-doped iron spinel catalysts. [•] SCR performance is affected by the redox cycle of Fe3+/Fe2+ in octahedral sites. [Copyright &y& Elsevier]

Abstract: A series of non-stoichiometric Fe–Ti spinel (Fe3−x Ti x )1−δ O4 were synthesized using a co-precipitation method and then developed as environmental-friendly and low cost catalysts for the selective catalytic reduction (SCR) of NO with NH3. As Ti was incorporated into γ-Fe2O3, the SCR reaction over (Fe3−x Ti x )1−δ O4 through the Langmuir–Hinshelwood mechanism was restrained. Therefore, the SCR activity of (Fe3−x Ti x )1−δ O4 (x ≠0) was less than that of γ-Fe2O3 at 150–250°C. However, the SCR reaction over (Fe3−x Ti x )1−δ O4 through the Eley–Rideal mechanism was promoted due to the incorporation of Ti. The SCR activity of (Fe3−x Ti x )1−δ O4 (x ≠0) was mainly related to the oxidative ability of Fe3+ cation on the surface, the concentration of NH3 adsorbed on the surface and the concentration of reducible Fe3+ cation on the surface. Although the oxidative ability of Fe3+ cation on the surface decreased due to the incorporation of Ti into γ-Fe2O3, the concentration of NH3 adsorbed on the surface and the concentration of reducible Fe3+ cation on the surface both increased. As a result, (Fe2Ti)0.8O4 showed excellent activity, selectivity, and H2O/SO2 durability for the SCR reaction at 300–400°C. [Copyright &y& Elsevier]

Lignite is widelyused as the fuel for coal-fired power plants, and its flue gas temperatureis about 50–100 °C higher than others. V2O5–WO3/TiO2is extremely restrictedin the selective catalytic reduction (SCR) of NO from the coal-firedpower plants burning lignite due to the drop of NOxconversion, low N2selectivity, and volatilityof vanadium pentoxide at high temperatures. Therefore, a more environmental-friendlySCR catalyst with excellent SCR activity and better N2selectivityat 350–450 °C should be developed for this application.In this work, sulfated Fe–Ti spinel catalyst was developedfor the SCR of NO from the coal-fired power plants burning lignite.The drop of NOxconversion at high temperatureswas mainly related to the simultaneous occurrence of the catalyticoxidization of NH3to NO during the SCR reaction. Ti wasincorporated into γ-Fe2O3to decease theoxidization ability of Fe3+on the surface, and the sitesfor −NH2adsorption and the active components for−NH2oxidization were separated after the sulfationto decrease the probability of the collision between −NH2adsorbed and Fe3+on the surface. They both inhibitedthe catalytic oxidization of NH3to NO over γ-Fe2O3. However, the SCR reaction over γ-Fe2O3was simultaneously restrained after the incorporationTi and the sulfation. Therefore, NOxconversionover γ-Fe2O3at high temperatures dependedon the ratio of NH3conversion through the catalytic oxidizationof NH3to NO to that through the SCR reaction. This ratiodecreased after the incorporation of Ti, and it further decreasedafter the sulfation, resulting in an obvious promotion of NOxconversion at high temperatures. Therefore, sulfatedFe–Ti spinel showed excellent SCR activity, N2selectivity,and H2O+SO2durability at 300–450 °C,which was suitable for the application in the coal-fired power plantsburning lignite. [ABSTRACT FROM AUTHOR]