Thermal behaviour of nickel(II) sulphate,nitrate and halide complexes containing ammine and ethylenediamine as ligands

Thermal behaviour of nickel amine complexes containing SO₄ ²⁻, NO₃ ⁻, Cl⁻ and Br⁻ as counter ions and ammonia and ethylenediamine as ligands have been investigated using simultaneous TG/DTA coupled with mass spectroscopy (TG/DTA–MS). Evolved gas analyses detected various transient intermediates during thermal decomposition. The nickel ammonium sulphate complex produces NH, N, S, O and N₂ species. The nickel ammonium nitrate complex generated fragments like N, N₂, NO, O₂, N₂O, NH₂ and NH. The halide complexes produce NH₂, NH, N₂ and H₂ species during decomposition. The ligand ethylenediamine is fragmented as N₂/C₂H₄, NH₃ and H₂. The residue hexaamminenickel(II) sulphate produces NiO with crystallite size 50 nm. Hexaammine and tris(ethylenediamine)nickel(II) nitrate produce NiO in the range 25.5 nm and 23 nm, respectively. The halide complexes produce nano sized metallic nickel (20 nm) as the residue. Among the complexes studied, the nitrate containing complexes undergo simultaneous oxidation and reduction.     

Chemical looping of metal nitride catalysts: low-pressure ammonia synthesis for energy storage

The activity of many heterogeneous catalysts is limited by strong correlations between activation energies and adsorption energies of reaction intermediates. Although the reaction is thermodynamically favourable at ambient temperature and pressure, the catalytic synthesis of ammonia (NH₃), a fertilizer and chemical fuel, from N₂ and H₂ requires some of the most extreme conditions of the chemical industry. We demonstrate how ammonia can be produced at ambient pressure from air, water, and concentrated sunlight as renewable source of process heat via nitrogen reduction with a looped metal nitride, followed by separate hydrogenation of the lattice nitrogen into ammonia. Separating ammonia synthesis into two reaction steps introduces an additional degree of freedom when designing catalysts with desirable activation and adsorption energies. We discuss the hydrogenation of alkali and alkaline earth metal nitrides and the reduction of transition metal nitrides to outline a promoting role of lattice hydrogen in ammonia evolution. This is rationalized via electronic structure calculations with the activity of nitrogen vacancies controlling the redox-intercalation of hydrogen and the formation and hydrogenation of adsorbed nitrogen species. The predicted trends are confirmed experimentally with evolution of 56.3, 80.7, and 128 μmol NH₃ per mol metal per min at 1 bar and above 550 °C via reduction of Mn₆N_2.58 to Mn₄N and hydrogenation of Ca₃N₂ and Sr₂N to Ca₂NH and SrH₂, respectively.     

Novel ruthenium based electrocatalyst for the convenient reduction of nitrogen-nitrogen bonds in azide to ammonia in aqueous solution

The interaction of azide (N ₃ ⁻ ) ion, at pH 5.3 with [Ru^III(EDTA) (H₂O)]⁻ (EDTA = ethylenediaminetetraacetate) was studied in aqueous solution by polarography and cyclic voltammetry. The product, [Ru^III(EDTA)(N₃)]²⁻ showed a multi-electron reduction step, which is polarographically reversible but, cyclic voltammetrically irreversible, in the potential range − 0.1 to − 0.2 V vs SCE. This reduction step, which was different from the one-electron reduction step of [Ru^III(EDTA)(H₂O)]; (E^1/2 = −0.113V vs SCE) was assigned to the reduction of the coordinated azide ion to ammonia by the irreversible transfer of electrons from Hg-electrode via ruthenium metal. Azide, at pH 5.3, was reduced, electrolytically, for the first time, to ammonia at Hg-pool cathode mediated by [Ru^III(EDTA) (N₃)]²⁻. The turnover number with respect to the formation of ammonia (moles of ammonia per mole of ruthenium per hour) was obtained from the constant potential electrolysis data. On the basis of experimental observations, a probable mechanism has been proposed for the electrocatalytic reduction of azide to ammonia in aqueous solution.     

Catalytic Performance of Spherical MCM-41 Modified with Copper and Iron as Catalysts of NH3-SCR Process

Spherical MCM-41 with various copper and iron loadings was prepared by surfactant directed co-condensation method. The obtained samples were characterized with respect to their structure (X-ray diffraction, XRD), texture (N₂ sorption), morphology (scanning electron microscopy, SEM), chemical composition (inductively coupled plasma optical emission spectrometry, ICP-OES), surface acidity (temperature programmed desorption of ammonia, NH₃-TPD), form, and aggregation of iron and copper species (diffuse reflectance UV-Vis spectroscopy, UV-Vis DRS) as well as their reducibility (temperature programmed reduction with hydrogen, H₂-TPR). The spherical MCM-41 samples modified with transition metals were tested as catalysts of selective catalytic reduction of NO with ammonia (NH₃-SCR). Copper containing catalysts presented high catalytic activity at low-temperature NH₃-SCR with a very high selectivity to nitrogen, which is desired reaction products. Similar results were obtained for iron containing catalysts, however in this case the loadings and forms of iron incorporated into silica samples very strongly influenced catalytic performance of the studied samples. The efficiency of the NH₃-SCR process at higher temperatures was significantly limited by the side reaction of direct ammonia oxidation. The reactivity of ammonia molecules chemisorbed on the catalysts surface in NO reduction (NH₃-SCR) and their selective oxidation (NH₃-SCO) was verified by temperature-programmed surface reactions.     

Synthesis and nitration of <Emphasis Type="Italic">N,N</Emphasis>´-bis(3-R-furoxan-4-yl)methylenediamines

A Mannich reaction of 4-amino-3-R-furoxans with paraformaldehyde in 10% aqueous H₂SO₄ led to the high yields of N,N′-bis(3-R-furoxan-4-yl)methylenediamines, whose structure (using R = Me as an example) was confirmed by X-ray diffraction study. The N,N′-bis-(3-R-furoxan-4-yl)methylenediamines obtained were nitrated to N,N′-dinitro-N,N′-bis-(3-R-furoxan-4-yl)methylenediamines upon the action of 100% HNO₃ in acetic or trifluoroacetic anhydride.     

Synthesis of ammonia in high-frequency discharges. II. Synthesis of ammonia in a microwave discharge under various conditions

The synthesis of ammonia from nitrogen-hydrogen plasma prepared using microwave discharge was studied by changing some experimental conditions, such as pressure (260–2600 Pa), power input (30–280 W), and nitrogen-hydrogen mixing ratio [H₂/(N₂+H₂)=0–1.0]. The ammonia yield increased with decreasing pressure and saturated at lower pressures. When the power input and the nitrogen-hydrogen mixing ratio were changed, the maximum yield of ammonia was obtained at the optimum experimental conditions (power input 150W; H₂/(N₂+H₂)0.75). Amounts of NH, H, and H₂ in the plasma also changed by changing the experimental conditions. From the changes in ammonia yield and amounts of NH, H, and H₂ by changing the experimental conditions, it is suggested that ammonia molecules are formed by the reaction of NH radicals not only with hydrogen atoms but also with hydrogen molecules. Otherwise, the formation and the decomposition of ammonia would occur simultaneously.     

Reaction scheme of ammonia synthesis in the ECR plasmas

The reaction scheme of ammonia synthesis in the ECR plasma apparatus teas investigated from both identifications of the species in the plasmas and the adsorbed species on the surface of a steel substrate placed in the plasmas. The adsorbed species were considerably different when different kinds of plasmas are used. NH, species were adsorbed on the steel substrate surface in the nitrogen-hydrogen plasma, and N₂ molecules were adsorbed in the nitrogen plasma. By the application of a negative bias potential on the substrate, the adsorption of N atom or Fe-N bond formation was identified on the steel substrate surface. When the stainless steel wall of the chamber was covered with aluminum foil, the yield of NH,, radicals, which were on both the substrate and in the plasma, decreased. By exposure of the substrate, on which N₂ molecules or N atoms adsorbed, to the hydrogen plasma, N₂ and N disappeared from the steel substrate surface, forming ammonia. Moreover, the adsorption of NH,, radicals disappeared when the stainless steel wall surface was covered with aluminum foil. Thus, the surface of the stainless steel wall acts as a catalyst in ammonia formation. The formation of ammonia in the nitrogen-hydrogen ECR plasma, in which the steel substrate served as the catalyst, is not only through the dissociative adsorption of excited nitrogen molecules but also through the dissociative adsorption of nitrogen molecular ions.     

Conversion of ammonia to dinitrogen in wastewater by Nitrosomonas europaea

Because Nitrosomonas europaea contains ammonia-oxidizing enzyme, nitrite reductase, and nitrous oxide reductase, the conversion of ammonia to dinitrogen was tried with different reaction conditions. In aerobic reaction conditions, ammonium was converted to nitrite (NO ₂ ⁻ ), while under oxygen-limiting or oxygen-free conditions, NO ₂ ⁻ -N formed from ammonia oxidation by N. europaea was reduced to N₂O and dinitrogen with 22% conversion. During denitrification, optimal pH for the production of N₂O and dinitrogen was found to be 7.0–8.0. Dinitrogen was not produced in acidic pH<7.0. A low partial oxygen pressure as well as oxygen-free conditions are favorable for high production of dinitrogen.     

Cyclothiomethylation of carboxylic acid hydrazides with aldehydes and H<Subscript>2</Subscript>S

The cyclothiomethylation of carboxylic acid hydrazides RCONHNH₂ (R = C₅H₄N, Ph, 2-MeOC₆H₄, or 4-HOC₆H₄CH₂) with formaldehyde and H₂S at 70 °C affords predominantly the corresponding N-(1,3,5-dithiazinan-5-yl)amides, whereas this reaction at 0–−50 °C gives a mixture of the latter compounds with 3-acyl-1,3,4-thiadiazolidines. N-(1,3,5-Dithiazinan-5-yl)-amides were selectively synthesized by the reaction of carboxylic acid hydrazides with formaldehyde and H₂S in the presence of BuONa in BuOH.     

Ab initio and density functional theory studies on the mechanism of nucleophilic vinylic substitution of 4<Emphasis Type="Italic">H</Emphasis>-pyran-4-one and 2-methyl-4<Emphasis Type="Italic">H</Emphasis>-pyran-4-one with ammonia

 Nucleophilic vinylic substitutions of 4H-pyran-4-one and 2-methyl-4H-pyran-4-one with ammonia were calculated by the B3LYP method using the 6-31G(d,p) basis set. Bulk solvent effects of aqueous solution were estimated by the polarized continuum and Poisson–Boltzmann self-consistent reaction field models using the 6-311+G(d,p) basis set. In the gas phase different mechanisms were found for the two reaction systems calculated. The reaction of 4H-pyran-4-one proceeds through enol, whereas a feasible path for the less reactive 2-methyl-4H-pyran-4-one is the mechanism through a keto intermediate. Addition of ammonia in concert with proton transfer is the rate-determining step ofthe reaction. The mechanism proceeding either by a bimolecular nucleophilic substitution (S_N2) or by one involving a tetrahedral zwitterionic intermediate is shown to be unlikely in the gas phase or nonpolar solution. The effects of bulk solvent not only consist in a reduction of the various activation barriers by about 25–40 kJ mol⁻¹ but also in a change in the reaction mechanism. Received 26 May 2002 / Accepted 26 July 2002 / Published online: 14 February 2003     

In-Flight Spheroidization of Alumina Powders in Ar–H<Subscript>2</Subscript> and Ar–N<Subscript>2</Subscript> Induction Plasmas

In-flight spheroidization of alumina powders in Ar–H₂ (H₂–7.6%, vol/vol) and Ar–N₂ (N₂–13.0%, vol/vol) RF induction plasmas was investigated numerically and experimentally. The mathematical model for the plasma flows incorporates the k– turbulence model, and that for particles is the Particle-Source-in-Cell (PSI-Cell) model. Experimental results demonstrate that spheroidized alumina particles are produced in both Ar–H₂ and Ar–N₂ RF plasmas, with different particle size distributions and crystal phases. Agreement between the predicted and measured particle size distributions is satisfactory under high particle feed rate conditions, while the results obtained for the Ar–H₂ plasma are better than those for the Ar–N₂ plasma. The discrepancy occurring in low feed rate conditions suggests that particle evaporation is an important factor affecting the plasma–particle heat transfer.     

Introduction of Primary Amino Groups on Poly(ethylene terephthalate) Surfaces by Ammonia and a Mix of Nitrogen and Hydrogen Plasma

With the aim of introducing primary amino groups on the surface of poly(ethylene terephthalate) (PET), two methods were compared—the use of ammonia or a combination of nitrogen and hydrogen low-pressure microwave plasma. Several plasma parameters were optimized on the reactor to increase the –NH₂ surface density, which was estimated by colorimetric titration and X-ray photoelectron spectroscopy (XPS). These techniques show that whatever the plasma treatment, almost 2 –NH₂/nm2 are incorporated on PET films. Emission spectroscopy highlighted a correlation between the density of primary amino groups and the ratio between an NH peak intensity and an Ar peak intensity (I_NH/I_Ar). Variation in surface hydrophilicity with aging in air after plasma treatment was monitored with contact angle measurements and showed a hydrophobic recovery. This was confirmed by XPS, which suggests also that surfaces treated by NH₃ plasma are more stable than surfaces treated by N₂/H₂.     

Calculation of partial molar volume of components in supercritical ammonia synthesis system

The partial molar volumes of components in supercritical ammonia synthesis system are calculated in detail by the calculation formula of partial molar volume derived from the R-K equation of state under different conditions. The objectives are to comprehend phase behavior of components and to provide the theoretic explanation and guidance for probing novel processes of ammonia synthesis under supercritical conditions. The conditions of calculation are H₂/N₂ = 3, at a concentration of NH₃ in synthesis gas ranging from 2% to 15%, concentration of medium in supercritical ammonia synthesis system ranging from 20% to 50%, temperature ranging from 243 K to 699 K and pressure ranging from 0.1 MPa to 187 MPa. The results show that the ammonia synthesis system can reach supercritical state by adding a suitable supercritical medium and then controlling the reaction conditions. It is helpful for the supercritical ammonia synthesis that medium reaches supercritical state under the conditions of the corresponding total pressure and components near the normal temperature or near the critical temperature of medium or in the range of temperature of industrialized ammonia synthesis. __________ Translated from Journal of Chemical Industry and Engineering, 57(7):1503–1507 [译自: 化工学报]     

Plasma chemical synthesis. II. Effect of wall surface on the synthesis of ammonia

The plasma synthesis of ammonia was stuided at pressures of 1–5 torr and flow rates of up to 200 torr cm³ min^–1 using Pyrex and silver surfaces cooled to 77 K. The N conversion to ammonia was about 13% in experiments in which the afterglow was trapped on the Pyrex surface. By quenching the plasma rather than the afterglow, the percent N conversion could be doubled using the Pyrex surface and quadrupled using the silver surface. Increasing the hydrogen pressure and/or hydrogen discharge cleaning decreased the percent N conversion; nitrogen discharge conditioning had no significant effect. With increasing nitrogen flow rate the percent N conversion decreased linearly in the quenched plasma reaction on the silver surface, suggesting nitriding and reduction by hydrogen to form ammonia. The exponential decrease of the percent N conversion in the quenched afterglow reaction on the Pyrex surface is explained by the formation and/or dissociation of adsorbed N₂ determining the ammonia yield at 77 K.     

Kinetics of oxidation of N,N-bis(salicylaldehyde-1,2-diaminoethane) cobalt(II) complex by periodate. Evidence for the inhibiting effect of copper(II)

A kinetic study of the oxidation of [Co(H₂L)(H₂O)₂]²⁺ (H₂L = N,N-bis (salicylaldehyde-1,2-diaminoethane) Schiff base) by periodate in aqueous solution was performed over pH (2.3–3.4) range, (0.1–0.5) mol dm⁻³ ionic strength and temperatures 20–35 °C for a range of periodate and complex concentrations. The reaction rate showed a first-order dependence on both reactants and increased with pH over the range studied. The effects of Cu(II) and Fe(II) on the reaction rate were investigated over the (1.0–9.0) × 10⁻⁵ mol dm⁻³ range. The reaction was inhibited as the concentration of Cu(II) increased, and it was independent on Fe(II) concentrations over the ranges studied. An inner-sphere mechanism is proposed for the oxidation pathways of both the protonated and deprotonated Co^II complex species.     

Bimetallic Cooperative Cleavage of Dinitrogen to Nitride and Tandem Frustrated Lewis Pair Hydrogenation to Ammonia

Although reductive cleavage of dinitrogen (N₂) to nitride (N^3?) and hydrogenation with dihydrogen (H₂) to yield ammonia (NH₃) is accomplished in heterogeneous Haber–Bosch industrial processes on a vast scale, sequentially coupling these elementary reactions together with a single metal complex remains a major challenge for homogeneous molecular complexes. Herein, we report that the reaction of a chloro titanium triamidoamine complex with magnesium effects complete reductive cleavage of N₂ to give a dinitride dititanium dimagnesium ditriamidoamine complex. Tandem H₂ splitting by a phosphine–borane frustrated Lewis pair (FLP) shuttles H atoms to the N^3?, evolving NH₃. Isotope labelling experiments confirmed N₂ and H₂ fixation. Though not yet catalytic, these results give unprecedented insight into coupling N₂ and H₂ cleavage and N?H bond formation steps together, highlight the importance of heterobimetallic cooperativity in N₂ activation, and establish FLPs in NH₃ synthesis.     

HPLC-ICP-MS and HPLC-ES-MS/MS characterization of synthetic seleno-arsenic compounds

Various toxicological and metabolic interactions have been reported to exist between arsenic and selenium. In the present study, synthetic seleno-arsenic compounds, potentially suitable for probing metabolic interactions between these two elements, were prepared and tentatively characterized by using high-performance liquid chromatography (HPLC)–electrospray tandem mass spectrometry and HPLC–inductively coupled plasma mass spectrometry. In analogy to the recently identified thio-arsenic species, which can be prepared from their corresponding oxo-arsenic species via reaction with H₂S, the seleno-arsenic compounds were also derived from oxo-arsenic compounds via reaction with H₂Se. Figure H₂Se bubbled into solutions containing oxo‐arsenosugars converts them into their seleno‐arsenosugar analogues.     

Synergistic effects of catalysts and plasmas on the synthesis of ammonia and hydrazine

The synergistic effects o1 driving frequency of the discharge and catalysis of iron and molybdenum wires when then are placed in nitrogen-h ydrogen radio-frequency and microwave plasmas mere investigated. The ammonia Yield increased in the plasmas prepared using both driving frequencies. but the hydrazine yield increased only in fire radio-frequency discharge with the catalysts. The direct adsorption of NH_x formed in the plasma on the catalyst surface followed by the formation of NH₃ and N₂H₄ are considered as a reaction scheme in the radio-frequency discharge. On the other hand, the adsorption of N atoms and/or formation of the metal- N bond favors the formation of ammonia but does not affect the hydrazine formation in the microwave discharge.     

Synthesis,characterization, and X-ray crystal structure of the manganese(III) complex Mn(Sal<Subscript>2</Subscript>hn)(CH<Subscript>3</Subscript>OH)(N<Subscript>3</Subscript>) [Sal<Subscript>2</Subscript>hn = N,N′-bis(salicylidene)-1,2-hexanediamine]

The new manganese(III) complex, Mn(Sal₂hn)(CH₃OH)(N₃), where Sal₂hn = N,N′-bis(salicylidene)-1,2-hexanediamine, was prepared from a reaction mixture containing Sal₂hn, MnCl₂ · 2H₂O, and NaN₃ (2: 1: 8 molar ratio) in methanol and characterized using elemental analysis, FT-IR spectroscopy, and X-ray single-crystal diffraction. In the title complex, the Mn(III) center is in a distorted octahedral coordination geometry with the basal plane formed by the N₂O₂ donors of the tetradentate Schiff base dianion; the two phenolate O atoms and the two imine N atoms are each mutually in the cis position. The azide ion and the O atom of the methanol molecule occupy the other two positions of the octahedron. The hydrogen bond O(3)-H(3O)⋯N(5) links the mononuclear Mn(Sal₂hn)(CH₃OH)(N₃) units into a 1D chain extended along the x axis. The crystal structure is further stabilized by C(7)-H(7)⋯N(3) and C(16)-H(16)⋯N(5) hydrogen bonds.     

Two-Temperature Two-Dimensional Non Chemical Equilibrium Modeling of Ar–CO<Subscript>2</Subscript>–H<Subscript>2</Subscript> Induction Thermal Plasmas at Atmospheric Pressure

Here the authors developed a two-dimensional two-temperature chemical non-equilibrium (2T-NCE) model of Ar–CO₂–H₂ inductively coupled thermal plasmas (ICTP) around atmospheric pressure (760 torr). Assuming 22 different particles in this model and by solving mass conservation equations for each particle, considering diffusion, convection and net production terms resulting from 198 chemical reactions, chemical non-equilibrium effects were taken into account. Species density of each particle or simply particle composition was also derived from the mass conservation equation of each one taking the non chemical equilibrium effect into account. Transport and thermodynamic properties of Ar–CO₂–H₂ thermal plasmas were self-consistently calculated using the first order approximation of the Chapman–Enskog method at each iteration point implementing the local particle composition and temperature. Calculations at reduced pressure (500 and 300 torr) were also done to investigate the effect of pressure on non-equilibrium condition. Results obtained by the present model were compared with results from one temperature chemical equilibrium (1T-CE) model, one-temperature chemically non equilibrium (1T-NCE) model and finally with 2T-NCE model of Ar–N₂–H₂ plasmas. Investigation shows that consideration of non-chemical equilibrium causes the plasma volume radially wider than CE model due to particle diffusion. At low pressure with same input power, presence of diffusion is relatively stronger than at high pressure. Comparison of present reactive model with non-reactive Ar–N₂–H₂ plasmas shows that maximum temperature reaches higher in reactive C–H–O molecular system than non-reactive plasmas due to extra contribution of reaction heat.