Catalytic Ammonia Decomposition Over Fe/Fe4N

The catalytic ammonia decomposition over iron and iron nitride, Fe₄N, under the atmosphere of ammonia–hydrogen mixtures of different amounts of ammonia in the temperature range of 400–550 °C by means of thermogravimetry has been studied. A differential tubular reactor with mixing has been used. The ammonia concentration in the gas phase during all the process was analysed. The balance between the inlet and outlet ammonia quantity has been used to determine a degree of ammonia conversion and the values of decomposition reaction rate. The activation energy of ammonia decomposition reaction over Fe and Fe₄N was found to be 68 and 143 kJ/mol, respectively.     

Effect of La2O3 on Ru/CeO2-La2O3 Catalyst for Ammonia Synthesis

A series of CeO₂-La₂O₃ supported ruthenium catalysts were prepared by co-precipitation method and the as-obtained samples were characterized by N₂ physisorption, X-ray diffraction, CO chemisorption, H₂-TPR, H₂-TPD and XPS. The activity test shows that ammonia concentration of the catalyst with 10% La is 13.9% at 10 MPa, 10,000 h^?1, 450 °C, which is 17% higher than that of Ru/CeO₂. La doping can improve the activity of Ru-ceria catalyst for ammonia synthesis by facilitating the reduction of oxygen which subsists in the cerium oxide surface. In addition, it can be realized that the test of catalyst stability proves the stability performance of Ru/CeO₂-La₂O₃ catalyst within the reaction time of 55 h.     

Propane Ammoxidation over Mo–V–Te–Nb–O M1 Phase Investigated by DFT: Elementary Steps of Ammonia Adsorption,Activation and NH Insertion into π-Allyl Intermediate

The selective ammoxidation of propane into acrylonitrile catalyzed by the bulk Mo–V–Te–Nb–O system has received significant attention because it is more environmentally benign than the current process of propene ammoxidation and relies on more abundant propane feedstock. The reaction mechanism is proposed to consist of a series of elementary steps including propane oxidative dehydrogenation, ammonia and O₂ activation, and NH_x insertion into C₃ intermediates. In this study density functional theory calculations have been performed to investigate the energetics of ammonia adsorption and activation in the proposed active center in the ab plane of the M1 phase. The formation of NH _x (x = 0, 1, 2, 3) species is found to be highly favored on reduced, oxo-depleted metal sites. The reduced Mo site is determined to be the most favorable site for ammonia activation by comparing the reaction energy profiles for the sequential dehydrogenation of ammonia on the various metal sites. The activation barrier for the initial H abstraction from ammonia was found to depend strongly on the surface sites that stabilize H and NH₂, and is as low as 0.28 eV when NH₂ is stabilized by the reduced Mo site and H is abstracted by the telluryl oxo group. The subsequent step of surface NH insertion into a π-allyl gas intermediate was also found to have a low activation energy barrier of 0.03 eV on the reduced Mo site.     

Electrodeposition of Co–Pd alloys from ammonia solutions and their catalytic activity for hydrogen evolution reaction

Investigations of the influence of electrolysis parameters such as the concentration of metal ammonia complexes, working electrode potential and temperature on the composition, structure and catalytic activity of synthesized alloys for water molecule reduction reaction in 2 M NaOH (T = 25 °C) were conducted. The alloys were deposited under potentiostatic conditions within potential range from ?0.7 to ?1.1 V in electrolytes of pH 9.5, containing ammonia complexes of cobalt(III) and palladium(II), [Co(NH₃)₆]³⁺ and [Pd(NH₃)₄]²⁺, of different concentration ratio. Structural changes in electrodeposited alloys were discussed based on results of X-ray diffraction measurements. An elemental analysis was performed using the energy-dispersive X-ray spectroscopy technique. Finally, based on results of galvanostatic measurements, the Tafel slope within the range of activation control for hydrogen evolution reaction was determined and mechanism of the process was discussed. The alloys presented low Tafel slope value, from 25.4 to 88.7 mV dec^?1. The alloy of the highest activity for hydrogen evolution reaction contained 31.2 at.% of Pd.     

OPTIMIZATION OF LEACHING OF COPPER FROM OXIDIZED COPPER ORE IN NH3-(NH4)2SO4 MEDIUM

Studies were carried out for selective leaching of Cu with simultaneous avoidance of iron dissolution during leaching of oxidized copper ore in an aqueous NH₃-(NH₄)₂SO₄ system. The effects of leaching parameters, such as ammonia concentration, ammonium sulphate concentration, leaching time, and solid-to-liquid ratio, were investigated on leaching of copper. A 2ⁿ factorial experimental design method in the dissolution experiments was used. In addition, the “Steepest Ascent” method was also applied to determine the optimum leaching conditions. It was observed that the most effective parameters on the leaching of copper were ammonia concentration and leaching time. Only 0.17% of iron in ore was dissolved in ammonia and ammonium sulphate medium. The optimum conditions established for maximum copper recovery were: ammonia concentration 2.824 mol L^?1, ammonium sulphate concentration 0.236 mol L^?1, solid-to-liquid ratio 0.167 g mL^?1, leaching time 2 h. Fixed parameters chosen in the experiments were: room temperature, average particle size 2.8 mm, stirring speed 500 rpm. Under the optimum conditions established for maximum copper recovery, the percentage of leached copper was 98.87.     

Synthesis of magnetic mesoporous silica composites via a modified Stöber approach

In this work, magnetic Fe₃O₄@mesoporous silica composites were synthesized by a microemulsion (oil-in-water/ethanol) approach which was applied with a modified Stöber reaction. Cetyl trimethyl ammonium bromide was employed as the surfactant, nano-Fe₃O₄ particles were dispersed in microemulsion. Tetraethyl orthosilicate (TEOS) formed oil drops, and ammonia solution facilitated the hydrolysis polymerization of TEOS. The diameters of the magnetic Fe₃O₄@mesoporous silica composites can be tuned within the range 120–380 nm by varying the ratio of ethanol/water and the amount of nano-Fe₃O₄ particles. Brunauer–Emmett–Teller surface areas of magnetic Fe₃O₄@mesoporous silica composites were determined to be within the range 490–759 m²/g and their pore sizes were around 2.3 nm as it was determined by Barrett–Joyner–Halenda method. Furthermore, the encapsulation of poorly water-soluble drugs within magnetic Fe₃O₄@mesoporous silica composites was investigated using protoporphyrin IX. Magnetic Fe₃O₄@mesoporous silica composites showed a drug loading within 22–68 mg/g, which can be an excellent drug delivery platform for photodynamic therapy.     

Ammonia Removal from Aqueous Solutions by Iranian Natural Zeolite

Abstract

The capability of Iranian natural clinoptilolite for ammonia removal from aqueous solutions has been thoroughly studied. Both batch and continuous (column) experiments were carried out. The viability of this natural zeolite in reducing the leakage of ammonia to the environment through waste water streams was a main focus of this research. Through the batch experiments, the effect of process variables such as the size of zeolite particles, pH, and ammonia concentration of the feed solution on the kinetics of ammonia uptake were investigated. Ammonia removal occurred rapidly and within the first 15 minutes of contact time, a major part of ammonia was removed from the solution. An adsorption capacity about 17.8 mg NH₄ ⁺/g zeolite at feed ammonia concentration of 50 mg/L was obtained and the optimum range for pH was achieved about 5.5–7.6. The adsorption capacity of clinoptilolite in the continuous mode was about 15.16 and 15.36 mg NH₄ ⁺/g zeolite for the original and regenerated types of clinoptilolite, respectively, where feed ammonium concentration was 50 mg/L. Increasing the feed ammonium concentration to 100 mg/L did not reduce the capability of the column for its ammonium removal and up to a bed volume (BV) of 85, there was only less than 1 mg/L ammonium in the column outlet. Presence of cations such as Ca²⁺, Mg²⁺ and Na⁺ in the feed solution reduced the clinoptilolite adsorption capacity to about 11.68 mg NH₄ ⁺/g zeolite. Regeneration experiments were carried out using concentrated sodium chloride solutions, as well as tap water. Where tap water was used as the regenerant, gradual release of ammonium from exhausted clinoptilolite was observed.     

Reaction Pathways for Ammonia Formation on Lean NOx Trap/Reduction System: A Spectroscopic Infrared Investigation

This study is devoted to an operando study of Pt–Rh/Al₂O₃–BaO lean-NO_x trap catalyst during the regeneration with H₂/CO reaction mixture. Particular attention was paid to the influence of CO coexisting with H₂ during the regeneration that can simulate the regeneration step by using reformate composed of CO and H₂. In rich H₂ mixture ammonia predominantly forms. As expected, strongly chemisorbed CO molecules over noble metals lower the efficiency of the trap at 150 °C. Successive hydrogenation of N atoms to ammonia predominates in our conditions. However, the comparison of the outlet gas composition with infrared spectral features also suggests a minor participation of isocyanate species (NCO) as possible intermediates in the production of ammonia especially for long regeneration duration in the absence of water. Interestingly, ammonia formation as reducing agent for the selective reduction of NO can stimulate practical applications for further coupling lean-NO_x trap with SCR catalysts.     

A Novel Method for Measuring Active Sites of Fe3O4 for WGS Reaction

Phase transformation among iron oxides was investigated. Pure magnetite material was obtained by reducing iron oxide with diluted hydrogen in a narrow temperature window and with steam to prevent over-reduction. A pulse chromatographic method with N₂O decomposition over magnetite surface to determine active sites of iron oxide based catalysts for water gas shift reaction has been developed. N₂O decomposes over activated Fe₃O₄ surface to N₂ and leaves oxygen species at oxygen vacancy on the catalyst surface, which is the same site for water gas shift reaction. Lower temperature for N₂O decomposition is required to avoid magnetite bulk oxidation. An oxygen coverage on the active sites θ = 1 corresponded to a surface stoichiometry of N₂O/Fe²⁺ = 0.5 was estimated. A linear correlation between water gas shift reaction rate and the quantity of decomposed N₂O over the corresponded catalysts was observed.     

Development and application of a simultaneous measurement method for gaseous ammonia and particulate ammonium in ambient air

Ammonia gas is one of the precursors contributing to the formation of secondary particulate ammonium via reactions with atmospheric acids, such as sulfuric and/or nitric acids, which are present in ambient air. In this study, a new instrument that is suitable for measuring ammonia gas and fine particulate ammonium (PM_2.5 NH₄⁺) concentrations simultaneously under ambient conditions was developed. A wetted frit sampler was connected in the back of a counter-current flow tube (CCFT) sampler, and the NH₃ gas and PM_2.5 NH₄⁺ samples were collected by CCFT and wetted frit samplers, respectively. An air sample was drawn through the samplers at a flow rate of 1.0 dm³ min^?1 and an absorption water flow rate of 120 mm³ min^?1. Then, the ammonium that formed in the absorption solution was detected by the indophenol method using a continuous flow analysis system. The estimated detection limits were 43 and 49 ng m^?3 for ammonia gas and PM_2.5 NH₄⁺, respectively. Notably, the ammonia gas was collected on the CCFT sampler with a collection efficiency of 98.5%, but most of the PM_2.5 NH₄⁺ passed through it and was captured on the wetted frit sampler with a collection efficiency of approximately 100%. The present method was applied to measure NH₃ gas and PM_2.5 NH₄⁺ at two urban sites: Osaka, Japan and Ho Chi Minh City, Vietnam. It was found that the simultaneous measurement method performed very well and that the measured concentrations were comparable with those obtained with the annular denuder method.

Copyright © 2016 American Association for Aerosol Research     

Crystal and Supramolecular Structure of a Novel Organotin Sulphate: {[(Ph3Sn)2SO4]2 · (H2O)3} · 2EtOH

A novel sulphate of organotin was synthesized by the reaction of triphenyltin chloride with silver sulphate. The structure of {[(Ph₃Sn)₂SO₄]₂ · H₂O)₃} · 2EtOH has been determined by X-ray crystallography. The crystal data parameters are as follows: monoclinic, space group Cc, a = 14.146(6), b = 23.844(11), c = 23.777(11) Å, Z = 4. The title compound displays a dimeric tetra-tin nuclear structure. The geometry about tin is trigonal bipyramidal with a trans-O₂SnC₃ stereochemistry about the metal. Hydrogen bonding between the oxygen atoms of the anion and the solvate water produces a graphite-like 3D network lattice.     

Efficient Esterification of Fatty Acids with Alcohols Catalyzed by Zr(SO4)2 · 4H2O Under Solvent-Free Condition

Zirconium sulfate (Zr(SO₄)₂ · 4H₂O) was an efficient catalyst for the esterification of fatty acids and alcohols under solvent-free condition. The esterification of fatty acid with branched alcohols using Zr(SO₄)₂ · 4H₂O catalyst gave a good yield of the corresponding ester. The zirconium sulfate Bronsted acid site was suggested to be the catalytically active species in this reaction. In addition, Zr(SO₄)₂ · 4H₂O compound is a potential green catalyst due to its high catalytic activity and low toxicity. This compound is also cost effective, easy to handle, is easily recovered by simple filtration and can be recycled for further reactions.     

Regeneration of 4-Chlorophenol Exhausted GAC with a Microwave Assisted Wet Peroxide Oxidation Process

To improve the performance of wet oxidation for the regeneration of GAC, a microwave assisted wet peroxide oxidation process has been applied for the regeneration of 4-chlorophenol exhausted GAC. The effects of various factors including reaction temperature, H₂O₂ dosage, reaction time, and addition of catalyst have been studied. The regeneration improves with the increase in reaction temperature, H₂O₂ dosage, and reaction time. The addition of Cu²⁺ further promotes the regeneration process. Under the conditions of temperature 150°C, H₂O₂ dosage 15 mmol, reaction time 20 min, Cu²⁺ concentration 20 mg/L, the regenerated GAC recovers 93.5% of its adsorption capacity. A nearly complete degradation of 4-chlorophenol in the aqueous phase is observed based on UV-vis and high-performance liquid chromatography spectra studies.     

The Denitridation of Nitrides of Iron, Cobalt and Rhenium Under Hydrogen

The denitridation behaviour of binary iron, cobalt and rehnium nitrides under H₂ /Ar has been investigated. The iron nitride was found to lose over 70 % of its as prepared nitrogen content at 400 °C. The cobalt nitride was completely denitrided at 250 °C. Rhenium nitride lost close to 90 % of its nitrogen at 350 °C. In addition, Co-Re₄ prepared by ammonolyis was investigated, whilst only traces of NH₃ were lost from this material under H₂/Ar at 400 °C, with H₂/N₂ it proved to be an active ambient pressure ammonia synthesis catalyst in accordance with previous literature.     

Modification of Ammonia Decomposition Activity of Ruthenium Nanoparticles by N-Doping of CNT Supports

The use of ammonia as a hydrogen vector has the potential to unlock the hydrogen economy. In this context, this paper presents novel insights into improving the ammonia decomposition activity of ruthenium nanoparticles supported on carbon nanotubes (CNT) by nitrogen doping. Our results can be applied to develop more active systems capable of delivering hydrogen on demand, with a view to move towards the low temperature target of less than 150?°C. Herein we demonstrate that nitrogen doping of the CNT support enhances the activity of ruthenium nanoparticles for the low temperature ammonia decomposition with turnover frequency numbers at 400?°C of 6200 LH₂ mol_Ru ^?1 h^?1, higher than the corresponding value of unmodified CNT supports under the same conditions (4400 LH₂ mol_Ru ^?1 h^??1), despite presenting similar ruthenium particle sizes. However, when the nitrogen doping process is carried out with cetyltrimethylammonium bromide (CTAB) to enhance the dispersion of CNTs, the catalyst becomes virtually inactive despite the small ruthenium particle size, likely due to interference of CTAB, weakening the metal–support interaction. Our results demonstrate that the low temperature ammonia decomposition activity of ruthenium can be enhanced by nitrogen doping of the CNT support due to simultaneously increasing the support’s conductivity and basicity, electronically modifying the ruthenium active sites and promoting a strong metal–support interaction.     

Synthesis,characterization and sintering of Si-C-N nano-powders via sodium reduction in liquid ammonia

Si-C-N nano-powders with tunable carbon content were synthesized through the reduction of silicon tetrachloride (SiCl₄) and trichloromethylsilane (SiCl₃CH₃) solution by sodium in liquid ammonia. The nano-powders contain two domains of structure, Si-C-N amorphous or continuous random networks (CRNs), and free carbon. The carbon content in Si_3+nC_nN₄ CRNs_, is tunable from n = 0 to n = 1. Free carbon will appeared with the increase of the C/Si mole ratio when C/Si is higher than 1/4. The crystallization of amorphous Si-C-N powders occurs at temperatures ranging from 1300 °C to 1500 °C depending on the carbon content. The additive-free dense Si-C-N ceramics with relatively low porosity were fabricated by Spark Plasma Sintering (SPS).     

Modelling NH<Subscript>3</Subscript> volatilisation within a urine patch using NZ-DNDC

Urea concentrations in urine patches deposited during animal grazing can be over ten times higher than typical fertiliser application rates, potentially leading to large ammonia (NH₃) losses. The process-based NZ-DNDC model was modified to better simulate soil pH changes and ammonia (NH₃) emissions following urine application using data collected from a New Zealand field trial. After modification, simulated 30-day NH₃ emissions decreased from 506 to 117 kg N ha^?1 compared to measured emissions of 78 ± 3 kg N ha^?1 (mean ± standard error) and the Nash–Sutcliffe Efficiency (NSE) for daily NH₃ emissions increased from ?7.11 to +0.97 for the parameterisation dataset. However, modified model correctly estimated the cumulative emissions for the first 7 days. Using the same parameterisation on an independent dataset from a nearby site gave cumulative 18-day NH₃ emissions of 84 kg N  ha^?1 compared to the measured 48 ± 2 kg N ha^?1 (mean ± standard error). However, the NSE for daily NH₃ emissions was ?0.71, indicating site specific parameterisation might be needed. The sensitivity of NH₃ emissions to ±5 and ±10% errors in 4 model parameters was tested. The sensitivities ranged from ?0.36 to +0.71. The highest sensitivity was to the rate of NH₃ transfer from the soil solution to the atmosphere and the lowest sensitivity was to the rate of urea hydrolysis.     

Use of the open-path TDL analyzer to monitor ammonia emissions from winter wheat in the North China Plain

The backward Lagrangian stochastic (BLS) model and open-path tunable diode laser (OPTDL) analyzer were used to monitor ammonia (NH₃) emissions from urea applied to winter wheat in the North China Plain. The high-temporal resolution measurements of ammonia concentrations provided an opportunity for estimating the diel patterns of ammonia emissions, as well as valuable information about the factors that influence NH₃ emissions. The results showed both large diel variability and daily variability in NH₃ volatilization, with NH₃ emissions highest during the daytime. The diel pattern of ammonia volatilization depended mainly on the diel variation of wind speed and soil temperature, while the overall pattern of NH₃ loss was strongly affected by soil moisture content, soil NH₄ ⁺-N concentration, wind speed and soil temperature. At the end of the measurement period, the cumulative NH₃ loss was 12.21–16.43 kg N ha^?1, calculated based on different time scale average Q _BLS. Due to sensitivity of the OPTDL analyzer, the estimated total ammonia loss was still doubtful in this study.     

A novel low-temperature firable La2Zr3(MoO4)9 microwave dielectric ceramic

A novel low-temperature fired La₂Zr₃(MoO₄)₉ microwave dielectric ceramic was successfully fabricated by a conventional solid-state reaction method. The powder compact was densified in air in the temperature range of 700–800 °C for 4 h. X-ray diffraction analysis indicated that all studied samples presented a single phase structure. Rietveld refinement results further confirmed that La₂Zr₃(MoO₄)₉ belonged to a trigonal system with space group R$\overline{3}$c. Scanning electron microscopy results revealed dense and homogeneous microstructure of La₂Zr₃(MoO₄)₉ ceramics as sintered in the temperature range of 725–800 °C. The La₂Zr₃(MoO₄)₉ ceramic sintered at 775 °C for 4 h possessed excellent microwave dielectric properties of relative permittivity ε_r ～ 10.8, quality factor Qxf ～ 50,628 GHz (at 10.45 GHz), and temperature coefficient of the resonant frequency τ_f ～ ?38.8 ppm/°C, showing great potentials for applications of low temperature co-fired ceramic technology.     

Potassium-Doped Ni–MgO–ZrO2 Catalysts for Dry Reforming of Methane to Synthesis Gas

Ni/K–MgO–ZrO₂ catalysts for dry reforming of methane, with a range of Mg/Zr ratios and each containing about 10 wt% Ni, were prepared via Ni nitrate impregnation on MgO–ZrO₂ supports synthesized by co-precipitation using K₂CO₃. It was found that a proportion of the potassium of the precipitant remained in the samples and improved the stability of the catalysts in the reaction. It was also shown that reduction of the catalysts at 1,023 K without calcination in air is necessary for stable and high activity; calcination in air at 1,073 K gives a deterioration of the catalytic properties, leading to rapid deactivation during the reaction. The order of the CH₄ conversions of the reduced catalysts after 14 h on stream was as follows: Ni/K–Mg₅Zr₂ ~ Ni/K–Mg ≥ Ni/K–Mg₂Zr₅ ? Ni/K–Zr. A catalyst with 0.95 wt% K on MgO–ZrO₂ with a Mg:Zr mole ratio of 5:2 showed the best resistance to deactivation. Experiments in a microbalance system showed that there was only negligible coke deposition on the surface of this sample. This behaviour was attributed to the presence of Ni nanoparticles with a diameter of less than 10 nm located on a MgO/NiO solid solution shell doped by K ions; this in turn covers a core of tetragonal ZrO₂ and/or a MgO/ZrO₂ solid solution. This conclusion was supported by EDS/TEM, XPS, XRD and H₂ chemisorption measurements.