Removal Of Nitrogen Oxides Research Articles

In situ IR spectroscopy study of NO removal over CuCe catalyst for CO-SCR reaction at different temperature

CO-SCR was considered as one of the most optimum technologies for synergistic removal of nitrogen oxides and carbon monoxide from flue gas. CuCe catalyst showed excellent NOx and CO catalytic activity in the range of 250–500 °C because of its unique physicochemical property. Herein, the mechanism of CuCe catalyst in the CO-SCR reaction at different temperature was studied via in situ DRIFTS characterization. The result indicated that the adsorbed CO species could react with gaseous NO molecules over CuCe catalyst at 150 ºC, implying that the E-R mechanism was obeyed at lower temperature. Moreover, the nitrate/nitrite species and adsorbed CO species could react with each other on the surface of CuCe catalyst at 350 ºC, indicating that the L-H mechanism was followed in the CO-SCR reaction at higher temperature. This work proposed the reaction mechanism of CuCe catalyst at different temperature for NO reduction by CO, which could provide a theoretical direction for the optimization of CuCe catalyst and promote its application in industrial production.

Modeling of a Two-Bed Reactor for Low-Temperature Removal of Nitrogen Oxides in Nitric Acid Production

In this study, the modeling of the low-temperature catalytic abatement of NOX and N2O from tail gases in a weak nitric acid plant utilizing a single-pressure 0.716 MPa system was performed. A one-reactor concept assumes that in the first bed, NOX is reduced by ammonia on a commercial vanadia–alumina catalyst, and in the second bed, N2O is decomposed on a proprietary nickel–cobalt catalyst. The kinetics of N2O decomposition on a Cs/Ni0.1Co2.9O4 catalyst was experimentally studied in an isothermal flow reactor. The reaction rate constants were determined by varying the residence time and temperature; these data formed the basis for modeling kinetics and heat and mass transport in an adiabatic reactor in which the low-temperature mitigation of nitrogen oxides occurred. Taking into account the given spatial limitations inside the reactor and the allowable temperatures, the layer heights were evaluated to ensure a residual NOX and N2O content of less than 50 ppm. Catalyst loading using layers in a commercial reactor was estimated for the tail-gas flow rates of 46,040–58,670 m3/h. Simulations showed that the optimum inlet temperature was 260 °C; in this case, the NOX and N2O conversion targets were achieved in the range of 46,040–58,670 m3/h while adhering to catalyst bed height and outlet temperature limitations.

Prominent difference in the deactivation rate and mechanism of V2O5/TiO2 under H2S or SO2 during selective catalytic reduction of NOx with NH3

Selective catalytic reduction (SCR) over V2O5/TiO2-based catalysts is the most efficient technology to remove nitrogen oxides from stationary sources, where H2S coexists with NOx under variable combustion conditions. For the first time, the poisoning effect of H2S was observed to be almost six-fold that of SO2. Catalyst deactivation under SO2 was mainly caused by ammonium bisulfate while sulfates, especially polymeric sulfate, were the main contributors to H2S poisoning. Theoretical calculations showed that the generation of sulfates was much more energetically favorable under H2S than under SO2, resulting in massive deposition of sulfates and serious damage to vanadyl (VO). Polymeric sulfate could inhibit the charge transfer between the occupied and unoccupied orbitals of VO and suppress NH3 activation, thereby significantly restraining SCR activity. Furthermore, unstable sulfur species were shown to be responsible for the temporary deactivation during H2S poisoning. This work provides crucial information for solving catalyst deactivation.

A Novel Method Based on Hydrodynamic Cavitation for Improving Nitric Oxide Removal Performance of NaClO2.

In the removal of nitric oxide (NO) by sodium chlorite (NaClO2), the NaClO2 concentration is usually increased, and an alkaline absorbent is added to improve the NO removal efficiency. However, this increases the cost of denitrification. This study is the first to use hydrodynamic cavitation (HC) combined with NaClO2 for wet denitrification. Under optimal experimental conditions, when 3.0 L of NaClO2 with a concentration of 1.00 mmol/L was used to treat NO (concentration: 1000 ppmv and flow rate: 1.0 L/min), 100% of nitrogen oxides (NOx) could be removed in 8.22 min. Furthermore, the NO removal efficiency remained at 100% over the next 6.92 min. Furthermore, the formation of ClO2 by NaClO2 is affected by pH. The initial NOx removal efficiency was 84.8-54.8% for initial pH = 4.00-7.00. The initial NOx removal efficiency increases as the initial pH decreases. When the initial pH was 3.50, the initial NOx removal efficiency reached 100% under the synergistic effect of HC. Therefore, this method enhances the oxidation capacity of NaClO2 through HC, realizes high-efficiency denitrification with low NaClO2 concentration (1.00 mmol/L), and has better practicability for the treatment of NOx from ships.

Recent advance for NOx removal with carbonaceous material for low-temperature NH3-SCR reaction

The purification of gaseous pollutants, especially for nitrogen oxides, from the combustion of fossil fuels has become a concern matter at present. Selective catalytic reduction (SCR) technology is proved an effective method to remove nitrogen oxides. The performance of catalysts, such as the improvement of anti-poisoning ability and low-temperature catalytic efficiency, become the main direction of current extensive research. Carbonaceous materials were widely applied in low-temperature catalysts for removal of NOx due to their various structures and rich surface functional groups, and had potential to expand the function to remove multipollutant. Herein, different carbonaceous materials, activated methods and carbon-based NH3-SCR catalysts were concluded, and the corresponding reaction mechanisms were discussed. In addition, the removal of double or three contamination components with carbon-based catalysts were also summarized and discussed. Finally, further development directions for carbonaceous material in pollutants control were proposed.

Simultaneous carbon dioxide sequestration and nitrate removal by Chlorella vulgaris and Pseudomonas sp. consortium

Carbon dioxide and nitrogen oxides are the main components of fossil flue gas causing the most serious environmental problems. Developing a sustainable and green method to treat carbon dioxide and nitrogen oxides of flue gas is still challenging. Here, a co-cultured microalgae/bacteria system, Chlorella vulgaris and Pseudomonas sp., was developed for simultaneous sequestration of CO2 and removal of nitrogen oxides from flue gas, as well as producing valuable microalgae biomass. The co-cultured Chlorella vulgaris and Pseudomonas sp. showed the highest CO2 fixation and NO3−-N removal rate of 0.482 g L−1d−1 and 129.6 mg L−1d−1, the total chlorophyll accumulation rate of 65.6 mg L−1 at the initial volume ratio of Chlorella vulgaris and Pseudomonas sp. as 1:10. The NO3−-N removal rate can be increased to 183.5 mg L−1d−1 by continuous addition of 0.6 g L−1d−1 of glucose, which was 37% higher than that of co-culture system without the addition of glucose. Photosynthetic activity and carbonic anhydrase activity of Chlorella vulgaris were significantly increased when co-cultured with Pseudomonas sp. Excitation–emission matrix (EEM) fluorescence spectroscopy indicated that the humic acid-like substances released from Pseudomonas sp. could increase the growth of microalgae. This work provides an attractive way to simultaneously treatment of CO2 and NOX from flue gas to produce valuable microalgal biomass.

Recent Advances in g-C3N4-Based Photocatalysts for NOx Removal

Nitrogen oxides (NOx) pollutants can cause a series of environmental issues, such as acid rain, ground-level ozone pollution, photochemical smog and global warming. Photocatalysis is supposed to be a promising technology to solve NOx pollution. Graphitic carbon nitride (g-C3N4) as a metal-free photocatalyst has attracted much attention since 2009. However, the pristine g-C3N4 suffers from poor response to visible light, rapid charge carrier recombination, small specific surface areas and few active sites, which results in deficient solar light efficiency and unsatisfactory photocatalytic performance. In this review, we summarize and highlight the recent advances in g-C3N4-based photocatalysts for photocatalytic NOx removal. Firstly, we attempt to elucidate the mechanism of the photocatalytic NOx removal process and introduce the metal-free g-C3N4 photocatalyst. Then, different kinds of modification strategies to enhance the photocatalytic NOx removal performance of g-C3N4-based photocatalysts are summarized and discussed in detail. Finally, we propose the significant challenges and future research topics on g-C3N4-based photocatalysts for photocatalytic NOx removal, which should be further investigated and resolved in this interesting research field.

Nano-particle Characteristic Emitted from Gasoline Direct Injection Engine Equipped with Non-Thermal Plasma Device

The impact of non-thermal plasma (NTP) on particulate matter (PM) removal, nitrogen oxide (NOx) reduction, and hydrocarbon species in exhaust gases from gasoline direct injection (GDI) engines using gasoline E20 fuel and a mean effective pressure (IMEP) of 6 bar. The experiments were conducted with an exhaust gas flow rate of 20 L/min, applying high voltage in the range of 0 to 10 kV (2 kV per step) at a frequency of 500 Hz. The results show that NTP reduces PM concentrations, particularly in the nucleation mode (10 nm particles). Maximum PM removal of approximately 83% However, with experimental results, compared to 0 kV, the production of particulate matter Aitken mode increased up to 19 times for a voltage increase of 10 kV, and NOx removal has been at a maximum of about 9.5%, with an energy density of 5 J/L at 10 kV. The effects of NTP on hydrocarbon species such as ethylene, propylene, acetylene, 1.3 butadiene, methane, and ethane have been slightly affected by increased high voltages.

Spontaneous intra-electron transfer within rGO@Fe2O3-MnO catalyst promotes long-term NOx reduction at ambient conditions.

Iron (Fe)-based catalysts are widely used for taming nitrogen oxides (NOx) containing flue gas, but the regeneration and long-term reusability remains a concern. The reusability can be acquired by external additives, and resultantly can not only increase the cost but can also add to process complexity as well as secondary pollutants. Herein, a self-sustainable material is designed to regenerate the catalyst for long-term reusability without adding to process complexity. The catalyst is based on reduced graphene-oxide impregnated by Fe2O3-MnO (rGO@Fe2O3-MnO; G-F-M) for spontaneous intra electron (e-)-transfer from Mn to Fe. The developed catalyst; G-M-F exhibited 93.7% NOx reduction, which suggests its high catalytic activity. The morphological and structure characterizations confirmed the Fe/Mn loading, contributing to e--transfer between Mn and Fe due to its conductivity. The synthesized G-F-M showed higher NOx reduction about 2.5 folds, than rGO@Fe2O3 (G-FeO) and rGO@MnOx (G-MnOx). The performance of G-M-F without and with an electrochemical system was also compared, and the difference was only 5%, which is an evidence of the spontaneous e- transfer between the Mn and Fe-NOx complex. The designed catalyst can be used for a long time without external assistance, and its efficiency was not affected significantly (<3.7%) in the presence of high oxygen contents (8%). The as-prepared G-M-F catalyst has great potential for executing a dual role NOx removal and self-regeneration of catalyst (SRC), promoting a sustainable remediation approach for large-scale applications.

Reaction Mechanism for the Removal of NOx by Wet Scrubbing Using Urea Solution: Determination of Main and Side Reaction Paths

Secondary problems, such as the occurrence of side reactions and the accumulation of by-products, are a major challenge in the application of wet denitrification technology through urea solution. We revealed the formation mechanism of urea nitrate and clarified the main and side reaction paths and key intermediates of denitrification. Urea nitrate would be separated from urea absorption solution only when the concentration product of [urea], [H+] and [NO3-] was greater than 0.87~1.22 mol3/L3. The effects of the urea concentration (5-20%) and reaction temperature (30-70 °C) on the denitrification efficiency could be ignored. Improving the oxidation degree of the flue gas promoted the removal of nitrogen oxides. The alkaline condition was beneficial to the dissolution process, while the acidic condition was beneficial to the reaction process. As a whole, the alkaline condition was the preferred process parameter. The research results could guide the optimization of process conditions in theory, improve the operation efficiency of the denitrification reactor and avoid the occurrence of side reactions.

Study on Precipitation Kinetics of Calcium Pyro-Vanadate and Thermodynamics of Vanadium Water System

Selective catalytic reduction (SCR) is a technology widely used in large coal-fired units to remove nitrogen oxides from flue gas, but it also generates a large number of waste catalysts every year. At present, the recovery of V from discarded SCR catalysts has good application prospects and environmental significance. In this paper, the kinetics and thermodynamics of vanadium precipitation process are described with the vanadium-containing liquid of waste denitration catalyst recovered by alkali leaching as raw material and CaCl2 as precipitant in order to further explore the mechanism of vanadium precipitation. The kinetics study showed that the crystallization process of calcium pyrovanadate can be well-described by Avrami kinetic model when the precipitation time is 95–130 min, and the vanadium precipitation temperature is 60–80 °C. After that, the Arrhenius equation was used to analyze the fitted kinetic data, and the apparent activation energy Ea of vanadium precipitation reaction was calculated to be 98.196 kJ/mol, and the pre exponential factor A = 8.59 × 1039 min−1. Thermodynamic study showed that when the pH of the vanadium water system is low, the +5 valence vanadium in the solution mainly exists in the form of VO2+ cation. When the pH is between 0–1, the solubility of vanadium reaches the minimum and then increases the solution pH again, and various polymerized anions are formed in the vanadium water system. When the temperature is 25 °C, the activity of vanadium in vanadium-containing solution is 10−1, the pH of solution is 8–12, and the existence form of +5 valence vanadium in solution is mainly HV2O73−. By analyzing the existing forms of V with different activities in a vanadium water system at 25 °C, it can be seen that with the decrease of V activity in liquid, the dominant region of polymerized vanadium-containing species in the potential pH diagram will disappear, indicating that vanadium mainly exists in the form of mononuclear ions in low-concentration vanadium-containing solutions, which is not conducive to precipitation. Therefore, in the process of precipitation of vanadium in solution, the concentration of V should be increased as much as possible.

Light‐Emitting Diode Visible‐Light‐Driven Photocatalytic Redox Reactions in Nitrogen Oxide Removal Using β‐Bi2O3/Bi/g‐C3N4 Prepared by One‐Step In Situ Thermal Reduction Synthesis

Traditional photocatalytic oxidation of nitrogen oxide (NO) may cause the more toxic NO2 generation after longtime reaction, and even the ideal final production nitrate may also inevitably cause the poisoning of photocatalysts. Thus, utilizing photocatalytic reduction to remove NO into N2 should be considered more practical but is still challenging currently. Herein, a novel S‐scheme β‐Bi2O3/Bi/g‐C3N4 heterojunction photocatalyst is developed via a one‐step in situ thermal reduction method. The photocatalytic degradation efficiency over this S‐scheme photocatalyst exhibits around 88.7% degradation rate for NO with little NO2 generation under light‐emitting diode light irradiation, which is significantly higher than that of the pristine g‐C3N4 (60%). Interestingly, both reduction of NO into N2 and oxidation of NO into NO3− exist synchronously in the system. The increased degradation efficiency and the efficient reduction pathway occurring should be ascribed to the enhanced generation, separation, and transfer of the photogenerated carriers through the Bi‐bridge S‐scheme heterojunction. This study has provided a new route for regulating the photocatalytic reaction pathway for NO removal through a simple synthesis method.

Hollow TiO2/Poly (Vinyl Pyrrolidone) Fibers Obtained via Coaxial Electrospinning as Easy-to-Handle Photocatalysts for Effective Nitrogen Oxide Removal.

Herein, we present a method for fabricating hollow TiO2 microfibers from Ti (OBu)4/poly (vinyl pyrrolidone) sol-gel precursors and their effects on denitrification as a photocatalyst for air purification. Various sizes of hollow TiO2 fibers were developed using coaxial electrospinning by controlling the core flow rate from 0 to 3 mL h-1. At higher flow rates, the wall layer was thinner, and outer and core diameters were larger. These features are correlated with physical properties, including specific surface area, average pore diameter, and crystalline structure. The increase in the core flow rate from 0 to 3 mL h-1 leads to a corresponding increase in the specific surface area from 1.81 to 3.95 µm and a decrease in the average pore diameter from 28.9 to 11.1 nm. Furthermore, the increased core flow rate results in a high anatase and rutile phase content in the structure. Herein, hollow TiO2 was produced with an approximately equal content of anatase/rutile phases with few impurities. A flow rate of 3 mL h-1 resulted in the highest specific surface area of 51.28 m2 g-1 and smallest pore diameter size of ~11 nm, offering more active sites at the fiber surface for nitrogen oxide removal of up to 66.2% from the atmosphere.

A new multi-component marine exhaust cleaning method using combined hydrodynamic cavitation and chlorine dioxide

Simultaneous desulfurization and denitration of ship exhaust is a challenging problem. To solve the problem, we proposed a novel non-circulation cleaning method for removing nitrogen oxides (NOx) and sulfur dioxide (SO2) using combined hydrodynamic cavitation and chlorine dioxide (ClO2). The SO2 and NO removal mechanism was studied. Experiments were carried out to determine the efficiency of combined hydrodynamic cavitation and ClO2 for exhaust desulfurization and simultaneous desulfurization and denitration. The results showed that hydrodynamic cavitation could effectively desulfurize. The simultaneous desulfurization and denitration performance of combined hydrodynamic cavitation and ClO2 process was significantly better than that of hydrodynamic cavitation alone. The study found that the presence of SO2 would promote denitration and also competed with NOx for ClO2. The effects of pressure difference (ΔP) before and after the hydrodynamic cavitation reactor, NO gas flow rate (QNO), 600 mg/L ClO2 feeding rate (ηClO2), and NO initial concentration (CNOinitial) on the denitration efficiency were further studied. The results revealed that around 95.0 % of NOx removal efficiency was reached. This study could provide important theoretical support for the industrial application of this technology.

A Review of Synergistic Catalytic Removal of Nitrogen Oxides and Chlorobenzene from Waste Incinerators

Emission of harmful gases, nitrogen oxides (NOx), and dioxins pose a serious threat to the human environment; so, it is urgent to control NOx and dioxin emissions. The new regulations for municipal solid waste incineration emissions set new stringent requirements for NOx and dioxin emission standards. Most of the existing pollutant control technologies focus on single-unit NOx reduction or dioxin degradation. However, the installation of separate NOx and dioxins removal units is space-consuming and costs a lot. Nowadays, the simultaneous elimination of NOx and dioxins in the same facility has been regarded as a promising technology. Due to the extremely high toxicity of dioxins, the less toxic chlorobenzene, which has the basic structure of dioxins, has been commonly used as a model molecule for dioxins in the laboratory. In this review, the catalysts used for nitrogen oxides/chlorobenzene (NOx/CB) co-removal were classified into two types: firstly, non-loaded and loaded transition metal catalysts, and their catalytic properties were summarized and outlined. Then, the interaction of the NH3-SCR reaction and chlorobenzene catalytic oxidation (CBCO) on the catalyst surface was discussed in detail. Finally, the causes of catalyst deactivation were analyzed and summarized. Hopefully, this review may provide a reference for the design and commercial application of NOx/CB synergistic removal catalysts.

Polyol-Mediated Synthesis of V2O5-WO3/TiO2 Catalysts for Low-Temperature Selective Catalytic Reduction with Ammonia.

We demonstrated highly efficient selective catalytic reduction catalysts by adopting the polyol process, and the prepared catalysts exhibited a high nitrogen oxide (NOX) removal efficiency of 96% at 250 °C. The V2O5 and WO3 catalyst nanoparticles prepared using the polyol process were smaller (~10 nm) than those prepared using the impregnation method (~20 nm), and the small catalyst size enabled an increase in surface area and catalytic acid sites. The NOX removal efficiencies at temperatures between 200 and 250 °C were enhanced by approximately 30% compared to those of the catalysts prepared using the conventional impregnation method. The NH3-temperature-programmed desorption and H2-temperature-programmed reduction results confirmed that the polyol process produced more surface acid sites at low temperatures and enhanced the redox ability. The in situ Fourier-transform infrared spectra further elucidated the fast absorption of NH3 and its reduction with NO and O2 on the prepared catalyst surfaces. This study provides an effective approach to synthesizing efficient low-temperature SCR catalysts and may contribute to further studies related to other catalytic systems.

Purification Technologies for NOx Removal from Flue Gas: A Review

Nitrogen oxide (NOx) is a major gaseous pollutant in flue gases from power plants, industrial processes, and waste incineration that can have adverse impacts on the environment and human health. Many denitrification (de-NOx) technologies have been developed to reduce NOx emissions in the past several decades. This paper provides a review of the recent literature on NOx post-combustion purification methods with different reagents. From the perspective of changes in the valence of nitrogen (N), purification technologies against NOx in flue gas are classified into three approaches: oxidation, reduction, and adsorption/absorption. The removal processes, mechanisms, and influencing factors of each method are systematically reviewed. In addition, the main challenges and potential breakthroughs of each method are discussed in detail and possible directions for future research activities are proposed. This review provides a fundamental and systematic understanding of the mechanisms of denitrification from flue gas and can help researchers select high-performance and cost-effective methods.

Lead-Free Cs3Bi2Br9 perovskite In-situ growth on 3D Flower-like g-C3N4 microspheres to improve photocatalytic performance

Nitrogen oxide (NOx) removal has long been a subject that has motivated researchers to develop a diverse range of techniques, including physical adsorption, biofiltration, low temperature plasma, selective catalytic reduction, and photocatalytic oxidation. In this work, Cs3Bi2Br9 lead-free perovskite was synthesized via in-situ growth on a 3D flower-like g-C3N4 microsphere, whichusesaseriesofCs3Bi2Br9/g-C3N4 (labeled as X% CBB/CN, where X = 5, 10, 20, 30, and 50) heterojunctions for the photocatalytic removal of NOx. The efficiency of NO removal was enhanced considerably, compared with that of the pristine elements, when irradiated with a 300 W Xe lamp with the concentration of NO at the ppb level. The results of photocurrent measurements and electrochemical impedance spectroscopy are consistent with the results of the NO removal test. Electron spin resonance results verified that ⋅OH and ⋅O2− are formed under visible light irradiation. We report the detailed mechanism for the photocatalytic process of NO removal by CBB/CN heterojunctions and provide insights into the potential applications of lead-free perovskite-based heterostructures in the field of photocatalysis.

Insights of Selective Catalytic Reduction Technology for Nitrogen Oxides Control in Marine Engine Applications

The international shipping industry is facing increasingly stringent limitations on nitrogen oxide (NOx) emissions. New solutions for reducing NOx emitted by marine engines need to be investigated to find the best technology. Selective Catalytic Reduction (SCR) is an advanced active emissions control technology successfully used in automotive diesel engines; it could be applied to marine engines with ad-hoc solutions to integrate it in the exhaust of large engines. In this study, a commercial SCR was tested at the exhaust of a diesel engine in inlet gas conditions typical of a marine engine. The SCR system consisted of a custom monolith (provided by Hug-Engineering AG) that enabled seamless integration for a broad range of engine sizes; the active phases were V2O5 (3 wt%)-WO3 (7 wt%)-TiO2 (75 wt%). The monolith was studied at the laboratory scale for its in-depth chemical/physical characterization and by means of an intermediate-scale engine, reproducing the exhaust gas conditions of a full-scale marine engine. The system’s effectiveness in terms of NOx removal for the selected engine operating conditions was evaluated in a wide range of temperature and NOx emissions values and for different quantities of the reduction agent (AdBlue or ammonia) added to exhaust gases. The investigated technological solution resulted in efficient NOx emission control from a marine engine.

Effect of substrate roughness on NOx removal of poly heptazine imides coated cement pastes exposed to washing and weathering

Developing photocatalytic coatings onto cementitious materials is an attractive approach to combat air pollution. However, the low photocatalysis durability of the photocatalytic cementitious materials is the main challenge for their large-scale implementation in aggressive outdoor environments. Here, a coating composed of poly heptazine imides (PHI) was applied onto hardened cement pastes with different substrate roughness for nitrogen oxides (NOx) abatement under artificial washing and natural weathering. The apparent appearance, micromorphology and chemical composition of the PHI-coated cement pastes were characterized via visual inspection, scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy and attenuated total reflectance–Fourier transform infrared analysis. It was found that increasing the substrate roughness improved the adhesion of PHI coating against the washing test, contributing to a higher photocatalytic efficiency of NOx removal at highly rough substrates after subjecting to the washing test. After the weathering tests, the NOx removal of PHI-coated cement pastes increased and then decreased slightly with the increasing substrate roughness; the highest photocatalytic efficiency was observed at a substrate roughness of 2.83 μm. The observations open a window for improving the durability of photocatalytic coatings applied onto cementitious materials under real-life conditions.