Continuous synthesis of metal nanoparticles in supercritical methanol

Metal nanoparticles were synthesized continuously in supercritical methanol (scMeOH) without using reducing agents at a pressure of 30 MPa and at various reaction temperatures ranging 150-400 °C. Wide angle X-ray diffraction (WAXD) analysis revealed that metallic nickel (Ni) nanoparticles were synthesized at a reaction temperature of 400 °C while mixtures of nickel hydroxide (α-Ni(OH)₂) and metallic Ni were produced at lower reaction temperatures of 250-350 °C. In contrast, metallic silver (Ag) nanoparticles were produced at reaction temperatures above 150 °C while metallic cupper (Cu) nanoparticles were produced at reaction temperatures above 300 °C. Mixtures of copper oxide (CuO and Cu₂O) and metallic Cu were produced at lower reaction temperatures of 250 °C. Scanning electron microscopy (SEM) showed that the particles size and morphology changed drastically as the reaction temperature increased. The average diameters of Ni, Cu and Ag particles synthesized at 400 °C were 119 ± 19 nm, 240 ± 44 nm, and 148 ± 32 nm, respectively. The scMeOH acted both as a reaction medium and a reducing agent. A possible reduction mechanism in scMeOH is also presented.     

Synthesis of Titania Pillared Saponite in Aqueous Solution of Acetic Acid

The preparation of TiO₂-pillared saponite was carried out in a CH₃COOH aqueous solution. Titanium ion species to intercalate into the interlayer of saponite were obtained by an addition of Ti(C₃H₇O)₄ to an aqueous solution of CH₃COOH and by subsequent aging of the solution for a prescribed time. Ti⁴⁺-intercalated saponite including organic materials was obtained by ion exchange. After the sample was calcined at 500°C in air, TiO₂-pillared saponite was obtained. The resulting TiO₂-pillared saponite (Ti-Sapo) possessed surface areas in the range 300–400 m²/g and a sharp pore size distribution with the pore radius of 1.2 nm. The basal spacing of the product heated at temperature >250°C was about 2.45 nm. The pillar height of TiO₂ in the Ti-Sapo was estimated to be 1.5 nm.     

IrO2-deposited Pt electrocatalysts for unitized regenerative polymer electrolyte fuel cells

An IrO₂/Pt electrocatalyst for the polymer electrolyte-type unitized regenerative fuel cell (URFC) was prepared by deposition of iridium oxide (IrO₂) particles on Pt black via a colloidal iridium hydroxide hydrate precursor, and URFC performance was examined. After the iridium hydroxide hydrate deposited Pt was calcined at 400 °C in air for 1 h, rutile-structure IrO₂ particles (20–50 nm dia.) were formed on Pt particle clusters. TEM and pore volume distribution analysis revealed that the microstructure of the deposited IrO₂/Pt catalyst was different from the mixed IrO₂/Pt catalyst. The cell using the deposited IrO₂/Pt (20 at % Ir) catalyst showed similar fuel cell performance with the mixed IrO₂/Pt electrode of higher Pt content (10 at % Ir) while maintaining water electrolysis performance. Consequently, 51% round-trip energy conversion efficiency at a current density of 300 mA cm^–2 was attained.     

Preparation of High-Performance Co3O4 Catalyst for Hydrocarbon Combustion from Co-Containing Hydrogarnet

Supported Co₃O₄ catalysts were prepared via the calcination of Co-containing hydrogarnet, (Ca_3-x Co _x )Al₂(SiO₄)_{3- y} (OH)_4y , at 400 °C. Such precursors with various extents of substitution were synthesized from the hydrothermal reaction of a stoichiometric mixture of calcium oxide, amorphous silica, alumina sol, and cobalt hydroxide at 200 °C. It was found that the catalyst consisted of Co₃O₄, CaO, and mayenite and exhibited a high activity for the combustion of propylene, benzene, and toluene at temperatures below 300 °C.     

X-ray absorption spectroscopy studies of nickel oxide thin film electrodes for supercapacitors

Nickel oxide films were synthesized by electrochemical precipitation of Ni(OH)₂ followed by heat-treatment in air at various temperatures (200-600 °C). Their structure and electrochemical properties were studied by cyclic voltammetry, X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). XRD results showed that the nickel oxide obtained at 250 °C or above has a crystalline NiO structure. The specific capacitance of the oxide depends on the heat-treatment temperature, showing a maximum value at 300 °C. XAS results revealed that the non-stoichiometric nickel oxide (Ni_1−xO) approached the stoichiometric NiO structure with increasing heat-treatment temperature due to the defect healing effect. The defective nature of the nickel oxide could be utilized to improve its specific capacitance for supercapacitor application.     

A novel CO and C3H8 sensor made of CuSb2O6 nanoparticles

Trirutile-type CuSb₂O₆ nanoparticles were synthesized by a simple and economical route, starting from copper nitrate, antimony chloride, ethylenediamine, and ethyl alcohol as solvent. The latter was evaporated by microwave radiation at 140 W. The precursor material was calcined at 200, 300, 400, 500, and 600 °C, and analyzed by powder XRD. The oxide phase was obtained at the last calcination step (600 °C), whose powders were analyzed by field-emission scanning electron (FE-SEM) and transmission electron (TEM) microscopies. Microrods, hexagonal microplates, and nanoparticles with an average size of ~ 51.2 nm were observed. A forbidden bandwidth of 3.41 eV was detected for the direct transition with UV–vis. Tests were carried out on pellets made of the powders in carbon monoxide (CO) and propane (C₃H₈) atmospheres at different concentrations and operating temperatures, obtaining high response at 300 ppm of CO and 500 ppm of C₃H₈, both at 300 °C.     

Microwave-enhanced catalytic degradation of phenol over nickel oxide

A mix-valenced nickel oxide, NiO_x, was prepared from nickel nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by sodium hypochlorite. Further, pure nickel oxide was obtained from the NiO_x by calcination at 300, 400 and 500 °C (labeled as C300, C400 and C500, respectively). They were characterized by thermogravimetry (TG), X-ray diffraction (XRD), nitrogen adsorption at −196 °C and temperature-programmed reduction (TPR). Their catalytic activities towards the degradation of phenol were further studied under continuous bubbling of air through the liquid phase. Also, the effects of pH, temperature and kinds of nickel oxide on the efficiency of the microwave-enhance catalytic degradation (MECD) of phenol have been investigated. The results indicated that the relative activity affected significantly with the oxidation state of nickel, surface area and surface acidity of nickel oxide, i.e., NiO_x (>+2 and S_BET = 201 m² g⁻¹) ≫ C300 (+2 and S_BET = 104 m² g⁻¹) > C400 (+2 and S_BET = 52 m² g⁻¹) > C500 (+2 and S_BET = 27 m² g⁻¹). The introduction of microwave irradiation could greatly shorten the time of phenol degradation.     

Low-temperature selective catalytic reduction of NO over MnOx/CNTs catalysts: Effect of thermal treatment condition

Carbon nanotubes (CNTs) supported manganese oxide catalysts were prepared through different thermal treatment routes and used for low-temperature selective catalytic reduction of NO with NH₃. The MnO_x/CNTs catalyst prepared by calcined the precursor in air at 300 °C showed lower NO conversions than that treated at 250 °C, while it showed higher NO conversions than the one calcined in nitrogen. BET, TGA, XRD and H₂-TPR results indicated that CNTs may impose effects on the oxidation state and redox ability of the manganese oxide and hence on the catalytic activity during the calcination process at given temperatures.     

Formation of fullerenes by pyrolysis of perchlorofulvalene and its derivatives

In a retro-synthetic approach, [60]fullerene might be accessible by condensing six fulvalene fragments. In order to explore the potential of such a route for direct synthesis of [60]fullerene we have investigated the pyrolysis of perchlorofulvalene (PCF). Low temperature pyrolysis of PCF at 250 °C resulted mainly in the formation of dimers, trimers, tetramers and products of subsequent intramolecular condensation of these oligomers. Increasing the temperature to 300-350 °C leads to the formation of perchlorinated polynuclear aromatic hydrocarbons. Pyrolysis at 400-450 °C gives a cross-linked polymer structure which is the result of intermolecular condensation of the polynuclear aromatic intermediates. Pyrolysis at higher temperatures (>500 °C) mainly leads to graphite. It was found that the two-step pyrolysis of PCF (heating first at 450 °C, after that at 750 °C) yielded a fullerene containing soot via an intermediate polynuclear aromatic net. High temperature rearrangement of the latter gave fullerenes C₆₀ and C₇₀. The best results were obtained when a PCF oligomer obtained by Ullmann condensation was used as a precursor. By two-step pyrolysis and further high vacuum sublimation of the soot the fullerenes C₆₀ and C₇₀ were obtained in extractable amounts.     

Reduction of NOx over a NOx-Trap Catalyst and the Regeneration Behaviour of Adsorbed SO2

A conventional NO _x -trap catalyst containing platinum, rhodium, barium and lanthanum was conditioned with oxygen at 500°C, preloaded with NO under standard oxidising conditions and then subjected to regeneration with the reductants H₂, CO and C₃H₆, either alone or as a mixture. Hydrogen is the most efficient reductant in terms of NO _x conversion efficiency and reductant usage efficiency. There is a temperature optimum for CO between 300 and 400°C and a catalyst loading optimum (mols reductant added)/(mols NO _x adsorbed) between 1.5 and 3.0. The behaviour of the catalyst towards sulphur poisoning was examined in supplementary trials with the adsorption of SO₂ in the presence or absence of water vapour. When water is not present in both adsorption and reduction steps, very stable sulphates are formed, unattacked by reductants even at 1000°C. Sulfates are more easily reduced when water is present in the reductant mixture.     

Nickel oxide/hydroxide nanoplatelets synthesized by chemical precipitation for electrochemical capacitors

Nickel hydroxide powder prepared by directly chemical precipitation method at room temperature has a nanoplatelet-like morphology and could be converted into nickel oxide at annealing temperature higher than 300 °C, confirmed by the thermal gravimetric analysis and X-ray diffraction. Annealing temperature influences significantly both the electrical conductivity and the specific surface area of nickel oxide/hydroxide powder, and consequently determines the capacitor behavior. Electrochemical capacitive behavior of the synthesized nickel hydroxide/oxide film is investigated by cyclic voltammetry and electrochemical impedance spectroscope methods. After 300 °C annealing, the highest specific capacitance of 108 F g⁻¹ is obtained at scan rate of 10 mV s⁻¹. When annealing temperature is lower than 300 °C, the electrical conductivity of nickel hydroxide dominates primarily the capacitive behavior. When annealing temperature is higher than 300 °C, both electrical conductivity and specific surface area of the nickel oxide dominate the capacitive behavior.     

Preparation of ordered mesoporous nickel oxide film electrodes via lyotropic liquid crystal templated electrodeposition route

A novel electrochemical route to fabricate ordered mesoporous metal oxide film electrodes has been investigated with particular reference to nickel oxide. Ordered mesoporous nickel oxide films are successfully synthesized by templated electrodeposition of H_I-e nickel hydroxide and followed by heat-treatment in air at various temperatures. The films are characterized physically by thermogravimetry (TG), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The applicability of this film as inexpensive and high-performance supercapacitor electrode material is demonstrated by the electrochemical characterization using cyclic voltammetry (CV) and chronopotentiometry technique. The specific capacitance of the nickel oxide film depends on the annealing temperature, showing a maximum value of 590 F g⁻¹ when the as-deposited film is heat-treated at 250 °C for 1.5 h.     

Fundamental Investigations of Thermal Aging Phenomena of Model NOx Storage Systems

Investigations of the aging behavior induced by high temperatures coupled with oxidizing atmosphere of model NO _x storage systems Ba/Al₂O₃ and Ba/CeO₂ are reported in this paper. The samples were prepared, calcined and exposed to temperatures between 500 and 1000 °C in air for 12 h for thermal aging. Samples were characterized with XRD, HRSEM, DSC-TGA-MS and BET analyses. In XRD investigations of all model systems calcined at 500 °C for 2 h, the NO _x storage component was present in form of BaCO₃. The release of CO₂ as a result of the decarbonization of the NO _x storage component at increased temperatures was verified by thermogravimetric investigations. In the case of Ba/Al₂O₃, already during calcination a partial reaction of the NO _x storage component with Al₂O₃ resulting in the formation of barium aluminate was observed. In the model system Ba/CeO₂ the decomposition of the barium carbonate started above 780 °C and the formation of a barium cerium mixed oxide was observed. The presence of the barium containing NO _x storage component has a strong influence on the specific surface area of the model NO _x storage systems. The morphology and crystallite size of CeO₂ modified with the barium containing NO _x storage component exhibited distinct changes compared to the unmodified oxide. The NO _x storage efficiency determined by model gas tests of freshly prepared and engine aged model NO _x storage catalysts correlates well with the above described observations.     

Synthesis of nanosized (Pb,Sr)TiO3 perovskite powders by coprecipitation processing

Nanosized perovskite lead strontium titanate (Pb_xSr_1−x)TiO₃ (PST) powders were successfully prepared by a simple coprecipitation method. Lead-strontium titanyl oxalate (PSTO) precursor was first synthesized at room temperature, and the precursor was then calcined at 600 °C for 1 h to produce the single phase perovskite PST powders. Characterization studies were carried out on the as-dried precursor and the calcined PST powders by various techniques. The results showed a strong dependence of the chemical composition of final PST powders on pH value in the coprecipitation reaction. PST powders with desired composition could be synthesized by adding 25 mol% excess Sr. PST particles were found to be spherical in nature with an average size of 10 nm.     

Effects of Lean/Rich Timing and Nature of Reductant on the Performance of a NOx Trap Catalyst

A NO _x trap catalyst was studied in a laboratory reactor under simulated diesel passenger car conditions. The effects of lean/rich duration and the nature of reductant are investigated. At 300°C, the average NO _x conversion decreases with increasing lean duration; conversely the NO _x conversion increases with increasing rich duration. The NO _x conversion at this temperature was found to be a direct function of reaction stoichiometry. That is, the quantity of trapped NO _x under lean conditions must be balanced by the quantity of reductant during the rich trap regeneration step. At extreme temperatures, other factors, reaction kinetics (at lower temperatures) and NO _x storage capacity (at higher temperatures), dominate the NO _x conversion process. Overall, carbon monoxide was found to be the most effective reductant. Hydrocarbon, e.g., C₃H₆, is effective at higher temperatures (T>350°C), while H₂ is more efficient than other reductants at low temperatures (T<200°C). The individual steps of the NO _x conversion process are discussed.     

Iron oxide supported sulfated TiO2 nanotube catalysts for NO reduction with propane

Sulfated TiO₂ nanotubes and a series of iron oxide loaded sulfated TiO₂ nanotubes catalysts with different iron oxide loadings (1 wt%, 3 wt%, 5 wt% and 7 wt%) were prepared and calcined at 400 °C. The physico-chemical properties of the catalysts were studied by using XRD, N₂-physisorption, Raman spectroscopy, SEM-EDX, TEM, XPS, and pyridine adsorption using FTIR and H₂-TPR techniques. It was observed that iron oxide was highly dispersed on the sulfated TiO₂ nanotube support due to its strong interaction. The activity of these catalysts in the catalytic removal of NO with propane was also studied in the temperature range of 300–500 °C. Highest activity (90% NO conversion) was observed with 5 wt% iron oxide supported on sulfated TiO₂ catalyst at 450 °C. Selective catalytic reduction of NO activity of the catalysts was correlated with iron oxide loading, reducibility, and the Brönsted and Lewis acid sites of the catalysts. The catalyst also showed good stability under studied reaction conditions that no deactivation was observed during the 50 h of reaction.     

Structural and magnetic characterization of MnxZn1 − xFe2O4 (x = 0.2; 0.35; 0.65; 0.8; 1.0) ferrites obtained by the citrate precursor method

In this work the microstructure and magnetic properties of Mn-Zn ferrites powders were investigated. Mn_xZn1 _− xFe₂O₄ powders where x = 0.2; 0.35; 0.5; 0.65; 0.8 and 1.0 were obtained by citrate precursor method. Citrate resin precursor was burned on air atmosphere at 400 °C for 3 h. Mn-Zn powders were calcined at 950 °C during 150 min under inert atmospheres: N₂ and rarefied atmosphere. Thermal analysis of precursor resin, phase evolution and microstructure of Mn-Zn ferrites powders were investigated by TG, DTA, XRD and SEM techniques. The powders calcined under rarefied atmosphere show spinel cubic structure and contamination of α-Fe₂O₃, while powders calcined under N₂ presents only the spinel cubic structure. Particle size was observed by SEM ranging from 80 to 150 nm. The magnetic properties were measured employing a vibrating sample magnetometer (VSM). It was observed that the saturation magnetization M_s increased with the increase of Mn content. The M_s of Mn_0.8Zn_0.2Fe₂O₄ calcined on rarefied atmosphere and Mn_0.8Zn_0.2Fe₂O₄ calcined on N₂ was 23.31 emu g⁻¹ and 56.23 emu g⁻¹, respectively.     

Ca3(PO4)2 coating of spherical Ni(OH)2 cathode materials for Ni-MH batteries at elevated temperature

Calcium phosphate was used for surface modification of spherical nickel hydroxide to improve its high temperature performance at the first time due to its low cost. The Ca₃(PO₄)₂ and Co(OH)₂ coated nickel hydroxides were prepared by precipitation of Ca₃(PO₄)₂ on the surface of spherical nickel hydroxide, followed by precipitation of Co(OH)₂ on its surface. The optimum coating content of calcium was around 2% (atomic concentration) to obtain high discharge capacity both at 25 and 60 °C. It was shown that the discharge capacity of nickel hydroxide at higher temperatures was improved by coating of Ca₃(PO₄)₂ and cobalt hydroxide. The high temperature performances of the sealed AA-sized nickel-metal hydride (Ni-MH) batteries using Ca/Co coated nickel hydroxide as positive electrodes were carried out, showing much better than those using uncoated or only Co(OH)₂ coated nickel hydroxide electrodes. The charge acceptance of the battery using 2% Ca and 2% Co coated nickel hydroxide reached 81% at 60 °C, where the charge acceptances for uncoated and only Co(OH)₂ coated nickel hydroxide were only 42 and 48%, respectively. It has shown that the Ca/Co coating is an effective way to improve the high temperature performance of nickel hydroxide for nickel-metal hydride batteries. It is a promising cathode material of Ni-MH batteries for EV applications due to the cost.     

TaCx Thin Films Prepared by Atomic Layer Deposition as Diffusion Barriers for Cu Metallization

TaC_x films were deposited by atomic layer deposition (ALD) using tris (neopentyl) tantalum dichloride, (Ta[CH₂C(CH₃)₃]₃Cl₂) and H₂ plasma as the precursor and reactant, respectively, at substrate temperatures ranging from 200°C to 400°C. The ALD–TaC_x films with the formation of nanocrystalline structures and a rock‐salt phase were confirmed by X‐ray and electron diffraction. The ALD temperature window was found to be 225°C–300°C with a growth rate of ~0.11 nm per cycle. The resistivity of the ALD–TaC_x films was dependent on the microstructural features, such as the grain size and crystallinity, as well as their composition (C/Ta ratio), and the presence of impurities in the films, which could be controlled by varying the deposition parameters, such as the deposition temperature and reactant pulse conditions. With increasing deposition temperature and reactant pulse time, Ta‐rich films with a low Cl impurity concentration and larger grain size were obtained. The film with a resistivity less than 400 μΩ cm was obtained at 300°C, which was within the ALD temperature window, by optimizing the H₂ plasma pulse time. The step coverage of the film deposited at 300°C was approximately 100% over the trench structure (top opening width of 25 nm) with an aspect ratio of ~4.5. The performance of the ALD–TaC_x films deposited under the optimized conditions was evaluated as a diffusion barrier for the Cu interconnects. The structure of Cu (100 nm)/ALD–TaC_x (5 nm)/ Si was stable without the formation of copper silicide after annealing at 600°C for 30 min.     

Synthesis of fluorine-graphite intercalation compounds by elemental fluorine and high oxidation-state transition-metal fluorides

Fluorine-graphite intercalation compounds have been synthesized using high purity fluorine gas and high oxidation-state transition-metal fluorides, AgF₃ and NiF₃, at room temperature and at −78 °C. At room temperature, a mixture of stage 1 + 2 − 4 compounds with compositions, C_4.2F to C_14.6F were obtained. On the other hand, stage 2–4 compounds with compositions C_5.6F to C_14.2F were synthesized at −78 °C. The fluorinating ability of AgF₃ and NiF₃ has been shown more clearly at room temperature because a small amount of fluorine was intercalated/absorbed into graphite at −78 °C without catalysts. XPS spectra show that ionic, nearly ionic, semi-covalent and covalent fluorines coexist in the C_xF samples, and that the covalency of CF bonding increases with decreasing stage number.