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Highlights: [•] Vanadia species suppress the reducibility and defect sites of ceria. [•] Polymeric VO x , ceria provide Lewis and CeVO4 provide Brønsted acid sites. [•] Polymeric VO x low energy barriers and CeVO4 increase rate constant. [•] The reaction mechanism depends on the temperature. [ABSTRACT FROM AUTHOR]

Abstract: (Fe3−x Mn x )1−δ O4 was synthesized using a co-precipitation method and then developed as a catalyst for the low temperature selective catalytic reduction (SCR) of NO with NH3. The SCR activity of (Fe3−x Mn x )1−δ O4 was clearly enhanced with the increase of Mn content. The results of in situ DRIFTS study demonstrated that both the Eley–Rideal mechanism (i.e. reaction of activated ammonia with gaseous NO) and the Langmuir–Hinshelwood mechanism (i.e. reaction of adsorbed ammonia species with adsorbed NO x species) might happen during the SCR reaction over (Fe3−x Mn x )1−δ O4. According to the kinetic analysis, the respective contribution of the Langmuir–Hinshelwood mechanism and the Eley–Rideal mechanism on the SCR reaction was studied. Only the adsorption of NO+O2 on (Fe2.8Mn0.2)1−δ O4 was promoted, so the Langmuir–Hinshelwood mechanism predominated over NO conversion on (Fe2.8Mn0.2)1−δ O4 especially at lower temperatures. Both the adsorption of NO+O2 and the adsorption of NH3 on (Fe2.5Mn0.5)1−δ O4 were obviously promoted, so NO conversion on (Fe2.5Mn0.5)1−δ O4 mainly followed the Eley–Rideal mechanism especially at higher temperatures. Both the nitrate route and the over-oxidization of adsorbed ammonia species contributed to the formation of N2O on (Fe2.8Mn0.2)1−δ O4 above 140°C. However, the formation of N2O on (Fe2.5Mn0.5)1−δ O4 mainly resulted from the over-oxidization of adsorbed ammonia species. Although the activity of (Fe2.5Mn0.5)1−δ O4 was suppressed in the presence of H2O and SO2, the deactivated catalyst can be regenerated after the water washing. [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]