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Selective catalytic reduction of nitrogen oxides (NO x ) with C 3 H 6 (C 3 H 6 -SCR) was investigated over NiO catalysts supported on different metal-oxides. A NiAlO x mixed oxide phase was formed over NiO/γ-Al 2 O 3 catalyst, inducing an immediate interaction between NiO x and AlO x species. Such interaction resulted in a charge transfer from Ni to Al site and the formation of Ni species in high oxidation state. In comparison to other NiO-loaded catalysts, NiO/γ-Al 2 O 3 catalyst exhibited the highest NO x conversion at temperature higher than 450 °C, but a poor C 3 H 6 oxidation activity due to the decreased nucleophilicity for surface oxygen species. By temperature-programed NO oxidation, it is indicated that nitrate species were rapidly formed and stably maintained at high temperature over NiO/γ-Al 2 O 3 catalyst. In situ transient reactions further verified the Langmuir-Hinshelwood mechanism for C 3 H 6 -SCR, where both gaseous NO and C 3 H 6 were adsorbed and activated on catalyst surface and reacted to generate N 2 . Due to the strong metal-support interaction over NiO/γ-Al 2 O 3 catalyst, both nitrate and C x H y O z intermediates were well preserved to attain high C 3 H 6 -SCR activity., (© 2022 Wiley-VCH GmbH.)

In this study, the poisoning effects of SO 2 on the V 2 O 5 -WO 3 /TiO 2 (1%VWTi) and CeO 2 -WO 3 /TiO 2 (5%CeWTi) selective catalytic reduction (SCR) catalysts were investigated in the presence of steam, and also the regeneration of deactivated catalysts was studied. After pretreating the catalysts in a flow of NH 3 + SO 2 + H 2 O + O 2 at 200 °C for 24 h, it was observed that the low-temperature SCR (LT-SCR) activity decreased significantly over the 1%VWTi and 5%CeWTi catalysts. For 1%VWTi, NH 4 HSO 4 (ABS) was the main product detected after the poisoning process. Both of NH 4 HSO 4 and cerium sulfate species were formed on the poisoned 5%CeWTi catalyst, indicating that SO 2 reacted with Ce 3+ /Ce 4+ , even in the presence of high concentration of NH 3 . The decrease of BET specific surface area, NO x adsorption capacity, the ratio of chemisorbed oxygen, and reducibility were responsible for the irreversible deactivation of the poisoned 5%CeWTi catalyst. Meanwhile, the LT-SCR activity could be recovered over the poisoned 1%VWTi after regeneration at 400 °C, but not for the 5%CeWTi catalyst. For industrial application, it is suggested that the regeneration process can be utilized for 1%VWTi catalysts after a period of time after NH 4 HSO 4 accumulated on the catalysts.

The performances of fresh and sulfated MnOx-CeO₂ catalysts for selective catalytic reduction of NOx by NH₃ (NH₃-SCR) in a low-temperature range (T < 300 °C) were investigated. Characterization of these catalysts aimed at elucidating the role of additive and the effect of sulfation. The catalyst having a Sn:Mn:Ce = 1:4:5 molar ratio showed the widest SCR activity improvement with near 100% NOx conversion at 110-230 °C. Raman and X-ray photoelectron spectroscopy (XPS) indicated that Sn modification significantly increases the concentration of oxygen vacancies that may facilitate NO oxidation to NO₂. NH₃-TPD characterization showed that the low-temperature NH₃-SCR activity is well correlated with surface acidity for NH3 adsorption, which is also enhanced by Sn modification. Furthermore, as compared to MnOx-CeO₂, Sn-modified MnOx-CeO₂ showed remarkably improved tolerance to SO₂ sulfation and to the combined effect of SO₂ and H₂O. In the presence of SO₂ and H₂O, the Sn-modified MnOx-CeO₂ catalyst gave 62% and 94% NOx conversions as compared to 18% and 56% over MnOx-CeO₂ at temperatures of 110 and 220 °C, respectively. Sulfation of SnO₂-modified MnOx-CeO₂ may form Ce(III) sulfate that could enhance the Lewis acidity and improve NO oxidation to NO₂ during NH₃-SCR at T > 200 °C.

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: (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]

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]