NO Removal Efficiency Research Articles

Methanol-assisted NO oxidation under an oxygen atmosphere for efficient denitration: Experiments and ReaxFF-MD simulations

The development of selective catalytic reduction technologies for controlling nitrogen oxide (NOx) emissions in flue gas is hampered by high equipment and catalyst costs. In this study, a catalyst-free and efficient denitration process using methanol and oxygen as reactants was developed. Various gas atmospheres with differing concentrations were investigated to remove NO without catalysts. The addition of methanol significantly enhanced NO removal efficiency, reaching 94.6 % at 550 °C, with 55.1 % of NO converted to NO2, which can be absorbed by downstream alkali solutions. Reactive force field molecular dynamics (ReaxFF-MD) simulations were employed to analyze the atomic level NO oxidation mechanism in the CH3OH/NO/O2/H2O homogeneous reaction system. The simulation revealed the generation pathway of three key oxidizing intermediates (OH, HO2, and H2O2) and their roles in NO oxidation. This study offers critical insights into developing a cost-effective denitration process, highlighting the potential for improved NOx emission control.

A superior Mn5CeTi5Ox catalysts for synergistic catalytic removal of chlorobenzene and NOx: Performance enhancement and mechanism studies

The transition metal titanium-doped Mn-Ce-Ox catalysts catalyst were employed to achieve synergetic removal of NO and CB at 180–220 °C. The Mn5CeTi5Ox catalyst with a molar ratio of Mn/Ce/Ti = 5:1:5 exhibits excellent activity, and the NOx and CB removal efficiencies reach 96 % and 89 % at 160–220 °C, respectively. The selectivity for N2 and CO2 are 93 % and 78 %, respectively. The N2-physisorption, NH3-TPD, H2-TPR and XPS results show that Ti doping makes the catalyst possess a mesoporous structure, suitable particle sizes, and excellent redox and Lewis site properties. All of these features contribute to the observed high NO and CB removal efficiency. The synergetic removal of CB and NO over Mn5CeTi5Ox results from the synergistic catalysis between the redox and the solid acid. On the one hand, in the synergistic removal process, CB and NH3 are competitively adsorbed on the catalyst surface, resulting in a decrease in the NH3-SCR activity. On the other hand, the removal of NO and CB has a synergetic effect. The byproduct NO2 produced by the NH3-SCR reaction promotes the oxidation of CB, which is beneficial for CB removal. Moreover, the consumption of NO2 indirectly promotes the NH3-SCR reaction, which partially compensates for the decrease in the NO removal efficiency caused by competitive adsorption between NH3 and CB. Ti doping promotes the participation of the SCR byproduct NO2 in the CBCO reaction and promotes the formation of maleic acid, an intermediate product of CB oxidation. In summary, the Mn5CeTi5Ox catalyst exhibits good activity for the synergistic removal of NOx and CB and is a promising candidate for the effective and economical removal of NO and CB during waste incineration.

Research over the effect of activated carbon treated with calcium nitrate solution on the catalytic ability in the reduction of Co(III)Triethylenetetramine

AbstractActivated carbon can be used as a catalyst for the reduction of Co(III)TETA to Co(II)TETA so as to maintain the ability of removing NO from gas stream with Co(II)TETA solution. Calcium nitrate has been utilized to treat activated carbon to improve its catalytic ability in the regeneration of Co(II)TETA. The biggest Co(III)TETA conversion is gained by the carbon being soaked in 0.3 mol/L calcium nitrate solution at 65°C for 12 h with a solid/liquid ratio of 1 g/50 mL followed being carbonized at 400°C for 2 h in nitrogen. The characterization with Fourier transform infrared spectroscopy, XPS, BET (Brunauer‐Emmett‐Teller) and Boehm titration indicates that the modification with calcium nitrate increases the specific surface area and acidic groups on activated carbon. The continuous experiments reveal that the NO removal efficiency obtained by the modified carbon is over 12% up to that by the original one.

Online in-situ modification of biochar for the efficient removal of elemental mercury and co-benefit of SO2/NO removal

In this study, non-thermal plasma discharge was proposed for online in-situ modification of biochar injected into coal-biomass co-combustion flue gas, aiming to achieve the combined removal of elemental mercury (Hg0), NO, and SO2 from flue gas. After plasma discharge, the pore structure of biochar was slightly improved whereas the surface morphology of biochar was almost unchanged. After plasma discharge under O2, SO2, and HCl atmospheres, the oxygen, sulfur, and chlorine contents of biochar were obviously increased. More exactly, additional functional groups were formed on the modified biochar surface, such as CO, C(O)OC, CS, and CCl. Compared with raw biochar, the biochar modified under HCl, SO2, O2, H2O and CO2 atmospheres exhibited higher Hg0 removal efficiency, and longer modification time resulted in better Hg0 removal performance. The optimal modification atmosphere and reaction temperature were the simulated flue gas (SO2 + HCl + CO2 + O2 + H2O + NO + N2) and 20 ℃-100 ℃, respectively. The modified biochar exhibited excellent resistance to SO2 and H2O. The addition of HCl, CO2, NO, and O2 contributed to Hg0 removal. The removal efficiency of NO and SO2 attained a maximum of 100 %. The Hg0 removal mechanism was further revealed, where CO, C(O)OC, CS, and CCl served as active components.

Synthesis of CdS QDs/NH2-Nb2O5 via electrostatic self-assembly method for highly efficient photocatalytic removal of NO and synchronous inhibition of NO2

A two-step electrostatic self-assembly method was used to first graft –NH2 groups onto the Nb2O5 followed by loading of CdS QDs onto the NH2-Nb2O5 to obtain CdS/NH2-Nb2O5. The performance of the samples under visible light was evaluated under simulated conditions of 25 °C and varying relative humidity (RHs). The results showed that with the increase of RH, the NO removal efficiency by CdS/NH2-Nb2O5 increased first and then decreased, reaching the maximum NO removal efficiency when RH = 50 %. The selectivity of NO2 on CdS/NH2-Nb2O5 (9.01 %) was significantly lower compared to that of Nb2O5 (24.44 %) and NH2-Nb2O5 (19.72 %). The introduction of –NH2 groups and CdS QDs significantly enhanced visible light absorption and improved the separation efficiency of photogenerated charge carriers. In-situ DRIFTS analysis revealed that Cd2+ served as an additional active site for NO adsorption. Furthermore, CdS had a relatively negative conduction band position, which was conducive to the generation of O2–, further inhibiting the generation of NO2. This work provides a new approach to the design and preparation of catalysts for photocatalytic oxidation of NO.

Na-doped nitride-rich carbon nitride for efficient photocatalytic NO abatement

Nitride-rich carbon nitride (C3N5) is gaining prominence as a substantial catalyst for photocatalytic reaction because of its narrow bandgap, extensive light responsiveness, and photocatalytic stability. To enhance the efficiency of photogenerated carrier separation in C3N5, we propose a strategy for Na-doped modification. Photocatalytic NO removal efficiency of C3N5/Na achieved 73.9 % under 15 % relative humidity, which is 3.5 times higher than that of C3N5. Besides, the NO removal efficiency of C3N5/Na maintained above 70 % even after six cycles under different relative humidities. Detailed analytical characterization revealed that Na doping of C3N5 not only increased its specific surface area by 5.5-fold but also modulated its energy band structure and molecular structure, leading to improved hole-carrier separation efficiency and enhancing the photocatalytic performance of C3N5/Na. ESR and reactive species trapping experiments confirmed that electrons and superoxide are the main reactive species, and modulation of the energy band structure accelerates the reaction. This work explains the effect of Na doping on C3N5 and provides a new strategy for designing efficient for photocatalytic treatment of air pollution.

Synergistic removal of NO and CO in industrial waste gas by Fe-modified Cu/TiO2 catalysts: The synergistic effect of metal oxides interaction

NH3-based selective catalytic reduction (NH3-SCR) combined with carbon monoxide (CO) catalytic oxidation is a productive way to synergistically remove nitrogen oxides (NOx) and CO from industrial waste gas. Catalyst is the undoubtedly centerpiece of the synergistic removal technology, which has aroused tremendous attention. Herein, in this investigation a variety of Cu/TiO2 catalysts modified by various metal oxides were prepared by impregnation method, and the excellent synergistic removal performance of Fe-modified Cu/TiO2 catalyst was observed. The Cu/TiO2 catalyst with a 7 wt% Fe doping amount exhibited the highest NO and CO removal efficiency (86 % for NO at 300 °C and over 98 % for CO from 300 ∼ 400 °C). Through a series of characterization techniques, it was discovered that Cu and Fe oxides interacted to evenly distribute them throughout the surface of TiO2 support, resulting in smaller particle size and abundant variable valence species (Cu+/Cu2+ and Fe2+/Fe3+) to enhance the redox performance of the catalysts. Moreover, the creation of additional surface chemisorbed oxygen, the adsorption of NO and CO, and the improvement of surface acidity were all facilitated by the electron transfer between various Cu and Fe species. In addition, in-situ diffuse reflectance infrared transform spectroscopy (in situ DRIFTS) results revealed the interaction between NH3-SCR and CO oxidation. This study proposes a viable approach to develop efficient catalysts for the synergistic removal of NO and CO in industrial applications.

Type-II heterojunction In2O3/TiO2 with highly efficient charge separation for boosted photocatalytic NO abatement

Photocatalytic NO degradation often suffers from sluggish charge carrier separation and low selectivity. Herein, a series of In2O3/TiO2 (P25) composites were synthesized to enhance NO abatement. Benefiting from the conspicuous synergistic effect between In2O3 and P25, the In2O3/P25 catalysts demonstrated more than double the NO elimination performance compared to pure P25 and In2O3. The In2O3/P25 sample with 75 wt% In2O3 (In-P25-75) achieved a NO removal efficiency of 51.7 %, higher than reported catalysts (30.0–49.0 %). It was the successful formation of type-II heterostructure that enabled intimate interfacial contact and provided ample electron transfer channels. Moreover, photoluminescence spectra and photoelectrochemical measurement confirmed the improved separation and inhibited recombination of photogenerated charge carriers in In-P25-75, thereby boosting the NO photocatalytic efficiency. ·O2− and ·OH radicals generated by photoinduced electron transfer to the conduction band of P25, along with the induced holes confined to the valence band of In2O3, facilitated the targeted deep oxidation of trace NO into NO3− rather than harmful NO2. This work discloses a promising strategy for the efficient removal of NO from the atmosphere by reducing the emission of hazardous intermediate NO2.

Study on Ship Exhaust Gas Denitrification Technology Based on Vapor-Phase Oxidation and Liquid-Phase Impingement Absorption

A system combining gas-phase oxidation and liquid-phase collision absorption for removing NO from marine diesel engine exhaust was proposed. This method was the first to utilize different physical states of the same mixed solution to achieve both pre-oxidation and impingement reduction absorption of exhaust gases. During the pre-oxidation stage, a mixture of (NH4)2S2O8 and urea solution was atomized into a spray using an ultrasonic nebulizer to increase the contact area between the oxidant and the exhaust gas, thereby efficiently pre-oxidizing the exhaust gas in the gas phase. In the liquid-phase absorption stage, the (NH4)2S2O8 and urea solution was used in an impingement absorption process, which not only enhanced gas–liquid mass transfer efficiency but also effectively inhibited the formation of nitrates. Experimental results showed that, without increasing the amount of absorbent used, the maximum NO removal efficiency of this method reached 97% (temperature, 343 K; (NH4)2S2O8 concentration, 0.1 mol/L; urea concentration, 1.5 mol/L; NO concentration, 1000 ppm; pH, 7; impinging stream velocity, 15 m/s), compared to 72% using the conventional liquid-phase oxidation absorption method. Additionally, this method required only the addition of a nebulizer and two opposing nozzles to the existing desulfurization tower to achieve simultaneous removal of sulfur and nitrogen oxides from the exhaust gas, with low retrofitting costs making it favorable for practical engineering applications.

Acid sites-CeOx doping CrZrCeOx catalyst with high SO2 resistance for marine SCR application: Surface analysis and mechanism study

This paper mainly talked about acid sites-CeOx doping CrZrCeOx catalyst with high SO2 resistance for marine NH3– SCR (selective catalytic reduction). The NO removal efficiency of the Cr:Zr:Ce = 8:2:1 catalyst reached 90 % with 500 ppm SO2 and 85 % with 1000 ppm SO2 for 20 h, respectively. It was inferred that the main roles of CeOx species were acid sites but not redox sites. CeOx addition promoted the SCR performance and SO2 resistance, which significantly changed the adsorbed species on the surface. CeOx acted as sacrifice sites to protect CrOx actives sites through reducing the combination of Cr and sulfates. The Cr:Zr:Ce = 8:2:1 catalyst followed Langmuir-Hinshelwood (L-H) mechanism and the reaction process was derived in this paper. It indicated that the Cr:Zr:Ce = 8:2:1 catalyst would be a promising marine SCR catalyst with good SO2 resistance in the future.

Asymmetric dual-chamber electrochemical reactor for reducing Fe(Ⅲ)EDTA to remove NOx by enhanced complexing absorption

The complexing absorption technology possesses broad application prospects in the efficient removal of pollutant NO from industrial flue gas. However, the absorbent Fe(Ⅱ)EDTA is readily oxidized to Fe(Ⅲ)EDTA by the inherent O2 in flue gas, which severely impairs denitrification efficiency due to the inability of Fe(Ⅲ)EDTA to absorb NO. Here, a novel asymmetric dual-chamber electrochemical reactor (ADER) was designed to efficiently reduce Fe(Ⅲ)EDTA to Fe(Ⅱ)EDTA. The key to high-efficient reduction was to improve the reaction kinetics utilizing a unique design of larger cathode–anode area ratio. Moreover, cloth served as separator simultaneously satisfied the needs of H+ transfer and diffusion limitation of Fe(Ⅱ)EDTA and Fe(Ⅲ)EDTA, thus safeguarding the reduction efficiency while avoiding membrane contamination. The reduction efficiency and current efficiency of Fe(Ⅲ)EDTA up to 78.05 and 98.19 % in ADER system, respectively, with energy consumption of 0.078 kWh/mol Fe(Ⅲ)EDTA. And the ADER systems coupled with complexing absorption exhibited excellent NO removal efficiencies exceeding 92 % even in the presence of O2. The ADER provided an efficient, convenient and low-cost strategy for the regeneration of absorbent Fe(Ⅱ)EDTA as well as NOx removal.

Remarkable improvement in photocatalytic activity of g-C3N4 for NO oxidation through surface hydroxylation

The nitrogen oxide emissions originating from combustion pose significant risks to the environment. Photocatalysis is considered an efficient and environmentally friendly strategy to alleviate this problem. Graphitic carbon nitride (g-C3N4) is regarded as one of the most promising organic photocatalytic materials for environmental purification. However, its small specific surface area, weak adsorption and high recombination rate of charge carriers result in low intrinsic photocatalytic activity. To overcome these obstacles, a hydrothermal treatment of dicyandiamide-derived g-C3N4 (DCN) at different temperatures (140–200 °C) was employed to enhance the photocatalytic activity for NO oxidation. The experimental results demonstrated a significant improvement in the photocatalytic oxidation removal rate of NO after a hydrothermal treatment. The optimal photocatalyst, DCN-180, treated at 180 °C, demonstrated the highest NO removal efficiency (65.0 %), which is twice the value of pristine DCN (32.5 %). Additionally, the formation of the toxic intermediate NO2 was effectively suppressed during the reaction. Photoelectrochemical tests revealed that DCN-180 exhibited higher photocurrent density and smaller impedance radius compared to the untreated g-C3N4 sample. Moreover, density functional theory (DFT) calculations confirmed that the DCN-180 sample showed a stronger ability to adsorb O2 and NO. The enhanced photocatalytic NO oxidation performance of DCN-180 has been primarily attributed to its enlarged specific surface area (from 10.7 to 35.5 m2 g−1), local polarization effect, reduced interfacial charge transfer resistance, and improved adsorption abilities for NO and O2 molecules. This study provides valuable insights for designing and preparing highly efficient g-C3N4 based photocatalysts through surface modification for photocatalytic NO purification.

Facile strategy to promote SO2‑resistance ability for NH3-SCR catalyst CeSnTiOx via copper sulfate-modified: Boost from a double reaction site

Constructing excellently SO2-resistence NH3-SCR catalyst is a challenge for achieving superior NOx removal efficiency at practical needs. In this work, the effect of sulfate modification on the performance of NH3-SCR on ordered mesoporous catalysts was carefully studied. The ordered mesoporous catalyst CeSnTiOx modified with copper sulfate with the weak-confined effect has been prepared successfully via vacuum impregnation. Interestingly, the NO removal efficiencies of CeSnTiOx modified with copper sulfate got greatly enhanced at 240 °C under the atmosphere of SO2, and the 5Cu-S/CeSnTiOx catalyst (5% loaded of copper sulfate) has shown excellent performance. A series of characterizations such as XRD, TEM, TG, Raman and in-situ DRIFTS of SO2 atmosphere were conducted to investigate the interactions on the catalyst surface of those reactant molecule. It was revealed that the copper sulfate-modified has realized the boost from double reaction sites (redox site and acid site) in the 5Cu-S/CeSnTiOx catalyst. The Cu-species can disturb the electron cycle of the catalyst and reduce the strong redox performance of Ce active site, which can inhibit the adsorption of SO2 effectively. Meanwhile, the S-species (from the SO42-) has changed the distribution of acid sites and the total acid content on the catalyst surface, which has realized the rapid SCR reaction. This work provides a facile but effective strategy for further design of highly efficient SO2-resistence SCR catalysts.

Mass transfer enhancement for simultaneous desulfurization and denitrification by a venturi reactor

Interphase mass transfer is acknowledged as the rate-limiting step of simultaneous desulfurization and denitrification by wet oxidation. For this issue, this study established a venturi reactor to facilitate interphase mass transfer between flue gas and absorbent (NaClO2 solution), and to improve the efficiency of simultaneous desulfurization and denitrification. The effects of flow rate of jet, NaClO2 concentration, initial pH of solution, SO2 and NO volume concentration on the efficiency of desulfurization and denitrification were investigated. The results showed that SO2 can be completely removed at all experimental conditions. The denitrification efficiency decreased as jet flow rate increased from 8.38 L/ min to 12.87 L/min. The denitrification efficiency and overall mass transfer coefficient increased as the NaClO2 concentration increased from 0.01 wt% to 0.025 wt%. When the pH of the absorbent decreased from 9 to 3, the denitrification efficiency was improved significantly. An increasing SO2 volume concentration promoted NO removal efficiency, while SO2 and NO competed to inhibit denitrification at NaClO2 deficiency. The denitrification efficiency firstly increased and then decreased, with an increasing NO volume concentration from 500 to 1700 ppm. This study provides an important theoretical basis for the industrial application of simultaneous desulfurization and denitrification in venturi reactors.

Theoretical and experimental studies of NO removal in alkaline H2O2 system

NO in flue gas is one of the atmospheric pollutants, and it is necessary to study effective NO removal technology. It was identified that the alkaline H2O2 system achieved over 98 % NO removal efficiency with a gas–liquid contact time of 3 s in this paper. This paper investigates the mechanism of NO removal in alkaline H2O2 solution through both experimental and theoretical calculations. The results reveal the NO removal process can be divided into three phases by the NaOH/H2O2 molar ratio. (1) The ∙O2– dominated phase, where trace metal Fe catalyzes ∙O2– radical generation from H2O2 as Fe (OH)2+, reacting primarily with NO to form ONOO–. The energy barrier for this process is1.299 kcal/mol, with a reaction rate constant of 9.12 E + 11 s-1M−1. (2) The HO2– dominated phase, HO2– was generated through OH– and H2O2 neutralization, which converts NO to NO2 and regenerating OH–. The energy barrier for HO2– reacting with NO is 3.833 kcal/mol, and the reaction rate constant is 2.07E + 10 s-1M−1. (3) The O22– dominated phase, O22– was a further ionization of HO2– and converting NO to NO2– directly. The energy barrier for this process is 7.079 kcal/mol, and the reaction rate constant is 1.49 E + 08 s-1M−1.

Study on removal of NO from flue gas by ferrous cysteine solution and analysis of reaction process

Wet denitrification technology has been extensively researched for its benefits in synergistically treating pollutants. As a representative complexing agent, ferrous cysteine (Fe2+(CyS)2) solution in the complex absorption method has attracted the attention of researchers. In this study, the influence of c(Fe2+):c(CySH) ratio, complexation time, initial pH value, and temperature on the NO removal efficiency and reaction process of Fe2+(CyS)2 in a bubbling reactor were investigated. The results highlighted the significance of the initial pH of the Fe2+(CyS)2 solution in denitrification efficiency, with higher pH leading to improved NO removal. The denitrification efficiency showed a volcano-like variation with increasing temperature and was not much affected by NO inlet concentration and Fe2+(CyS)2 solution complexation time. Under optimal conditions, the denitrification efficiency remained above 80 % for 3 h of continuous reaction, peaking at 98.4 %. Calculations of NO absorption capacity indicated the regeneration of Fe2+(CyS)2 solutions. Testing with iodometric and bromine-ferrous titration methods revealed that the reaction product of cysteine is cystine, maintaining material balance before and after the reaction. Experimental results validate Fe2+(CyS)2 as an effective and stable denitrification method, laying the foundation for potential industrial application.

Performance, mechanism, and kinetics of NO removal using ligand-enhanced UV-Fenton driven by O2 from flue gas

Wet free radical advanced oxidation technology such as Fenton reaction is thought to be a very efficient method to remove NO from flue gas, but it requires the consumption of additional oxidants to achieve high removal efficiency. For this purpose, a ligand-enhanced UV-Fenton system without additional oxidants was proposed for NO removal. Three common chelating ligands, EDTA, NTA, and Citrate, were selected to promote UV-Fenton reaction for NO removal. The NO removal performance, mechanism, and kinetics of three different ligand-enhanced photochemical Fenton systems including EDTA/UV/Fe(II), NTA/UV/Fe(II), and Citrate/UV/Fe(II), were studied. Results showed that ligand addition can greatly promote a NO removal in the UV-Fenton system, in the following order of efficiency: EDTA > NTA > Citrate. The mechanism research indicated that these ligands not only enhanced NO oxidation removal by promoting the generation of •OH, but also provided NO complexation removal, which synergized oxidative denitrification and complexation denitrification in the same reaction system, greatly promoting wet NO removal. NO from simulated flue gas was mainly converted into NO3−, NO2−, NH4+, N2, and N2O through synergistic complexation-oxidation. The optimum ratio of ligand to Fe(II) was 1:1 for EDTA and NTA and 3:1 for citrate. NO removal efficiency was increased and then decreased with the increase in pH value or O2 concentration. The low temperature was found to be favorable for NO removal. Furthermore, the kinetics demonstrated that the L/UV/Fe(II) system reaction was a pseudo-first-order process involving nitric oxide. Finally, compared with other Fenton and Fenton-like denitrification systems, EDTA(NTA)-enhanced UV-Fenton system had shown great priority in terms of removal performance, absorbent cost, and waste disposal.

Surface tailoring on bifunctional CuOx/MnO2 catalyst to promote the selective catalytic reduction of NO with NH3 and oxidation of CO with O2

NO and CO are two primary pollutants in the sintering flue gas emission, posing significant challenges for the treatment. Under oxygen-enriched conditions, CO was easily oxidized to CO2 before participating in CO-SCR reaction as a reducing agent. Consequently, NH3-SCR technology coupled with CO oxidation reaction is a promising approach for simultaneous NO and CO removal. In this study, a series of bifunctional CuOx/MnO2 catalysts were synthesized using a combine of hydrothermal and wet impregnation methods, and their catalytic performance for simultaneous removal of NO and CO was assessed. CuOx/α-MnO2 catalyst displayed outstanding catalytic activity for both NO and CO, achieving over 80 % NO removal efficiency and 96 % CO conversion rate at 150 °C, while CuOx/β-MnO2 catalyst exhibited poor catalytic activity in the entire temperature range. Moreover, the interplay between the NH3-SCR and CO catalytic oxidation reactions was also explored. XPS results revealed that the concentration of Mn4+ and Cu+ species significantly influenced the catalytic activity of the catalysts for the simultaneous removal of NO and CO. Particularly, the presence of Mn4+ species promoted “fast SCR” reaction, whereas Cu+ species demonstrated higher reactivity for both NO reduction and CO oxidation. In situ DRIFTS analysis of transient reactions revealed that the L-H mechanism was followed over CuOx/α-MnO2 catalyst in the NH3-SCR reaction, while both the M-K and L-H mechanisms were observed in CO catalytic oxidation reaction.

Tailoring tunnel-type potassium-free manganese oxide catalyst via cerium substitution for catalytic NO reduction with NH3 at ultra-low temperatures

Manganese oxide (KMn8O16, K-MO) was widely used for selective catalytic reduction (SCR) denitration due to its superior ability for activating and converting NO to N2 with NH3. However, the harmful K+ in its tunnel structure tends to consume NH3, leading to limited low-temperature activity and stability. Herein, a Ce substitution strategy was developed for the preparation of K-free Ce-MO for NH3-SCR. As-prepared Ce-MO exhibits a high NOx conversion (95%) at an ultra-low temperature of 75°C, with negligible activity decay within 60 h. Systematic characterizations elucidate the important role of Ce substitution in improvement of catalytic efficiency and stability for NO removal. The introduction of Ce not only eliminates harmful K+ and improves the stability of the catalyst, but also enhances the removal efficiency of NOx by the generation of oxygen vacancies. In addition, the formation of intermediate NH4NO3 is critical to improving the catalytic efficiency and stability over Ce-MO base on in-situ DRIFTS. This work provides a favorable strategy for the preparation of free-K tunnel-type manganese oxide catalyst for denitration with high activity and superior stability at ultra-low temperature.

Strongly reducing NaHS regenerates Fe(II)EDTA for efficient NO removal with high cycling performance under high oxygen conditions

Fe(II)EDTA can remove NO efficiently, but it has not been industrially applied. This is because the oxygen present in the flue gas will oxidize Fe(II)EDTA and Fe(II)EDTA-NO to Fe(III)EDTA and deactivate them. In order to solve this problem, this paper innovatively proposes to use NaHS to reduce Fe(III) EDTA, because NaHS has high reducing ability and low price. Therefore, a series of experimental conditions were explored in order to obtain the best reaction setup. The results indicate that increasing the concentrations of NaHS, temperature, and pH enhances the rate of NaHS reduction. The mechanism of the increase in reduction rate was studied in depth using potentiometric titration. It was found that an increase in OH- concentration will generate S8 precipitate, which is beneficial to the forward progress of the reaction and promotes the large-scale production of the active component Fe2+. Oxygen is an inevitable factor in actual flue gas, so this study innovatively proposed a kinetic model under aerobic conditions and used this model to predict the trend of Fe(III)EDTA reduction by NaHS. On this basis, NO removal experiments were conducted under high oxygen conditions. After 15 cycles, the reduction performance of NaHS was still very high, and the NO removal rate was higher than 70%. The reason for this phenomenon is that the stabilizer exists in a form that is conducive to the removal of NO by the active component Fe2+. Therefore, this study provides theoretical guidance for promoting the industrial application of Fe(II) EDTA technology for NO removal.