FTIR spectroscopic study of the gas-phase reaction of HO2 with H2CO

The reaction of formaldehyde with HO₂ radicals in the presence of O₂ and NO₂ has been studied in a 420 ℓ reaction chamber at 0° C in 533 mbar of synthetic air. Reactants and products were measured by FTIR absorption spectrometry-Additional evidence is presented for the formation of the HOCH₂OO radical as the primary reaction product, by the IR spectroscopic identification of its NO₂ recombination product HOCH₂OONO₂. By computer simulation of the concentration-time profiles of HO₂NO₂, H₂CO and HOCH₂OONO₂, the rate constants (0°C, 533 mbar, M = air) k₁ = (1.1 ± 0.4) × 10^-13 cm³ s^-1 and k_-1 = 20_-10⁺²⁰ s^-i have been derived for the reactions (1, -1) HO₂ + H₂CO ⇌ HOCH₂OO.     

Mass spectrometric in-situ determination of NO2 in gas mixtures by resonance enhanced multiphoton ionisation

One- and two-colour photoionisation spectra for NO₂ have been investigated using a time of flight mass spectrometer as detector to find the most efficient REMPI process for analytical applications. Two different inlet systems have been employed: a pulsed supersonic jet expansion stage and a flow reactor. Selective and sensitive mass spectrometric determinations of free NO₂ have been possible even in the presence of high concentrations of organic nitrates, HNO₃ and other NO₂ precursors. Employing two-colour (1+1′+1) excitation using a concentration of HNO₃≤5·10¹⁴ molecules/cm³ a detection limit of 5·10¹¹ molecules/cm³ has been found for NO₂ whereas in the absence of HNO₃ a detection limit of 5·10¹⁰ molecules/cm³ is reported.     

Optical and morphological characterization of bispyrazole thin films for gas sensing applications

The optical gas recognition capabilities of thin film layer of 4-[bis[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-amino]phenol deposed on quartz substrates were studied. The dynamic gas responses to the following analytes have been investigated as air pollutants (SO₂, NO₂, CO, CH₄ and NH₃). The spin-coated bispyrazole layer appears to have reversible response towards SO₂ and a very low and irreversible response to NO₂. The selectivity of the thin film based on bispyrazole layer with respect to other analytes was also examined and the present data show that the thin sensing layer in the presence of CO, CH₄ and NH₃ in low concentration does not influence its optical properties.     

Products of the gas-phase reactions of aromatic hydrocarbons: Effect of NO2 concentration

The formation yields of selected products of the OH radical-initiated reactions of toluene, o-xylene, and 1,2,3,-trimethylbenzene have been measured in the absence of NO_x and in the presence of varying concentrations of NO and NO₂. The formation yield of o-cresol from toluene increased from 0.123 ± 0.022 in the absence of NO_x to 0.160 ± 0.008 for an average NO₂ concentration of 1.7 × 10¹⁴ molecule cm³. The formation yield of 2,3-butanedione from o-xylene was 0.092 ± 0.013 in the absence of NO_x, and in the presence of NO_x decreased from 0.16 at an average NO₂ concentration of (7–8) × 10¹² molecule cm^?3 to 0.09 at an average NO₂ concentration of ca. 7 × 10¹³ molecule cm^?3. The formation yield of 2,3-butanedione from 1,2,3-trimethylbenzene increased from 0.18 in the absence of NO_x to 0.444 ± 0.053 in the presence of ca. (0.16–3.6) × 10¹³ molecule cm^?3 of NO₂. These product data are consistent with literature kinetic data showing that the hydroxycyclohexadienyl radicals formed by OH radical addition to the aromatic ring react with both O₂ and NO₂ and with the NO₂ reaction rate constants being ca. 10⁵ higher than the O₂ reaction rate constants at room temperature. Under typical tropospheric conditions the reactions of the hydroxycyclohexadienyl radicals with O₂ will dominate over their reactions with NO₂. © 1994 John Wiley & Sons, Inc.     

Investigations into the response of an optical gas sensor based on polymeric LB films

The response of an NO₂ sensing system based on LB films of a polysiloxane with azobenzene chromophoric side-chains has been investigated. Changes in absorbance on exposure to 100 ppm NO₂ have been recorded using UV-visible absorption spectroscopy from which changes in extinction coefficient (Δ k ≈ 0.033 at 500 nm) have been determined. Shallow angle X-ray reflectivity (SAXR) studies indicate a change in layer thickness from 2.10nm in air to 2.31 nm in 10000 ppm NO₂ together with loss of Bragg detail. Changes in real refractive index (Δn ≈ 0.107 over most of the visible region) for films in air and 100 ppm NO₂ have been deduced from reflectance spectra.     

The kinetics and mechanisms of the HO2-NO2 reactions; the significance of peroxynitric acid formation in photochemical smog

Peroxynitric acid has been identified by Fourier transform, infrared, long-path spectroscopy as a product of the UV-irradiated dilute mixtures of HONO, CO, No_x in synthetic air at 24 ± 2°C. The characteristic peaks of this compound are identical to those observed by Niki, in irradiated Cl₂, H₂, NO₂, air mixtures and Hanst, in irradiated Cl₂, CH₂O, NO₂, air mixtures. The concentration of the reactants and products of the HONO, CO, NO_x, air system have been determined as a function of irradiation time. The changes observed were computer simulated using a combination of thirty elementary reactions. The data suggests that both reactions (1) and (2) occur as a result of HO₂-NO₂ interactions in the gas phase: HO₂ + NO₂ å HONO + O₂ (1); HO₂ + NO₂(+M) å HO₂NO₂(+M)(2). The data give the preliminary estimates: k₁/k₂ ≈0.7 ±0.4; k₁/k₃ ≈ 0.043 ± 0.02; k₂/k₃ ≈ 0.058 ± 0.02, where reaction (3) is: HO₂ + NO å HO + NO₂. These data and computer simulations of sunlight-irradiated, NO_x, hydrocarbon, aldehyde-polluted atmospheres suggest that peroxynitric acid may be formed in urban atmospheres at rates which are comparable to those observed for peroxyacetyl nitrate (PAN), and it is concluded that HO₂NO₂ may contribute to the “oxidant” found in these atmopheres.     

A spectroscopic study of the equilibrium NO2 + NO3 + M 2 N2O5 + M and the kinetics of the O3/N2O5/NO3/NO2/ air system

The equilibrium constant, K_eq of the reaction NO₂ + NO₃ + M 2 N₂O₅ + M has been determined for a small range of temperatures around room temperature in air at 740 torr by direct spectroscopical measurements of NO₂, NO₃, and N₂O₅. At 298 K, K_eq was determined as (3.73 ± 0.61) × 10⁻¹¹ cm³ molecule⁻¹. Averaging this and 11 other independent evaluations of K_eq yields K_eq = (3.31 ± 0.82) × 10⁻¹¹ cm³ molecule⁻¹, where the uncertainty is given as one standard deviation. The kinetics of the O₃/NO₂/N₂O₅/NO₃/ air system was studied in a static chamber at room temperature and 740 torr total pressure. Evidence of a unimolecular decay reaction of NO₃, NO₃ → NO + O₂, was found and its rate coefficient was estimated as (1.6 ± 0.7) × 10⁻³ s⁻¹ at 295 ± 2 K.     

Reactions of naphthalene in N2O5?NO3?NO2? air mixtures

The reactions of naphthalene in N₂O₅? NO₃? NO₂? N₂? O₂ reactant mixtures have been investigated over the temperature range 272–297 K at ca. 745 torr total pressure and at 272 K and ca. 65 torr total pressure using long pathlength Fourier transform infrared absorption spectroscopy. 2,3-Dimethyl-2-butene was added to the reactant mixtures at 272 K to rapidly scavenge the NO₃ radicals both initially present in the added N₂O₅ and formed from the thermal decomposition of N₂O₅ during the reactions. The data obtained in the presence and absence of added 2,3-dimethyl-2-butene showed that napthalene undergoes initial reaction with the NO₃ radical to form an NO₃-naphthalene adduct, which either rapidly decomposes back to the reactants (at a rate of ca. 5 × 10⁵ s^?1 at 298 K) or reacts exclusively with NO₂ to form products. When NO₃ radicals, N₂O₅ and NO₂ are in equilibrium, this overall process is kinetically equivalent to reaction of naphthalene with N₂O₅, and previous kinetic and product studies have indeed assumed the reactions of naphthalene and alkyl-substituted naphthalenes in N₂O₅? NO₃? NO₂? air mixtures to be with N₂O₅, and not with NO₃ radicals.     

Synthesis and characterization of three Cd(II) Schiff-base macrocyclic N3O2 complexes

Three polyamine ligands of N1-(2-nitrobenzyl)-N1-(2-aminoethyl)ethane-1,2-diamine (L₁), N1-(2-nitrobenzyl)-N1-(2-aminoethyl)propane-1,3-diamine (L₂) and N1-(2-nitrobenzyl)-N1-(3-aminopropyl)propane-1,3-diamine (L₃) were synthesized and their cyclocondensation with 2-[2-(2-formyl phenoxy)ethoxy]benzaldehyde (L₄) in the presence of various metal(II) ions was examined. These reactions only in the presence of a stoichiometric amount of cadmium(II) nitrate gave the related cadmium(II) macrocyclic Schiff-base complexes. In all the other cases no cyclic complexes have been obtained and metal(II) polyamines were the only products. The complexes have been studied with IR, ¹H NMR, ¹³C NMR, DEPT, COSY, HMQC and microanalysis. The crystal structures of [Cd(NO₃)(L₅)(μ-NO₃)Cd(NO₃)(L₅)]0.5Cd(NO₃)₄ (1) and [CdL₅(NO₃)(CH₃OH)]ClO₄ (2) have been also determined.     

Investigation on the thermal behaviour of Mg(NO3)2·6H2O I. The decomposition behaviour

The decomposition mechanism of Mg(NO₃)₂·6H₂O was studied by means of simultaneous TG, DTG and DTA method combined with EGA technique under conventional and quasi isothermal-quasi isobaric conditions. It has been found that Mg(NO₃)₂·6H₂O melts at 89 °C in a congruent way. The solution formed begins to boil at 147 °C. The water loss process of the salt hydrate and the decomposition process of the Mg(NO₃)₂ always overlap to some extent. Accordingly, Mg(NO₃)₂ of stoichiometric composition cannot be prepared thermally, because the compound always contains some basic salt. The last part of water departs in the vicinity of 270 °C with extreme rapidity. In contrast to expectations the compound decomposes in pure “self-generated” atmosphere at a temperature lower by about 80 °C than in the presence of air which contains a small amount of the gaseous decomposition product.     

Synthesis,characterization and thermal behaviour of Fe4(OH)11NO3·2H2O

A new iron basic salt, Fe₄(OH)₁₁NO₃·2H₂O, has been prepared by partially hydrolyzing a solution of Fe(NO₃)₃·9H₂O with urea. The X-ray powder diffraction pattern has been indexed within a monoclinic cella=9.99(3) ?,b=9.48(2) ?,c=3.074(3) ? andβ=90.57(1)°. Thermal decomposition reactions in still air and nitrogen flow have been studied by DTA and TG analysis, and the intermediate and final products have been characterized by X-ray diffraction and IR spectroscopy. When this material is thermally decomposed in an X-ray high temperature diffraction chamber, pure iron is formed at 900 °C together with Fe(III) and Fe(II) oxides.

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Zusammenfassung Mittels Hydrolyse einer L?sung von Fe(NO)₃)₃·9H₂O mit Karbamid wurde das neue basische Eisensalz Fe₄(OH)₁₁NO₃·2H₂O dargestellt. Aus einem R?ntgenpulververfahren resultierena=9,55(3) ?,b=9,48(2) ?,c=3,074(3) ? undβ=90,57(1)° für eine monozyklische Zelle. Mittels DTA- und TG-Untersuchungen wurden die thermischen Zersetzungsreaktionen an Luft und im Stickstoffflu? untersucht und die Zwischen- und Endprodukte mit r?ntgendiffraktionsverfahren und IR-Spectroskopie charakterisiert. Bei einer thermischen Zersetzung dieses Stoffes in einer Hochtemperatur-r?ntgendiffraktionskammer wird bei 900 °C elementares Eisen zusammen mit Fe(II)- und Fe(III)-oxiden gebildet.

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Резюме Частичным гидролизо м раствора соли Fe(NO₃)₃ · 9H₂O с мочевиной получен а новая основная соль Fe₄(OH)₁₁NO₃ · 2Н₂О, для которой методо м порошкового рентген оструктурного анализа была установ лена моноклинная стр уктура с параметрами ячейкиа=9,55(3) А,b=9,48(2) ?,c=3,074(3) ? иβ=90,57(1)°. Термиче ское разложение соли изучено методом ДТА и ТГ в динамическо й атмосфере воздуха и азота, а образующиеся промеж уточные и конечные продукты ре акции были охарактер изованы рентгенофазовым ана лизом и ИК спектроскопией. ˉПри термическом разложе нии соли в высокотемпературно й рентгено-диффракци онной камере при 900° образует ся чистое железо вмес те с оксидами двух- и трехвалентного желе за.

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The authors are greateful to Dr. R. M. Rojas for his helpful suggestions.     

Catalytic oxidation of 1-hexene with molecular oxygen by iridium nitro complexes

The oxidation of 1-hexene by molecular oxygen catalyzed by iridium(III) complexes, [Ir(CH₃CN)_5−xCl_x(NO₂)]^2−x (x=0, 1, or 2) has been studied in acetonitrile under P(O₂)=1.5 atm and T=100°C. [Ir(CH₃CN)₅(NO₂)](PF₆)₂ oxidizes 1-hexene to 1,2-epoxyhexane. Complex [Ir(CH₃CN)₄Cl(NO₂)]PF₆ oxidizes 1-hexene to 2,3-epoxyhexane only in the presence of [Pd(PhCN)₂(Cl)₂] (an olefin activator). In contrast to the cationic complexes, the neutral complex [Ir(CH₃CN)₄Cl₂(NO₂)] oxidizes 1-hexene to 2-hexanone only in the presence of [Pd(PhCN)₂(Cl)₂].     

Studies on kinetics and mechanism of initial thermal decomposition of nitrocellulose

The thermal decomposition of nitrocellulose (NC) 12.1% N, has been studied with regard to kinetics, mechanism, morphology and the gaseous products thereof, using thermogravimetry (TG), differential thermal analysis (DTA), IR spectroscopy, differential scanning calorimetry (DSC) and hot stage microscopy. The kinetics of the initial stage of thermolysis ofNC in condensed state has been investigated by isothermal high temperature infrared spectroscopy (IR). The decomposition ofNC in KBr matrix in the temperature range of 142–151°C shows rapid decrease in O?NO₂ band intensity, suggesting that the decomposition of NC occurs by the rupture of O?NO₂ bond. The energy of activation for this process has been determined with the help of Avrami-Erofe'ev equation (n=1) and is ≈188.35 kJ·mol^?1. Further, the IR spectra of the decomposition products in the initial stage of thermal decomposition ofNC, indicates the presence of mainly NO₂ gas and aldehyde.     

A smog chamber and modeling study of the gas phase NOx–air photooxidation of toluene and the cresols

An experimental and modeling study of irradiated toluene–NO_x–air, toluene–benzaldehyde–NO_x–air, and cresol–NO_x–air mixtures at part-per-million concentrations has been carried out. These mixtures were irradiated at 303 ± 1 K in a 5800-liter Teflon-lined, evacuable environmental chamber, with temperature, humidity, light intensity, spectral distribution, and the concentrations of O₃, NO, NO₂, toluene, PAN, formaldehyde, benzaldehyde, o-cresol, m-nitrotoluene, and methyl nitrate beingmonitored as a function of time. For the toluene and toluene–benzaldehyde–NO_x–air runs a variety of initial reactant concentrations were investigated. Cresol–NO_x–air runs were observed to be much less reactive in terms of O₃ formation and NO to NO₂ conversion rates than toluene–NO_x–air runs, with the relative reactivity of the cresol isomers being in the order meta » ortho > para. The addition of benzaldehyde to toluene–NO_x–air mixtures decreased the reactivity, in agreement with previous studies. Alternative mechanistic pathways for the NO_x photooxidations of aromaticsystems in general are discussed, and the effects of varying these mechanistic alternatives on the model predictions for the toluene and o-cresol–NO_x–air systems are examined. Fits of the calculations to most of the experimental concentration–time profiles could be obtained to within the experimental uncertainty for two of the mechanistic options considered. In both cases it is assumed that (1) O₂ adds to the OH–toluene adduct ～75% of the time forming, after a further addition of O₂, a C₇ bicyclic peroxy radical, and (2) this C₇ bicyclic peroxy radical reacts with NO ～75% of the time to ultimately form α-dicarbonyls and conjugated γ-dicarbonyls (e.g., methylglyoxal + 2-butene-1,4-dial) and ～25% of the time to form organic nitrates. The major uncertainties in the mechanisms concern (1) the structure of the bicyclicperoxy intermediate, and (2) the γ-dicarbonyl photooxidation mechanism. Good fits to the o-cresol concentration–time profiles in the toluene–NO_x runs are obtained if it is assumed that o7-cresol reacts rapidly with NO₃ radicals. However, it is observed that the model underpredicts nitrotoluene yields by a factor of ～10, but this is in any case a minor product. It is concluded that further experimental work will be required toadequately validate the assumptions incorporated in the aromatic photooxidation mechanisms presented here.     

Role of nitrogen dioxide in the oxidation of diesel soot on promoted mixed catalysts with fluorite and perovskite structures

The oxidation of soot on catalysts with the perovskite and fluorite structures (including platinum-promoted catalysts) in the presence and in the absence of NO₂ was studied using in situ IR spectroscopy and temperature-programmed techniques (TPR, TPD, and TPO). It was found that, as a rule, the temperature of the onset of soot oxidation considerably decreased upon the addition of NO₂ to a flow of O₂/N₂, whereas the amount of oxygen consumed in soot oxidation considerably increased. To explain these facts, we hypothesized that the initiation of soot combustion in the presence of NO₂ was related to the activation of the NO₂ molecule through the formation (at a low temperature) and decomposition (at a high temperature) of nitrate structures on the catalyst. Superequilibrium amounts of NO₂ resulted from the decomposition of nitrate complexes immediately on the catalyst for soot combustion. Based on a comparison between catalyst activities and data obtained by TPR and the TPD of oxygen, a conclusion was drawn that the presence of labile oxygen in the catalyst is a necessary but insufficient condition for the efficient occurrence of a soot oxidation reaction in the presence of NO₂. The introduction of platinum as a constituent of the catalyst increased the amount of labile oxygen and, as a consequence, increased the amount of highly reactive nitrate complexes. As a result, this caused a decrease in the temperature of the onset of soot combustion.     

Experimental investigation of chamber-dependent radical sources

While environmental chamber data have been widely used to generate and validate computer models of the chemistry occurring in polluted atmospheres, the effects of the chambers on the gas-phase chemistry being studied have been poorly characterized. In order to investigate such chamber effects, a series of NO_x—air irradiations, with trace levels of organics present to monitor OH radical concentrations, have been carried out in four different environmental chambers (ranging in volume from ～100 to 40,000 L) at varying temperatures, humidities, pressures, and reaction conditions. In addition, a number of control experiments have been carried out to validate the technique for measuring OH radical levels in these irradiations. The data show that unknown sources of OH radicals are present in all of the chambers studied. The data are consistent with the presence of two distinct radical sources: (1) the photolysis of initially present HONO, whose importance increases with increasing NO₂/NO concentration ratios, but which is a minor contributor to the overall radical flux after 30–60 min of irradiation, and (2) a constant (for these NO_x—air irradiations) radical source which dominates beyond approximately the first 60 min of irradiation. The radical input rates, after the first ∽30–60 min of irradiation, are independent of the NO concentration, increase with increasing temperature, humidity, and NO₂ concentration, are proportional to light intensity, and are dependent on the chamber employed. Although the exact nature of this radical source is still undetermined, results of experiments reported here allow a number of possible mechanisms to be ruled, out, and these are discussed.     

Field Measurement of NO2 and RNO2 by Two-Channel Thermal Dissociation Cavity Ring Down Spectrometer

A two-channel thermal dissociation cavity ring down spectroscopy (CRDS) instrument has been built for in situ, real-time measurement of NO₂ and total RNO₂ (peroxy nitrates and alkyl nitrates) in ambient air, with a NO₂ detection limit of 0.10 ppbv at 1 s. A 6-day long measurement was conducted at urban site of Hefei by using the CRDS instrument with a time resolution of 3 s. A commercial molybdenum converted chemiluminescence (Mo-CL) instrument was also used for comparison. The average RNO₂ concentration in the 6 days was measured to be 1.94 ppbv. The Mo-CL instrument overestimated the NO₂ concentration by a bias of +1.69 ppbv in average, for the reason that it cannot distinguish RNO₂ from NO₂. The relative bias could be over 100% during the afternoon hours when NO₂ was low but RNO₂ was high.     

Kinetics and nitro-products of the gas-phase OH and NO3 radical-initiated reactions of naphthalene-d8, Fluoranthene-d10, and pyrene

The kinetics and nitroarene product yields of the gas-phase reactions of naphthalene-d₈, fluoranthene-d₁₀, and pyrene with OH radicals in the presence of NO_x and in N₂O₅? NO₃? NO₂? air mixtures have been investigated at 296 ± 2 K and atmospheric pressure of air. Using a relative rate method, naphthalene-d₈ was shown to react in N₂O₅? NO₃? NO₂? air mixtures a factor of 1.22 ± 0.10 times faster than did naphthalene, with the 1- and 2-nitronaphthalene-d₇ product yields being similar to those of 1- and 2-nitronaphthalene from naphthalene. From the measured PAH concentrations and the nitroarene product yields, formation yields of 2-, 7-, and 8-nitrofluoranthene-d₉ and 2- and 4-nitropyrene of 0.03, 0.01, 0.003, 0.005, and 0.0006, respectively, were determined from the OH radical-initiated reactions. Effective rate constants for the reactions of fluoranthene-d₁₀ and pyrene with N₂O₅ in N₂O₅? ;NO₃? NO₂? air mixtures of ca. 1.8 × 10^?17 cm³ molecule^?1 s^?1 and ca. 5.6 × 10^?17 cm³ molecule^?1 s^?1, respectively, were derived. Formation yields of 2-nitrofluoranthene-d₉ and 4-nitropyrene of ca. 0.24 and ca. 0.0006, respectively, were estimated for these reaction systems. 2-Nitropyrene was also observed to be formed in these N₂O₅? NO₃? NO₂ reactions, but was found to be a function of the NO₂ concentration and, therefore, would be a negligible product under ambient NO₂ concentrations. These product and kinetic data are consistent with ambient air measurements of the nitroarene concentrations.     

Kinetics and mechanism of the oxidation of carbon by NO2 in the presence of water vapor

The kinetics and mechanism of the oxidation of carbon by NO₂ in absence and presence of water vapor were studied in a fixed bed reactor. The rate of carbon oxidation by NO₂ is enhanced in the presence of water vapor in the range of temperature 300–400°C. The benefit effect of water is attributed to the intermediate formation of traces of nitric and nitrous acids, which enhance the rate of the carbon oxidation without modifying the global mechanism reaction. Therefore, water acts as a catalyst for the carbon oxidation by NO₂. A kinetic mechanism derived from this parametric study shows a decrease in the activation energy of carbon oxidation by NO₂ in the presence of water vapor. This result is in agreement with the experimental observation. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 236–244, 2009     

DEEP CATALYTIC OXIDATION OF BENZENE IN THE PRESENCE OF SEVERAL VOLATILE ORGANIC COMPOUNDS ON METAL OXIDES AND Pt/Al2O3 CATALYSTS

Oxidation of benzene into CO₂ in air has been studied in the temperature range of 300-673 K on supported metal oxides and on 0.7% Pt/Al₂O₃, in the absence and in the presence of several Volatile Organic Compounds (VOCs). On the metal oxides, the deep oxidation of benzene is strongly inhibited in presence of VOCs and O-containing VOCs lead to more toxic VOCs (i.e: acetaldehyde).