Pressure dependence of secondary ion emission from selected 3d, 4d, and 5d transition metals under N2O, NO, and NO2

The reactant gas pressure dependence of secondary ion emission from surfaces of polycrystalline Cr, Fe, Co, Mo, Rh, W, Re, and Ir under the action of N₂O, NO and NO₂ was observed by means of moderate dynamic SIMS. The mass spectra for constant reactant gas pressure indicate the existence of two different groups of transition metals showing either dissociative or partial molecular adsorption behavior. This is confirmed at least above some suitable reactant gas pressure. Besides some special details (Fe/NO; Co/NO) several of the relative secondary ion intensities vs. reactant gas pressure exhibit similar curvature as for O₂, thus indicating the NO_x gases to be modified sources of oxygen. At higher pressures molecular secondary ions with and without metal atoms come to be appreciable.     

Pressure dependence of secondary ion emission from selected 3d, 4d, and 5d transition metals under N2O, NO, and NO2

The reactant gas pressure dependence of secondary ion emission from surfaces of polycrystalline Cr, Fe, Co, Mo, Rh, W, Re, and Ir under the action of N₂O, NO and NO₂ was observed by means of moderate dynamic SIMS. The mass spectra for constant reactant gas pressure indicate the existence of two different groups of transition metals showing either dissociative or partial molecular adsorption behavior. This is confirmed at least above some suitable reactant gas pressure. Besides some special details (Fe/NO; Co/NO) several of the relative secondary ion intensities vs. reactant gas pressure exhibit similar curvature as for O₂, thus indicating the NO_x gases to be modified sources of oxygen. At higher pressures molecular secondary ions with and without metal atoms come to be appreciable. Received: 28 May 1997 / Revised: 2 February 1998 / Accepted: 4 February 1998     

The electronic structure of N4O62+ and the bonding interaction of NO+ and NO3−

The results are reported of an MO-SCF-CNDO/2 study of the experimental and optimal geometries of the N₄O₆²⁺ion cluster. The calculations are shown to support the stable existence of the N₄O₆²⁺ complex and the suggestion of its discoverers [1] on the role of NO⁺ in the N₂O₄ solutions. The proposed interpretation of the bonding interaction explains why the shortest N β O distances are found with the NO⁺ ions which have their nitrogen atoms displaced out of the NO₃^? plane.     

N2O as an intermediate for the formation of N2 during SCR (NO): stationary and transient conditions

Platinum-based catalysts can be used for the selective reduction of NO_x in lean burn conditions, but they form undesirably high quantities of N₂O. In this study conducted under stationary and transient conditions, we attempted to better understand the mechanism of SCR (NO) over Pt. We found that N₂ selectivity increased with contact time, that significant quantities of N₂ were formed when N₂O was used as the reactant, and that N₂O was formed more quickly than N₂ when NO was used as the reactant. These results led us to propose a kinetic model in which adsorbed N₂O is an intermediate for NO reduction into N₂.     

On the structure and photodissociation of cluster ions in the gas phase. (N2) (O2+) and (NO)2+

Results are presented for two experiments on N₂O₂⁺ cluster ions formed via the reactions O₂⁺ + N₂ + M → (N₂) (O₂⁺) + M (i), and NO⁺ + NO + M → (NO)₂⁺ + M (ii). In the first experiment the N₂O₂⁺ clusters are collisionally dissociated. The resulting collision-induced dissociation (CID) spectra show almost exclusively O₂⁺ and N₂⁺ products from N₂ O₂⁺ formed via the first reaction, and almost exclusively NO⁺ products from N₂O₂⁺ formed via the second reaction. In the second experiment, single-photon photodissociation of N₂O₂⁺ ions produced by both reactions (i) and (ii) was investigate using 514.5 and 634 nm radiation. The results indicate that the N₂O₂⁺ cluster from reaction (i) cannot be photodissociated while the N₂O₂⁺ cluster from reaction (ii) undergoes photodissociation at both wavelengths. These experiments indicate that two distinct N₂O₂⁺ cluster ions exist and that reactions (i) and (ii) selectively produce the two ions.     

The heterogeneous formation of N2O in the presence of acidic solutions: Experiments and modeling

We investigated the heterogeneous processes that contribute towards the formation of N₂O in an environment that comes as closely as possible to exhaust conditions containing NO and SO₂ among other constituents. The simultaneous presence of NO, SO₂, O₂, and condensed phase water in the liquid state has been confirmed to be necessary for the production of significant levels of N₂O. The maximum rate of N₂O formation occurred at the beginning of the reaction and scales with the surface area of the condensed phase and is independent of its volume. The replacement of NO by either NO₂ or HONO significantly increases the rate constant for N₂O formation. The measured reaction orders in the rate law change depending upon the choice of the nitrogen reactant used and were fractional in some cases. The rate constants of N₂O formation for the three different nitrogen reactants reveal the following series of increasing reactivity: NO < NO₂ < HONO, indicating the probable sequential involvement of those species in the elementary reactions. Furthermore, we observed a complex dependence of the rate constant on the acidity of the liquid phase where both the initial rate as well as the yield of N₂O are largest at pH=0 of a H₂SO₄/H₂O solution. The results suggest that HONO is the major reacting N(III) species over a wide range of acidities studied. The N₂O formation in synthetic flue gas may be simulated using a relatively simple mechanism based on the model of Lyon and Cole. The first step of the complex overall reaction corresponds to NO oxidation by O₂ to NO₂ mainly in the gas phase, with the presence of both H₂O and active surfaces significantly accelerating NO₂ production. Subsequently, NO₂ reacts with excess NO to obtain HONO which reacts with S(IV) to result in N₂O and H₂SO₄ through a complex reaction sequence probably involving nitroxyl (HON) and its dimer, hyponitrous acid. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet: 29 : 869–891, 1997.     

Conversion of NO in NO/N2, NO/O2/N2, NO/C2H4/N2 and NO/C2H4/O2/N2 Systems by Dielectric Barrier Discharge Plasmas

An experimental study on the conversion of NO in the NO/N₂, NO/O₂/N₂, NO/C₂H₄/N₂ and NO/C₂H₄/O₂/N₂ systems has been carried out using dielectric barrier discharge (DBD) plasmas at atmospheric pressure. In the NO/N₂ system, NO decomposition to N₂ and O₂ is the dominating reaction; NO conversion to NO₂ is less significant. O₂ produced from NO decomposition was detected by an on-line mass spectrometer. With the increase of NO initial concentration, the concentration of O₂ produced decreases at 298 K, but slightly increases at 523 K. In the NO/O₂/N₂ system, NO is mainly oxidized to NO₂, but NO conversion becomes very low at 523 K and over 1.6% of O₂. In the NO/C₂H₄/N₂ system, NO is reduced to N₂ with about the same NO conversion as that in the NO/N₂ system but without NO₂ formation. In the NO/C₂H₄/O₂/N₂ system, the oxidation of NO to NO₂ is dramatically promoted. At 523 K, with the increase of the energy density, NO conversion increases rapidly first, and then almost stabilizes at 93–91% of NO conversion with 61–55% of NO₂ selectivity in the energy density range of 317–550 J L⁻¹. It finally decreases gradually at high energy density. A negligible amount of N₂O is formed in the above four systems. Of the four systems studied, NO conversion and NO₂ selectivity of the NO/C₂H₄/O₂/N₂ system are the highest, and NO/O₂/C₂H₄/N₂ system has the lowest electrical energy consumption per NO molecule converted.     

用T-jump/FTIR研究MnCP、NiCP和PbCP的快速热分解(英)

0IntroductionCarbohydrazideisahydrazinederivativewithwhitecrystalofstrongreducingbehaviors.Becauseithasmanycoordinationatoms(fournitrogenatomsandoneoxygenatom),carbohydrazidecan,therefore,beusedasmultidentateligand.Itscoordinationcom鄄poundiswidelyusedint…     

Kinetics of the reactions of isopropoxy radicals with NO,NO2, and O2

A fluorescence excitation spectrum of (CH₃)₂CHO (isopropoxy radical) is reported following photolysis of isopropyl nitrite at 355 nm. Rate constants for the reaction of isopropoxy with NO, NO₂, and O₂ have been measured as a function of pressure (1–50 Torr) and temperature (25–110°C) by monitoring isopropoxy radical concentrations using laser-induced fluorescence. We have obtained the following Arrhenius expressions for the reaction of isopropoxy with NO and O₂ respectively: (1.22±0.28)×10^?11 exp[(+0.62±0.14 kcal)/RT]cm²/s and (1.51±0.70)×10^?14 exp[(?0.39±0.28)kcal/RT]cm³/s where the uncertainties represent 2σ. The results with NO₂ are more complex, but indicate that reaction with NO₂ proceeds more rapidly than with NO contrary to previous reports. The pressure dependence of the thermal decomposition of the isopropoxy radical was studied at 104 and 133°C over a 300 Torr range using nitrogen as a buffer gas. The reaction is in the fall-off region over the entire range. Upper limits for the reaction of isopropoxy with acetaldehyde, isobutane, ethylene, and trimethyl ethylene are reported.We have performed the first LIF study of the isopropoxy radical. Arrhenius parameters were measured for the reaction of i-PrO with O₂, NO, NO₂, using direct radical measurement techniques. All reactions are in their high-pressure limits at a few Torr of pressure. The rate constant for the reactions of i-PrO with NO and NO₂ reactions exhibit a small negative activation energy. Studies of the i-PrO + NO₂ reaction produce data which indicate that O(³P) reacts rapidly with i-PrO. Unimolecular decomposition studies of i-PrO indicate that the reaction is in the fall-off region between 1 and 300 Torr of N₂ and the high-pressure limit is above 1 atmosphere of N₂.     

Etude par RPE de l'Ion NO2−2 dans une apatite nitrée

A calcium phosphate apatite which contains some different nitrogen oxides is studied by the ESR technique. NO^2?₂ ions are evidenced and characterized. They stay in the apatite channels with their OO direction along the channel axis. ESR experiments at different temperatures show that these ions rotate around this axis when the temperature becomes higher than that of liquid nitrogen.     

Secondary ion emission of selected transition metals under nitrogen oxides

The emission of various positive secondary ions has been investigated for polycrystalline targets of Ti, V, Cr, Nb, Ta, Co, Ni, Cu, Pd and Pt, which were bombarded by Ar⁺ ions under dynamic SIMS (DSIMS) conditions in the presence of the gaseous nitrogen oxides N₂O, NO and NO₂ at fixed pressure and under residual gas. Besides ions of the Me⁺ type several fragmentary ions (e.g. N⁺, O⁺, NO⁺, MeN⁺ and MeO⁺) and also cluster ions Me _x O _y ⁺ (x 2, 0 y 2) were detected. Signals of a more molecular type with respect to the reactant gas, e.g. MeNO⁺, were only found for Co, Ni, Cu, Pd and Pt. From this, one may infer that for the other targets the nitrogen oxides will exist preferentially in a dissociatively adsorbed state at the metal surface. Several aspects of secondary ion emission can be explained assuming a different degree of oxidation for the metals under the influence of reactant gas.Part of the dissertation     

Effect of sol-gel derived Al2O3-ZrO2 and Al2O3-TiO2 oxides on the selectivity of NO reduction by CO under oxidizing conditions

The role of Al₂O₃-ZrO₂ and Al₂O₃-TiO₂ sol-gel prepared supports in the activity of platinum for the NO reduction by CO under oxidizing conditions has been studied. ²⁷Al MAS-NMR spectra have shown the formation of pentacoordinate Al^V in alumina-zirconia support. ZrO₂ or TiO₂ crystalline phases cannot be identified by XRD diffraction, suggesting the formation of nanosized structures supported on alumina. When the reaction was carried out in presence of oxygen, large amounts of NO₂ were observed on Pt/Al₂O₃-ZrO₂catalyst, while the formation of N₂O is more prononced on Pt/Al₂O₃-TiO₂ catalyst. The effect of water during NO reduction is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Infrared studies of the diatomic molecules O2, N2, NO and H2 adsorbed on Fe2O3

An infrared spectroscopic study of the diatomic molecules O₂, N₂, NO and H₂ adsorbed under different conditions on Fe₂O₃ has been performed.Complex patterns of absorption on both α-Fe₂O₃ and γ-Fe₂O₃ activated in O₂ at high temperature are assigned to vibrations of two different chemisorbed O₂ species.N₂ molecules do not interact with “oxygen rich” α-Fe₂O₃ surfaces, but give N₂O^? and N₂O₂^2? species when chemisorbed on evacuated surfaces.NO molecules give complex patterns of absorption, depending on the gas pressure. Three different types of nitrate structures can be identified, as well as NO, NO^? and cis-N₂O₂ chemisorbed species. Chemisorbed water molecules are formed by contact of H₂ with Fe₂O₃ surfaces even at room temperature.     

Vibrational emission of NO2 from the reaction of NO with O3

Vibrational chemiluminescence in the Δν₁ = Δν₃ = ?1 band of NO₂ is observed both in the O + NO and O₃ + NO reactions and shown to be emitted by molecules with up to 11 000 cm^?1 of vibrational energy. Quenching rate constants of NO₂³ are estimated ranging from about 6 × 10^?14 for Ar to about 3 × 10^?12 cm³ s^?1 for NO₂. The ratio of vibrational to electronic emission is 0.06 ± 0.03 for O + NO and 5.3 ± 1.0 for O₃ + NO. It is suggested that vibrationally excited NO₂ is a major product of that channel of the O₃ + NO reaction which forms ground-state NO₂(²A₁) directly.     

Theoretical study on reactions of cyclic-N3 with NO, NO2 and Cl2

In this article, we report our detailed mechanistic study on the reactions of cyclic-N₃ with NO, NO₂ at the G3B3//B3LYP/6-311+G(d) and CCSD(T)/aug-cc-pVTZ//QCISD/6-311+G(d)+ZPVE levels; the reactions of cyclic-N₃ with Cl₂ was studied at the G3B3//B3LYP/6-311+G(d) and CCSD(T)/aug-cc-pVTZ//QCISD/6-31+G(d)+ZPVE levels. Both of the singlet and triplet potential-energy surfaces (PESs) of cyclic-N₃ + NO, cyclic-N₃ + NO₂ and the PES of cyclic-N₃ + Cl₂ have been depicted. The results indicate that on singlet PESs cyclic-N₃ can undergo the barrierless addition–elimination mechanism with NO and NO₂ forming the respective dominant products N₂ + ¹cyclic-NON and ¹NNO(O) + N₂. Yet the two reactions on triplet PESs are much less likely to take place under room temperature due to the high barriers. For the cyclic-N₃ + Cl₂ reaction, a Cl-abstraction mechanism was revealed that results in the product cyclic-N₃Cl + Cl with an overall barrier as high as 14.7 kcal/mol at CCSD(T)/aug-cc-pVTZ//QCISD/6-31+G(d)+ZPVE level. So the cyclic-N₃ radical could be stable against Cl₂ at low temperatures in gas phase. The present results can be useful for future experimental investigation on the title reactions.     

Transient Spark Discharge Generated in Various N2/O2 Gas Mixtures: Reactive Species in the Gas and Water and Their Antibacterial Effects

Reactive species generated in the gas and in water by cold air plasma of the transient spark discharge in various N₂/O₂ gas mixtures (including pure N₂ and pure O₂) have been examined. The discharge was operated without/with circulated water driven down the inclined grounded electrode. Without water, NO and NO₂ are typically produced with maximum concentrations at 50% O₂. N₂O was also present for low O₂ contents (up to 20%), while O₃ was generated only in pure O₂. With water, gaseous NO and NO₂ concentrations were lower, N₂O was completely suppressed and HNO₂ increased; and O₃ was lowered in O₂ gas. All species production decreased with the gas flow rate increasing from 0.5 to 2.2 L/min. Liquid phase species (H₂O₂, NO₂￣, NO₃￣, ^·OH) were detected in plasma treated water. H₂O₂ reached the highest concentrations in pure N₂ and O₂. On the other hand, nitrites NO₂￣ and nitrates NO₃￣ peaked between 20 and 80% O₂ and were associated with pH reduction. The concentrations of all species increased with the plasma treatment time. Aqueous ^·OH radicals were analyzed by terephthalic acid fluorescence and their concentration correlated with H₂O₂. The antibacterial efficacy of the transient spark on bacteria in water increased with water treatment time and was found the strongest in the air-like mixture thanks to the peroxynitrite formation. Yet, significant antibacterial effects were found even in pure N₂ and in pure O₂ most likely due to high ^·OH radical concentrations. Controlling the N₂/O₂ ratio in the gas mixture, gas flow rate, and water treatment time enables tuning the antibacterial efficacy.

     

Catalytic reduction of nitrogen monoxide with propene over Nb/TiO2 mixed mechanically with Mn2O3

Selective catalytic reduction of nitrogen monoxide (NO) over a catalyst of mechanically mixed Nb/TiO₂ and Mn₂O₃ (Mn₂O₃+Nb/TiO₂) in an oxidizing atmosphere with propene (C₃H₆) was studied. The Mn₂O₃+Nb/TiO₂ catalyst showed high activity for the reduction of NO to N₂. The maximum conversion of NO to N₂ was observed at 200∼300°C, with about 80% reduction of NO to N₂. Mn₂O₃ enhanced the formation of NO₂ from NO and the activation of propene to react with NO₂ for reduction to N₂.     

A boundary for reaction mechanisms within the transition metals interacting with nitrogen oxides is observed in DSIMS experiments

Summary Dynamic secondary ion mass spectrometry (DSIMS) investigations have been carried out with Cr, Mn, Fe, Co, Mo, Rh, W, Re, Os and Ir under 4 mPa N₂O, NO and 3 mPa NO₂ as reactant gases. Results indicate similar behaviour in adsorption for Cr, Mn, Fe, Mo, W on the one hand and for Co, Rh, Os and Ir on the other. For the first group of metals the nitrogen oxide molecules are always totally destroyed in adsorption whereas the second group shows evidence for surface compounds such as MeNO (Me=metal) indicating only a partial dissociation in the case of N₂O and NO₂, and molecular adsorption under NO respectively. Re does not belong uniquely to either group because it reacts with N₂O and NO₂ dissociatively whereas under NO only partial dissociation is observed.Abbreviations SIMS Secondary ion mass spectrometry - SSIMS Static SIMS - AES Auger electron spectroscopy - EELS Electron energy-loss spectroscopy - LEED Low energy electron diffraction - TDS Thermal desorption spectroscopy - XPS, UPS X-ray/Ultraviolet photoelectron spectroscopy     

Structural and Magnetic Study of N2, NO,NO2, and SO2 Adsorbed within a Flexible Single‐Crystal Adsorbent of [Rh2(bza)4(pyz)]n

The crystalline one‐dimensional compound, [Rh^II₂(bza)₄(pyz)]_n ( 1 ) (bza=benzoate, pyz=pyrazine) demonstrates gas adsorbency for N₂, NO, NO₂, and SO₂. These gas‐inclusion crystal structures were characterized by single‐crystal X‐ray crystallography as 1 ?1.5 N₂ (298 K), 1 ?2.5 N₂ (90 K), and 1 ?1.95 NO (90 K) under forcible adsorption conditions and 1 ?2 NO₂ (90 K) and 1 ?3 SO₂ (90 K) under ambient pressure. Crystal‐phase transition to the P space group that correlates with gas adsorption was observed under N₂, NO, and SO₂ conditions. The C2/c space group was observed under NO₂ conditions without phase transition. All adsorbed gases were stabilized by the host lattice. In the N₂, NO, and SO₂ inclusion crystals at 90 K, short interatomic distances within van der Waals contacts were found among the neighboring guest molecules along the channel. The adsorbed NO molecules generated the trans‐NO???NO associated dimer with short intermolecular contacts but without the conventional chemical bond. The magnetic susceptibility of the NO inclusion crystal indicated antiferromagnetic interaction between the NO molecules and paramagnetism arising from the NO monomer. The NO₂ inclusion crystal structure revealed that the gas molecules were adsorbed in the crystal in dimeric form, N₂O₄.     

Nitrite and Nitrate Production by NO and NO2 Dissolution in Water Utilizing Plasma Jet Resembling Gas Flow Pattern

This study investigated the reactive dissolution of nitric oxide (NO) and nitrogen dioxide (NO₂) mixtures in deionized water. The dissolution study was carried out in a flat surface type gas–liquid reaction chamber utilizing a gas flow-pattern resembling plasma jets which are often used in biomedical applications. The concentration of NO and NO₂ in the gas mixtures was varied in a broad range by oxidizing up to 800 ppm of nitric oxide in Ar carrier gas with variable amount of ozone. The production of nitrite (NO₂^?) and nitrate (NO₃^?) in the water was proportional to treatment time up to 50 min. The concentration of NO₃^? was a power function of gas phase NO₂ while the concentration of NO₂^? increased approximately linearly with gas phase NO₂. The formation of NO₂^? and NO₃^? could be described by reactions between dissolved NO₂ and NO in the water while the production rate was determined by diffusion-limited mass transport of nitrogen oxides to the bulk of the liquid. At higher NO₂ concentrations, the formation of dinitrogen tetraoxide (N₂O₄) increased the formation rate of NO₂^? and NO₃^?. The identified mass transport limitation by diffusion suggests that convection of water created by the gas jet is insufficient and dissolution of nitrogen oxides can be increased by additional mixing. In respect of practical applications, the ratio of NO₂^? /NO₃^? in water could be varied from 0.8 to 5.3 with treatment time and gas phase NO₂ and NO concentrations.