Specific Surface Area Of Samples Research Articles

Controllable syntheses of α- and δ-MnO2 as cathode catalysts for zinc-air battery

Four MnO2 samples were synthesized through a simple reaction of KMnO4 with high-purity graphite in different concentrations of sulfuric acid at low temperature. Their morphology, crystal structure and performance as cathode catalysts of zinc-air battery were investigated with X-ray diffraction (XRD), Fourier transformation infrared spectrometer (FTIR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) and electrochemical tests. It is found that the crystal structure and the morphology of the synthesized samples depend on the sulfuric acid concentration. The synthesized samples have large specific surface area and exhibit excellent performance compared to the commercial electrolytic manganese dioxide (γ-MnO2). Two varieties of manganese dioxides, δ-MnO2 (the as-prepared samples a and b) and α-MnO2 (the as-prepared sample c and d), were obtained when using low and high sulfuric acid concentration, respectively. Higher sulfuric acid concentration favors the agglomeration of the particles. The specific surface area of samples a, b, c, d, and γ-MnO2 is 83.2, 81.1, 88.5, 86.8, and 43.5m2g−1, corresponding to discharge capacity of zinc-air batteries is 169.5, 160.3, 175.2, 171.5, and 112.2mAh, respectively.

Effect of Slimes on Iron Ores Flotation

The presence of slimes is, in general, harmful to the flotation of iron ores, affecting the selectivity and the quality of the concentrates, besides causing an increase in reagents consumption. This work describes the behavior of different iron ore types from the Iron Quadrangle, Brazil, with respect to desliming in hydrocyclones and flotation, including a study on the dispersion degree as a function of pH. Flotation experiments were performed at different slimes contents (designated as by-pass) aiming at assessing the influence of this variable on the selectivity. The different ore types present differences in chemical and mineralogical composition and also in size distribution. The content of slimes not removed in the desliming stage (by-pass) affects differently the selectivity of each ore type. Some ores keep the selectivity constant for all levels of by-pass, but present a reduction in phosphorus grade in the concentrate for reduced by-pass levels. Other types respond to the reduction of by-pass with increased selectivity. As a general rule, by-pass levels lower than 4% lead to a stable behavior concerning selectivity, yielding low phosphorus content in the concentrate. The behavior of each ore type is related to the chemical and mineralogical composition and size distribution of the slimes and also to the dispersion degree of the ore. Preliminary tests indicated that the specific surface area of samples with different by pass levels can explain the flotation behavior.

Preparation of Mo-Embedded Mesoporous Carbon Microspheres for Friedel–Crafts Alkylation

Herein we report the preparation of Mo-embedded mesoporous carbon microspheres (Mo@C) in which molybdenum trioxide (α-MoO3) phase as high as 42% can be included. The precursor solid synthesized from a hydrothermal route consists of highly dispersed molybdenum dioxide (MoO2) crystals with the size of 3–6 nm. Carbonization of this solid precursor strengthens the sphere structure and generates micro- and mesopores within the resultant biphasic nanocomposite. Upon the carbonization, some of the MoO2 nanocrystals are further reduced to Mo2C. The oxidation states of encapsulated molybdenum can be tuned to Mo6+ (i.e., α-MoO3) by calcination in air at 300 °C without causing loss of carbonaceous matrixes. With this treatment, more mesopores are generated and specific surface area of sample is increased to 371 m2/g. Interestingly, the surface of these nanocomposites is amphiphilic due to copresence of hydrophilic and hydrophobic groups, which favors the particle dispersion. The α-MoO3 embedded mesoporous carbon mic...

The characteristics of the nanosized η-TiO2 polymorph

The nanosized η-TiO2 polymorph was prepared by the hydrolysis of titanyl sulfate (TiO)SO4 · xH2SO4 · yH2O. η-TiO2 was studied by X-ray diffraction, X-ray photoelectron spectroscopy, IR spectroscopy, and Raman spectroscopy. Characteristic X-ray data and distinguishing Raman spectrum features were found for η-TiO2,. The surface of η-TiO2 samples contained adsorbed OH− particles and water molecules or water molecules of crystal hydrates. The free specific surface area of samples with crystallite sizes of L = 50 (4) and 60 (5) A was S = 10.17 (9) and 15.6 (1) m2/g. The characteristics of samples with η-TiO2 were favorable for their use as photocatalysts and adsorbents.

Mechanochemistry of hexagonal boron nitride: 1. Destruction and amorphization during mechanical treatment

The regularities of the mechanical activation of hexagonal boron nitride are analyzed using the X-ray diffraction, IR spectroscopy, transmission electron microscopy, dynamic light scattering, and adsorption methods. At the initial state of mechanical activation, the main process is material destruction. At this stage, the specific surface area increases to 400 m2/g and crystallographically oriented nanosized needles are formed. At the same time, boron nitride crystal structure is disordered with an increase in interplanar distance d(002). The disordering is assumed to be due to a shift along planes (001). At a specific dose of supplied mechanical energy above 6–8 kJ/g, the disordering processes dominate and the material is amorphized. At this stage, the specific surface area of samples decreases.

A thermogravimetric and FT-IR study of the reduction by H2 of sulfated Pt/CexZr1−xO2 solids

The nature, concentration and reducibility by H2 of sulfate species formed from SO2 oxidation were studied over a range of Pt/CexZr1−xO2 catalysts using infrared spectroscopy and thermogravimetry. Ionic sulfates were formed over ceria and Ce-containing catalysts, even at high Zr content. The sample-specific surface area, the presence of platinum and the zirconium proportion affected the rate and extent of formation of sulfate in the bulk of the materials. Sulfate reduction by H2 first occurred at the CexZr1−xO2 surface. Bulk-like S-containing species subsequently migrated towards the surface to continuously replace surface sulfates removed by the reduction. The temperature required for sulfate migration as well as that necessary for sulfate reduction increased with the Zr content. The amount of stored sulfur is closely linked to the specific surface area of the sample. Finally, we have clearly shown that thermogravimetry was an appropriate technique for evaluating the oxygen storage capacity (OSC) of sulfated ceria–zirconia mixed oxides, despite the additional complexity due to the presence of sulfate compounds and various reduced S-species that can be formed during sample reduction.

The influence of thermal treatment on the properties of sorbents prepared from water conditioning precipitates

Sorbent samples based on the thermally activated precipitate formed in iron removal from under-ground water (water conditioning wastes) were studied by low-temperature nitrogen adsorption and thermal and X-ray analysis. The precipitate was found to be a material with a developed porous structure (the specific surface area of the initial sample was 229.9 m2/g). Calcining at 300°C decreased the specific surface area of the samples by 1.6–1.7 times and increased the volume of sorbing pores by 1.6 times. The precipitate material largely contained iron phases. An increase in the temperature of calcining contributed to deeper crystallization of the main phase, α-Fe2O3.

Synthesis of Fe3O4-based catalysts for the high-temperature water gas shift reaction

The water gas shift reaction is an essential process to adjust the CO/H2 ratio in the industrial production of hydrogen. FeCr catalysts have been widely used in this reaction at high temperature but have environmental and safety concerns related to chromium content. In this work, the replacement of chromium by molybdenum in magnetite-based catalysts is studied. The materials were prepared by oxidation–precipitation and wet impregnation and they were characterized using X-ray powder diffraction, X-ray fluorescence, transmission electron microscopy, and temperature programmed reduction. Specific surface areas of samples were also measured. The results obtained indicate that molybdenum increases thermal stability of the magnetite active phase and prevents metallic iron formation during the reaction. The oxidation–precipitation method allows obtaining the material directly in the active phase and molybdenum is incorporated into magnetite lattice.

Effect of the mechanochemical treatment of a V2O5/MoO3 oxide mixture on its properties

The mechanochemical treatment of a V2O5/MoO3 oxide mixture (V/Mo = 70/30 at %) was performed in planetary and vibratory mills under varying treatment times and media. The resulting samples were characterized using XRD analysis, micro-Raman spectroscopy, and XPS; their specific surface areas and catalytic activities in n-butane and benzene oxidation reactions were determined. It was found that the treatment of the oxide mixture in water resulted in chaotic degradation of the parent oxides, a decrease in crystallite sizes, and an increase in the specific surface area at a sufficiently uniform oxide distribution over the sample. The treatment in ethanol was accompanied by an anisotropic deformation of the V2O5 crystal by layer sliding in parallel to the vanadyl plane (010) and a chaotic degradation of MoO3 crystals. This process was accompanied by the partial nonuniform supporting of vanadium oxide crystals onto the surface of molybdenum oxide to increase the V/Mo ratio on the sample surface. In this case, the particle size of oxides decreased and the specific surface areas of samples increased. It was found that the treatment of the oxide mixture in air (dry treatment) resulted in the most significant decrease in the sizes of V2O5 and MoO3 crystals and a growth in the specific surface area. The amorphization of the parent oxides and the formation of MoV2O8 were observed as the treatment time was increased; in this case, an excess of amorphous vanadium oxide was supported onto the surface of this compound. It was found that, in all types of mechanochemical treatment, the binding energies of the core electrons of vanadium and molybdenum remained almost unchanged to indicate the constancy of the oxidation states of these elements. Mechanochemical treatment resulted in an increase in the activity of the samples in n-butane and benzene oxidation reactions and in an increase in the selectivity of maleic anhydride formation. In this case, an increase in the specific catalytic activity of the samples correlated with a decrease in the crystallite size of vanadium oxide, whereas selectivity correlated with an increase in the relative concentration of the V2O5 plane (010). In these reactions, samples after dry treatment exhibited a maximum activity, which can be related to the formation of MoV2O8.

On the issue of structure-chemical features of silicon oxides and thermal emission of singlet oxygen

Special features of the chemical structure of silicon oxides were analyzed by the methods of vibrational and electronic spectroscopy and it was found that cationic (Si-Si) and anionic (O2 and O3) sublattices contain isolated individual Si-CO oscillators, including electron-excited oscillators, and homoatomic bonds. By means of chromatographic and sorption-calorimetric analyses inverse dependence of singlet oxygen specific thermal emission on specific surface area of samples was found that corresponds to volume generation of excited states.

Synthesis and characterization of carbon-supported nanoparticles for catalytic applications

Metallic and carburized tungsten nanoparticles have been prepared using WCl 6 as precursor. The synthesis steps lead from tungsten hexachloride to tungsten carbide following the sequence WCl 6 → W 0 → α-W 2C → WC. These different compounds have been mainly characterized by X-ray diffraction, TEM observations and adsorption measurements. The total reduction of tungsten hexachloride can be completed at T = 973 K. The carburizing of the metallic lattice into carbide WC is observed at 1223 K although incomplete. At this temperature, crystal growth phenomena appear which are not desired for catalysis applications. The synthesis of nanoparticles supported on activated carbon is accompanied by a decrease of the specific surface area of samples, especially during high temperature carburizing.

SO2 Storage by CuTa2O6: Synergetic Oxidative Sorption

SO2 storage was performed on CuTa2O6 and its derivatives by repeating the cycle of oxidative sorption (SO2, 1000 ppm; O2, 3%) and reductive desorption (H2, 10%). Tantalum promoted the sorption of SO2 on CuTa2O6, and the synergetic oxidative sorption of copper and tantalum was investigated after several cycles. Observation of the specific surface areas of samples revealed that SO2 was absorbed also in the bulk of catalysts through synergetic oxidative sorption. XRD observation showed that the samples undergoing synergetic oxidative sorption were amorphous. Through observation of ammonia-TPD, it was found that the samples were comparable to super acid. Synergetic oxidative sorption was investigated on the physical mixture of copper oxide and tantalum oxide, as well as on the mixed oxides of CuO and MO (M = Nb, Cr, Ti and Zr).

Preparation, Characterization, and Performance of Alumina-Supported Nanostructured Mo−Phosphide Systems

A series of γ-Al2O3-supported molybdenum phosphide catalysts containing fixed Mo-loading (9.9 wt %) and variable P amounts (1.5−9.6 wt %) were prepared by temperature-programmed reduction (TPR) from their oxide precursors in hydrogen. The effect of the P/Mo atomic ratio on the structure of the molybdenum phosphide materials was studied by SBET, XRD, HRTEM, TPD−NH3, H2 chemisorption, XPS, and 31P- and 27Al-MAS NMR techniques. The reactions involved in the transformation of oxide precursor to Mo−phosphide were followed by TPR. Specific surface areas of samples subjected to reduction at 1123 K were rather high (210−263 m2 g-1). These catalysts were tested in the gas-phase hydrodesulfurization (HDS) of dibenzothiophene (DBT) at 553 K and 3.4 MPa. All Mo−phosphide catalysts were more active than a molybdenum sulfide sample with the same Mo-loading. The Mo−phosphide catalysts with P/Mo ratios of 1 and 1.1 were found to be the most active among the catalysts studied. The activity drop observed for higher P-loadi...

Preparation of ZrO<sub>2</sub> and Al<sub>2</sub>O<sub>3</sub> Thin-Films on Stainless Steel by Spray Pyrolysis

We have investigated the deposition of ZrO2 and Al2O3 films on a stainless steel (SS) substrate by spray pyrolysis method. The ZrO2 films were deposited from aqueous solution of zirconium dinitrate oxide. For Al2O3 films, a boehmite sol was used. The specific surface areas of samples were determined by the BET-method and sample surfaces were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. The spray pyrolysis method permits the preparation of ZrO2 and Al2O3 thin films on SS with good adhesion. This method enables preparation of oxide layers with relatively high specific surface area, suitable for applications as catalysts supports.

Effects of Palladium Loading on the Response of Thick Film Flame-made ZnO Gas Sensor for Detection of Ethanol Vapor

ZnO nanoparticles doped with 0-5 mol% Pd were successfully produced in asingle step by flame spray pyrolysis (FSP) using zinc naphthenate and palladium (II)acetylacetonate dissolved in toluene-acetonitrile (80:20 vol%) as precursors. The effect ofPd loading on the ethanol gas sensing performance of the ZnO nanoparticles and thecrystalline sizes were investigated. The particle properties were analyzed by XRD, BET,AFM, SEM (EDS line scan mode), TEM, STEM, EDS, and CO-pulse chemisorptionmeasurements. A trend of an increase in specific surface area of samples and a decrease inthe dBET with increasing Pd concentrations was noted. ZnO nanoparticles were observed asparticles presenting clear spheroidal, hexagonal and rod-like morphologies. The sizes ofZnO spheroidal and hexagonal particle crystallites were in the 10-20 nm range. ZnOnanorods were in the range of 10-20 nm in width and 20-50 nm in length. The size of Pdnanoparticles increased and Pd-dispersion% decreased with increasing Pd concentrations.The sensing films were produced by mixing the particles into an organic paste composedof terpineol and ethyl cellulose as a vehicle binder. The paste was doctor-bladed ontoAl2O3 substrates interdigitated with Au electrodes. The film morphology was analyzed bySEM and EDS analyses. The gas sensing of ethanol (25-250 ppm) was studied in dry air at400°C. The oxidation of ethanol on the sensing surface of the semiconductor wasconfirmed by MS. A well-dispersed of 1 mol%Pd/ZnO films showed the highest sensitivityand the fastest response time (within seconds).

Crystallization processes of Li2O–Ga2O3–SiO2–NiO system glasses

Crystallization processes of Li2O–Ga2O3–SiO2–NiO system glasses have been studied by X-ray diffraction, differential calorimetry and optical absorption. Transparent glass-ceramic containing LiGa5O8:Ni2+ as the sole crystalline phase has been obtained from glass with the composition of 13Li2O–23Ga2O3–64SiO2–0.1NiO (in mol%) by the heat treatment in the temperature range from 923 to 953K. It was revealed that the specific surface area of samples enhances crystallization of LiGaSi2O6 but obstructed that of LiGa5O8. LiGa5O8 grew to nano-sized crystallites dispersed in the glass matrices and did not affect the transparency seriously. In contrast, LiGaSi2O6 grew to crystallites with diameters more than 100nm on the surface and made the glasses opaque. Optical absorption measurements revealed that doped Ni2+ occupied five-folded trigonal bipyramidal sites in the as-quenched glass matrices but six-folded octahedral sites of precipitated LiGa5O8 in the glass-ceramics. It was confirmed that transparent glass-ceramic containing Ni2+:LiGa5O8 was effectively obtained by the heat treatment at a temperature of 953K for 10h.

The Use of Carbon Nanofiber Electrodes Prepared by Electrospinning for Electrochemical Supercapacitors

Poly(acrylonitrile) (PAN) solutions in dimethylformamide (DMF) were electrospun into webs consisting of 300 nm ultrafine fibers. High-surface area carbon nanofiber webs were prepared by oxidatively stabilized electrospun PAN fibers, followed by activation at 800°C with steam for different times. The specific surface areas of samples ranged from 460 to 1160 m 2 /g. The specific capacitances from the samples ranged from 133 to 75 F/g, depending on the activation time. The results provided a simple and economical means that could substantially enhance the capacitance of the carbon materials.

The synthesis and microstructure of morph-genetic TiC/C ceramics

Wood is a natural material with a novel and ordered hierarchical structure. In the present work, it is used as a bio-template to produce morph-genetic TiC/C ceramics. This is obtained by infiltrating the carbon preform pyrolyzed from wood with tetrabutyl titanate. It was subsequently sintered at 1400 °C to produce the final ceramic structure. By observing the microstructure under the scanning electron microscope and the transmission electron microscope, the morph-genetic TiC/C ceramics are shown retaining the complex morphology of the original template structure. The crystalline TiC was formed through the reaction of tetrabutyl titanate with carbon preform, and it was distributed mainly at the surface layer of the cellular wall. During the conversion of wood into carbon preform, the specific surface area of samples increased from 28.2 to 35.7 m 2 g −1, and its porosity also increased from 64.4% to 80.3%. However, during the conversion of carbon preform into morph-genetic ceramics, the specific surface area of samples decreased from 35.7 to 33.8 m 2 g −1, and its porosity also decreased from 80.3% to 76.5%. At the synthesis process, the variation of pore-size distribution is mainly in the range from 0.1 to 1 μm.

Formation and catalytic characterization of various rare earth phosphates

Various rare earth phosphates [rare earth elements: R = La, Ce, Pr, Nd, Sm, Yb, and Y; phosphates: Monazite-type, Xenotime-type, Rhabdophane-type, and Weinshenkite-type orthophosphates RPO4, polyphosphate R(PO3)3, and ultraphosphate RP5O14] were synthesized by heating the mixtures of each rare earth oxide and diammonium hydrogenphosphate or phosphoric acid. The compositions of rare earth phosphates were determined by XRD, FT-IR, and TG–DTA. Catalytic properties were studied as one of properties of various rare earth phosphates. Specific surface areas of samples were measured by the BET method. Acid strengths and amounts of acidic sites were measured using several indicators by n-butylamine titration. Acidic properties were also confirmed by adsorption of ammonia. Various rare earth phosphates were characterized by catalytic activities on dehydration reaction of 2-propanol, cracking/dehydrogenation reaction of cumene, and isomerization reaction of butene. The characterization of catalysts was discussed with regard to type of rare earth elements, type of phosphates, and type of phosphorus resources.

Effect of preoxidation and sintering on properties of ilmenite concentrates

The paper examines the effects of preoxidation and sintering on the phase composition, specific surface area, morphology and reducibility of ilmenite concentrates. Samples were preoxidised in air or sintered in argon by temperature-programmed heating to temperatures of 600–1400°C at a ramping rate of 300°C/h. In the concentrates preoxidised at temperatures up to 800°C, ilmenite formed an intermediate product, Fe 2O 3·2TiO 2, which decomposed into Fe 2O 3 and TiO 2. At temperatures above 800°C, pseudorutile was transformed into ferric pseudobrookite and rutile. Haematite recombined with rutile to form pseudobrookite at temperatures above 1000°C. When samples were heated in an argon atmosphere, ferric–ferrous pseudobrookite solid solution was formed from ilmenite and pseudorutile. Preoxidation and sintering at temperatures above 600°C caused a sharp decrease in the specific surface area of samples. The specific surface area decreased by more than 97% when samples were heated to 1200°C. Preoxidation enhanced while sintering retarded the reduction of iron oxides in ilmenite concentrates by methane–hydrogen gas mixtures in the temperature range of 550–800°C. Both preoxidation and sintering increased the temperature required to reduce titanium oxides. At high temperatures, such as 1200°C, the effects of preoxidation and sintering on isothermal reduction of ilmenites were negligible.