Manganese based catalysts are highly active in the NH3-SCR reaction for NOx removal. Unfortunately, manganese oxides can be easily deactivated by sulfur dioxide in the flow gas, which has become the main obstacle for their practical applications. To address this problem, we presented a green and facile method for the synthesis of multi-shell Fe2O3@MnOx@CNTs. The morphology and structural properties of the catalysts were systematically investigated. The results revealed that the MnOx@CNT core-shell structure was formed during the chemical bath deposition, while the outermost MnOx species were transformed to Fe2O3 after the galvanic replacement reaction. The formation of the multi-shell structure induced the enhancement of the active oxygen species, reducible species as well as adsorption of the reactants, which brought about excellent de-NOx performance. Moreover, the Fe2O3 shell could effectively suppress the formation of the surface sulfate species, leading to the desirable SO2 resistance to the multi-shell catalyst. Hence, the synthesis protocol could provide guidance for the preparation and elevation of manganese based catalysts.

Design of multi-shell Fe2O3@MnO(x)@CNTs for the selective catalytic reduction of NO with NH3: improvement of catalytic activity and SO2 tolerance.

A series of Ti-Nb binary oxide were synthesized by co-precipitation as supports to prepare Cu/Ti-Nb mixed oxide catalysts through wetness impregnation. The novel catalyst 0.8%Cu/Ti 2 NbO x exhibited an excellent catalytic activity and N 2 selectivity with a broad operation temperature (250–425 °C) under a gas hourly space velocity (GHSV) of 177,000 h −1 for the selective catalytic reduction of NO x with NH 3 . A series of analytical techniques including high resolution transmission electron microscopy (HRTEM), N 2 -physisorption, X-ray diffraction (XRD), Laser Raman spectra (LRS), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), NH 3 temperature-programmed desorption (NH 3 -TPD), H 2 temperature-programmed reduction (H 2 -TPR) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) were used to investigate the correlations among catalyst structure, surface properties and catalytic performance. For the support Ti 2 NbO x , the specific surface area was larger than that of TiO 2 , promoting the high dispersion of the active component. Also, the surface acid sites were increased by addition of niobium oxide species and the redox capability of the support was enhanced by doping copper species. Moreover, the introduction of copper species effectively enhanced the catalytic performance within 225–400 °C. The copper species mainly existed as isolated Cu 2+ and non-isolated Cu + and the isolated Cu 2+ ions played a significant role in the high NH 3 -SCR performance over 0.8%Cu/Ti 2 NbO x catalyst. Hydrothermal aging treatment experiment demonstrated that 0.8%Cu/Ti 2 NbO x catalyst had an excellent hydrothermal stability. In addition, water vapor or/and SO 2 had a slightly reversible inhibition influence on the catalytic performance over 0.8%Cu/Ti 2 NbO x , indicating that it was a promising candidate for NH 3 -SCR catalyst in the future practical application. The reaction pathway over 0.8%Cu/Ti 2 NbO x catalyst followed both Eley-Rideal mechanism and Langmuir-Hinshelwood mechanism at 225 °C.

Promotional synergistic effect of Cu and Nb doping on a novel Cu/Ti-Nb ternary oxide catalyst for the selective catalytic reduction of NOx with NH3

A series of tungsten-modified Cu0.02Fe0.2TiOx catalysts (Cu0.02Fe0.2WaTiOx; a = 0.01, 0.02, and 0.03) was synthesized by sol-gel method. Their catalytic activities were investigated for the selective catalytic reduction (SCR) of NO with NH3, in the presence/absence of 5 vol.% H2O. The characterization techniques of XRD, BET, Raman, H2-TPR, NH3-TPD, XPS, in situ DRIFTS, and kinetic studies were used to reveal the effect of tungsten modification on the redox and acidity of the Cu0.02Fe0.2WaTiOx catalysts. The relationship among the species composition, acid property, and oxidation-reduction behavior of the Cu0.02Fe0.2WaTiOx catalysts was established. Results demonstrated that a moderate amount of tungsten doping can markedly enhance the specific surface area, improve the abundant Bronsted and Lewis acid sites, and tune the surface species composition, which all benefited high-performance catalysis. Water/sulfur resistance also improved because of the excellent acidity levels. Among the Cu0.02Fe0.2WaTiOx catalysts, Cu0.02Fe0.2W0.02TiOx showed the highest NO conversion, a wide reaction-temperature window (235–520 °C) with >90% NO conversion, high N2 selectivity, and high water/sulfur resistance even in the presence of 5 vol.% H2O. Moreover, Cu0.02Fe0.2W0.02TiOx retained its outstanding catalytic activity under a rather high gas hourly space velocity (GHSV) of 100,000 h−1. In conclusion, the combined effects of redox and sufficient acidities on catalytic activity played key roles in superior SCR performance and water/sulfur durability. Furthermore, the NH3-SCR reaction over Cu0.02Fe0.2W0.02TiOx may follow the Eley–Rideal reaction pathway according to the in situ DRIFTS and kinetic studies results.

Effect of W on the acidity and redox performance of the Cu0.02Fe0.2WaTiOx (a = 0.01, 0.02, 0.03) catalysts for NH3-SCR of NO

Low temperature selective catalytic reduction (SCR) is an efficient and promising technology to transform NOx into N2 from flue gases, which has broad application prospects. However, the vulnerability of low temperature DeNOx catalysts to poisoning by SO2 and H2O restricts their industrial application. Therefore, it is vitally important to develop new low temperature DeNOx catalysts that resist poisoning. This paper reviews the mechanisms of SO2 & H2O poisoning of low temperature SCR catalysts, the strategies for improving the resistance of low temperature SCR catalysts to SO2 & H2O poisoning, application of theoretical calculations in the development of SO2 & H2O resistant low temperature SCR catalysts as well as novel ideas for developing poisoning resistant low temperature SCR catalysts. Moreover, the studies dealing with the regeneration of low temperature DeNOx catalysts are also included. Based on the problems detailed in this review, the challenges and the emphasis for future research in this area are also proposed. We believe that this review will provide an excellent foundation and good guidance for the future design and the development of improved SO2 & H2O-tolerant low temperature DeNOx catalysts.

Research progress, challenges and perspectives on the sulfur and water resistance of catalysts for low temperature selective catalytic reduction of NOx by NH3

New ceria and sulfate co-modified V2O5-TiO2 aerogel catalysts were developed, using the one-step sol gel method associated with the supercritical drying process, for Diesel DeNOx technology. N2 adsorption-desorption, XRD, H2-TPR, NH3-TPD, Raman and DRUV-Vis spectroscopy were employed to probe the physico-chemical properties of TiO2, V2O5-TiO2, V2O5-CeO2-TiO2 and V2O5-CeO2-TiO2-SO42− aerogel materials. XPS was used to obtain further information about the oxidation states of the active sites on the surface of the novel V2O5-CeO2-TiO2-SO42− aerogel catalyst. The characterization results showed the successful synthesis of a new generation of well nanostructured aerogel catalysts with high surface area, large porosity and good thermal stability. V, Ce and SO42− actives species were found highly dispersed on TiO2 surface and their presence strongly influenced the surface acidity and the redox properties of the aerogel catalysts. Sulfate anions created strong acid sites and most probably contributed to the stabilization of V and Ce surface species at their 4 + and 3 + oxidation state, respectively. In the SCR-NO by NH3 under oxygen rich conditions, V2O5-TiO2 aerogel catalyst exhibited low NO conversions in 150–500 °C temperature range. The addition of cerium significantly increased the NO conversion at low temperature (220–400 °C). However, the simultaneous incorporation of cerium and sulfate has led to a novel V2O5-CeO2-TiO2-SO42− nanostructured aerogel catalyst with superior catalytic performances, at high temperature (450–500 °C), with respect to V2O5-WO3/TiO2 commercial one (EUROCAT).

Novel V 2 O 5 -CeO 2 -TiO 2 -SO 4 2− nanostructured aerogel catalyst for the low temperature selective catalytic reduction of NO by NH 3 in excess O 2

A synergy between FeOX and CuOX was confirmed in FeCuOX/TiO2-hBN composites for selective catalytic reduction of NO with NH3. Accordingly, the reducibility of composites was modified to promote the NO to NO2 oxidation but suppress the NH3 to NO over oxidation, which is of benefit to the NO reduction. Also the optimal operation temperature could be controlled by tuning the Fe:Cu atomic ratio, and Fe10Ti85BN5, Fe7.5Cu2.5Ti85BN5 and Fe2.5Cu7.5Ti85BN5 achieved the best NO removal above 90% at 375 °C, 300 °C and 250 °C, respectively. From the NO2 and NH3 adsorption behaviors over FeCuOX/TiO2-hBN, the reaction followed Langmuir–Hinshelwood mechanism below 275 °C, but followed Eley–Rideal mechanism above 350 °C. The influence of SO2 on NO removal was found to be temperature dependent, at temperature below 325 °C, slight deactivation was observed, while a promotion was achieved above 350 °C.

Synergy between FeOX and CuOX in FeCuOX/TiO2-hBN composites for NO reduction with NH3

The invention discloses a method for inhibiting low-temperature denitration catalyst poisoning caused by SO2. A NO oxidation device is arranged at a flue gas inlet of a selective catalytic reduction (SCR) denitration facility, 5-70% of NO in flue gas is oxidized into NO2 by the NO oxidation device, the flue gas containing NO2 is fed into the SCR denitration facility at a space velocity of 1000-200000h and the flue gas is subjected to denitration purification at a temperature of 50-300 DEG C. Through a reaction of NO2 obtained by oxidation of NO and an ammonium salt deposited on the surface of the low-temperature denitration catalyst, the method can effectively inhibit SO2-ammonia gas reaction-caused deposition of ammonium salts such as ammonium sulfate and ammonium sulfite on the surface of the low-temperature denitration catalyst thereby inhibiting SO2-caused low-temperature SCR denitration catalyst poisoning so that a service life of the low-temperature denitration catalyst is prolonged and a SCR denitration operation cost is reduced.

Method for inhibiting low-temperature denitration catalyst poisoning caused by SO2

Catalyst for removing nitrogen oxide in high-temperature flue gas containing sulfur oxide and preparation method

Temperature-dependent effects of SO2 on selective catalytic reduction (SCR) of NO by NH3 over a TiO2 and carbon nanotubes (CNTs) supported iron–copper oxides catalyst were examined. At temperature below 300 °C, deposition of sulfites and sulfates on the catalyst surface suppressed NH3 adsorption, NO adsorption, and oxidation, which induced catalyst deactivation. The deposited sulfite/sulfates could be partially removed by 400 °C postannealing, which regenerated the catalyst. At temperature above 350 °C, NO adsorption was promoted by SO2 introduction, and suppression of NH3 adsorption also minimized the side reaction of NH3 oxidation, which increased the NO removal efficiency from 68% to 80% through reaction between adsorbed NO and gaseous NH3.

Temperature-Dependent Effects of SO2 on Selective Catalytic Reduction of NO over Fe–Cu–OX/CNTs–TiO2 Catalysts

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Synergy between FeOX and CuOX in FeCuOX/TiO2-hBN composites for NO reduction with NH3

Method for inhibiting low-temperature denitration catalyst poisoning caused by SO2

Catalyst for removing nitrogen oxide in high-temperature flue gas containing sulfur oxide and preparation method

Temperature-Dependent Effects of SO2 on Selective Catalytic Reduction of NO over Fe–Cu–OX/CNTs–TiO2 Catalysts