NO Removal Research Articles

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.

Long-term performance of wastewater gardens: follow-up on the status of the wastewater garden in Temacine – Algeria

ABSTRACT This work investigated the long-term performance of a small wastewater garden (WWG) system for treating municipal wastewater, which has been operating continuously since 2007. The studied system consisted of a horizontal subsurface flow (HFCW) and treated a flow rate of 15 m3/day. Results from 15 years of operation showed that the system has an average removal efficiency of 90.76, 85.12, 89.43, 66.87, 94.74, and 94.74% for total suspended solids (TSS), chemical oxygen demand (COD), biochemical oxygen demand (BOD5), nitrites (NO2–), nitrates (NO3–), and orthophosphates (PO43−), respectively. The high efficiency of the WWG plant was achieved during 2018–2022 compared to the two first years of operation (apart from the TSS). It was noted that the removal of BOD5, NO2–, NO3–, and PO43− has been improved in the last years of operation. The elimination COD remained relatively consistent between the initial and present period of operation. The finding confirms the high efficiency in the long-term operation of municipal wastewater treatment. Thus, it can serve as a suitable solution for small communities, especially in arid climate areas.

Mechanism of NO removal by CO + NH3 coupling in iron–manganese/activated carbon catalysts at medium and low temperatures

Mechanism of NO removal by CO + NH3 coupling in iron–manganese/activated carbon catalysts at medium and low temperatures

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.

Recent Progress and Future Prospects of Metal‐Organic Frameworks for Adsorption, Separation and Catalytic Removal of NOx and N2O

Recent Progress and Future Prospects of Metal‐Organic Frameworks for Adsorption, Separation and Catalytic Removal of NO_x and N₂O

MXene quantum dots decorated g-C3N4/BiOI heterojunction photocatalyst for efficient NO deep oxidation and CO2 reduction

The photocatalytic performance of g-C3N4 is greatly limited by the severe charge recombination due to its s-triazine unit structure. Hence, enhancing the separation of photogenerated carriers is the pivotal factor for high-efficiency photocatalysis of g-C3N4. In this work, we construct a MXene quantum dots (MQDs) decorated BiOI/g-C3N4p-n heterojunction photocatalyst. The interfacial charge separation and transfer are substantially promoted, due to the synergistic effect of the internal electric field (IEF) of BiOI/g-C3N4 heterojunction and strong electron-withdrawing capability of MQDs. Furthermore, the introduction of BiOI with a low band gap and MQDs with large specific areas and rich surface terminals lead to enhanced light absorption and active sites. As a result, the ternary g-C3N4/MQDs/BiOI photocatalyst achieves a much higher NO removal rate of 42.23 % and discharges less NO2 intermediate than the individual and binary ones. Meanwhile, the g-C3N4/MQDs/BiOI photocatalyst also exhibits the most effective CO2 photoreduction, with a CO production rate of 57.8 μmol·g−1·h−1 and a CH4 production rate of 3.6 μmol·g−1·h−1, surpassing all other photocatalysts in this study. In addition, the designed composite photocatalyst shows remarkable stability. The photocatalytic mechanisms are studied by the trapping experiment and in-situ Fourier Transform Infrared (FTIR) Spectra. This work paves a new avenue for enhancing charge separation and thus improving performances of g-C3N4-based photocatalysts by integrating a p-n heterojunction and a co-catalyst, which would accelerate commercial deployment of emerging photocatalysts.

Variable contribution of wastewater treatment plant effluents to downstream nitrous oxide concentrations and emissions

Abstract. Nitrous oxide (N2O), a potent greenhouse gas and ozone-destroying agent, is produced during nitrogen transformations in both natural and human-constructed environments. Wastewater treatment plants (WWTPs) produce and emit N2O into the atmosphere during the nitrogen removal process. However, the impact of WWTPs on N2O emissions in downstream aquatic systems remains poorly constrained. By measuring N2O concentrations at a monthly resolution over a year in the Potomac River estuary, a tributary of the Chesapeake Bay in the eastern United States, we found a strong seasonal variation in N2O concentrations and fluxes: N2O concentrations were larger in fall and winter, but the flux was larger in summer and fall. Observations at multiple stations across the Potomac River estuary revealed hotspots of N2O emissions downstream of WWTPs. N2O concentrations were higher at stations downstream of WWTPs compared to other stations (median: 21.2 nM vs. 16.2 nM) despite the similar concentration of dissolved inorganic nitrogen, suggesting the direct discharge of N2O from WWTPs into the aquatic system or a higher N2O production yield in waters influenced by WWTPs. Meta-analysis of N2O measurements associated with WWTPs globally revealed variable influence of WWTPs on downstream N2O concentrations and emissions. Since wastewater production has increased substantially with the growing population and is projected to continue to rise, accurately accounting for N2O emissions downstream of WWTPs is important for constraining and predicting future global N2O emissions. Efficient N2O removal, in addition to dissolved nitrogen removal, should be an essential part of water quality control in WWTPs.

Study on the Effects of Fe Doping on C‐ZFe Catalyst for Catalytic Removal of NO from the Low‐Temperature Flue Gas

AbstractThe denitrification efficiency of carbon‐based zero valent iron catalyst (C‐ZFe) for low‐temperature selective catalytic reduction (SCR) (<140°C) highly depends on the structural species of iron oxide (FexOy) and the physicochemical properties of the catalyst. In the study, we investigated the main factors affecting the low‐temperature denitrification efficiency of C‐ZFe such as temperature, iron content and O2. The results showed that the average NOX conversion was 72.6 % at 135°C when the space velocity was 459 h−1 and the mass ratio of carbon to iron was 15 % to 85 %. The surface morphology and structure of C‐ZFe were characterized by the surface area and pore size distribution measurements, X‐ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and X‐ray photoelectron spectroscopy (XPS). The results indicated that the iron on the catalyst surface was oxidized by O2 to Fe2O3, which could retain NO and then formed intermediate products. NO entered the mesoporous structure along C‐ZFe surface and proceeded a catalytic reduction reaction with the adjacent carbon.

The in-situ fabricated Bi nanoparticles on the BiOBr efficiently inhibit the production of toxic by-product NO2 during the photocatalytic NO oxidation

In this study, bismuth nanoparticles (NPs) are reduced in-situ on the BiOBr surface to enhance the electron transfer rate. The formation of Bi NPs is directly confirmed by characterizations such as XRD, TEM and XPS. Meanwhile, UV–Vis, PL characterization analysis and DFT theoretical calculation suggest that Bi NPs not only broaden the photoresponse range but also form a fast charge-transfer channel with the BiOBr. The results demonstrate that the NO removal rate of the optimal sample (BiOBr-1.5) is about 48.93%, which is 6.5 times that of the original BiOBr, and almost no toxic by-product NO2 is produced. This study provides a valuable strategy for designing photocatalysts that remove NO while effectively suppressing toxic by-products.

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.

Integration of SiC Membrane and CePO4 Catalyst for the Simultaneous Efficient Removal of Dust and NO

Integration of SiC Membrane and CePO₄ Catalyst for the Simultaneous Efficient Removal of Dust and NO

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.

Direct Eight-Electron N2O Electroreduction to NH3 Enabled by an Fe Double-Atom Catalyst.

N2O is a dominant atmosphere pollutant, causing ozone depletion and global warming. Currently, electrochemical reduction of N2O has gained increasing attention to remove N2O, but its product is worthless N2. Here, we propose a direct eight-electron (8e) pathway to electrochemically convert N2O into NH3. As a proof of concept, using density functional theory calculation, an Fe2 double-atom catalyst (DAC) anchored by N-doped porous graphene (Fe2@NG) was screened out to be the most active and selective catalyst for N2O electroreduction toward NH3 via the novel 8e pathway, which benefits from the unique bent N2O adsorption configuration. Guided by theoretical prediction, Fe2@NG DAC was fabricated experimentally, and it can achieve a high N2O-to-NH3 Faradaic efficiency of 77.8% with a large NH3 yield rate of 2.9 mg h-1 cm-2 at -0.6 V vs RHE in a neutral electrolyte. Our study offers a feasible strategy to synthesize NH3 from pollutant N2O with simultaneous N2O removal.

Pulsed Laser‐Initiated Dual‐Catalytic Interfaces for Directed Electroreduction of Nitrite to Ammonia

Green and highly selective synthesis of ammonia (NH3) via electrochemical reduction reaction of toxic nitrite (NO2−RR) in a neutral electrolyte is a feasible solution for energy and environmental issues. Dual‐nature electrocatalysts combining metal and metal‐derived materials are crucial for enhancing the selectivity parameter and efficacy of this reaction. Here, Pd‐, Pt‐, Ru‐, and Ir‐decorated Co3(PO4)2 (CoPi) composites with a robust metal–support interaction are obtained via the one‐pot pulsed laser ablation in liquid method. Among the designed composites, Ir–CoPi affords ≈100% Faradaic efficiency, mass balance, and selectivity toward NH3 product at sufficiently low potentials. Further, it affords the highest NH3 yield rate of 19.13 mg h−1 cm−2 with 78.1% removal of toxic NO2− with a rate constant kapp = 0.31 mm min−1 under −1.6 V versus Ag/AgCl. In situ experiments and theoretical investigations reveal the underlying mechanisms responsible for this outstanding performance of Ir–CoPi, which can be accredited to the generation of specific active sites on the Ir component. Insights derived from the evolving intermediate reactive species provide new opportunities for large‐scale NH3 production through electrochemical techniques, density functional theory calculations, and the improvement of the corresponding industrial processes.

Optimization of Photothermal Catalytic Reaction of Ethyl Acetate and NO Catalyzed by Biochar-Supported MnOx-TiO2 Catalysts.

The substitution of ethyl acetate for ammonia in NH3-SCR provides a novel strategy for the simultaneous removal of VOCs and NO. In this study, three distinct types of biochar were fabricated through pyrolysis at 700 °C. MnOx and TiO2 were sequentially loaded onto these biochar substrates via a hydrothermal process, yielding a family of biochar-based catalysts with optimized dosages. Upon exposure to xenon lamp irradiation at 240 °C, the biochar catalyst designated as 700-12-3GN, derived from Ginkgo shells, demonstrated the highest catalytic activity when contrasted with its counterparts prepared from moso bamboo and loofah. The conversion efficiencies for NO and ethyl acetate (EA) peaked at 73.66% and 62.09%, respectively, at a catalyst loading of 300 mg. The characterization results indicate that the 700-12-3GN catalyst exhibits superior activity, which can be attributed to the higher concentration of Mn4+ and Ti4+ species, along with its superior redox properties and suitable elemental distribution. Notably, the 700-12-3GN catalyst has the smallest specific surface area but the largest pore volume and average BJH pore size, indicating that the specific surface area is not the predominant factor affecting catalyst performance. Instead, pore volume and average BJH pore diameter appear to be the more influential parameters. This research provides a reference and prospect for the resource utilization of biochar and the development of photothermal co-catalytic ethyl acetate and NO at low cost.

Core-shell organic frameworks to activate peroxymonosulfate for the simultaneous removal of SO2 and NO

Advanced oxidation process is a simple and cost-effective approach for the simultaneous removal of SO2 and NO from the flue at low temperatures. Herein, two core–shell hierarchical metal organic frameworks (MOFs), namely FeBDC@CuBDC (Iron terephthalate@Copper terephthalate) and FeBDC@CuBTC (Iron terephthalate@Copper triphenylenetriate), were successfully synthesized through Cu partial exchange and the secondary growth on surface of FeBDC, respectively. These MOFs were utilized to activate efficiently peroxymonosulfate (PMS). In the two MOFs, the metals existed in multiple valence states, specifically Fe(II)/Fe(III) and Cu(I)/Cu(II), favoring the high catalytic activity. In these MOFs/PMS solutions, more than 85% NO was removed and SO2 was completely eliminated. FeBDC@CuBTC and FeBDC@CuBDC were recovered and regenerated for at least 5 cycles. The high catalytic activity of these MOFs was attributed to the high content of Fe(II)/Cu(I) achieved by the rapid reduction of Fe(III)/Cu(II) with O2•-. Through the analysis of reactive oxygen species in the MOFs/PMS, it was observed the NO removal was influenced by both free radical processes (SO4•-,•OH) and non-free radical processes(1O2), whereas the SO2 removal was controlled primarily by free radical processes (SO4•- and •OH).

Acidified SiO2 Supported Fe-based Bimetal Oxide Catalyst with Resistance to High-Level Alkali Poisoning for CO Selective Catalytic Reduction of NO Removal of NOx

Acidified SiO₂ Supported Fe-based Bimetal Oxide Catalyst with Resistance to High-Level Alkali Poisoning for CO Selective Catalytic Reduction of NO Removal of NO_<i>x</i>

Efficient photocatalytic decomposition of NO and mechanism insight enabled by NaBH4-reduced N(ligancy-3)-vacancy-rich-graphitic carbon nitride

Vacancy defect engineering is an effective means to improve the performance of g-C3N4 photooxidation for NO removal. In this paper, flake graphite-phase g-C3N4 is prepared by thermal polycondensation. Then g–C3N4–x (x = 0, 0.5, 1.0, 1.5, and 2.0) containing various amounts of vacancies of nitrogen atoms with (3 coordination number) ligancy 3 (N(ligancy-3)) was prepared by NaBH4 reduction at room temperature. The introduction of N vacancies in g-C3N4 narrowed the forbidden gap, enhanced optical absorbance, optimized photo exciton separation and migration, and functioned as traps to mitigate the recombination of photogenerated electron-hole pairs. As a result, g–C3N4–x shows a superior NO removal performance, especially g–C3N4–1.5, which exhibits a high NO removal rate of 66.7 %, excellent resistance to the by-product NO2, and excellent stability. The free-radical seizure experiments and electron paramagnetic resonance (EPR) studies proved the superiority of superoxide radicals, electrons and holes as the prominent free radicals in the photocatalytic NO removal process. In situ diffuse infrared Fourier transform spectroscopy (DRIFTS) confirmed that the cis-dimer (NO)2 produced from NO adsorption on the surface of g–C3N4–1.5 is an important intermediate. Additionally, NO2− is observed as an intermediate and a primary product, and NO3− is identified as the key product of NO photocatalytic oxidation. DFT calculations showed that the N(ligancy-3) vacancy introduces impurity energy levels in g-C3N4 and shortens the electron migration path. The adsorption calculation of NO demonstrated that g–C3N4–N(ligancy-3) exhibits good adsorption and conversion of NO. This study provides a practical defect engineering for the g-C3N4 to remediate environmental pollution.

Hydrochars derived from real organic wastes as carbonaceous precursors of activated carbons for the removal of NO from contaminated gas streams

The improvement of air quality in densely-populated urban regions constitutes an environmental challenge of increasing concern. In this respect, the abatement of NO emissions, primarily emanating from combustion processes associated with motor-vehicles, along with industrial/domestic combustion systems, represents one of the main problems. Here, three hydrochars from diverse organic residues were used as activated carbon precursors for their evaluation in the NO removal in two potential application scenarios. Hydrochars were physically activated at 800 °C with pure-CO2 or diluted-O2. These materials were tested in a lab-scale biofilter at different conditions (NO concentration, temperature, relative humidity, NO-containing gas and carbon particle size) and in a larger-scale biofilter to evaluate the long-term NO removal capacity. Hydrochar-derived carbons present a relatively well-developed micro- and mesoporous structure, with BET areas of up to 421 m2/g, and a variety of oxygen surface functionalities (carboxylic, lactone, carbonyl and quinone groups), especially concerning CO2-activated carbons. These exhibited an excellent behaviour at low NO concentration (5 ppmv) between 25 and 75 °C with removal capacities of ≈97 % and > 82 %, respectively; and still good-performance (≈66 %) in a more concentrated gas (120 ppmv). Whilst, carbons obtained by diluted-O2 activation from the same hydrochars, evidenced a higher removal capacity loss at high NO concentration. The O2 presence in the gas stream was confirmed as a crucial factor in the NO elimination, since both co-adsorb on the carbon surface favouring NO oxidation to NO2. Besides, the humidity in the airstream diminished the NO removal capacity from 0.88 to 0.51 mgNO/gcarbon, but still remained at 0.54 mgNO/gcarbon, when the carbon (in pellet) was operated at larger-scale biofilter in 9-fold longer test under humid air. Therefore, this study highlights the potential of renewable carbons to serve as cost-effective component in urban biofilters, to mitigate NO emissions from exhaust gases in biomass boilers and urban semi-close areas.

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.