Decomposition Of Nitrogen Oxides Research Articles

Mechanism of heterogeneous reduction of NO over graphite-supported single-atom Fe catalyst: DFT study

The mechanism of nitrogen oxide (NO) reduction over graphite carbon-supported single-atom iron (Fe) catalyst (Fe/G) was investigated by density functional theory (DFT) and transition state theory (TST). The catalyst deactivation was also analyzed. The results revealed that the NO reduction, based on the Eley-Rideal (E-R) mechanism, underwent four stages including N2O formation and release as well as N2 formation and release. However, the NO reduction only involved two stages according to Langmuir-Hinshelwood (L-H) mechanism: N2 formation and release. Furthermore, for the E-R mechanism, the rate-controlling step was NO reduction, where a NO molecule was adsorbed on an Fe atom with an N, O-down structure with energy barrier of 15.5 kJ/mol, lower than that of other paths. Energy barrier analysis indicated that the energy barrier for the reduction of reactive oxygen species was higher than that for the formation of N2. Reactive oxygen species remaining on the surface of Fe atoms after NO decomposition inhibited the adsorption and reduction of NO, leading to catalyst deactivation due to the absence of active sites. The single-atom Fe species promoted the NO reduction. Kinetic analysis results suggested that, upon increasing the reaction temperature, the NO reduction rate increased more significantly than the reactive oxygen transfer rate.

Method of neutralization of nitrogen oxides in area of low-temperature plasma

In the production of 1 ton of oxalic acid, 2000 m3 of gases with an average content of 2–2.5% of nitrogen oxides are emitted into the atmosphere. The existing methods of air purification from nitrous gases have a number of disadvantages and therefore cannot be widely used in industry. Based on theoretical and experimental studies, a new method for the thermal decomposition of nitrogen oxides has been developed, which provides for the sanitary purification of waste gases in the production of oxalic acid, up to the maximum permissible concentrations. The process of thermal decomposition of nitrogen oxides in the temperature range from 500 to approximately 50000С has been studied. To achieve such temperatures, an arc plasma torch with a tungsten cathode and a copper anode was used. The degree of decomposition was determined by measuring the NO concentration at the inlet and outlet by the evacuated flask method. The effects of gaseous (hydrogen, ammonia, methane, natural gas), liquid (kerosene, gasoline, fuel oil), and solid reducing agents (coke, coal, graphite) on the decomposition reaction of nitrogen oxides were also studied.

Direct NO decomposition over Rh-supported catalysts for exhaust emission control

Direct nitrogen oxide decomposition (DND) is a promising alternative to the selective catalytic reduction (SCR) of nitrogen oxides for emissions control, as it eliminates the need to inject reductants such as urea/ammonia. The present study investigates the implementation of Rh-supported metal oxides for the DND reaction. Rh supported on each of PrOX, TiO2, Al2O3, and CeO2 were characterized, and we found that initially the catalytic activity on Rh/PrOX and Rh/TiO2 was very high, though it deactivated over time due to strong poisoning by adsorbed oxygen. This deactivation by oxygen poisoning was verified through in-situ DRIFTS, XPS, NEXAFS, O2-TPD measurements and density functional theory (DFT) calculations, respectively. This catalytic deactivation was positively regenerated by reductive treatments with CO or H2. This study discovers the mechanism of DND deactivation and regeneration over Rh-supported metal oxides, which will provide significant insight into further development of DND.

Bone powder decorated TiO2 and ZnO nanoparticles: The first investigation of NOx degradation by solar light and visible light-driven photocatalyst

This study performed the transformation of food waste and resin into the valuable photocatalyst which was applied in the NOx decomposition. Bone waste was used as the agricultural waste because of its high CaCO3 compositions. In this study, heterojunction composites were synthesized by calcination ZnO and TiO2 with chicken bone and pork bone (ZnO@Pb, ZnO@Cb, TiO2@Pb and TiO2@Cb). The degradation of NOx can be obtained from 63.30% to 81% under solar light irradiation from the concentration of NOx at 550 ppb. TiO2 decorated with pork bone under visible light gives the best NOx removal efficiency at 70%, with the concentration of NOx at 1800 ppb (1.8 ppm). Furthermore, the trapping experiments confirm that h+ and e− have an impact on the degradation of NOx. The addition of bone waste also shortened the band gap of TiO2/ZnO from 0.649 to 1.266 eV with the microcube formation. This study provides important information on cost-less catalysts for degrading nitrogen oxide (NOx) under solar light and visible light.

Catalytic Direct Decomposition of NOx Using Non-Noble Metal Catalysts

Nitrogen oxides (NOx) gases, such as nitrous oxide (N2O), nitrogen oxide (NO), and nitrogen dioxide (NO2), are considered the most hazardous exhausts exhaled by industries and stationary and non-stationary application engines. Investigation of catalytic decomposition of NO has been carried out on copper ion exchanged with different bases, such as COK12, Nb2O5, Y-zeolite, and ZSM5. The catalytic decomposition of NO is widely accepted as an excellent method for the abatement of NO. However, the catalyst that achieves the highest reactivity in terms of NO decomposition is still a matter of research. The present paper aims to extend the research on the reactivity of non-noble metal-based catalysts using the direct decomposition method to remove NO from diesel engine exhaust. The reactivity of catalysts was observed in a quartz fixed bed reactor of 10 mm diameter placed in a furnace maintained at a temperature of 200 °C to 600 °C. The flow of NO was controlled by a mass flow controller, and the gas chromatography technique was used to observe the reactivity of the catalysts. Analysis showed that adding Cu to COK12, Nb2O5, Y-zeolite, and ZSM5 supports resulted in a rise in NO decomposition compared to stand-alone supports. Further experimental trials on the performance of Cu-ZSM5 at varying flow rates of NO showed that the NO decomposition activity of the catalyst was higher at lower flow rates of NO.

Numerical modeling of the co-firing process of an in situ steam-torrefied biomass with coal in a 230 MW industrial-scale boiler

This paper presents the CFD modeling results of the torrefied maize straw co-firing with sub-bituminous coal in various mass ratios in the industrial scale boiler, to recognize possible application issues of the coal substitution with upgraded biomass. The steam torrefaction of biomass took place in a pilot in a counter-flow torrefaction reactor fed with superheated steam from the OP-230 (Rafako, Poland) boiler. Using a TGA, it was possible to analyze the combustion indexes and synergy effects after burning the torrefied biomass-coal mixtures. Additionally, a kinetic model of pyrolysis devolatilization was established and used in the modeling along with Ansys Fluent kinetics of the coal and gas-phase combustion models. Due to the numerical modeling, it was possible to determine the temperature distribution in the boiler's furnace chamber, the heat flux densities, the simulated distribution of carbon monoxides and carbon dioxide concentration, and the decomposition of nitrogen oxides resulting from co-combustion. Steam torrefied biomass indicates higher combustion activity compared to coal, ignites easier, and burns more intensely with better combustion stability. A synergistic effect between the coal-torrefied blend was observed. According to numerical analysis, it was found that with the increase of the share of torrefaction in the fuel mixture, the share of unburned fuel in fly ash increases. Additionally, an increased share of the torrefied biomass in the fuel blend from 30% to 40% results in a slight increase in the molar NO concentration in the furnace chamber. The authors strongly recommend the continuation of work on further investigation of the co-firing of the coal with torrefied biomass in the pre-mixed blends injected through all burners.

Self-Cleaning Cement-Based Building Materials

The modern rhythm of human life leads to well-known problems, which are air, water and soil pollution and climate warming. An increase in the power of industries and vehicles leads not only to atmospheric pollution by-products of incomplete fuel combustion but also to various microscopic particles that form aerosols, which carry an obvious danger to human health and also pollute the buildings’ facades. An environmentally friendly building material with a hybrid method “Nano-titania gradient” was developed. This method consists of forming a gradient of n-TiO2 particles concentration in the composite since the physical properties of the composite are always inextricably linked to the geometry. To increase the efficiency of the photocatalytic process, a method of surface sensitization of titanium dioxide with the use of graphene oxide was proposed, which contributed to an increase in the overall photosensitivity. Thus, the decomposition of nitrogen oxide by volume with the modified surface increased by 27% in comparison with the classic titanium dioxide, and the decomposition of volatile organic substances increased by 32%. It was found that for the facade plate made with surface-sensitized TiO2, the process of self-cleaning is completed after 3 h after the irradiation start. The modern rhythm of human life leads to well-known problems, which are air, water and soil pollution and climate warming. Using the theory of percolation, the concentration range of the photocatalyst content was calculated. To facilitate the material, waste cellulose was introduced. To increase the efficiency of the photocatalytic process, a method of surface sensitization of titanium dioxide (SS TiO2) with the use of graphene oxide was proposed. The analysis of the experimental-statistical models of the compressive strength shows that the optimum content of TiO2 was in the range from 0.8 to 1.1%, and cellulose from 0.4 to 0.8%, the optimum content of SS TiO2 was in the range from 0.7 to 1.1%, and cellulose from 0.4 to 0.8%. Analysis of the experimental and statistical model of the bending strength shows that the optimal content of TiO2 and SS TiO2 was in the range of 0.6 to 1.0%, and cellulose from 0.4 to 0.8%. When studying the structure of composites, it was found that titanium dioxide was sorbed on the surface of swollen cellulose fibers and remained there after the process of cement hydration. The effectiveness of the method of surface sensitization of titanium dioxide by combining it with graphene oxide was shown. Thus, the decomposition of nitrogen oxide by volume with the modified surface increased by 27% in comparison with the classic titanium dioxide, and the decomposition of volatile organic substances increased by 32%. It was found that for the facade plate made with surface-sensitized TiO2, the process of self-cleaning was completed after 3 h after the irradiation start.

Tin dioxide nanomaterial-based photocatalysts for nitrogen oxide oxidation: a review.

Semiconducting SnO2 photocatalyst nanomaterials are extensively used in energy and environmental research because of their outstanding physical and chemical properties. In recent years, nitrogen oxide (NOx) pollutants have received particular attention from the scientific community. The photocatalytic NOx oxidation will be an important contribution to mitigate climate change in the future. Existing review papers mainly focus on applying SnO2 materials for photocatalytic oxidation of pollutants in the water, while studies on the decomposition of gas pollutants are still being developed. In addition, previous studies have shown that the photocatalytic activity regarding NOx decomposition of SnO2 and other materials depends on many factors, such as physical structure and band energies, surface and defect states, and morphology. Recent studies have been focused on the modification of properties of SnO2 to increase the photocatalytic efficiency of SnO2, including bandgap engineering, defect regulation, surface engineering, heterojunction construction, and using co-catalysts, which will be thoroughly highlighted in this review.

Dioxygen Activation Kinetics over Distinct Cu Site Types in Cu-Chabazite Zeolites

Cu-exchanged zeolites activate dioxygen to form active sites for partial methane oxidation (PMO), nitrogen oxide decomposition, and carbon monoxide oxidation. Apparent rates of O2 activation depend both on the intrinsic kinetics of distinct Cu site types and the distributions of such sites within a given zeolite, which depend on the density and arrangement of the framework Al atoms. Here, we use hydrothermal synthesis methods to control the arrangement of framework Al sites in chabazite (CHA) zeolites and, in turn, the distinct Cu site types formed. Time-resolved in situ resonance Raman spectroscopy reveals the kinetics of O2 adsorption and activation within these well-defined Cu-CHA materials and the concomitant structural evolution of copper-oxygen (CuxOy) complexes, which are interpreted alongside Cu(I) oxidation kinetics extracted from in situ X-ray absorption spectroscopy (XAS). Raman spectra of several plausible CuxOy species simulated using density functional theory suggest that experimental spectra (λex = 532 nm) capture the formation of mono(μ-oxo)dicopper species (ZCuOCuZ). Transient experiments show that the timescales required to form CuxOy structures that no longer change in Ra-man spectra correspond to the durations of oxidative treatments that maximize CH3OH yields in stoichiometric PMO cycles (approximately 2 h). Yet, these periods extend well beyond the timescales for the complete conversion of the initial Cu(I) intermediates to their Cu(II) states (<0.3 h, reflected in XANES spectra), which demonstrates that CuxOy complexes continue to evolve structurally following rapid oxidation. The dependence of ZCuOCuZ formation rates on O2 pressure, H2O pressure, and temperature are consistent with a mechanism in which ZCuOH reduce to form ZCu+ sites that bind molecular oxygen and form ZCu-O2 intermediates. Subsequent reaction with proximate ZCu+ form bridging peroxo dicopper complexes that cleave O-O bonds to form ZCuOCuZ in steps facilitated by water. These data and interpretations provide evidence for the chemical processes that link rapid and kinetically irrelevant Cu oxidation steps (frequently probed by XAS and UV-Vis spectroscopy) to the relatively slow genesis of reactive Cu complexes that form CH3OH during PMO. In doing so, we reveal previously unrec-ognized complexities in the processes by which Cu ions in zeolites activate O2 to form active CuxOy complexes, which under-score the insight afforded by judicious combinations of experimental and theoretical techniques.

Integration of hydrogen production and greenhouse gas treatment by utilizing nitrogen oxide as sweep gas in a solid oxide electrolysis cell

Solid oxide electrolysis cells (SOECs) for hydrogen production are generally operated at a thermoneutral voltage, a voltage at which the cell does not generate or require additional heat. When an SOEC is operated above the thermoneutral voltage, it consumes more electrical energy. However, operating below the thermoneutral voltage cools the cell and results in a temperature gradient within the electrode because of the endothermic reaction. To prevent these phenomena, an SOEC requires additional heat input to maintain a constant temperature. Recently, nitrous oxide has become a global concern because of its high global-warming potential. In this study, we propose the use of nitrogen oxide instead of air or pure oxygen as the sweep gas for SOEC operation, integrating the hydrogen production and greenhouse gas treatment. This study investigated the influence of different types of sweep gas on the heat demand of water electrolysis. To examine this SOEC system, we conducted a simulation study, and the effects of operating conditions and cell geometrical parameters on the system performance were analyzed in detail. With the heat released from the decomposition of nitrogen oxide, operation of the SOEC below the thermoneutral voltage and a higher hydrogen production efficiency are achieved.

The issue of improving the efficiency of nitrogen oxide neutralization systems in diesel internal combustion engines

The most effective method of reducing nitrogen oxides in diesel exhaust gas is selective purification by the SCR-NH3 method. The method uses ammonia released during thermolysis and hydrolysis of a urea solution when it is injected through a nozzle into a neutralizer. This method has a relatively low efficiency of cleaning the exhaust gas from nitrogen oxides. The main factor hindering the achievement of high efficiency of the NOx neutralization system is the insufficiently high temperature during the implementation of this process. The article analyzes various ways to increase the efficiency of the neutralization process and proposes a new method for neutralizing NOx by using urea injection into the cylinders of the internal combustion engine at the expansion stroke in a diesel internal combustion engine. Efficiency can be achieved due to a higher exhaust gas temperature in the cylinder of the internal combustion engine and an increase in the time of the process of thermolysis and hydrolysis of urea. The kinetics of the decomposition of nitrogen oxides, the process of NH3 oxidation, and the calculation of temperature conditions in the cylinder of a diesel internal combustion engine at the exhaust cycle are considered. The experience of neutralization of NOx contained in the flue gases of thermal power plants, where NOx purification takes place at high temperatures without the use of a catalyst, is analyzed. It is shown that the modernization of the SCR-NH3 process, due to the injection of urea at the exhaust stroke in a diesel internal combustion engine, will simplify the existing method of NOx neutralization and at the same time obtain additional advantages for a modern high-speed engine.

Modeling of nitrogen oxides formation in a diesel

Mathematical modeling is an integral part of any scientific and technical research. In the modern world, it is necessary to improve computer technology, calculation methods and programs in order to improve a particular technology. The article offers a mathematical model of formation and decomposition of nitrogen oxides in the engine cylinder and at the time of opening the exhaust valve. The research object was a two-cylinder four-stroke air-cooled diesel engine D-21 running on methyl alcohol and methyl ether of rapeseed oil. These fuels are renewable and differ significantly in their chemical properties from petroleum diesel fuel. Owing to this, their use significantly reduces the emissions of toxic agents such as nitrogen oxides and soot. Theoretical studies have shown high convergence with the data obtained as a result of bench tests.

Dynamic inferential NO x emission prediction model with delay estimation for SCR de-NO x process in coal-fired power plants.

The selective catalytic reduction (SCR) decomposition of nitrogen oxide (de-NOx) process in coal-fired power plants not only displays nonlinearity, large inertia and time variation but also a lag in NOx analysis; hence, it is difficult to obtain an accurate model that can be used to control NH3 injection during changes in the operating state. In this work, a novel dynamic inferential model with delay estimation was proposed for NOx emission prediction. First, k-nearest neighbour mutual information was used to estimate the time delay of the descriptor variables, followed by reconstruction of the phase space of the model data. Second, multi-scale wavelet kernel partial least square was used to improve the prediction ability, and this was followed by verification using benchmark dataset experiments. Finally, the delay time difference method and feedback correction strategy were proposed to deal with the time variation of the SCR de-NOx process. Through the analysis of the experimental field data in the steady state, the variable state and the NOx analyser blowback process, the results proved that this dynamic model has high prediction accuracy during state changes and can realize advance prediction of the NOx emission.

Pregled reakcija azotnih oksida pri sagorevanju fosilnih goriva u atmosferi

This paper discusses the reactions of formation and decomposition of nitrogen oxides during fossil fuel combustion and in the atmosphere. Information about the chemical processes of pollutant formation and decomposition is the basis for the development of theoretical models of pollutant emissions. The information also provides a clearer picture about the primary factors influencing emissions. Nitrogen oxides are pollutants that damage human health, living and nonliving nature, and material property.

CeO2–MxOy (M = Fe, Co, Ni, and Cu)-Based Oxides for Direct NO Decomposition

Direct decomposition of nitrogen oxides (NOx) into N2 and O2 offers the ideal route to catalytic removal of this air pollutant that contributes to photochemical smog and acid rain. Direct decomposi...

Kinetics of the nitrogen oxides reaction with coke carbon in a low-temperature swirl furnace process

The work is devoted to the increase of ecological parameters of organic fuel burning process in power boilers combustion chambers. The technological method of nitrogen oxides decomposition on the surface of carbon particles with the formation of environmentally safe carbon dioxide and molecular nitrogen in low-temperature swirl combustion is considered. A methodology, a mathematical model and a program for calculating the process of a fuel combustion under conditions of multiple circulation, with periodic return of fuel particles to zones with the initial concentration of oxygen, are developed. It is shown that the stepwise supply of the oxidizer to the flare leads to a decrease in the generation of toxic nitrogen oxides, the formation of reducing zones, and the decomposition of the formed nitrogen oxides on the surface of burning coke particles. It has been established that the amount of decomposed nitrogen oxides depends on the surface area of the reacting fuel particles, as well as the time of their stay in the swirl zone of the low-temperature swirl furnace. With the use of calculated results, emissions of nitrogen oxides of reconstructed boilers are reliably predicted.

Direct Decomposition of NOx over TiO2 Supported Transition Metal Oxides at Low Temperatures

TiO2 supported transition metal oxides were investigated for the direct decomposition of nitrogen oxides (NOx) at lower temperatures. The results showed that the catalytic performance strongly depends on the kind of transition metal oxide deposited on the TiO2. Among the various catalysts examined, Mn/TiO2 and Co/TiO2 exhibited relatively high NOx conversion at lower temperatures in the presence of 3 vol % O2. The oxygen in the reaction stream had a positive impact on the NOx decomposition over the Mn/TiO2 catalyst. We have not observed any TiO2 phase conversion from anatase to rutile in the Mn/TiO2 during the NOx decomposition reaction at different temperatures (100–350 °C). NOx decomposition activity was shown to be governed by the surface labile oxygen rather than the gas phase oxygen. The Mn/TiO2 catalyst exhibited a good resistance to 10 vol % H2O and 100 ppm of SO2.

Enhanced photocatalytic NOx decomposition of visible-light responsive F-TiO2/(N,C)-TiO2 by charge transfer between F-TiO2 and (N,C)-TiO2 through their doping levels

Composite type photocatalyst F-TiO2/(N,C)-TiO2 consisted of anatase-type TiO2 with fluorine-doping (F-TiO2) and TiO2 with nitrogen and carbon-doping ((N,C)-TiO2) was prepared by simple physical mixing to exhibit higher visible-light responsive photocatalytic nitrogen oxide (NOx) decomposition activity than those of F-TiO2 and (N,C)-TiO2. Transient absorption measurement clarified that the composite possessed longer carrier lifetime compared to that of each material (F-TiO2 or (N,C)-TiO2), resulting in higher photocatalytic activity. In the composite, photoexcited holes and electrons, which are not in impurity level but in valence and conduction band, respectively, should photocatalytically decompose NOx, judging from the redox potential of O2/O2･− and the band positions of F-TiO2 and (N,C)-TiO2. The mechanism for higher visible-light photocatalytic activity, or longer carrier lifetime can be explained by charge transfer between F-TiO2 and (N,C)-TiO2 through their impurity levels. The charge transfer should make photoexcited carries spatially separated to enhance the photocatalytic activity.

Catalytic Decomposition of Nitrogen Oxides by Bimetallic Catalysts Synthesized by Dielectric Barrier Discharge Plasma Technology

Nitrous oxide (N2O) is a common greenhouse gas and urgent need to be contained. Direct catalytic decomposition of N2O by high activity catalyst into N2 and O2 is a low-cost and harmless method. Bimetallic catalysts show good catalytic activity in many classes of reactions, and plasma technologies, applied to prepare of catalyst, are considered to be a promising method. In our contribution, DBD cold plasma is applied to synthesize Rhodium and Cobalt bimetallic catalysts for catalytic N2O decomposition. The influence of cobalt and rhodium content on N2O decomposition activity shows that the optimal amount of metal is determined as 5wt. % cobalt and 0.5wt. % rhodium loaded on Al2O3. The best working voltage is determined as 18kV. The results indicated that the Rh/Al2O3 catalysts prepared by atmospheric-pressure DBD cold plasma showed smaller size and high dispersion of Rh particles, so that the metal-support interaction and the catalytic activity are enhanced. Atmospheric-pressure DBD cold plasma is proved to be an environmentally friendly and efficient method for preparing high performance Rhodium and Cobalt bimetallic catalysts for catalytic N2O decomposition.

Introduction of low-temperature swirl technology of burning as a way of increase in ecological of low power boilers

Work is devoted to the solution of problems of energy efficiency increase in low power boilers at combustion of solid fuel. The technological method of nitrogen oxides decomposition on a surface of carbon particles with education environmentally friendly carbonic acid and molecular nitrogen is considered during the work of a low-temperature swirl fire chamber. Based on the analysis of physical and chemical processes of a fuel chemically connected energy transition into thermal, using the diffusive and kinetic theory of burning modern approaches the technique, mathematical model and the settlement program for assessment of plant ecological indicators when using a new method are developed. Alternative calculations of furnace process are carried out, quantitative assessment of nitrogen oxides emissions level of the reconstructed boiler is executed. The results of modeling and experimental data have approved that the organization of swirl burning increases overall performance of a fire chamber and considerably reduces emissions of nitrogen oxides.