Synthesis of ordered mesoporous Pd/carbon catalyst with bimodal pores and its application in water-mediated Ullmann coupling reaction of chlorobenzene

Heterogeneous palladium catalysts have been supported on the ordered mesoporous carbons (Pd/OMC) with bimodal pores which are prepared by the surfactant-templating approach. Characterization using XRD, TEM, XPS, H₂ chemisorption, and N₂ sorption techniques reveals that the Pd/OMC catalysts have the ordered 2-D hexagonal mesostructure (space group of p6mm), extremely high surface areas (~1800 m²/g), large pore volumes (~1.64 cm³/g), bimodal pores (6.3 nm of primary mesopores and 1.7 nm of secondary mesopores inside the pore walls), hydrophobic carbon surface, and small metal particles well-dispersed inside the secondary small mesopores. This catalyst exhibits a high yield of 43% for biphenyl from the Ullmann coupling reaction of chlorobenzene in water at 100 °C without assistance of any phase transfer catalyst and can be reused up to 10 times, providing potential opportunities for industrial applications such as coupling and hydrogenation reactions.     

Preparation and characterization of SnO2 nanoparticles incorporated into talc porous materials (TPM)

Tin oxide (SnO₂) particles incorporated into porous material with different Sn/Si molar ratios were prepared. Talc was mechanically milled and subsequently leached to prepare talc porous material (TPM) which was used as host for incorporating SnO₂ nanoparticles. The SnO₂ incorporated TPM (SnO₂/TPM) samples were characterized by X-ray diffraction (XRD), high-resolution TEM (HRTEM), Fourier transformation infrared spectroscopy (FT-IR) and N₂ adsorption techniques. The specific surface area and pore volume decrease significantly from 260 m²/g and 0.51 ml/g for TPM sample to 178 m²/g and 0.32 ml/g for SnO₂/TPM sample with Sn/Si molar ratio of 0.4, respectively. Both of them can be attributed to the presence of SnO₂ particles within the pores of the SnO₂/TPM samples.     

Crack growth resistance of fluoroelastomer vulcanizates filled with particulate and fibre filler

Crack growth characteristics of fluoroelastomer vulcanizates filled with carbon black (size: 30 nm) and short Kevlar fibre (6 mm length) under static and dynamic conditions have been evaluated. The fibre reinforced vulcanizate shows higher J _c values (80 kJ m^–2) than both the carbon black filled sample (44 kJ m^–2) and the control (15 kJ m^–2). However, under dynamic fatigue conditions, the black filled sample is stronger.     

Effect of calcination on the microstructures of titania nanoparticles prepared in W/O microemulsions

Monodispersed titania nanoparticles were prepared from reacting TiOCl₂ with NH₄OH in water/Triton X-100/n-hexanol/cyclohexane microemulsions. The effect of calcination on the microstructures of the particles was investigated. The particles synthesized were amorphous, transformed into the anatase phase at 300°C, and further into the rutile phase at 850°C. The crystallite size of the particles was 9.7 to 35.6 nm in the temperature range between 300 and 900°C. Secondary particles, agglomerates of finer primary particles, were about 20 nm in size at 200°C and increased markedly by a factor of 10 to 20 at 900°C due to a significant interagglomerate densification. With increasing calcination temperature from 300 to 900°C, the specific surface area of the particles decreased rapidly from 317.5 to 8.4 m²/g, whereas the average pore radius increased considerably from 2.9 to 31.8 nm as the result of shrinkage of the agglomerates, destruction of the minute intercrystallite pores, and interagglomerate densification.     

Synthesis of uniformly porous NiO/ZrO2 particles

Porous NiO-ZrO₂ particles were successfully synthesized using a spray-drying method with polystyrene latex (PSL: 400 nm) as a template and starting materials that included NiO powder (7 nm) and ZrO₂ sol (1.2 nm). Porous particles with an average diameter of 4.5 μm and nearly spherical, narrow pores with an average size of ∼300 nm were obtained from the precursor at a pH of 3.7. The Brunauer, Emmett and Teller (BET) surface area of the prepared particles was relatively high—about 27 m²/g. When the solution pH was increased to 9.7, the particle morphology became completely spherical, indicating that the morphology of prepared particles can be controlled by adjusting the pH. Calcinations at 900 and 1200 °C were carried out to estimate the thermal stability of the prepared particles, which had shrinkage of less than 36%. The existence of these pores means that various applications, such as electrodes and catalysts, will be possible for the prepared particles.     

Influence of carbon precursors on thermal plasma assisted synthesis of SiC nanoparticles

Nanosized SiC was synthesized by solid state method using silicon and carbon powders followed by non-transferred arc thermal plasma processing. X-ray diffraction (XRD) analysis revealed that activated carbon has highest reactivity while graphite has lowest activity in the crystallization of SiC through solid state method. The reactivity was dependent on surface area of carbon source and activated carbon with highest surface area (590.18 m² g⁻¹) showed highest reactivity, whereas graphite with least surface area (15.69 m² g⁻¹) showed lowest reactivity. The free silicon content was decreased with increasing reaction time as well as carbon mole ratio. Scanning electron microscope (SEM) study showed that the shape and size of synthesized SiC depends on the shape and size of carbon source. SiC nanoparticles within 500 nm were formed for carbon black while bigger particles (∼5 μm) were formed for activated carbon and graphite. Plasma processing of these solid–solid synthesized SiC resulted into the formation of well dispersed, ultrafine SiC nanoparticles (30–40 nm) without any structural modification. Thermal plasma processing resulted into the increase in crystallite size of SiC.     

椰壳活性炭孔结构对Li-S电池性能的影响

以椰壳为原料,采用化学活化法制备不同比表面积和孔结构的活性炭,通过改变制备工艺参数来调节活性炭的比表面积和孔结构。将活性炭负载60%(质量分数)硫后,作为锂硫电池的正极材料,研究活性炭孔结构对锂硫电池性能的影响。结果表明:随着活性炭比表面积的增加,中孔比例增加,锂硫电池比容量逐步提高。其中,当活化剂与炭化料的质量比为4时,活性炭的比表面积达到2900m2/g,中孔率达到15.36%。在电流密度为200mA/g时,首次放电比容量高达1294.5mAh/g,循环100次后的可逆比容量仍然高达809.3mAh/g。     

Hydrogen Storage in Carbon-Based Nanostructured Materials

Carbon nanostructures represent a revolution in science and hold the potential for a large range of applications because of their interesting electrical, mechanical, and optical properties. Multiwall carbon nanotubes and carbon nanofibers of herringbone formation were grown by chemical vapor deposition on different catalysts from a number of hydrocarbon sources. After the total or particle removal of the catalyst system, the carbon nanostructures were analyzed for hydrogen uptake. Six samples of nanofibers grown on a Pd-based catalyst system (with a surface area of 425–455 m²/g) were controlled oxidized in air, such that they had different ratios of Pd/C varying from 0.05 to 0.9 mole ratio. The hydrogen uptake experiments were performed volumetrically in a Sievert-type installation and showed that the quantity of desorbed hydrogen (for pressure intervals ranging from 1 to 100 bars) by the carbon nanostructures free of any metal catalyst particles was between 0.04 and 0.33% by weight. For the samples of nanofibers that contained Pd in various Pd/C ratios, palladium revealed catalytic properties and supplied atomic hydrogen at the Pd/C interface by dissociating the H₂ molecules. The results show a direct correlation between the Pd/C ratio and the quantity of hydrogen absorbed by these samples. A saturation value of about 1.5 wt.% was reached for a high ratio of about 1:1 of Pd/C. The multiwall carbon nanotubes grown on a Fe:Co:CaCO₃ catalytic system and purified by acid cleaning and air oxidation showed a hydrogen uptake value of 0.1 to 0.2 wt.%.     

Preparation and electrochemical characteristics of mesoporous carbon spheres for supercapacitors

Mesoporous carbon spheres serving as electrode materials for supercapacitors were synthesized by a facile polymerization-induced colloid aggregation method using melamines as a carbon precursor and commercial colloidal silica as a silica source for hard template. After the carbonization of as-formed resins-template composites at 1000 °C and the removal of the silica template by hydrofluoric acid, the resulting mesoporous carbon spheres with a diameter size of ∼5 μm, specific surface area (up to 1280 m²/g) and uniform pore size as large as 30 nm could be obtained. Due to the enriched nitrogen content and the large pore size of the mesoporous carbon spheres affecting the surface wettability, resistance, and ion diffusion process in the pores, the mesoporous carbon spheres showed a high specific capacitance of 196 F/g in 5 mol/l H₂SO₄ electrolytes at a discharge current density of 1 A/g.     

AN INVESTIGATION ON THE OPTICAL PROPERTIES OF CARBON BLACK,FULLERITE, AND OTHER CARBONACEOUS MATERIALS IN RELATION TO THE SPECTRUM OF INTERSTELLAR EXTINCTION OF LIGHT

ABSTRACT

In this work, the optical properties in the UV-VIS of three carbon blacks having specific surface area from 145 to 7?m²/g and produced with furnace or thermal processes have been studied. The results have been compared to the optical properties (in the same spectral range) of C₆₀ fullerene photopolymer, to fullerite i.e., the carbon soot containing fullerenes and to a sample of carbonaceous matter containing carbyne. The scope of the work was to verify if any of the carbonaceous matter studied was able to match the interstellar extinction spectrum which shows a “bump” at 217.5?nm and which was originally attributed to interstellar graphitic particles. None of the materials studied has shown a peak at 217.5?nm. All the carbonaceous materials studied show maxima of absorption from 252 to 267?nm with the exclusion of C₆₀ photopolymer which has a completely peculiar and different spectrum from all other materials with three maxima at 271, 389 and 510?nm. All the carbon materials studied do not match the 217?nm peak, hence, cannot be considered the carrier of the interstellar “bump” but may be present in some circumstellar shells of late type stars, where the peaks at 240–250?nm have been recorded and attributed to a more ordered and partially graphitized carbonaceous matter. In the discussion, the matrix effect, the particle size, and the clumping of the material studied have been considered as cause of the shift of the peak to longer wavelength.

The carbon black samples have also been extracted with pentane or ethanol and the polycyclic aromatic hydrocarbons (PAH) identified have been discussed in the frame of recent works and in relation to the role that they play in the interstellar medium as potential carriers of the diffuse interstellar bands (DIBS).     

Preparation of nanoporous TiO2 film with large surface area using aqueous sol with trehalose

The precursor solutions containing TiO₂ sol for nanoporous films were prepared by hydrolyzing titanium(IV) isopropoxide and adding trehalose dihydrate. The porous and thick TiO₂ film was prepared by dip-coating technique on glass substrate and heating at 500 °C. The maximum thickness of the film prepared by one-run dip-coating was ca. 740 nm. The film was composed of nanosized particles (10–20 nm) and pores (7 nm). The specific surface area and porosity of the film were 163 m²/g and 65%, respectively.     

Microstructure and corrosion resistance of Ni-based alloy laser coatings with nanosize CeO2 addition

Abstract

Micron-size Ni-base alloy (NBA) powders were mixed with both 1.5 wt.% (hereinafter %) micron-size CeO₂ (m-CeO₂) and also 1.5% and 3.0% nano-size CeO₂ (n- CeO₂) powders. These mixtures were coated on low-carbon steel (Q235) by 2.0 kW CO₂ laser cladding. The effects on the microstructures, phases and electrochemical corrosion of the coatings upon the addition of m- and n- CeO₂ powders to NBA (m- and n- CeO₂ /NBA) have been investigated. The results showed that a smooth coating was prepared under suitable processing parameters (P= 2.0 kW, V= 180 mm min^{- 1}) by adding 1.5% n- CeO₂. In addition to the primary phases of γ-Ni, Cr₂₃ C₆ and Ni₃ B in the Ni-base alloy coating, CeNi₃ was formed in Ni-base alloy coatings with both n- CeO₂ and m-CeO₂ particles, and CeNi₅ appeared in the coating upon decreasing the size of CeO₂ particles. Well-developed dendrites were observed in the Ni-base alloy coating; directional dendrites grew at the interface in the coating upon the addition of m-CeO₂, whereas fine and multioriented dendrites grew upon decreasing the size of CeO₂ particles to the nanoscale. Actinomorphic dendrites and compact equiaxed dendrites grew from the interface to near the surface upon increasing the content of n- CeO₂ from 1.5 to 3.0%. In strongly acidic HNO₃ solution, the severe corrosion of dendrites occurred and there were many corrosion pits in the Ni-base alloy coating; intercrystalline corrosion also has a dominant role upon the addition of m-CeO₂, whereas uniform corrosion occurs in the coating as the size of CeO₂ particles is decreased to nanoscale.     

Optical and photocatalytic properties of the Fe-doped TiO2 nanoparticles loaded on the activated carbon

In this work, Fe-doped (1?wt%) TiO₂ loaded on the activated carbon nano-composite was prepared using a sol-gel method. A prepared nano-composite was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), BET surface area, Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) spectroscopy and UV–Vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the nano-composite was evaluated through degradation of synthetic textile wastewater, reactive red 198, under visible light irradiations. The XRD result indicated that the TiO₂ nano-composite contained only anatase phase. The surface area of the TiO₂ increased from 48?m²/g to 100?m²/g through the fabrication of the nano-composite. The FE-SEM results indicate that the TiO₂ particles with an average particle size of 35–70?nm can be deposited homogeneously on the activated carbon surface. DRS showed that the Fe doping in the TiO₂ -activated carbon nano-composite induced a significant red shift of the absorption edge and then the band gap energy decreased from 3.3 to 2.9?eV. Photocatalytic results indicated that the photocatalytic activity of the Fe doped TiO₂ increased under visible light irradiation in the presence of the activated carbon.     

Field-activated,pressure-assisted combustion synthesis of tungsten carbide–nickel composites

The field-activated, pressure-assisted combustion synthesis (FAPACS) process, which combines the simultaneous synthesis and densification of materials, was utilized to produce WC–10 wt.% Ni composites from reactant mixtures of W, Ni, and different carbon sources. The product composition, density, and microhardness of WC–Ni composites fabricated through the FAPACS process were investigated. The results show that the Vickers microhardness and toughness were 1287 kg/mm² and 7.8 MPa m^1/2 for the product made with activated carbon, and 1424 kg/mm² and 5.9 MPa m^1/2 with carbon black.     

Synthesis of hollow silica spheres SBA-16 with large-pore diameter

Hollow silica SBA-16 spheres with cubic ordered mesoporous shells were synthesized by an emulsion-templating method, using Pluronic F127 as a structure-directing agent, tetraethyl orthosilicateas as a silica source and heptane as a cosolvent in the presence of NH₄F. The size of these spheres is in the range of 10 to 30 μm. The shell is about 700 nm thick and consists of large pores, ~ 9 nm in diameter, arranged in a cubic order. After calcination, the spheres maintain their mesoporosity and show a high surface area of 822 m²/g. The formation mechanism of the silica hollow spheres is discussed.     

Effect of the SiO2/TiO2 ratio on the solid acidity of SiO2-TiO2/montmorillonite composites

SiO₂-TiO₂/montmorillonite composites with varying SiO₂/TiO₂ molar ratios were synthesized and the effect of the SiO₂/TiO₂ ratio on the solid acidity of the resulting composites was investigated. Four composites with SiO₂/TiO₂ molar ratios of 0, 0.1, 1 and 10 were synthesized by the reaction of colloidal SiO₂-TiO₂ particles prepared from alkoxides with sodium-montmorillonite at room temperature. The composites showed slight expansion and broadening of the XRD basal reflection, corresponding to the intercalation of fine colloidal SiO₂-TiO₂ particles into the montmorillonite sheets and incomplete intercalation to form disordered stacking of exfoliated montmorillonite and colloidal SiO₂-TiO₂ particles. The colloidal particles crystallized to anatase in the low SiO₂/TiO₂ composites but remained amorphous in the high SiO₂/TiO₂ composites. The specific surface areas (S_BET) of the composites measured by N₂ adsorption ranged from 250 to 370 m²/g, considerably greater than in montmorillonite (6 m²/g). The pore size increased with decreasing SiO₂/TiO₂ molar ratio of the composites. The NH₃-TPD spectra of the composites consisted of overlapping peaks, corresponded to temperatures of about 190 and 290 °C. The amounts of solid acid obtained from NH₃-TPD were 186-338 μmol/g in the composites; these values are higher than in the commercial catalyst K10 (85 μmol/g), which is synthesized by acid-treatment of montmorillonite. The present sample with SiO₂/TiO₂ = 0.1 showed the highest amount of acid, about four times higher than K10.     

Iron oxide nanopowders prepared by the electroexplosion of wire

We have studied the effect of process parameters (supplied energy, oxygen concentration in the gas mixture, and others) on the particle size and yield of iron oxide nanopowder obtained by the electroexplosion of wire. Under optimal conditions, up to 25% of the particles in the powder were 15–20 nm in size (specific surface of up to 100 m²/g). Using several independent characterization techniques, we determined the phase composition, elemental composition, and structure of the material in the bulk and on the surface of the particles. The majority phase in the powder (90–98 wt %) is the metastable oxide γ-Fe₂O₃, which is sufficiently stable under ordinary storage conditions. The powder also contains the stable oxide α-Fe₂O₃. The effect of annealing in air and helium on the phase composition and carbon content of the powder is examined. The results are interpreted in terms of redox and diffusion processes.     

Effects of carbon content on mechanical properties of 5%Mn steels exhibiting transformation induced plasticity

Abstract

A series of highly ductile, high strength steels exhibiting transformation induced plasticity due to retained austenite was developed by varying the carbon content in the range 0·01–0·4 wt-% in 5 wt-%Mn based steel. For up to 0·l%C the mechanical properties are insensitive to cooling rate after intercritical heating, but afurther increase in carbon content causes a large sensitivity to the cooling rate, owing to carbide precipitation occurring during slow cooling. By suppressing this carbide precipitation with water quenching after the intercritical holding, an excellent combination of tensile strength (1580 MN m^?2) and uniform elongation (21%) was attained at 0·3%C in this series.

MST/1964     

Preparation of zirconia and silicon carbide whisker biphasic powder mixtures by carbothermal reduction of zircon powders

Carbothermic reduction of zircon powders has been studied under argon and nitrogen gas pressures of 0.15 MPa in order to obtain biphasic composite powder mixtures containing zirconia and silicon carbide whiskers. The reduction has been carried out using different mole ratios of carbon and zircon. Carbon was used in the form of activated charcoal (specific surface area 1000 m²g^–1) or carbon black (specific surface area 300 m²g^–1). Whilst complete decomposition to m-ZrO₂ was obtained in the argon atmosphere at 1700 °C, under the nitrogen atmosphere the conversion was incomplete even at 1700 °C. However, the extent of conversion to zirconia at 1650 °C under nitrogen was found to be more than that under argon gas. In a few cases, particularly under the nitrogen atmosphere, minor amounts of other forms of zirconia e.g., tetragonal (t)-ZrO₂ or orthorhombic (o)-ZrO₂ were formed along with the major monoclinic (m)-ZrO₂ phase. The rate of reaction was found in general to increase with an increase in the carbon content. The studies particularly indicate that activated charcoal is a better reducing agent than carbon black owing probably to its enormous surface area. Further, it was also noted that cobalt chloride and sodium chloride act as a catalyst and a space forming agent respectively. They aid silicon carbide whisker formation and growth and hence the reaction is appreciably accelerated and reaches completion at 1650 °C in the argon atmosphere.     

Tuning the pore size and structure of mesoporous carbons synthesized using an evaporation-induced self-assembly method

Mesoporous carbons (MCs) have been prepared by the carbonization of reverse triblock copolymer-phloroglucinol/formaldehyde resin composites, which were themselves formed by hydrogen-bonding interaction through the evaporation-induced self-assembly method. The microstructure of MCs was analyzed by nitrogen adsorption isotherms and transmission electron microscope. The results showed that the pore size could be readily tailored from 4.7 to 17.8 nm by simply varying the weight ratios of formaldehyde and surfactants while the amounts of the other reactants were kept constant. The highest surface area and pore volume of MCs are 410 m²/g and 0.77 cm³/g, respectively. Moreover, the pore structure also can be controlled as ink-bottle or cylinder type.