Low-temperature Selective Catalytic Reduction Activity Research Articles

Promoting effect of polyoxometallic acid modification on the NH3-SCR performance of Mn-based catalysts

The strong oxidation capabilities of Mn sites render Mn-based catalysts showing high activities of selective catalytic reduction (SCR) at temperatures < 250℃, but simultaneously lead to the generation of by-product N2O with strong greenhouse effect. The activity-N2-selectivity trade-off was a prevalent observation in the development of Mn-based SCR catalysts. Here, a polyoxometallic acid enhancement strategy was devised to simultaneously promote the N2 selectivity and low-temperature SCR (LT-SCR) activity of Mn-based metal oxide catalysts, where the introduction of uniformly dispersed phosphomolybdic acid (HPMo) tuned the oxidation capabilities and enhanced NH3 adsorption-storage capability of catalysts. The combination of transient reaction, in-situ DRIFTS analysis and DFT calculations revealed that the main origin of N2O on the Mn-based catalysts was the deep oxidation of NH3, which was inhibited by the interaction between HPMo and Mn sites. Additional NH3 molecules adsorbed by the abundant acid sites supplied by HPMo further facilitated the SCR reaction. This strategy could guide the design of high-activity and high-selectivity LT-SCR catalysts for industrial denitration.

Enhanced low-temperature selective catalytic reduction (SCR) activity and H2O and SO2 resistance of flower-like SmMnOx and SmMnOx-rGO catalysts

Reed flower-like SmMnOx and cauliflower-like SmMnOx-rGO catalysts were successfully synthesized by a coprecipitation-coupled solvothermal method for selective catalytic reduction (SCR) of NOx. The NOx conversion of the two catalysts is more than 90% in the temperature range of 75–200 °C, and the N2 selectivity of SmMnOx-rGO is above 90%. Moreover, both of them exhibit more than 62% of resistance to H2O and SO2 at a very low temperature of 100 °C, much superior than the fluffy spherical SmMnOx prepared by coprecipitation method. The strong synergy between Mn and Sm endowed by the flower-like structure contributes to a low degree of crystallization, a high ratio of (Mn3++Mn4+)/Mn, more chemisorbed oxygen species, strong redox ability, and more Lewis acid sites, hence effectively enhancing low-temperature SCR activity and resistance to H2O and SO2. In addition, the decreased ratio of Mn4+/Mn after rGO doping hinders the side reaction of NH3 oxidation, thus enhancing the N2 selectivity of rGO-doped SmMnOx catalyst.

3D-printing of attapulgite monoliths with superior low-temperature selective catalytic reduction activity: the influence of thermal treatment

This study provides a facile strategy for 3D-printing of attapulgite monoliths with superior low-temperature NH3-SCR performance under thermal treatment.

Iron-based denitration catalyst derived from Fenton sludge: Optimization analysis of selective dealkalization and influence mechanism of calcination temperature

Fenton sludge from sewage treatment plants is a kind of hazardous waste that causes serious harm to the ecological environment. In this study, the potential of preparing a novel selective catalytic reduction (SCR) denitration (deNOx) catalyst was evaluated through selective dealkalization followed by calcination using Fenton sludge. The effects of water leaching, carbon dioxide leaching, and acid leaching methods (organic and inorganic acid) on Fenton sludge dealkalization were studied, taking the total dealkalization and active component retention rates and deNOx efficiency as comprehensive considerations. Results showed that acid leaching method has the best leaching effect on free alkali and chemically combined alkali, the order of dealkalization rates was FSH2SO4 (94.23%)>FSHCl (92.18%)>FSHNO3 (89.93%)>FSCH3COOH (81.07%). Through comprehensive comparison, FSHCl exhibited the best catalytic active and excellent selective dealkalization performance, achieving relatively high total dealkalization rate while retaining the active components to the greatest extent (86.73%). On this basis, the effects of calcination temperature on catalytic activity, as well as physical and chemical properties of the catalyst were studied. The MFS-450 catalyst exhibited the largest surface area (76.53 m2/g), pore volume (0.23 cm3/g), abundant oxygen-containing functional groups, excellent surface acidity (0.779 μmol/m2), and redox properties (5.07 mmol/g). Besides, it has the best low-temperature SCR activity and the widest reaction temperature window, with nitrogen oxide (NOx) conversion exceeding 90% at temperatures between 293 and 471 °C. This research contributes a representative example of converting Fenton sludge into valuable materials and may open a new avenue to synthesizing high-activity SCR catalyst from low-cost feedstocks.

Boosting low-temperature selective catalytic reduction of NO with NH3 of V2O5/TiO2 catalyst via B-doping

A series of B-doped V2O5/TiO2 catalysts has been prepared the by sol-gel and impregnation methods to investigate the influence of B-doping on the selective catalytic reduction (SCR) of NOx with NH3. X-ray diffraction, Brunauer-Emmett-Teller specific surface area, scanning electron microscope, X-ray photoelectron spectroscopy, temperature-programmed reduction of H2 and temperature-programmed desorption of NH3 technology were used to study the effect of the B-doping on the structure and NH3-SCR activity of V2O5/TiO2 catalysts. The experimental results demonstrated that the introduction of B not only improved the low-temperature SCR activity of the catalysts, but also broadened the activity temperature window. The best SCR activity in the entire test temperature range is obtained for VTiB2.0 with 2.0% doping amount of B and the NOx conversion rate is up to 94.3% at 210 °C. The crystal phase, specific surface area, valence state reducibility and surface acidity of the active components for the as-prepared catalysts are significantly affected by the B-doping, resulting in an improved NH3-SCR performance. These results suggest that the V2O5/TiO2 catalysts with an appropriate B content afford good candidates for SCR in the low temperature window.

Manganese oxide nanorod catalysts for low-temperature selective catalytic reduction of NO with NH3.

MnOx nanorod catalysts were successfully synthesized by two different preparation methods using porous SiO2 nanorods as the template and investigated for the low-temperature selective catalytic reduction (SCR) of NO with NH3. The catalysts were characterized by scanning electron microscopy, transmission electron microscopy, nitrogen adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, and NH3 temperature-programmed desorption. The results show that the obtained MnOx-P nanorod catalyst prepared by redox precipitation method exhibits higher NO removal activity than that prepared by the solvent evaporation method in the low temperature range of 100–180 °C, where about 98% NO conversion is achieved over MnOx(0.36)-P nanorods. The reason is mainly attributed to MnOx(0.36)-P nanorods possessing unique flower-like morphology and mesoporous structures with high pore volume, which facilitates the exposure of more active sites of MnOx and the adsorption of reactant gas molecules. Furthermore, there is a lower crystallinity of MnOx, higher percentage of Mn4+ species and a large amount of strong acid sites on the surface. These factors contribute to the excellent low-temperature SCR activity of MnOx(0.36)-P nanorods.

Improved hydrothermal durability of Cu-SSZ-13 NH3-SCR catalyst by surface Al modification: Affinity and passivation

To improve the hydrothermal durability of Cu-SSZ-13 selective catalytic reduction (SCR) catalyst, a thin Al2O3 modification layer was coated on the external surface of Cu-SSZ-13 by a chemical liquid deposition (CLD) method. The high-temperature SCR activity of the Al-modified Cu-SSZ-13 can be maintained upon 750–800 °C hydrothermal aging, and over-oxidation of NH3 is largely inhibited. Based on H2-TPR and EPR results, it is revealed that CuAl2O4-like species forms upon Al modification and converts further to CuAlO2-like species during aging, while the accumulation of CuO-like species is inhibited. The high affinity of Al-containing species (i.e., Al2O3 and CuAl2O4-like species) with Cu(OH)2 is suggested by DFT calculations, indicating that Cu(OH)2 detached from ion-exchange sites are captured by Al to form CuAlO2-like species instead of CuO-like species. The passivation of detached Cu species by coated Al leads to somewhat weakened low-temperature SCR activity, but successfully preserves the high-temperature SCR performance upon aging, which can be applied to high-temperature SCR scenarios.

Molybdenum oxide as an efficient promoter to enhance the NH3-SCR performance of CeO2-SiO2 catalyst for NOx removal

Selective catalytic reduction (SCR) of NOx with NH3 has been widely used for the removal of NOx. Because of the inevitable disadvantages of conventional V2O5-WO3(MoO3)/TiO2 catalysts such as poor low-temperature SCR activity and toxicity of vanadium, as well as the high-cost and over-strong NH3 adsorption of zeolite catalysts, the development of efficient and non-toxic metal oxide SCR catalysts is highly demanded. Previously, we have developed an environmentally-benign CeO2-SiO2 mixed-oxide SCR catalyst (CeSi2), which exhibited superior SO2 resistance ability. However, the low-temperature SCR activity on CeSi2 was not that satisfactory. In this work, we proposed a new strategy of Mo doping to improve the low-temperature SCR activity on CeSi2, which was very crucial for its practical application. By a simple co-precipitation method, a homogenous Mo-Ce-Si mixed-oxide catalyst was prepared. The Mo doping could significantly enhance the NH3-SCR activity on CeSi2 below 250 °C, and the optimal catalyst was Mo0.1CeSi2, which could achieve 80% NOx conversion at 200 °C. Mo0.1CeSi2 also exhibited superior N2 selectivity and resistance to SO2/H2O poisoning. Via a series of characterizations, it was found that the redox properties and surface acidity on CeSi2 by Mo doping, which accounted for the enhanced low-temperature NH3-SCR activity on Mo0.1CeSi2. The reaction mechanism on Mo0.1CeSi2 was also fully revealed by in situ DRIFTS experiments. This work provided a new insight for the development of efficient low-temperature SCR catalysts with superior SO2 resistance ability.

Water: A promoter of ammonia selective catalytic reduction over copper-exchanged LTA zeolites

Negative effects of water on the hydrothermal stability of ammonia (NH3) selective catalytic reduction (SCR) catalysts are well known. Thus, developing water-resistant, zeolite-based transition metal catalysts like copper (Cu) for mitigating nitrogen oxides from mobile sources is very challenging. Here we show that water markedly facilitates the migration of copper ions from sterically inaccessible sod cage to the readily accessible lta one through six-membered rings within a copper-exchanged high-silica Cu-LTA zeolite. We also show that this ubiquitous molecule promotes the low-temperature SCR activity of the Cu-LTA catalyst with a plausible reaction [H2O-Cu-NH3]+ intermediate. We anticipate that water might play a beneficial role in nitrogen oxides removal over metal-containing zeolites for cleaner air via tuning the active sites and reaction pathways.

Lead poisoning and regeneration of Mn-Ce/TiO2 catalysts for NH3-SCR of NOx at low temperature

The effect of lead on the catalytic performance of Mn-Ce/TiO2 catalysts in the selective catalytic reduction (SCR) of NOx with ammonia at low temperature was investigated; with the help of nitrogen sorption, XRD, FT-IR spectroscopy, H2-TPR and NH3-TPD characterization, the causes of lead poisoning and acid regeneration were clarified. The results indicate that the doping of Pb in Mn-Ce/TiO2 leads to a significant decrease of the low-temperature SCR activity; with a Pb loading of 11%, the conversion of NO over Mn-Ce/TiO2 at 180°C decreases from original 100% on the fresh catalyst to 44% on the Pd-poisoned catalyst. The presence of Pb may reduce the content of active Mn4+ and Ce3+ species on the Mn-Ce/TiO2 catalyst, which suppresses the redox cycle of Mn4+ + Ce3+ ↔ Mn3+ + Ce4+; moreover, the decrease of surface acidity on the Mn-Ce/TiO2 catalyst by the doping of Pb is also disadvantageous to the adsorption and activation of NH3. The Pd-poisoned Mn-Ce/TiO2 can be regenerated by nitric acid treatment; after the regeneration, the catalytic activity of Mn-Ce/TiO2 in NH3-SCR of NO is almost completely recovered and even exceeds that of the fresh catalyst at 80–150°C. The nitric acid treatment can restore the redox capacity of Mn-Ce/TiO2, increase the surface area, and create new acid sites, which contribute to recovery of the activity of Pb-poisoned Mn-Ce/TiO2 catalyst in NH3-SCR.

Promotional effect of ion-exchanged K on the low-temperature hydrothermal stability of Cu/SAPO-34 and its synergic application with Fe/Beta catalysts

Kions were introduced onto Cu/SAPO-34 catalysts via the ion-exchange process in order to improve their stability under low-temperature hydrothermal aging. The changes in structure and copper-species contents of these catalysts upon hydrothermal aging were probed in order to investigate their effects on selective catalytic reduction (SCR) activity. For the fresh Cu/SAPO-34 catalysts, K ions had little influence on the chabazite framework but effected their acidities by exchanging with acid sites. After hydrothermal aging, the structural integrity and amount of active sites decreased on pure Cu/SAPO-34. While the K-loaded catalysts showed improved chabazite structure, acidity, and active site conservation with increasing K loading. However, although the 0.7 wt% K catalyst maintained the same crystallinity, active site abundance, and low-temperature SCR activity as the fresh catalyst upon aging, an apparent decrease in SCR activity at high temperature was observed because of the inevitable decrease in the number of Bronsted acid sites. To compensate for the activity disadvantage of K-loaded Cu/SAPO-34 at high temperature, Fe/Beta catalysts were co-employed with K-loaded Cu/SAPO-34, and a wide active temperature window of SCR activity was obtained. Thus, our study reveals that a combined system comprising Fe/Beta and K-loaded Cu/SAPO-34 catalysts shows promise for the elimination of NOx in real-world applications.

The poisoning mechanism of gaseous HCl on low-temperature SCR catalysts: MnOx−CeO2 as an example

The degradation of catalyst properties, rather than the deposition of NH4Cl, was the main reason for the deactivation of the MnCe low-temperature SCR (selective catalytic reduction) catalyst under HCl atmosphere. Cl ions prefer to be located at the oxygen vacancies around Mn cations on the MnCe surface. The adsorbed Cl ions could further promote the formation of oxygen vacancies. Therefore, the active Mn sites on the surface of MnCe would be quickly covered by Cl ions when HCl was present and thus promote the formation of Brønsted acid sites. However, the ionic NH4+ adsorbed on the Brønsted acid sites of MnCe and MnCe − Cl were not fully utilized in the SCR reaction. Meanwhile, the reactivity of the coordinated NH3 bonded with Lewis acid sites was significantly restrained by HCl due to the significant inhibition of the redox performance. Overall, HCl could obviously restrain the low-temperature SCR activity of MnCe.

The role of the Cu dopant on a Mn3O4 spinel SCR catalyst: Improvement of low-temperature activity and sulfur resistance

Mn-based oxides are regarded as one of the most promising catalysts for selective catalytic reduction (SCR) of NOx by NH3 at low temperatures, but their applications are extremely restricted by the irreversible poisoning of SO2. Improving the SO2 tolerance of Mn-based catalyst has longtime received the most attentions from both academia and industry. In this work, a series of Cu-modified Mn3O4 spinels were synthesized, and the roles of the Cu dopant were investigated. The (Cu1.0Mn2.0)1–δO4 spinel showed both excellent SCR performance and SO2 resistance at low temperature. Cu doping improved the BET surface area, the quantities of active Mn4+ and the acid sites of Mn3O4 spinels, all of which contributed to the increase in low-temperature SCR activity. The formation of MnSO4 was mainly responsible for the irreversible deactivation of the Mn3O4 spinel upon exposure to SO2. DFT calculations suggested that SO2 was more likely to be adsorbed as “–Mn–O–S–O–Mn–” on Mn3O4 and (Cu1.0Mn2.0)1–δO4 spinels. Therefore, the formation of MnSO4 on the (Cu1.0Mn2.0)1–δO4 spinel was significantly mitigated by Cu doping, mainly due to reduced amounts of adjacent Mn. Moreover, resulting from the electronic transfer between copper and manganese cations within the spinel lattice (Cu2+ + Mn3+ ⇄ Mn4++ Cu+), the (Cu1.0Mn2.0)1–δO4 spinel retained a high surface ratio of Mn4+/Mntotal, which maintained an excellent low-temperature SCR activity under the SO2-containing condition. This work shows that doping with the low–valence dopant of Cu can significantly improve the low-temperature SCR activity and SO2 tolerance of the Mn3O4 spinel, which could be a strategy for the further design of Mn-based SCR catalysts.

Investigation of low-temperature selective catalytic reduction of NOx with ammonia over Cr-promoted Fe/AC catalysts.

Fe/activated coke (AC) and Cr-Fe/AC catalysts with AC as a supporter and Cr and Fe as active components were prepared by an impregnation method for low-temperature selective catalytic reduction (SCR) of NO with NH3. The effects of Cr addition and its concentrations on the deNOx performance of Fe/AC catalysts were studied at low temperature. The Cr addition promotes the low-temperature SCR activity of the 8Fe/AC catalyst and the 8Fe6Cr/AC catalyst has the best low-temperature SCR deNOx performance, which the NOx conversions are greater than 90% at 160-240 °C. The 8Fe6Cr/AC catalyst has good water resistance. However, when 100 ppm SO2 was introduced into the reaction gas, its deNOx efficiency drops to 45% at 180 °C. To clarify the specific effects of Cr addition on the NOx conversions and sulfur poisoning, the Cr-Fe/AC catalysts were characterized by X-ray diffraction, BET, H2 temperature-programmed reduction, NH3 temperature-programmed desorption, X-ray photoelectron spectroscopy, and Fourier infrared spectroscopy. The addition of Cr into Fe/AC catalysts greatly increases the BET surface area and the number of weak and medium-strong acid sites on the catalyst surface and improves the ratio of Fe3+/Fe2+. These factors enhance the NOx conversion of 8Fe/AC catalyst. The formed sulfates and hydrogen sulfates cover the active sites on the catalyst surface, which lead to the sulfur poisoning of the 8Fe6Cr/AC catalyst. Graphical abstract.

The promotion effect of Cr additive on CeZr2Ox catalyst for the low-temperature selective catalytic reduction of NOx with NH3

A sequence of Cr-modified CeZr2Ox catalysts were synthesized through the co-precipitation way and applied in selective catalytic reduction (SCR) of NOx with ammonia. The optimal catalyst (Cr1CeZr2Ox) exhibited the excellent NH3-SCR activity and high SO2 resistance. From the characterization results, Cr species in Cr1CeZr2Ox could suppress the formation of ZrO2 crystals, which could also contribute to stronger surface acidity and reducibility. Besides, more Ce3+ and surface adsorbed oxygen species were observed on Cr1CeZr2Ox catalyst. On the basis of in situ DRIFT experiments, it could be confirmed that the NH3-SCR process on Cr1CeZr2Ox was promoted through Langmuir-Hinshelwood (L-H) mechanism. Besides, the improved NO oxidation and more ad-NOx and ad-NH3 also played a vital role for the superior low-temperature SCR activity of Cr1CeZr2Ox.

Impact of Hydrothermal Aging on SO2 Poisoning over Cu-SSZ-13 Diesel Exhaust SCR Catalysts

The impact of hydrothermal aging on SO2 poisoning over Cu-SSZ-13 selective catalytic reduction (SCR) catalysts were investigated in this study. The catalyst samples were hydrothermally aged at various temperatures for SO2 poisoning and characterized by SO2 temperature-programmed desorption (SO2-TPD), X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), and NH3-TPD. The performance evaluations were also performed to illustrate the impact on SCR activity and oxidation. The results showed that the Cu-SO4-like species decreased in the 750 °C aged sample via copper migration, while they increased in the 850 °C aged sample due to CuOX/CuAlOX formation. The low-temperature SCR activity and oxidation decreased due to sulfur poisoning. For the sulfated sample, however, it was determined that NOX conversion was slightly higher on the mildly hydrothermally aged sample. Furthermore, desulfation is easier for the mildly hydrothermally aged sample but more difficult for the severely hydrothermally age...

Morphology control of manganese-based catalysts for low-temperature selective catalytic reduction of NOx

The low-temperature selective catalytic reduction (SCR) of NOx by ammonia is an efficient purification technique to eliminate NOx from stationary combustion sources. In this paper, the different exposed crystal facets of α-MnO2 catalyst were controllably synthesized by using of capping agents of PVP, P123, HAc and CTAB. It was found that all α-MnO2 catalyst prepared using various capping agents are with the same nanorods morphology but different exposed crystal facets. The structure-activity relationship of the catalyst was investigated and the exposed crystal facets showed strong effects of on its activity of SCR for deNOx. The α-MnO2 catalyst with exposed (200) facets has the highest surface acidity, strongest NH3 and NO adsorption and therefore the best low-temperature SCR activity, with 98% NO conversion at 160 °C.

Metal oxide-confined interweaved titania nanotubes M/TNT (M = Mn, Cu, Ce, Fe, V, Cr, and Co) for the selective catalytic reduction of NOx in the presence of excess oxygen

A series of metal oxide confined titania nanotube M/TNT (M = Mn, Cu, Ce, Fe, V, Cr and Co) catalytic formulations were successfully synthesized using hydrothermal method followed by wet impregnation technique. The resulting materials were investigated for the low temperature Selective Catalytic Reduction (SCR) of NOx with NH3 in the presence of excess oxygen (10 vol.%). The prepared catalysts exhibit remarkable deNOx potential at temperatures as low as 100 °C and in a wide temperature range from 100 to 350 °C. Compared to manganese oxide supported on conventional TiO2, the synthesized Mn/TNT catalyst exhibits superior activity. Interestingly, the surface texture and tubular morphology of Mn/TNT catalyst greatly promotes the NOx conversion in the temperature regime of 100–300 °C. Our BET results of the as-prepared catalysts demonstrated that this is an effective synthesis for the generation of high specific surface area (421 m2/g) titania nanotubes. High resolution transmission electron microscopy (HR-TEM) results revealed the formation of tubular structure and multi-walled layer construction in the pristine titania nanotube (TNT), Mn/TNT and Ce/TNT samples. The relative atomic percentage value of Mn4+/Mn3+ and Ce3+/Ce4+ characterized by deconvoluted XPS spectra was considerably high for the Mn/TNT (Mn4+/Mn3+ = 2.15) and Ce/TNT catalysts (Ce3+/Ce4+ = 0.79), respectively. The existence of abundant surface Mn4+ species apparently contributes to the remarkable low-temperature SCR activity over our Mn/TNT catalyst. The H2-TPR results are in good accordance with our XPS results, with MnO2 being the prevailing phase and the increased reduction potentials of manganese appear to be the reason for the high deNOx activity of the Mn/TNT catalyst at low-temperatures. Vanadia based catalyst (V/TNT) formulations exhibit monolayer isolated species present over the support where V5+ is the dominant oxidation state. Titania nanotubes confined vanadium oxide catalyst demonstrates a broad operation temperature window attributed to the high dispersion of active species on the support.

New Insight into SO2 Poisoning and Regeneration of CeO2-WO3/TiO2 and V2O5-WO3/TiO2 Catalysts for Low-Temperature NH3-SCR.

In this study, the poisoning effects of SO2 on the V2O5-WO3/TiO2 (1%VWTi) and CeO2-WO3/TiO2 (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 NH3 + SO2 + H2O + O2 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, NH4HSO4 (ABS) was the main product detected after the poisoning process. Both of NH4HSO4 and cerium sulfate species were formed on the poisoned 5%CeWTi catalyst, indicating that SO2 reacted with Ce3+/Ce4+, even in the presence of high concentration of NH3. 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 NH4HSO4 accumulated on the catalysts.

Improved catalytic activity and N2 selectivity of Fe–Mn–O x catalyst for selective catalytic reduction of NO by NH3 at low temperature

FeO x , MnO x and Fe–Mn–O x catalysts were prepared by the co-precipitation method and used for the selective catalytic reduction (SCR) of NO x by NH3 at low temperature. Fe–Mn–O x catalyst showed the best catalytic activity and above 80% NO x conversion was obtained at 50–150 °C. Nearly 80% N2 selectivity of Fe–Mn–O x catalyst was acquired at the whole temperature range. The excellent low-temperature SCR activity and N2 selectivity were ascribed to the abundant surface acid sites, the formation of Fe–O–Mn species, co-existence of multiple valence states (Mn4+, Mn3+ and Mn2+) and the proper redox ability. In addition, the interaction between Fe and Mn species over the Fe–Mn–O x catalyst was responsible for the improvement of SCR performance and N2 selectivity. Fe–Mn–O x catalysts were prepared by the co-precipitation method and used for the selective catalytic reduction (SCR) of NO x by NH3 at low temperature. The formation of Fe–O–Mn species contributed to the co-existence of multiple valence states (Mn4+, Mn3+, Mn2+, Fe3+ and Fe2+), resulting in an increase in catalytic activity and N2 selectivity. Besides, the abundance of acid sites was responsible for the superior N2 selectivity.