Gas-phase NO Research Articles

Heterogeneous photochemical aging of soot by NO2 under simulated sunlight

The aging process of soot in the atmosphere can significantly influence its physical and chemical properties. Here, the heterogeneous photochemical aging of soot by NO2 under simulated sunlight was investigated using in situ attenuated total internal reflection infrared spectroscopy. It was observed that simulated sunlight can enhance the aging process of soot by NO2. The photochemistry of soot with NO2 led to the formation of various nitro compounds and oxygen-containing species on the soot surface. The photolysis of the surface nitro compounds resulted in various carbonyl groups and gas-phase NO and HONO. The photochemical aging depended on the NO2 concentrations and combustion conditions of soot production. The soot samples with high content of organic carbon (OC) showed high photochemical reactivity towards NO2. This means that the active species mainly belong to OC components, which mainly consist of various polycyclic aromatic hydrocarbons (PAHs) and some unidentified components.

Measurement of Nitrosamine and Nitramine Formation from NOx Reactions with Amines during Amine-Based Carbon Dioxide Capture for Postcombustion Carbon Sequestration

With years of full-scale experience for precombustion CO(2) capture, amine-based technologies are emerging as the prime contender for postcombustion CO(2) capture. However, concerns for postcombustion applications have focused on the possible contamination of air or drinking water supplies downwind by potentially carcinogenic N-nitrosamines and N-nitramines released following their formation by NO(x) reactions with amines within the capture unit. Analytical methods for N-nitrosamines in drinking waters were adapted to measure specific N-nitrosamines and N-nitramines and total N-nitrosamines in solvent and washwater samples. The high levels of amines, aldehydes, and nitrite in these samples presented a risk for the artifactual formation of N-nitrosamines during sample storage or analysis. Application of a 30-fold molar excess of sulfamic acid to nitrite at pH 2 destroyed nitrite with no significant risk of artifactual nitrosation of amines. Analysis of aqueous morpholine solutions purged with different gas-phase NO and NO(2) concentrations indicated that N-nitrosamine formation generally exceeds N-nitramine formation. The total N-nitrosamine formation rate was at least an order of magnitude higher for the secondary amine piperazine (PZ) than for the primary amines 2-amino-2-methyl-1-propanol (AMP) and monoethanolamine (MEA) and the tertiary amine methyldiethanolamine (MDEA). Analysis of pilot washwater samples indicated a 59 μM total N-nitrosamine concentration for a system operated with a 25% AMP/15% PZ solvent, but only 0.73 μM for a 35% MEA solvent. Unfortunately, a greater fraction of the total N-nitrosamine signal was uncharacterized for the MEA-associated washwater. At a 0.73 μM total N-nitrosamine concentration, a ~25000-fold reduction in concentration is needed between washwater units and downwind drinking water supplies to meet proposed permit limits.

Local ammonia storage and ammonia inhibition in a monolithic copper-beta zeolite SCR catalyst

Selective catalytic reduction of NO with NH3 was studied on a Cu-beta zeolite catalyst, with specific focus on the distributed NH3 capacity utilization and inhibition. In addition, several other relevant catalyst parameter distributions were quantified including the SCR zone, or catalyst region where SCR occurs, and NO and NH3 oxidation. We show that the full NH3 capacity (100% coverage) is used within the SCR zone for a range of temperatures. By corollary, unused NH3 capacity exists downstream of the SCR zone. Consequently, the unused capacity relative to the total capacity is indicative of the portion of the catalyst unused for SCR. Dynamic NH3 inhibition distributions, which create local transient conversion inflections, are measured. Dynamic inhibition is observed where the gas phase NH3 and NO concentrations are high, driving rapid NH3 coverage buildup and SCR. Accordingly, we observe dynamic inhibition at low temperatures and in hydrothermally aged states, but predict its existence very near the catalyst front in higher conversion conditions where we did not specifically monitor its impact. While this paper addresses some general distributed SCR performance parameters including Oxidation and SCR zone, our major new contributions are associated with the NH3 capacity saturation within the SCR zone and dynamic inhibition distributions and the associated observations. These new insights are relevant to developing accurate models, designs and control strategies for automotive SCR catalyst applications.

Desferrioxamine inhibits protein tyrosine nitration: Mechanisms and implications

Tissues are exposed to exogenous and endogenous nitrogen dioxide (NO2), which is the terminal agent in protein tyrosine nitration. Besides iron chelation, the hydroxamic acid (HA) desferrioxamine (DFO) shows multiple functionalities including nitration inhibition. To investigate mechanisms whereby DFO affects 3-nitrotyrosine (3-NT) formation, we utilized gas-phase NO2 exposures, to limit introduction of other reactive species, and a lung surface model wherein red cell membranes (RCM) were immobilized under a defined aqueous film. When RCM were exposed to NO2 covered by +/– DFO: (i) DFO inhibited 3-NT formation more effectively than other HA and non-HA chelators; (ii) 3-NT inhibition occurred at very low[DFO] for prolonged times; and (iii) 3-NT formation was iron independent but inhibition required DFO present. DFO poorly reacted with NO2 compared to ascorbate, assessed via NO2 reactive absorption and aqueous-phase oxidation rates, yet limited 3-NT formation at far lower concentrations. DFO also inhibited nitration under aqueous bulk-phase conditions, and inhibited 3-NT generated by active myeloperoxidase “bound” to RCM. Per the above and kinetic analyses suggesting preferential DFO versus NO2 reaction within membranes, we conclude that DFO inhibits 3-NT formation predominantly by facile repair of the tyrosyl radical intermediate, which prevents NO2 addition, and thus nitration, and potentially influences biochemical functionalities.

Surface-Catalyzed Chlorine and Nitrogen Activation: Mechanisms for the Heterogeneous Formation of ClNO, NO, NO2, HONO, and N2O from HNO3 and HCl on Aluminum Oxide Particle Surfaces

It is well-known that chlorine active species (e.g., Cl(2), ClONO(2), ClONO) can form from heterogeneous reactions between nitrogen oxides and hydrogen chloride on aerosol particle surfaces in the stratosphere. However, less is known about these reactions in the troposphere. In this study, a potential new heterogeneous pathway involving reaction of gaseous HCl and HNO(3) on aluminum oxide particle surfaces, a proxy for mineral dust in the troposphere, is proposed. We combine transmission Fourier transform infrared spectroscopy with X-ray photoelectron spectroscopy to investigate changes in the composition of both gas-phase and surface-bound species during the reaction under different environmental conditions of relative humidity and simulated solar radiation. Exposure of surface nitrate-coated aluminum oxide particles, from prereaction with nitric acid, to gaseous HCl yields several gas-phase products, including ClNO, NO(2), and HNO(3), under dry (RH < 1%) conditions. Under humid more conditions (RH > 20%), NO and N(2)O are the only gas products observed. The experimental data suggest that, in the presence of adsorbed water, ClNO is hydrolyzed on the particle surface to yield NO and NO(2), potentially via a HONO intermediate. NO(2) undergoes further hydrolysis via a surface-mediated process, resulting in N(2)O as an additional nitrogen-containing product. In the presence of broad-band irradiation (λ > 300 nm) gas-phase products can undergo photochemistry, e.g., ClNO photodissociates to NO and chlorine atoms. The gas-phase product distribution also depends on particle mineralogy (Al(2)O(3) vs CaCO(3)) and the presence of other coadsorbed gases (e.g., NH(3)). These newly identified reaction pathways discussed here involve continuous production of active ozone-depleting chlorine and nitrogen species from stable sinks such as gas-phase HCl and HNO(3) as a result of heterogeneous surface reactions. Given that aluminosilicates represent a major fraction of mineral dust aerosol, aluminum oxide can be used as a model system to begin to understand various aspects of possible reactions on mineral dust aerosol surfaces.

Production of Gas Phase NO2 and Halogens from the Photochemical Oxidation of Aqueous Mixtures of Sea Salt and Nitrate Ions at Room Temperature

Nitrate and halide ions coexist in a number of environmental systems, including sea salt particles, the Arctic snowpack, and alkaline dry lakes. However, little is known about potential synergisms between halide and nitrate ions. The effect of sea salt on NO(3)(-) photochemistry at 311 nm was investigated at 298 K using thin films of deliquesced NaNO(3)-synthetic sea salt mixtures. Gas phase NO(2), NO, and halogen products were measured as a function of photolysis time using NO(y) chemiluminescence and atmospheric pressure ionization mass spectrometry (API-MS). The production of NO(2) increases with the halide-to-nitrate ratio, and is similar to that for mixtures of NaCl with NaNO(3). Gas phase halogen production also increased with the halide-to-nitrate ratio, consistent with NO(3)(-) photolysis yielding OH which oxidizes halide ions in the film. Yields of gas phase halogens and NO were strongly dependent on the acidity of the solution, while that of NO(2) was not. An additional halogen formation mechanism in the dark involving molecular HNO(3) is proposed that may be important in other systems such as reactions on surfaces. These studies show that the yield of Br(2) relative to NO(2) during photolysis of halide-nitrate mixtures could be as high as 35% under some atmospheric conditions.

Selective catalytic reduction of NOx with methanol over supported silver catalysts

Methanol is a potential renewable fuel for the transport sector and is thus interesting to study as reducing agent for NOx in hydrocarbon assisted selective catalytic reduction (HC-SCR). The effect of catalyst composition on the lean NOx reduction during methanol-SCR conditions was investigated. In particular silver supported on alumina and ZSM-5 were in focus and parameters that can improve the NOx reduction performance, i.e. the C/N molar ratio and the addition of hydrogen, were specifically studied. Five catalysts were prepared (H-ZSM-5, Ag/H-ZSM-5, Pd/Ag/H-ZSM-5, γ-Al2O3 and Ag-Al2O3) and compared in flow reactor experiments. The Ag-Al2O3 (2wt% Ag, sol–gel) sample was found to give higher NOx reduction compared to the other tested samples, where important factors are suggested to be the support material, the preparation method and the Ag loading. The NOx reduction over Ag-Al2O3 with methanol is proposed to proceed by adsorbed nitrates or nitrites (or gas phase NO2) reacting with adsorbed acetate or formaldehyde like species forming adsorbed RNO2 or RONO, with subsequent conversion into NCO, CN, RNH2 or NH3, with final desorption of N2 and COx (or HCHO). The addition of hydrogen and an increase of the supplied methanol concentration resulted in an increased NOx reduction mainly over the Ag-Al2O3 sample, where the addition of hydrogen also extended the active temperature interval towards lower temperatures. Another effect of the addition of hydrogen was formation of more oxidized carbon containing reaction products. The Ag-Al2O3 catalyst prepared by the sol–gel method, including freeze-drying of the formed gel, is concluded to be the most promising candidate of the tested catalysts for methanol-SCR.

Pathways for N2 and N2O Formation during the Reduction of NOx over Pt–Ba/Al2O3 LNT Catalysts Investigated by Labeling Isotopic Experiments

Mechanistic aspects involved in the formation of N2 and of N2O during the reduction of gas-phase NO and of NOx stored over a model PtBa/Al2O3 NSR catalyst are investigated using unlabeled ammonia and labeled NO. The reduction of the stored NOx species (labeled nitrites and nitrates) with NH3 leads to the selective formation of N2 as a major product and of small amounts of nitrous oxide. Based on the nitrogen isotopic distribution, it appears that N2 formation occurs primarily through the statistical coupling of N-atoms formed by dissociation of NOx- and NH3-related surface intermediates, although an SCR-pathway (involving the coupling of NH3- and NO-derived ad-species) is also likely to occur. It appears as well that the formation of nitrous oxide involves either the coupling of two adsorbed NO molecules or the recombination of an adsorbed NO molecule with an adsorbed NHx fragment.

17O excess transfer during the NO2 + O3 → NO3 + O2 reaction

The ozone molecule possesses a unique and distinctive (17)O excess (Δ(17)O), which can be transferred to some of the atmospheric molecules via oxidation. This isotopic signal can be used to trace oxidation reactions in the atmosphere. However, such an approach depends on a robust and quantitative understanding of the oxygen transfer mechanism, which is currently lacking for the gas-phase NO(2) + O(3) reaction, an important step in the nocturnal production of atmospheric nitrate. In the present study, the transfer of Δ(17)O from ozone to nitrate radical (NO(3)) during the gas-phase NO(2) + O(3) → NO(3) + O(2) reaction was investigated in a series of laboratory experiments. The isotopic composition (δ(17)O, δ(18)O) of the bulk ozone and the oxygen gas produced in the reaction was determined via isotope ratio mass spectrometry. The Δ(17)O transfer function for the NO(2) + O(3) reaction was determined to be: Δ(17)O(O(3)∗) = (1.23 ± 0.19) × Δ(17)O(O(3))(bulk) + (9.02 ± 0.99). The intramolecular oxygen isotope distribution of ozone was evaluated and results suggest that the excess enrichment resides predominantly on the terminal oxygen atoms of ozone. The results obtained in this study will be useful in the interpretation of high Δ(17)O values measured for atmospheric nitrate, thus leading to a better understanding of the natural cycling of atmospheric reactive nitrogen.

Enhancement mechanism of SO2 removal with calcium hydroxide in the presence of NO2

The enhancement mechanism of SO2 removal by the presence of NO2 under low temperature and humid conditions was studied in a fixed bed reactor system. The presence of NO2 in the flue gas can enhance SO2 removal. The interaction between SO2 and NO2 in gas phase could not explain the effect of NO2 on SO2 removal under low-temperature and humid conditions. When Ca(NO3)2 and Ca(NO2)2 as additive were added on the surface of sorbent, the desulfurization activity of sorbent decreased. However, the sorbent pretreated by NO2 for a moment has higher SO2 removal. The oxidization of SO32− to SO42− and the evolution of sorbent surface structure in the presence of NO2 can explain the enhancement of SO2 removal by the presence of NO2. HSO3− and SO3− reacted with NO2 to form sulfate, which can accelerate the hydrolysis of SO2. The reaction between NO2 and Ca(OH)2 can make the unreacted sorbet under the SO2 removal product exposed to the reactant gas.

Kinetic study of NO reduction on carbon-supported chromium catalysts

Direct reduction of NO on carbon supported chromium catalyst and in the presence of reducing agent, such as C3H6 and CO, has been studied. For the direct NO reduction on the catalyst, a kinetic study has been carried out considering that adsorption of NO takes place on an activated chromium site. This activated chromium site, an oxygen deficient chromium catalysts, is generated by the reaction between a chromium site and an unstable carbon site, obtained by decomposition of carbon–oxygen complexes. The following step was the dissociative chemisorption of adsorbed NO by a neighboring carbon site. The rate determining step for the direct NO reduction is the formation of CO2, associated to the chromium catalyst regeneration. In the presence of a reducing agent, the proposed mechanism considers the chemisorption of C3H6 or CO on the chromium site, followed by the activation (reduction) of this site to obtain an oxygen-deficient species, which interacts with NO in gas phase, when propylene is used as reducing agent. The presence of CO favors other reaction pathway for the regeneration of the chromium catalyst, increasing the activity. Both models represent reasonably well the experimental data. XPS and thermodynamic results support the validity of the models proposed.

Modelled and measured concentrations of peroxy radicals and nitrate radical in the U.S. Gulf Coast region during TexAQS 2006

Measurements of total peroxy radicals (HO2 + RO2) and nitrate radical (NO3) were made on the NOAA research vessel R/V Brown along the U.S. Gulf Coast during the TexAQS 2006 field campaign. The measurements were modelled using a constrained box-model based upon the Master Chemical Mechanism (MCM). The agreement between modelled and measured HO2 + RO2 was typically within ∼40% and, in the unpolluted regions, within 30%. The analysis of the model results suggests that the MCM might underestimate the concentrations of some acyl peroxy radicals and other small peroxy radicals. The model underestimated the measurements of NO3 by 60–70%, possibly because of rapid heterogeneous uptake of N2O5. The MCM model results were used to estimate the composition of the peroxy radical pool and to quantify the role of DMS, isoprene and alkenes in the formation of RO2 in the different regions. The measurements of HO2 + RO2 and NO3 were also used to calculate the gas-phase budget of NO3 and quantify the importance of organic peroxy radicals as NO3 sinks. RO2 accounted, on average, for 12–28% of the total gas-phase NO3 losses in the unpolluted regions and for 1–2% of the total gas-phase NO3 losses in the polluted regions.

UVA/Vis-induced nitrous acid formation on polyphenolic films exposed to gaseous NO2

Photochemical processes on ground and airborne surfaces have been suspected to lead to production of HONO in the sunlit lower troposphere, e.g. upon light activation of humic acids followed by reaction with adsorbed NO(2). Here, we used tannic and gentisic acids as proxies for atmospheric polyphenolic compounds to obtain further insights into the photoenhanced NO(2) conversion to HONO, which is a significant tropospheric hydroxyl radical (OH) source. The coated wall flow tube technique was used in combination with online detection of gas-phase HONO and NO(x) under different irradiation conditions. Photoenhanced HONO formation rates of 0.1 to 2 ppbv s(-1) were measured upon NO(2) (0-400 ppbv) uptake on tannic and gentisic acid coatings under irradiation with UV light. The data allow identification of three pathways of light-induced HONO formation: (I) photolysis of a nitroaromatic intermediate formed by a non-photochemical process in the dark, with a photolysis frequency of 10(4) s(-1) at 2 × 10(20) photons m(-2) photon flux; (II) direct photo-oxidation, presumably through electron or hydrogen transfer of the excited substrate; and (III) sensitized electron or hydrogen transfer as suggested before but also demonstrated for visible irradiation here. Aging of tannic acid under oxygen in the dark led to products which promoted light-induced HONO formation in the visible.

A theoretical investigation of gas phase NO 3 initiated nitration of p-cresol

The reaction mechanisms for nitration of p-cresol (4-methylphenol) initiated by the NO 3 radical are investigated theoretically. We have considered two reaction mechanisms: addition-elimination and hydrogen abstraction. Density functional theory methods employing the B3LYP and BB1K exchange-correlation functionals combined with the basis set 6-311+G(d,p) were employed for the geometry optimization of the stationary points along the reaction path. The energies have been refined using the coupled cluster singles and doubles method including a perturbative correction due to triples excitations (CCSD(T)). The barrier heights for these reaction paths are calculated in order to identify the reaction channel. The reaction path where the NO 3 radical is added to the C1 position and the NO 2 radical to the C2 position has the lowest energy barrier for the elimination of the HNO 3 and the transition state is better stabilized than any of the other transition states describing elimination.

On the pH dependence of photo-induced volatilization of nitrogen oxides from frozen solutions containing nitrate

[1] Photochemically induced emissions from the surfaces of snow and ice crystals are known to alter the composition of the troposphere. In particular, photolysis of the nitrate anion in snow and ice has been shown to yield NOx (= NO + NO2) and nitrous acid (HONO) in the gas-phase; photolysis of HONO and NOx alters the oxidative balance of the atmosphere and increases the rate of formation of the greenhouse gas ozone. We report here that the photochemical release of NO2 from irradiated frozen solutions containing nitrate anion is promoted by acidic conditions similar to those found in moderately polluted environments. In unbuffered ice or under basic conditions (pH 9.5), the main gas-phase nitrogen oxide observed was NO2 (>95% relative to odd nitrogen, or NOy). The yield of gas-phase NO2 increases with decreasing pH (measured prior to freezing) in the range from 9.5 to 4.5. At pH 4.5 and lower, acidic nitrogen oxides, mainly HONO and nitric acid (HONO2), are observed in the gas-phase, as well as trace amounts of peroxynitric acid (HO2NO2) and peroxynitrous acid (HO2NO). We propose that the acid-promoted increase in the rate of NO2 release involves formation of HOONO as a volatile intermediate. This acid-promoted pathway for conversion of condensed-phase NO3− to gas-phase NO2 is currently not considered in atmospheric chemistry and aerosol models but may be a significant and overlooked aerosol nitrate volatilization pathway.

TGF-β2reduces nitric oxide synthase mRNA through a ROCK-dependent pathway in airway epithelial cells

Exhaled NO (eNO) is a potential noninvasive biomarker of inflammation in asthma. The significant intersubject variability of eNO within clinically similar patients has contributed to its limited clinical application. Arginase and NO synthase (NOS) utilize the same substrate (l-arginine) and contribute to the fibrotic and inflammatory features of asthma, respectively. Interestingly, TGF-β(2) can increase the expression of arginase, stimulates fibrosis, and is overexpressed in asthma. We hypothesized that TGF-β(2)-enhanced arginase activity would decrease gas phase NO release from lung epithelial cells by limiting l-arginine availability for NOS. Our results show that TGF-β(2) (5 ng/ml) significantly enhances total arginase activity up to two- to threefold in both primary small airway epithelial cells (SAECs) and the A549 cell line. Preincubation with TGF-β(2) prior to cytokine (IL-1β, TNF-α, and IFN-γ, 10 ng/ml each) stimulation decreases gas phase NO release to baseline levels (from 1.66 ± 0.52 to 0.30 ± 0.12 pl·s(-1)·cm(-2) and from 0.27 ± 0.03 pl·s(-1)·cm(-2) to near zero in SAEC and A549 cells, respectively). Addition of arginase inhibitor (N(ω)-hydroxy-nor-l-arginine) or small interfering RNA only partly reverses the reduction. In contrast, Rho-kinase (ROCK) pathway inhibitor (Y-27632) completely recovers the cytokine-induced NO flux in the present of TGF-β(2). Inducible NO synthase (iNOS) mRNA and protein levels change in a similar trend as NO release from the cells. We conclude that TGF-β(2) impacts cytokine-induced NO production in airway epithelial cells by reducing iNOS mRNA and protein levels through a ROCK-dependent pathway.

A DFT study of the NO adsorption on Pd n ( n = 1–4) clusters

We report a density-functional study of some properties of the adsorption process of the NO molecule on small palladium clusters ( n = 1–4). The interaction between NO and the Pd n clusters is studied on various adsorption sites. Both, NO and Pd n geometrical relaxations are taken into account. The significant conformational reconstruction of the metallic cluster upon NO adsorption induces a large decrease of the NO adsorption energy. Nevertheless, the N–O binding energy is strongly weakened when the molecule is adsorbed on the small Pd n clusters due essentially to an electrostatic repulsion between both N and O atoms. The possible dissociation process of NO on Pd 4 cluster is then investigated within two processes: the NO molecule does not dissociate on Pd 4 with process (i) (dissociation of the isolated gas phase NO molecule followed by the adsorption of both nitrogen and oxygen atoms on the cluster). Process (ii) which presents three successive steps (adsorption of the NO molecule, dissociation of the NO molecule adsorbed on Pd 4, adsorption of the O atom on the cluster) is studied in details and we propose a reaction pathway locating transition states and intermediate species. The activation energy for process (ii) is high and the dissociation of the NO molecule on the Pd 4 cluster is thus highly improbable.

NOx storage and reduction on a SrTiCuO3 perovskite catalyst studied by operando DRIFTS

The behaviour of a perovskite SrTiCuO3 as NSR catalyst has been studied by simultaneous DRIFTS and activity measurement. The amount of NOx stored on the perovskite SrTiCuO3 (41μmol/m2 at 300°C) is much higher, when compared on a surface area basis, than on noble metal-containing reference catalysts (0.3–23μmol/m2). The perovskite SrTiCuO3 is able to perform both the NO oxidation to NO2 and the NOx storage, and copper enhances both the NO oxidation and NOx chemisorption capacities of copper-free SrTiO3 perovskite. During NOx chemisorption on SrTiCuO3, the following process have been identified (i) NO chemisorption and nitrite formation or NO oxidation to gas phase NO2 and further chemisorption of NO2 with nitrites or nitrates formation, (ii) nitrite oxidation to nitro and/or nitrates, and (iii) nitro and/or nitrate decomposition with release of NO2. NOx chemisorption at 300°C is more effective than chemisorption at 350°C, while regeneration at 350°C is more effective than regeneration at 300°C because: (i) decreased NOx slip (only for CO regeneration) and (ii) maintains the same chemisorption capacity of the perovskite after regeneration. H2 is a better reductant than CO, and the differences between both reducing gases are much higher at 300°C than at 350°C.

Nitration of particle-associated PAHs and their derivatives (nitro-, oxy-, and hydroxy-PAHs) with NO3 radicals

Theheterogeneousreactionsoftypicalpolycyclicaromatichydrocarbons(PAHs)andtheirderivatives(nitro-, oxy-, and hydroxy-PAHs) adsorbed on azelaic acid particles with NO3 radicals are investigated using a flowtube reactor coupled to a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). The mono-nitro-, di-nitro-, and poly-nitro-products from successive nitro-substitution reactions of PAHs and their derivatives are observed in real time with VUV-ATOFMS. 9-Nitroanthracene, anthraquinone, anthrone, 9,10-dinitroanthracene, 2-, 4-, and 9-nitrophenanthrene,1-nitropyrene,1,3-,1,6-, and1,8-dinitropyrene,7-nitrobenzo[a]anthracene,andbenzo[a]anthracene-7,12-dioneare identifiedbyGC/ MS analysis of the reaction products of PAHs and their derivatives coated on the inner bottom surface of the conical flasks with NO3 radicals. Other oxygenated products are tentatively assigned. 1-Nitropyrene is the only mono-nitrated product detected in the reaction of surface-bound pyrene with gas-phase NO3 radicals. This phenomenon is different from what has been observed in previous studies of the gas-phase pyrene nitration, showing that 2-nitropyrene is the sole nitration product. The experimental results may reveal the discrepancies between the heterogeneous and homogeneous nitrations of pyrene.

A kinetic model of standard selective catalytic reduction of NO by NH3 on single sites

Reduction of NO by NH3 in the presence of O2 may occur on single Fe or Cu atoms or dimers incorporated into the inner walls of zeolite. One of the likely schemes of this reaction implies the formation of N2 and H2O through the reaction of gas-phase NO and adsorbed NH3. The steady-state kinetics corresponding to this scheme was recently analyzed by the author assuming that the reaction runs on single metal atoms. In this work, the author presents a model including two metal atoms. Under the practically important conditions, the kinetics predicted by the one- and two-site models are demonstrated to be similar. In particular, both models allow one to interpret the apparent reaction orders observed experimentally.