NOx Gas Research Articles

Boosting visible-light-driven photocatalysis of nitrogen oxide degradation by Mott–Schottky Pd/TiO2 heterojunctions

One of the main air pollutants is NOx gas, which is emitted into the atmosphere by burning fossil fuels and vehicle exhaust. The application of the photocatalytic technique to mitigate the concentration of NOx in the atmosphere is preferable because it is environmentally friendly, simple, and inexpensive method. In this work, palladium nanoparticles (Pd NPs) were decorated on TiO2 nanotubes (TNTs) by gamma-ray irradiation, and degradation of nitrogen monoxide (NO) was applied to evaluate the photocatalysis of the as-prepared Pd/TNT materials under atmospheric conditions. The results demonstrated that the Pd/TNT material with a 14 kGγ dose is the best photocatalyst, achieving 53.30 % NO removal efficiency, which is 1.6 times greater than that of pure TNTs. Furthermore, the decomposition of NO on the Pd/TNT catalysts also generated less NO2 poisoning under both solar and visible light conditions. Additionally, they possess desirable properties such as reusability, low toxicity, and high apparent quantum efficiency (AQE).

MODELING OF COAL-BASED COMPOSITE BRIQUETTES IN ORDER TO REDUCE SULFUR EMISSIONS INTO THE ATMOSPHERE

The tendency to abolish, to obtain heat from coal in order to reduce atmospheric pollution, leads to the closure of coal deposits. The alternative for obtaining heat, especially in the category of heating smaller residential buildings, with wood pellets, although acceptable from an ecological point of view, has its drawbacks, if one takes into account the scale of the required amount of energy and the role of the forest in purifying the air. Wood pulp and coal as basic energy carriers have hydrocarbon compounds. So, in both cases COx and NOx gases appear as gaseous products. The difference is in their scale. Unlike wood, coal also contains sulfur compounds, which makes it an environmentally unacceptable fuel. By adding a certain amount of wood pulp and additives to the coal mass, in this work, pyrophyllite shale, the impact on the energy and ecological aspects of heat release of such a complex fuel mixture was investigated. The ecological aspect is accentuated through the release of sulfur from coal. The mixture was subjected to the briquetting process, and the obtained samples were tested with relevant parameters, primarily the obtained lower heat value and sulfur content (SOx) in these products. The obtained results are very optimistic with both parameters mentioned above and can be a guide for further research for this idea. Key words: coal, wood sawdust, briquette, calorific value, sulfur, ecology.

Seasonal oxidative dynamics and isotopic fractionation of NOx and SO2 in Ostrava, Czech Republic: Insights from stable isotope analysis

The city of Ostrava, NE Czech Republic, is known for its industrial pollution. It has well-characterized emission sources and stable air movement patterns. These features are conveniently used to generalize on atmospheric NOx and SO2 oxidation processes. In 2021, we conducted a series of sampling campaigns to assess the isotopic fractionation conducive to NO3− and SO42− aerosols in PM10. These sampling campaigns were timed to capture varying atmospheric conditions, including climatic inversion periods, providing also insights into urban emission dynamics over the course of the year. Gaseous NOx and SO2 were collected on passive filters, while their oxidized forms, NO3− and SO42, were captured on PM10 particle filters, enabling us to analyze the transformation dynamics of these pollutants. Isotopic analyses distinguished the sources of NOx emissions—coal combustion (δ15N = −3‰) and vehicular emissions (δ15N = −7 ‰)—and allowed quantifying isotope fractionation during their conversion to NO3− (εNOx-NO3- = 11.5 ± 1.15 ‰). This fractionation, however, was influenced by seasonal variations, and appears to be notably affected by NH4NO3 decomposition during warmer months. The correlation of the NO3− to NOx ratio with PM10 and atmospheric moisture highlighted the interplay between particulate matter and humidity in relevant atmospheric transformations. Similarly, for SO2, primarily emitted from coal combustion (δ34S = −2‰), we identified distinct fractionation patterns during oxidation to SO42− encompassing both kinetic (εSO2-H2O = −1.3 ± 0.5‰) and equilibrium (εSO2- SO42- = 2.24 ± 0.67‰) effects. The SO42−/SO2 ratio was correlated with PM10 but showed no dependence on humidity. Significantly, atmospheric inversion conditions accelerated oxidation, modifying the fractionation patterns for both NOx (εNOx-NO3- = 7‰) and SO2 (εSO2- SO42-= −0.9 ± 0.3‰). Our methodology elucidates pivotal mechanisms in atmospheric pollution transformation, underlined by the tracing of NOx and SO2 to aerosol conversions via δ15N and δ34S isotopic analyses. The isotope fractionation underscores equilibrium processes in oxidation reactions, while the effect of PM10 and humidity reveals the complexity of these atmospheric oxidative transformations. The role of wet deposition in removing SO2 highlights an essential pathway in the atmospheric sulfur cycle.

Investigation effects of different calorific values and operating conditions on biogas flame: a CFD study

ABSTRACT This study investigates different biogas fuels’ and operating conditions’ effects on flame temperatures and emissions (CO, CO2, NOx, and soot). Different calorific values (15.580, 17.880, 20.430, 23.080, and 26.230 MJ/kg) were obtained by changing methane content. Furthermore, various gas pressure (0.5, 1, 2, and 3 atm), excess air coefficient (1.4, 1.8, 2.5, and 4), and oxygen values (21, 23, 25, and 27%) were simulated for 8.6 kW thermal capacity furnace. Increasing the calorific value of biogas fuels, CO, NOx, and soot emissions and flame length tend to increase, while CO2 decreases. Increasing gas pressure, flame temperature, and CO2, CO, and NOx decrease, while soot emissions tend to increase. As a result of the decrease in the air excess coefficient from 4.0 to 1.4, there is a increase in the flame temperature, flame length, and soot, CO, CO2, and NOx emissions. On the other hand, oxygen content from 21% to 27% oppositely affected these parameters, excluding flame length.

Highly selective sensing of toxic NOx gases for environmental monitoring using Ru-doped single walled TiO2 nanotube: A density functional theory study

Applying density functional theory simulations, in this study, we examine the sensing properties of Ru-TNT surface towards NOx molecules such as NO and NO2. The obtained results show that Ru doping creates a large-spin density over the Ru-TNT surface, which hints at an increase in the adsorption energy of NOx molecules. The electronic properties of the Ru-TNT surface are significantly altered after NO and NO2 molecule adsorption, as proven by the larger change in the energy gap values. Moreover, the selectivity study indicates that the Ru-TNT is capable of selectively sensing the NOx molecules in the presence of other gases, e.g., CO2, CO, NH3 and H2O. Using an external positive electric field can resist the strong anchoring of NOx molecules over the Ru-TNT surface, suggesting that material recovery is feasible. Thus, the Ru-TNT structure can be applied as a selective, sensitive, and promising ambient temperature gas sensor for NOx molecules.

Normalised similarity assessment to inform grouping of advanced multi-component nanomaterials by means of an Asymmetric Sigmoid function

This manuscript presents a procedure for similarity assessment as a basis for grouping of multi component nanomaterials (MCNMs). This methodology is an adaptation of the approach by Zabeo et al. (2022), which includes an impactful change: the calculated similarities are normalised in the [0,1] domain by means of asymmetric Logistic scaling to simplify comparisons among properties' distances. This novel approach allows for grouping of nanomaterials that is not affected by the dataset, so that group membership will not change when new candidates are included in the set of assessed materials. It can be applied to assess groups of MCNMs as well as mixed groups of multi and single component nanomaterials as well as chemicals. To facilitate the application of the proposed methodology, a software script was developed by using the Python programming language, which is currently undergoing migration to a user-friendly web-based tool. The presented approach was tested against a real industrial case study provided by the Andalusian Innovation Centre for Sustainable Solution (CIAC): SiO2-ZnO hybrid nanocomposite used in building coatings, which is designed to facilitate photocatalytic removal of NOx gases from the atmosphere. The results of applying the methodology in the case study demonstrated that ZnO is dissimilar from the other candidates mainly due to its different dissolution profiles.

Treating NOx gas Pollution by Visible Light Photocatalytic Reaction of S-doped TiO2 Nanotubes

Treating NOx gas Pollution by Visible Light Photocatalytic Reaction of S-doped TiO2 Nanotubes

Theoretical insight into NO formation and reduction at biochar N-sites: Influence of different oxygen-containing functional groups

Biochar is a cost-efficient and promising porous carbonaceous material for the efficient removal of flue gas NOx. The N-site located at the edge of biochar can be a crucial gateway for NO reduction to N2 or for NO formation by oxidation, which can be significantly affected by the oxygen-containing functional groups (OFGs) on the biochar edge. However, the roles of different OFGs in N-site-involved reactions remain elusive. Based on the biochar characterization results, reasonable theoretical models of biochar with different N-sites and OFGs were constructed. Subsequently, the effects of distinct OFGs on the interaction between NO and N-sites as well as the NO liberation from N-sites were elucidated, by employing density functional theory (DFT) and electronic structure analysis. The results reveal that all OFGs, encompassing -CHO, -COOH, and -OH, manifest their roles through the direct inherent electrostatic properties of O/H in OFGs (O*/H*) or altering the reactivity of edge atoms indirectly. For pyridinic nitrogen (N-6) at the zigzag edge, unsaturated (-CHO, -COOH)/saturated (-OH) OFGs inhibit/enhance NO reduction with N-6 by electrostatic properties of O*/H*, and all OFGs inhibit NO generation from N-6. Besides, all OFGs enhance the NO reduction with pyrrolic nitrogen (N-5) at the armchair edge while inhibiting the release of NO, by influencing the edge activity. The present study gives a mechanism insight into the roles of distinct OFGs in reactions involving biochar N-sites.

Fulvic acid and fermentation agent optimize in situ composting by reducing antibiotic resistance genes abundances and altering succession of bacterial communities

The use of biostimulants to enhance microbial activity has been extensively reported. However, their regulatory properties on the ecological security of in situ composting have not yet been fully elucidated. Here, the effects of two biostimulants (fermentation agent [FM] and fulvic acid [FA]) on in situ composting were investigated under field conditions. The abundances of antibiotic resistance genes (ARGs), as well as those of the microbial communities and the activities of enzymes, were comprehensively investigated. The addition of biostimulants significantly reduced the abundances of streptomycin and sulfonamide resistance genes by 79%–97% and decreased the abundance of Gammaproteobacteria. This was particularly true for species that are members of the Enterobacteriaceae and contain many ARGs. The addition of biostimulants promoted the succession of bacterial communities toward enhancing the solubility of phosphorus, promoting the degradation of aromatic compounds, and reducing the emissions of NOx gas. The application of FA and FM resulted in distinct bacterial network structures, and many negative correlations were associated with ARGs in the temperature subnetwork in the FM treatment. This study provides an effective strategy for the in situ treatment of agricultural waste and underscores the significance of biostimulants in improving the biological safety of medium-temperature in-situ composting.

E-Nose for Piston Ring and Cylinder Block Condition Detection of Motorcycle Engine Based on MyRIO LabVIEW Programming

This study has created a system capable of identifying the condition of the piston ring and cylinder block of a 4-stroke motorcycle engine using petrol or similar through exhaust emissions. Multisensory gas, sensitive to changes in CO, CO2, NOx, and HC gas elements and compounds, is installed as an input to the exhaust channel and integrated using LabVIEW programming on the NI myRIO module. Multisensory data is processed using the FFT and the backpropagation method to classify whether the piston rings and engine cylinder block are in good or damaged condition. Tests have been carried out on motorbikes with piston rings and engine cylinder blocks that are in good, damaged, or unknown condition. During the test, the target error value for motorcycles with piston rings and engine cylinder blocks in good or damaged condition is less than 1%. The system can distinguish the condition of the piston ring and cylinder block of a motorcycle engine that is 100% optimal and 100% damaged with an error of 0% compared to the compression test method, and the maximum error is 20% Compared to the technician's manual method. Ten motorcycles were randomly tested in unknown conditions; 50% were in good condition, and 50% were damaged. For further development, an electronic nose system can detect engine combustion conditions and damage to cylinder rings and 4-stroke motorbike engine blocks based on exhaust emissions.

Unveiling the Computational Insights into Na‐Decorated Hydrogen‐Substituted Graphdiyne for Efficient Tracing and Trapping of Nitrogen and its Oxides

Addressing air pollution is a critical concern, particularly in the context of tracing and trapping nitrogen and its oxides (N2, N2O, NO, NO2) emitted from fuel combustion. In this context, this study delves into the potential of recently discovered Hydrogen-substituted Graphdiyne (HsGDY) and to enhance its adsorption capabilities by incorporating sodium (Na) metal atom computationally. Herein, the strategic sites for Na atom decoration on HsGDY is identified and the most stable site R1 with Eads = −0.820 eV is chosen for subsequent NOx adsorption studies. Through DFT calculations, we assess the adsorptive capacity of NOx gases onto both HsGDY and Na-decorated HsGDY (NaHsGDY) slabs. In particular NO2 gas molecule with Eads = −2.537 eV emphasizes greater adsorption over NaHsGDY slab. Analysis of electronic properties reveals significant reduction in the energy gap (Eg) of the NaHsGDY, indicating heightened reactivity toward NOx gases thereby resulting in substantial increase in the slab’s conductivity. Additionally, charge density difference and Löwdin charge analyses provides consistent evidence supporting enhancement in charge transfer during NOx gases adsorption after Na decoration. The NaHsGDY slab demonstrates high selectivity, sensitivity, and superior performance than HsGDY slab, positioning it as a promising candidate for targeted NOx gas molecules detection.

Establishing Z-scheme Bi2WO6/g-C3N4 interfaces toward efficient photocatalytic performance of NOx under visible light

NOx gas is released from automobile emissions and fossil fuel combustion. The photocatalytic method was applied to address environmental issues, notably NOx air pollution because of environmentally friendly, low cost, and utilized solar light irradiation. In this work, a Z-scheme Bi2WO6/g-C3N4 heterojunction photocatalyst was successfully synthesized by a hydrothermal method at 180 °C for 12 h. Combining g-C3N4 with Bi2WO6 promoted two oxidation (over Bi2WO6) and reduction (over g-C3N4) sites, enhancing the photocatalytic activity of the g-C3N4 single-component system. The sample contains 20 wt% of Bi2WO6, becoming the best excellent photocatalytic activity at approximately 43.45% in 30 minutes of visible light irradiation. In addition, the photogenerated electron (e−) and hole (h+) were determined as primary agents. The high stability of Bi2WO6/g-C3N4 photocatalysts was demonstrated by little change in photocatalytic performance over five cycles of photocatalytic measurements. The NOx removal mechanism and the intermediate generation were proposed to understand the reaction process better.

Parametric Optimization for Highly Sensitive ZnO Based NOX Gas Sensor

Parametric Optimization for Highly Sensitive ZnO Based NOX Gas Sensor

Study on the Performance and Emissions of Triple Blends of Diesel/Waste Plastic Oil/Vegetable Oil in a Diesel Engine: Advancing Eco-Friendly Solutions

To provide technical and economical solutions regarding management of plastic waste, which is constantly increasing worldwide, this study addresses the possibility of using plastic oils (PO) obtained from these plastic wastes as biofuels. To this end, the replacement of the fossil diesel employed in internal combustion diesel engines with triple diesel/PO/vegetable oil mixtures has been investigated. Sunflower (SO) and castor oil (CO) mixed with PO in the most appropriate proportion are evaluated as pure vegetable oils (SVO). Thus, diesel/PO/SVO triple blends were prepared, characterized, and then tested on a diesel engine operating as electricity generator, evaluating power output, consumption, and exhaust emissions. The obtained results show that, with the incorporation of relatively small quantities of pure, non-edible vegetable oils, in double mixtures of PO/SO and PO/CO, an effective alternative fuel for transport is obtained, that allows for 100% of fossil diesel to be replaced. In fact, with these double PO/SVO biofuel mixtures, higher engine power values and lower consumption levels are obtained than those achieved with fossil diesel. Regarding exhaust emissions, these are produced with a slightly greater opacity than with fossil diesel, but there are lower values of carbon gases as a whole (CO + CO2) and in NOx gases.

Ammonia marine engine design for enhanced efficiency and reduced greenhouse gas emissions

Pilot-diesel-ignition ammonia combustion engines have attracted widespread attentions from the maritime sector, but there are still bottleneck problems such as high unburned NH3 and N2O emissions as well as low thermal efficiency that need to be solved before further applications. In this study, a concept termed as in-cylinder reforming gas recirculation is initiated to simultaneously improve the thermal efficiency and reduce the unburned NH3, NOx, N2O and greenhouse gas emissions of pilot-diesel-ignition ammonia combustion engine. For this concept, one cylinder of the multi-cylinder engine operates rich of stoichiometric and the excess ammonia in the cylinder is partially decomposed into hydrogen, then the exhaust of this dedicated reforming cylinder is recirculated into the other cylinders and therefore the advantages of hydrogen-enriched combustion and exhaust gas recirculation can be combined. The results show that at 3% diesel energetic ratio and 1000 rpm, the engine can increase the indicated thermal efficiency by 15.8% and reduce the unburned NH3 by 89.3%, N2O by 91.2% compared to the base/traditional ammonia engine without the proposed method. At the same time, it is able to reduce carbon footprint by 97.0% and greenhouse gases by 94.0% compared to the traditional pure diesel mode.

Study on the Optimized Matching of VNT and EGR Systems in a Diesel Engine

An experimental investigation of the coupling relationship between the VNT (Variable Nozzle Turbine) and EGR (Exhaust Gas Recirculation) systems was carried out in this study on a four-valve common-rail diesel engine in bench tests, as well as a transient optimization of the VNT and EGR control strategies. It was found that the overall level of NOX and flue gas emissions decreased with decreasing VNT opening. When the opening of the EGR valve was in the range of 5%-10%, the NOX and soot emissions could be reduced simultaneously by decreasing the VNT opening; the response of the intake volume was greatly improved by modifying the coordinated control strategy by boosting the control strategy under the acute load step condition; the NOX emission was significantly reduced by 6% overall, and the soot was reduced by 22.8% and the CO2 emission was improved in the transient-optimized WLTC test cycle. Therefore, by coupling the VNT and EGR systems and optimizing them transiently, emissions of pollutants during rapid engine acceleration can be decreased.

Experimental Study on Flame Chemical Composition of Coal and Ammonia Gas-Solid Jet in Flat Flame Burner.

Ammonia as a fuel to partially or completely replace fossil fuels is one of the effective ways to reduce carbon dioxide, and the research on ammonia coal cocombustion is of great significance. The combustion characteristics of ammonia are very different from those of pulverized coal, resulting in the ignition and emission characteristics of ammonia and pulverized coal gas flow that is different from traditional pulverized coal flame. In this paper, the effect of pulverized coal concentration in coal and ammonia mixed combustion jet on the ignition distance and gas-phase components at different positions of the jet flame were studied experimentally on the flat flame burner, and the conditions of ignition and ignition stability of coal and ammonia gas-solid fuel were expounded. It was found that the ammonia mixed with pulverized coal changed the temperature field of the flat flame burner and therefore the ignition characteristics of the jet were changed. The ignition delay time at the same jet speed was positively correlated with the pulverized coal concentration, but when the pulverized coal concentration continued to decrease, the influence on the ignition delay time gradually became smaller. The composition of coal ammonia gas-solid fuel changed the heat transfer path and share during combustion, and finally, the flame temperature was negatively correlated with the concentration of pulverized coal. Therefore, the reduction of the pulverized coal concentration was conducive to the stable combustion of coal ammonia mixed fuel. When HAB = 100 mm, the conversion rate of fuel N to NOx per unit mass of coal ammonia mixture increased with the increase of pulverized coal concentration. The NOx production amount first increased and then decreased with the increase of pulverized coal concentration, and the amount of N2O and NO2 decreased rapidly with the increase of HAB. The proportion of NOx in NO exceeded 94%, which was conducive to achieving low nitrogen combustion of coal and ammonia gas-solid fuel. In general, the O2 concentration in the ammonia coal jet flame decreased, the flue gas temperature, and NOx and CO generation increased after mixing ammonia, and the optimal pulverized coal concentration in this experiment was 0.41 kgc/kga (mass ratio of pulverized coal to the sum of N2 and NH3).

Assessment of the Ambient Air Quality of Sangli City, Maharashtra, vis-à-vis National Ambient Air Quality Standards (NAAQS)

Assessment of ambient air quality is important to formulate short-term and long-term plans to mitigate air pollution. This study attempts to present an ambient air quality assessment for Sangli City, located at 16.85° N, and 74.58° E. The assessment is done through ambient air quality data measured over three ambient air quality monitoring stations located in residential, commercial, and industrial zones of Sangli City. The data was collected from 2009 to 2017 under the National Air Quality Monitoring Program of the Central Pollution Control Board (CPCB), India. The observed concentrations of gaseous pollutants, SO2 and NOx, and respirable particulate matter are compared with the concentration levels prescribed by the National Ambient Air Quality Standards (NAAQS) in 2009. The concentration levels of particulate matter are quite on the higher side of the prescribed standards. The levels of NOx are almost approaching the prescribed values, whereas SO2 levels are well within the margin. We have also studied seasonal variations in the pollutants during the study period. In general, the air quality in Sangli City is quite undesirable during the mid-winter to mid-summer period. The study is useful for common men to increase awareness. It also forms baseline data and is useful for local and central government to design appropriate strategies to apply corrective measures, protect health, and promote environmental protection.

Investigation of two dimensional‐MoS2/reduced graphene oxide electrode for applications of NOx gas sensors

AbstractIntroductionTo generate GO and rGO nanoparticles, high‐temperature thermal reduction and the Hummers' technique were both employed. A GO sample is heated and turned into rGO nanopowder. A MoS2 precursor is then added to make a MoS2/rGO composite structure.ObjectivesThe themes of this research work consist of (1) preparation of molybdenum disulfide (MoS2) powder produced by hydrothermal method and sulfurization reaction; (2) graphene oxide (GO) nanoparticles prepared by Hummers' method, compounded with MoS2 to form molybdenum disulfide/reduced graphene oxide (MoS2/rGO) powder in order to reduce the working temperature of a gas sensing process; (3) evaluation of effects of MoS2 and MoS2/rGO sensing devices for NO and NO2 (NOx) gas detection.Results and conclusionWhen tested under various gas concentration and ambient temperature conditions, the NOx gas concentration is 10 ppm, and the working temperature is 150°C, the response value obtained reaches 14.4. In this study, MoS2; a member of two‐dimensional (2D) transition metal sulfide materials, was applied as the main body of the sensing material, and rGO was used as a functional additive. For creating new gas sensing devices, significant progress has been made in creating and designing NOx gas sensing devices for MoS2/rGO composite materials.

Insight into the Alkali Resistance Mechanism of FeMoTiOx Catalysts for NH3 Selective Catalytic Reduction of NO: Self-Defense Effects of MoOx for Alkali Capture.

The deactivation of selective catalytic reduction (SCR) catalysts caused by alkali metal poisoning remains an insurmountable challenge. In this study, we examined the impact of Na poisoning on the performance of Fe and Mo co-doped TiO2 (FeaMobTiOx) catalysts in the SCR reaction and revealed the related alkali resistance mechanism. On the obtained Fe1Mo2.6TiOx catalyst, the synergistic catalytic effect of uniformly dispersed FeOx and MoOx species leads to remarkable catalytic activity, with over 90% NO conversion achieved in a wide temperature range of 210-410 °C. During the Na poisoning process, Na ions predominantly adsorb on the MoOx species, which exhibit stronger alkali resistance, effectively safeguarding the FeOx species. This preferential adsorption minimizes the negative effect of Na poisoning on Fe1Mo2.6TiOx. Moreover, Na poisoning has little influence on the Eley-Rideal reaction pathway involving adsorbed NHx reacting with gaseous NOx. After Na poisoning, the Lewis acid sites were deteriorated, while the abundant Brønsted acid sites ensured sufficient NHx adsorption. As a benefit from the self-defense effects of active MoOx species for alkali capture, FeaMobTiOx exhibits exceptional alkali resistance in the SCR reaction. This research provides valuable insights for the design of highly efficient and alkali-resistant SCR catalysts.