Fe–Ti spinel for the selective catalytic reduction of NO with NH3: Mechanism and structure–activity relationship

A series of non-stoichiometric Fe–Ti spinel (Fe3−xTix)1−δO4 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−xTix)1−δO4 through the Langmuir–Hinshelwood mechanism was restrained. Therefore, the SCR activity of (Fe3−xTix)1−δO4 (x ≠ 0) was less than that of γ-Fe2O3 at 150–250 °C. However, the SCR reaction over (Fe3−xTix)1−δO4 through the Eley–Rideal mechanism was promoted due to the incorporation of Ti. The SCR activity of (Fe3−xTix)1−δO4 (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.

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► (Fe2Ti)0.8O4 showed an excellent SCR performance at 300–400 °C.
► The SCR reaction through the L–H mechanism was restrained due to Ti incorporation.
► The SCR reaction over Fe–Ti spinel mainly followed the E–R mechanism.
► The SCR reaction through the E–R mechanism was promoted due to Ti incorporation.