NO Oxidation Research Articles

Potensi Ancaman dan Upaya Mitigasi Emisi Gas Rumah Kaca di Sektor Pertanian Indonesia : Tinjauan Sistematis atas Literatur

Agriculture in Indonesia is a vital sector that can fulfill food needs and provide livelihoods. However, agriculture also contributes to greenhouse gas (GHG) emissions. Indonesia's agricultural sector contributes around 14% of emissions globally and 7% nationally. Greenhouse gas emissions such as methane gas CH4, carbon dioxide CO2, and nitrous oxide N2O are generated from agricultural activities ranging from land preparation, fertilization, transportation of agricultural products, to processing in factories. These greenhouse gas emissions influence the climate change that occurs and affect the increase in temperature and rainfall patterns. In mitigation efforts, this study noted several steps taken. Energy conversion, such as the use of biogas from animal manure can reduce CH4 emissions and the use of pellets from palm waste processing can reduce CO2 emissions. Reforestation with special carbon-absorbing plants to reduce CO2 emissions. The use of organic fertilizers as a partial replacement for inorganic fertilizers is useful in reducing CH4 and N2O emissions. Through this systematic review, it is expected to contribute to the understanding of the role of the agricultural sector in greenhouse gas emissions in Indonesia and provide insight into mitigation efforts that can be applied in achieving sustainable agriculture.

Atomically dispersed Mn sites on TiO2(B) microspheres enables efficient photocatalytic abatement of NOx

While photocatalytic technology has been recognized as an effective means for removing low-concentration NOx in ambient atmosphere, it still faces the challenge of the deep oxidation in high efficiency. In many cases, the release of more toxic NO2 byproduct appeared to be inevitable during the photocatalytic oxidation of NO. Herein we report that the atomically dispersed MnOx cocatalyst on TiO2(B) microspheres could significantly enhance the deep oxidation of NOx under mild photocatalytic conditions (1 mW/cm2 UV-A light, 1 L/min flow rate). At an initial NO concentration of 0.35 ppm, ca. 67.15% of NO is oxidized on the MT-0.5 sample, which is 2.76 times higher than the pristine TiO2(B) sample. More importantly, the release of NO2 is suppressed by 2.11 times. Comprehensive spectral analyses suggest that atomically dispersed MnOx effectively promotes the charge separation of photogenerated carriers in TiO2(B), even better than MnOx nanoparticles-loaded TiO2(B). EPR and in-situ FTIR analyses illustrate that atomically dispersed MnOx-loaded TiO2(B) sample exhibits excellent low concentration NOx abatement performance, thus providing a rational mechanism for the NO deep oxidation pathway. This study not only provides a unique approach for preparing non-noble metal atomically dispersed co-catalysts, but also affords an effective means for efficient photocatalytic NO degradation.

Synergistic effect of oxygen-containing and nitrogen-containing groups on promoting low-temperature denitration over non-metallic carbon-based catalyst

Oxygen-containing and nitrogen-containing groups on the surface of non-metallic carbon-based catalysts have been regarded as active sites for NH3 selective catalytic reduction (NH3-SCR) of nitrogen oxides (NOx) at low temperature. In this study, series of AC-xO-yN catalysts were prepared via grafting oxygen-containing and/or nitrogen-containing groups on active carbon (AC). The activity test results showed that the denitration efficiency of AC-5O-0 N and AC-0O-4 N catalyst were only 20 and 44 % at a temperature of 120 °C and a GHSV of 4500 h−1, respectively, while the activity of the AC-5O-4 N catalysts reached 97 % at the same condition, indicating that the oxygen-containing and nitrogen-containing groups exhibited a superior synergistic effect in facilitating the low-temperature NH3-SCR denitration reaction. Characterization results revealed that the oxygen-containing groups (mainly carboxyl and lactone groups) contribute to NH3 adsorption and activation, while the nitrogen-containing groups (especially pyridine nitrogen groups) could promote NO adsorption and oxidation. The co-existence of oxygen-containing and nitrogen-containing groups can synergistically advance the low-temperature NH3-SCR denitration reaction on the surface of the AC catalyst via a fast SCR route. This work might provide insight into designing and preparing non-metallic carbon-based catalysts with high denitration performance.

Metal-free β zeolite used as an efficient NH3-SCR catalyst can achieve complete immunity to SO2: Unique design strategy of sulfur-resistant catalyst

Sulfur oxides present in flue gas can deactivate metal oxide catalysts or metal cation exchange zeolite catalysts used in NH3-SCR, as the deposition of (NH4)2SO4/NH4HSO4 and metal sulfate can obstruct and damage active sites, respectively. The physical poisoning of the (NH4)2SO4/NH4HSO4 deposition can be prevented by selecting an appropriate reaction temperature range (reversible), while chemical poisoning caused by the sulfation of active sites is challenging to avoid and can permanently deactivate the catalyst (irreversible). This research addresses the issue of irreversible catalyst deactivation resulting from sulfur poisoning by employing metal-free β zeolite without redox sites, which effectively prevents redox site sulfation at its source and shields the catalyst from physical poisoning by operating at moderate to high temperatures. This metal-free β zeolite with an appropriate pore structure exhibited exceptional deNOx activity, N2 selectivity, stability, and sulfur resistance at 300 °C. The NO oxidation experiment and DFT analysis demonstrated that the specific pore structure of β zeolite functioned as a sub-nano reactor, facilitating the oxidation of NO to NO2, thereby triggering the subsequent series catalytic reaction of “fast” SCR. Even in an atmosphere with a high concentration of 300 ppm SO2, the β zeolite catalyst maintained over 80 % NOx conversion after 130 h. The slight reduction in activity was attributable to the inhibitory influence of SO2 on the collision reaction between NO and O2; however, SO2 did not have any poisonous impact on the catalyst. The unique design strategy found in present work provides valuable insights for the sulfur resistance of metal-free zeolites used in NH3-SCR process, and provides a new idea for the design of completely sulfur-resistant catalysts.

Bimetallic MOF derived mesoporous structure of Ru doped SnO2 enable high-sensitivity gas sensors for triethylamine in high humidity

Mesoporous metal oxides have been reported as promising semiconductor gas sensing materials, showing great potential in detecting volatile organic compound (VOC) pollutants in the air. Here, we present the use of mesoporous Ru doped SnO2 oxide semiconductor, derived from a bimetallic organic framework (MOF), as a composite material for high-performance TEA gas sensing. Mesoporous structure of bimetallic MOF-derived composites synthesised using a one-step method, has a high porosity and large specific surface area (69.48 m2 g−1), which can enhance the number of sensing reaction sites and improve its capturing ability for the target gas. Moreover, the in-situ substitution of Ru3+ ions for Sn4+ ions can adjust the carrier concentration. Therefore, the synthesized mesoporous 0.4 mol% Ru-SnMOF@SnO2 exhibits high sensitivity, excellent selectivity, fast response kinetics, and good long-term stability for TEA sensing at 250 °C. Exceptionally, there is still an impressive response (S = 125.5–100 ppm) to triethylamine at 80 % RH. The relative humidity was set at 25 °C.

Operating parameters analysis of a nitric acid plant to increase production and reduce NOx gases emission

In this work the influence of some operating parameters of a medium pressure nitric acid plant producing 54,000 t/year was studied in order to evaluate its influence over the absorption column efficiency. The target is to increase nitric acid production and reduce NOx emissions. The nitric acid plant was simulated using ProSimPlus HNO3. The parameters considered in the analyses were: secondary air molar flow rate; absorption column operating pressure; cooling water temperature and absorption water molar flow rate. Parameters were evaluated individually and the best results were combined in a multi-parameter analysis evaluating different optimized scenarios, including the possibility of increasing the amount of ammonia injected in the system and the addition of a plug flow reactor (PFR), which is a new approach to improve NO oxidation. Considering a base case, the best scenario obtained was able to reduce NOx emissions in 55 % while increasing nitric acid production in 18 %, using the following set of parameters: 20 kmol.h − 1 of additional ammonia; a 40 m3 PFR; cooling water at 5 °C; 172 kmol.h − 1 of absorption water and 345 kmol.h − 1 of secondary air. The results obtained in this work contribute to provide practical insights for optimum absorption stage operation in a real nitric acid plant.

Ligand-induced reaction mechanism regulation on Sr/Nb2O5 for high-efficiency selective photocatalytic NO oxidation

Developing highly efficient photocatalysts that selectively convert NO pollutants to NO3¯ while storing metabolic nitrogen for crops remains a great challenge. Simultaneously, there is a dearth of research investigating the relationship between the chemical environment and the activity of catalytic sites. Herein, an efficient impregnation approach to access atomically dispersed Sr single atoms supported on Nb2O5 is reported; meanwhile, various ligands (-Cl, -Br, -OH) are employed to customize the local structure. The results show that Cl-Sr/Nb2O5 exhibits excellent catalytic performance in eliminating NO, which is significantly superior to other catalysts. The introduction of Sr atom and ligand increases the energy barrier of NO2 formation, thus improving the selectivity of converting NO to NO3¯. This study highlights the importance of precisely designing the catalytic site at the atomic level, and the obtained insights may serve as a valuable guide for developing future catalyst designs.

Three-dimensional ordered macroporous LaFe1-xMnxO3 with high stability for efficient NO oxidation and sulfur resistance.

NOx is an air pollutant that affects human health. A series of perovskite catalysts with different ratios of lanthanum, iron, and manganese and a three-dimensional ordered microporous structure was prepared, and the strongest catalytic performance was obtained with the LaFe0.1Mn0.9O3 catalyst. LaFe0.1Mn0.9O3 possesses the greatest number of oxygen vacancies and reached 77% NO oxidation conversion at 250 °C, with the highest NO oxidation conversion of 99% at 318 °C. This work provides a promising non-precious metal catalyst for NO oxidation and soot combustion.

Visible light photocatalytic NOx removal with suppressed poisonous NO2 byproduct generation over simply synthesized triangular silver nanoparticles coupled with tin dioxide.

The treatment or conversion of air pollutants with a low generation of secondary toxic substances has become a hot topic in indoor air pollution abatement. Herein, we used triangle-shaped Ag nanoparticles coupled with SnO2 for efficient photocatalytic NO removal. Ag triangular nanoparticles (TNPs) were synthesized by the photoreduction method and SnO2 was coupled by a simple chemical impregnation process. The photocatalytic NO removal activity results show that the modification with Ag TNPs significantly boosted the removal performance up to 3.4 times higher than pristine SnO2. The underlying roles of Ag TNPs in NO removal activity improvement are due to some advantages of Ag TNPs. Moreover, the Ag TNPs contributed photogenerated holes as the main active species toward enhancing the NO oxidation reaction. In particular, the selectivity toward green products significantly improved from 52.78% (SnO2) to 86.99% (Ag TNPs/SnO2). The formation of reactive radicals under light irradiation was also verified by DMPO spin-trapping experiments. This work provides a potential candidate for visible-light photocatalytic NO removal with low toxic byproduct generation.

Mechanism and Physiological Relevance of Xanthine Oxidase as Nitrate Reductase in Mammalian Organism: An Overview

In living organisms nitric oxide radical is produced by the enzymes NO synthases, with consequent oxidation to nitrate by several oxidation/reduction pathways. The end step of NO oxidation is the formation of nitrite and nitrate, which after their formation enter a reduction phase of NO cycle, thereby playing a physiologically important role of NO donors. However, while in plants and microorganisms the key pathway of nitrate/nitrite reduction is the functioning of the enzymes nitrate reductases (NRs), mammalian organism lacks NRs enzymes. Instead, in mammals, the reduction of nitrates and nitrites occurs by several other, both enzymatic and non-enzymatic, pathways. Based on the present knowledge, one of the key enzymes involved in the nitrate/nitrite reduction process is xanthine oxidoreductase (XOR). XOR is capable of reducing organic and inorganic nitrates and nitrite, and the role of XOR in NO3 - → NO2 - → ·NO pathway is most studied as compared to other enzymes with nitrate reductase activity. The functions of XOR, the mechanisms of nitrate/nitrite reduction by this enzyme and their physiological relevance will be outlined in this mini review.

Alkali metal enhanced cerium manganese-based three-dimensional ordered macroporous catalyst for NO oxidation and soot combustion

Alkali metal can control the redox potential of the reaction system, modify the surface electronic structure, improve the stability of catalyst. Herein, we dop the alkali metal into cerium manganese-based...

An experimental and modeling study on homogeneous oxidative coupling of methane utilizing N2O as oxidant

Experimental and kinetic modeling studies were performed to investigate the homogeneous oxidative coupling of methane utilizing nitrous oxide as the oxidant (N2O-OCM). The experiments were performed in a jet stirred reactor at atmospheric pressure and temperatures of 773–1173 K. Synchrotron vacuum ultraviolet photoionization mass spectrometry was used to achieve comprehensive and isomer-resolved identification of major products and nitrogenous, carbonyl and hydrocarbon intermediates. To interpret the experiments, a detailed kinetic model was developed by extending the widely used hydrocarbon growth mechanisms. Rate of production and sensitivity analyses were performed to provide a deep insight into the complex reaction network. The results demonstrate that N2O dissociation is the rate-controlling step, and the mild oxidation of N2O effectively reduces the production of CO2 as byproduct and meanwhile improves the selectivity of C2 species. In the presence of N2O, CH3 can actively participates in H-abstraction reactions of C2H6 and C2H4, besides the self-coupling reactions. Due to chain-propagation competition reactions (N2O+H=N2+OH and N2O+H=NH+NO), NH3 and NO exhibit low concentrations. The detailed formation pathways for NH3 and NO were elaborated, and the evolution routes of carbonyl intermediates in the presence of N2O were analyzed. Benzene formation is found mainly through C3 self-recombination and C5 ring reforming reactions. Finally, comparative analysis with O2-OCM reveals that the presence of oxygen promotes the conversion of CH3 to CH2O and deep oxidation of C2H3, explaining the lower C2 yield of O2-OCM. The inherent limitation of the C2 yield of N2O-OCM primarily arises from the reaction of C2H4 and O, as well as the subsequent reaction CH2(S)+N2O=CH2O+N2. The experiment observations confirmed the existence of C2 carbonyl intermediates such as ketene and acetaldehyde. The study highlights the notable role of O2 molecular and O atoms in the homogeneous OCM and offers kinetic support for the OCM reaction process with catalysts.

Building a database system of greenhouse gas emissions from concentrated domestic wastewater treatment plants in urbans of the Northern region to prepare for Vietnam's carbon market

In the field of wastewater treatment, a quality-assured carbon database system will serve as a basis for determining greenhouse gas emission quotas and aiming to prepare Vietnam's carbon market in the period from now to 2025. This article presents the results of calculations to determine the volume of greenhouse gas emissions (including emissions of methane CH4 and nitrous oxide N2O) from concentrated domestic wastewater treatment plants in urbans of the region North. The inventory calculation period is determined from the official operation of the plant to 2024. Total CH4 and N2O emissions during the calculation period of 29 plants correspond to normal emission scenarios (BAU) is 378.0 and 79.7 x 106 tons CO2e, low emission scenario is 363.8 and 6.4 x 106 tons CO2e, high emission scenario is 476.1 and 13,103.9 x 106 tons CO2e. On this basis, state management agencies as well as local authorities can propose the most appropriate and effective strategic directions for green growth urban development.

Positive effects of the Sr doping on LaCoO3 perovskites for simultaneous catalytic oxidation performances of NO and Hg0

LaCoO3 perovskite, with a general formula of ABO3, have received significant attention as environmental functional catalysts for NO and Hg0 oxidation owing to their compositional adjustability and chemical stability. Structural modifications of the perovskite have been performed through the substitution of La atoms at the A-site with atoms of different ion radii to enhance the oxidation ability. In this study, herein, a series of La1–xSrxCoO3 (x = 0.1–0.5) perovskites were synthesized, resulting in a transition from the R–3C rhombohedral phase structure to the Pm-3m cubic phase. Sr doping was effective in improving the oxidation of NO and Hg0. The improved catalytic activity was attributable to the generation of more electronegative Co3+ and the higher content of surface-adsorbed oxygen species. Moreover, Sr doping enhanced the redox performance and reduced the reaction temperature. Notably, SrCO3 species were the main factors responsible for the reducing the activation of La1–xSrxCoO3 (x = 0.1–0.5) perovskites, which could be detected when the Sr doping content exceeded 0.4. This study provides a screening strategic idea for the designing highly active perovskite catalysts.

Enhanced simultaneous oxidation of Hg0 and NO with SO2 resistance by dual single-atom Co-Cu incorporated g-CN nanocomposites

The simultaneous catalytic oxidation of Hg0 and NO within coal-fired plants is crucial in abating diverse pollutants. Nevertheless, conventional catalysts often encounter challenges, such as diminished oxidation efficiency at lower temperatures and competitive adsorption with other gaseous components, particularly SO2, to remove Hg0 and NO. A nanocomposite catalyst, Co-Cu/g-CN, was developed to address these issues, featuring dual single-atom doping of Co and Cu in graphitized carbon nitride (g-CN). Surface characterization techniques and theoretical calculations confirmed that Co and Cu single atoms were successfully incorporated into the g-CN structure. Moreover, this innovative catalyst exhibited a strong metallic interaction between the dual single atoms, which led to an increased production number of superoxides (O2−), albeit with a slightly reduced oxidizing ability. The trade-off in the active centers of O2− ultimately enhanced the oxidation capability of Hg0 and NO owing to the augmented number of O2−. Co-Cu/g-CN demonstrated complete Hg0 removal efficiency and achieved 81.3% NO removal efficiency at 200–250 °C. Both theoretical analysis and DRIFTS investigation revealed that the competitive adsorption of SO2 over O2− was significantly weakened due to the reduced oxidizing ability of O2−. Additionally, the Cu single atoms acted as sacrificial sites for sulfate species, thereby preserving the catalytic activity of Co single atoms for NO oxidation. This research provides a valuable dual single-atom-catalyst fabrication strategy for addressing flue-gas NOx and Hg0 pollution.

Mechanism of O2-promoted NO adsorption on activated carbon: An experimental and computational study

Activated carbon can be used to control NOx emissions in low-temperature flue gas, while improving its performance is challenging. NO adsorption on activated carbon was found significantly promoted with the presence of O2. Based on the analysis of NO adsorption characteristics under different atmospheres and corresponding desorption characteristics, NO oxidation, NO2 migration and further conversion on activated carbon are proposed to cause the significant increase in NO adsorption capacity. Quantum chemical calculations conducted on the adsorption and reaction pathways of NO, O2, and NO2 on different carbonaceous models clarified that the pathway of O2-promoted NO adsorption on activated carbon can be divided into two stages. In the first stage, O2 adsorbs on active carbon atoms near the hydroxyl functional group and undergoes an oxidation reaction with gaseous NO to generate NO2. In the second stage, the desorbed NO2 is re-absorbed on the saturated carbon atoms; the N-down adsorption configuration of NO2 will not convert, while the O-down adsorption configuration of NO2 will oxidize the active site to form C-O and release NO; the C-O further reacts with the gaseous NO2 to form NO3- which stably remains. There are two types of active sites involved in the pathway. The active carbon atoms near the hydroxyl functional groups mainly play a catalytic role in the oxidation of NO, while the saturated carbon atoms mainly store nitrogen-containing components. The results can help improve the performance of activated carbon in adsorbing NO in low-temperature flue gas.

Enhanced Low-Temperature Activity and Hydrothermal Stability of Ce-Mn Oxide-Modified Cu-SSZ-39 Catalysts for NH3-SCR of NOx

Cu-SSZ-39 zeolite with an AEI structure exhibits excellent hydrothermal stability and can be a potential alternative to Cu-SSZ-13 zeolite SCR catalysts for NOx removal in diesel vehicles. However, the inferior low-temperature performance of Cu-SSZ-39 leads to substantial NOx emissions during the cold-start period, impeding its practical application. In this study, Ce-Mn oxide-modified Cu-SSZ-39 catalysts (CeMnOx/Cu-SSZ-39) and references (CeO2/Cu-SSZ-39 and MnOx/Cu-SSZ-39) were prepared by the ion-exchange of Cu ions followed by impregnation of the oxide precursors, with the aim of enhancing the NH3-SCR performance at low temperatures. The modified catalysts exhibited improved low-temperature activity and hydrothermal stability compared to the unmodified counterpart. In particular, CeMnOx/Cu-SSZ-39 showed the highest activity among the three catalysts and achieved NOx conversions above 90% within the temperature range of 180 °C to 600 °C, even after undergoing hydrothermal aging at 800 °C. Experimental results indicated that the synergistic effect between Ce and Mn in CeMnOx improves the redox properties and acidity of the catalyst due to the presence of Ce3+, Mn4+, and abundant adsorbed oxygen species, which facilitate low-temperature SCR reactions. Furthermore, the interaction of CeMnOx with Cu-SSZ-39 stabilizes the zeolite framework and hinders the agglomeration of Cu species during the hydrothermal aging process, contributing to its exceptional hydrothermal stability. The kinetics and NO oxidation experiments demonstrated that CeMnOx provides access to fast SCR reaction pathways by oxidizing NO to NO2, resulting in a significant increase in low-temperature activity. This study provides novel guidelines for the design and preparation of Cu-SSZ-39 zeolite with outstanding SCR performance over a wide temperature range.

Efficient photocatalytic NO removal with inhibited NO2 formation and catalyst loss over sponge-supported and functionalized g-C3N4

Though photocatalytic purification of NO has been widely studied, how to avoid secondary pollution during gas-solid reaction is still a challenge, especially in inhibiting the formation of toxic intermediates (NO2) and avoiding the blow away of powdery photocatalyst. Herein, we proposed a one-step solvothermal method to prepare melamine sponge (MS) supported and functionalized g-C3N4 (CN), which simultaneously realizes the inhibition of NO2 formation and catalyst loss. Sodium hydroxide, which plays a dual role, has been introduced during the preparation of supported photocatalyst. Specifically, sodium atom, as the modifier of performance, could facilitate the randomly distributed charge of pristine CN to be converged, which accelerates the adsorption/activation of reactants for efficient and deep NO oxidation. Hydroxyl group, as the binder between CN and MS, induces the interaction by forming hydrogen bonds, which contributes to the firm immobilization of powdery photocatalyst. The supported sample exhibits outstanding NO removal rate (58.90%) and extremely low NO2 generation rate (1.41%), and the mass loss rate of photocatalyst before and after reaction is less than 1%. The promotion mechanism of performance also has been elaborated. This work takes environmental risks as a prerequisite to propose a feasible strategy for perfecting the practical application of photocatalytic technology.

Low temperature oxidation of diesel soot particles over one-dimensional 2 × 3 tunnel-structured Na2Mn5O10 catalysts

Tunnel-structured manganese oxides have drawn widespread research attention due to their excellent oxidation properties for the soot oxidation reaction. In this study, a series of romanechite Na2Mn5O10 catalysts with a 2 × 3 tunnel structure were synthesized via a facile hydrothermal method. The as-synthesized catalysts were investigated using X-ray diffraction, scanning and transmission electron microscopy, H2 and soot temperature-programmed reduction, O2 temperature-programmed desorption, NO temperature-programmed oxidation, X-ray photoelectron spectroscopy, and other measurements. Among all the catalysts, the Na1MnyOδ-120 catalyst exhibited the best catalytic performance for soot combustion, with T10, T50, and T90 values of 281 ℃, 317 ℃, and 343 ℃, respectively, which were considerably reduced to 271 ℃, 310 ℃, and 335 ℃ in the existence of 10% H2O. The results of multiple characterization methods indicated that the Na2Mn5O10 catalysts exhibit good reducibility, strong oxygen adsorption and activation capacity, and NO to NO2 oxidation ability. Moreover, the active sites (Mn and oxygen vacancies) and reaction mechanism (Langmuir–Hinshelwood) were also revealed by in-situ DRIFT and density functional theory calculations results. This study details a new strategy for the design and synthesis of efficient soot oxidation catalysts with practical application prospects.

Simultaneously accomplishing selective catalytic reduction of NO and catalytic oxidation of CO in a catalyst coupling system

Considering that nitrogen oxides (NOx) and carbon monoxide (CO) usually meantime exist in industrial flue gas, it is meaningful to develop a collaborative control technology for the simultaneous purification of NOx and CO. In this work, the catalysts xCu-1V-5W/Ti were evaluated in the simultaneously selective catalytic reduction by NH3 (NH3-SCR) and CO oxidation. The introduction of CuO provided the active sites for the oxidation of CO, while inhibited the NH3-SCR process and facilitated the generation of N2O by-product at high temperature. Accordingly, a catalyst coupling system was designed by employing 1V-5W/Ti and 2Cu-1V-5W/Ti catalysts in one reactor, and high NO conversion (>90 %) and CO removal efficiency (>80 %) could be simultaneously realized within 350–500 °C. This work would provide valuable insights for achieving simultaneous removal of NOx and CO using the catalyst coupling method.