NO O2 Research Articles

Modified mesoporous Y zeolite catalyzed nitration of azobenzene using NO2 as the nitro source combined with density functional theory studies

A modified mesoporous Y zeolite (Fe–Y) is developed for high ortho regioselective nitration of azobenzene under a NO2–O2 system.

Environmental Characteristics of Modern Systems of Domestic Use of Fuel. Part 1

The analysis of the environmental component of the processes of natural gas burning in atmospheric burners of domestic gas stoves has been carried out. The computational and experimental studies of the harmful substances formation by combustion of natural gas have been performed. The chemical equilibrium of the NO–O2–NO2 system was considered. The thermodynamic analysis of transformation of the system during a process of natural gas (methane-air mixture) combustion has been tested. Despite an essential (sometimes – by the order(s)) difference between the thermodynamically equilibrium concentration of the nitrogen oxides [NOx]eq and the local, actually measured values [NOx] = [NO] + [NO2], the [NO]eq values could be served as the qualitative indicators of actual values of [NOx] concentrations. In the combustion processes natural gas and other fuels combustion at high temperatures [NO] >> [NO2] for both equilibrium and measured concentrations. By moderate and low local temperatures up to 600 K the equilibrium concentration [NO2]eq → [NO]eq in order of magnitude. Under some compositions of burning mixture the correlation could be set as [NO2] >> [NO], resulting in great danger for the human health. With regard to the formation of particularly toxic NO2 effluents observed in some cases, an influence of the reaction temperature and the composition of the combustible mixture on the possibility of nitrogen dioxide formation in the combustion products have been analyzed. A methodology for the experimental study of the harmful emissions formation has been proposed while the computerized firing rig has been developed for studying the combustion of hydrocarbon gases in burners of household stoves. An influence of the coefficient of primary air excess on the СО, NO, NO2 formation has been revealed and the possibility of appearance the emissions of a high concentration of nitrogen dioxide has been demonstrated.

Nanostructure changes in diesel soot during NO2–O2 oxidation under diesel particulate filter-like conditions toward filter regeneration

Development of the regeneration process on diesel particulate filters requires a better understanding of soot oxidation phenomena, especially its relation to soot nanostructure. Nitrogen dioxide (NO2) is known to play an essential role in passive regeneration by oxidizing soot at low temperatures, especially in the presence of oxygen (O2) in the exhaust. However, change in soot nanostructure due to oxidation by NO2–O2 mixtures has not received much attention. This work focuses on nanostructure evolution during passive regeneration of the diesel particulate filter by oxidation of soot at normal exhaust gas temperatures (300°C–400°C). High-resolution transmission electron microscopy of partially oxidized model carbons (R250, M1300, arc-generated soot) and diesel soot under NO2–O2 mixtures is used to investigate physical changes in nanostructure correlating with the material’s behavior during oxidation. Microscopy reveals the changing nanostructure of model carbons during oxidation while fringe analysis of the images points to the differences in the structural metrics of fringe length and tortuosity of the resultant structures. The variation in oxidation rates highlights the inter-dependence of the material’s reactivity with its structure. NO2 preferentially oxidizes edge-site carbon, promotes surface oxidation by altering the particle’s burning mode with increased overall reactivity of NO2+O2 resulting in inhibition of internal burning, typically observed by O2 at exhaust gas temperatures.

Oxidation-derived maturing process of soot, dependent on O2–NO2 mixtures and temperatures

Oxidizer- and temperature-dependent soot properties were investigated to better understand soot oxidation process. For this work, partially oxidized Printex-U samples as surrogate soot, under three different O2–NO2 mixtures, were analyzed by using the high resolution-transmission electron microscope, Raman microscope and Fourier transform infrared spectroscopy- attenuated total reflectance. The results show that the maturing process was much dependent on NO2 content in the O2–NO2 mixture: with no NO2 added, soot oxidized through the internal-burning out process, whereas with increased NO2 in the mixture, soot tended to oxidize through the external burning process. As the NO2 content increased, the preferential oxidation of less-ordered carbon crystallites decreased and as a result the maturing process was delayed. Internal burning-out process by O2 only was also verified at various temperatures and with actual engine soot such as diesel soot and gasoline direct-injection (GDI) soot by TEM observations. Despite similar internal burning-out process, however, it was shown that oxidation at increased temperature resulted in relatively less-ordered soot, implying that soot maturing process was delayed with temperature. Since soot oxidation rate increased with temperature, the increase in oxidation temperature seems to diminish preference on short-ranged crystallites like more efficient O2–NO2 cases.

Diesel soot oxidation by nitrogen dioxide, oxygen and water under engine exhaust conditions: Kinetics data related to the reaction mechanism

Abstract Experimental studies on diesel soot oxidation under a wide range of conditions relevant for modern diesel engine exhaust and continuously regenerating particle trap were performed. Hence, reactivity tests were carried out in a fixed bed reactor for various temperatures and different concentrations of oxygen, NO2 and water (300–600 °C, 0–10% O2, 0–600 ppm NO2, 0–10% H2O). The soot oxidation rate was determined by measuring the concentration of CO and CO2 product gases. The parametric study shows that the overall oxidation process can be described by three parallel reactions: a direct C–NO2 reaction, a direct C–O2 reaction and a cooperative C–NO2–O2 reaction. C–NO2 and C–NO2–O2 are the main reactions for soot oxidation between 300 and 450 °C. Water vapour acts as a catalyst on the direct C–NO2 reaction. This catalytic effect decreases with the increase of temperature until 450 °C. Above 450 °C, the direct C–O2 reaction contributes to the global soot oxidation rate. Water vapour has also a catalytic effect on the direct C–O2 reaction between 450 °C and 600 °C. Above 600 °C, the direct C–O2 reaction is the only main reaction for soot oxidation. Taking into account the established reaction mechanism, a one-dimensional model of soot oxidation was proposed. The roles of NO2, O2 and H2O were considered and the kinetic constants were obtained. The suggested kinetic model may be useful for simulating the behaviour of a diesel particulate filter system during the regeneration process.

Catalytic effect of platinum on the kinetics of carbon oxidation by NO2 and O2

The effect of a commercial Pt/Al2O3 catalyst on the oxidation by NO2 and O2 of a model soot (carbon black) in conditions close to automotive exhaust gas aftertreatment is investigated. Isothermal oxidations of a physical mixture of carbon black and catalyst in a fixed bed reactor were performed in the temperature range 300–450°C. The experimental results indicate that no significant effect of the Pt catalyst on the direct oxidation of carbon by O2 and NO2 is observed. However, in presence of NO2–O2 mixture, it is found that besides the well established catalytic reoxidation of NO into NO2, Pt also exerts a catalytic effect on the cooperative carbon–NO2–O2 oxidation reaction. An overall mechanism involving the formation of atomic oxygen over Pt sites followed by its transfer to the carbon surface is established. Thus, the presence of Pt catalyst increases the surface concentration of –C(O) complexes which then react with NO2 leading to an enhanced carbon consumption. The resulting kinetic equation allows to model more precisely the catalytic regeneration of soot traps for automotive applications.

Analysis of the structural parameters controlling the temperature window of the process of SCR-NOx by low paraffins over metal-exchanged zeolites

Catalytic activity of H- and FeH-ferrierite (FER) zeolites with iron content from 50 to 4000ppm in NO–NO2 equilibration and SCR of NOx by propane was measured, both in NO2-poor and NO2-rich streams. The activity of FeH-FER in SCR in NO2-poor streams depends strongly on the Fe content; this relationship is valid down to traces of iron, while no such correlation was indicated in NO2-rich streams. This was rationalized by realizing the negligible activity of zeolite protons for NO–NO2 equilibration. Accordingly the SCR activity of H-FER in NO2-poor streams necessitates presence of iron traces. In the NO2–O2–propane mixtures a process in absence of zeolite catalyst initiating propane oxidation and NO2→NO conversion, but without N2 formation, was evidenced at temperatures over 350°C. It is suggested that such a radical process participate in characteristic narrow temperature window for NOx reduction by propane.

Enhancement effects of methanol on the reactivity for methane partial oxidation in the gas phase reaction of CH4–O2–NO2

The partial oxidation of methane in the gas phase reaction of CH4–O2–NO2 was enhanced with the addition of a small amount of methanol; the selectivity of methanol at the same level of CH4 conversion was enhanced in the presence of methanol which showed this effect exclusively in the presence of NO2.

Thermal stability of carbonyl radicals Part I. Straight-chain and branched C4 and C5 acyl radicals

The competition between thermal decomposition (kdis) and O2 addition (kO2) of linear and branched C4 and C5 alkanoyl (R-C(•)O, R=alkyl) radicals has been studied in a photochemical reaction chamber made from stainless steel (v=12 L). RCO radicals were prepared by continuous photolysis of Br2–RC(O)H–O2–NO2–N2 mixtures at wavelengths 420 nm. The products CO and RC(O)O2NO2 were analyzed by long-path IR absorption using an FT-IR spectrometer. Rate constant ratios kdis/kO2 were determined at 317 K for n-butyryl, n-pentanoyl, 3-methylbutyryl, 2-methylpropionyl and 2-methylbutyryl and at 6 temperatures between 293 and 317 K for 2,2-dimethylpropionyl (=pivaloyl, t-butyl-CO) radicals. Total pressures were 1 bar (M=N2+O2). Adopting the literature value of kO2 for acetyl, unimolecular decomposition rate constants kdis were derived from the measured ratios kdis/kO2. kdis at 298 K, 1 bar, M=O2+N2 increases by factors of 35, 54 and 24 for each H atom in CH3CO which is consecutively replaced by a methyl group (corresponding to increasing branching of R). For the unimolecular decomposition of 2,2-dimethylpropionyl radicals, the Arrhenius expression kdis(t-butyl-CO)=6.0×1012 exp(−41.6 kJ mol−1/RT) s−1 (2σ) was derived for the temperature range 293–317 K and a total pressure of 1 bar (M=N2+O2). The results on kdis/kO2 show that even for the thermally most unstable of the carbonyl radicals studied in this work, i.e. 2,2-dimethylpropionyl, only 1.8% decompose rather than add O2 at 298 K and 1 bar in dry air.

The enhancement effects of added methanol on methane-selective oxidation in the gas phase reaction of CH4–O2–NO2

The reactivity of the selective oxidation of methane in the gas phase reaction of CH4–O2–NO2 was enhanced by the addition of a small amount of methanol. The selectivity of methanol produced at the same level of methane conversion was enhanced by adding a small amount of methanol in the feed gas. The enhanced effect of methanol addition was restricted to methane conversion in the presence of NO2. The enhancement effect was obtained more effectively when the ratio of methanol to NO2 was near to 1, at which higher concentration of both methanol and NO2 a significant enhancement was shown. Theoretical calculations concluded as follows: CH3OH + NO2→CH2OH + HNO2 was the predominant step of hydrogen abstraction from methanol. HO2 was then produced by CH2OH + O2→CH2O + HO2. CH4 + HO2→CH3 + H2O2 was the key reaction to enhance the reactivity of methane. HO2 + OH→H2O + O2 brought about an OH radical dissipation reaction to stabilize the produced methanol from the following decomposition reaction: CH3OH + OH→CH2OH + HO2 .

Nitration of nonactivated arenes with a ternary system NO–NO2–O2. Mechanistic implications of the Kyodai-nitration

The ternary mixture NO–NO2–O2 has been found to be more effective than the binary mixture NO2–O2 as a nitrating agent for nonactivated arenes, such as toluene and chlorobenzene; the results may be rationalized in terms of an initial electron transfer mechanism in which nitrogen trioxide, formed from nitrogen monoxide and dioxygen, oxidizes the arene to its radical cation.

Reaction Mechanism of the Photooxidation of the Toluene–NO2–O2–N2 System in the Gas Phase

Abstract Photooxidation of the toluene (34 ppm)–NO2(8–207 ppm)–N2 and/or O2(1 atm) system has been studied in a 67 dm3 reaction chamber. The reaction was initiated by O(3P) atoms formed in the photolysis of NO2. The main products were benzaldehyde, cresols, benzyl nitrate, m-nitrotoluene, 6-nitro-o-cresol, and 2-nitro-p-cresol. Their relative yields were studied as functions of reactant concentrations. The formation mechanisms of the products were proposed on the basis of the reactions of O(3P) and OH radicals with toluene in the presence of NO2 and O2.