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BET Surface Area (bet + surface_area)
Selected AbstractsThe Effect of Surface Area and Crystal Structure on the Catalytic Efficiency of Iron(III) Oxide Nanoparticles in Hydrogen Peroxide DecompositionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2010Cenek Gregor Abstract Iron(II) oxalate dihydrate has been used as a readily decomposable substance for the controlled synthesis of nanosized iron(III) oxides. The polymorphous composition, particle size and surface area of these iron oxide nanoparticles were controlled by varying the reaction temperature between 185 and 500 °C. As-prepared samples were characterized by XRD, low-temperature and in-field Mössbauer spectroscopy, BET surface area and the TEM technique. They were also tested as heterogeneous catalysts in hydrogen peroxide decomposition. At the selected temperatures, the formed nanomaterials did not contain any traces of amorphous phase, which is known to considerably reduce the catalytic efficiency of iron(III) oxide catalysts. As the thickness of the sample (, 2 mm) was above the critical value, a temporary temperature increase ("exo effect") was observed during all quasi-isothermal decompositions studied, irrespective of the reaction temperature. Increasing the reaction temperature resulted in a shift of the exo effect towards shorter times and an increased content of maghemite phase. The maghemite content decreases above 350 °C as a result of a thermally induced polymorphous transition into hematite. The catalytic data demonstrate that the crystal structure of iron(III) oxide (i.e. the relative contents of maghemite and hematite) does not influence the rate of hydrogen peroxide decomposition. However, the rate constant increases monotonously with increasing sample surface area (and decreasing thermolysis temperature), reaching a maximum of 27,×,10,3 min,1(g/L),1 for the sample with a surface area of 285 m2,g,1. This rate constant is currently the highest reported value of all known iron oxide catalytic systems and is even slightly higher than that observed for the most efficient catalyst reported to date, which has a significantly larger surface area of 337 m2,g,1. This surprisingly high catalytic activity at relatively low surface area can be ascribed to the absence of a amorphous phase in the samples prepared in this study. Taking into account these new findings, the contributions of the key factors highlighted above (surface area, particle size, crystal structure, crystallinity) to the overall activity of iron oxides forhydrogen peroxide decomposition are discussed. [source] Microporous activated carbon spheres prepared from resole-type crosslinked phenolic beads by physical activationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Arjun Singh Abstract Microporous activated carbon spheres (ACSs) with a high specific Brunauer,Emmet,Teller (BET) surface area were prepared from resole-type spherical crosslinked phenolic beads (PBs) by physical activation. The PBs used as precursors were synthesized in our laboratory through the mixing of phenol and formaldehyde in the presence of an alkaline medium by suspension polymerization. The effects of the gasification time, temperature, and flow rate of the gasifying agent on the surface properties of ACSs were investigated. ACSs with a controllable pore structure derived from carbonized PBs were prepared by CO2 gasification. Surface properties of ACSs, such as the BET surface area, pore volume, pore size distribution, and pore diameters, were characterized with BET and Dubinin,Reduchkevich equations based on N2 adsorption isotherms at 77 K. The results showed that ACSs with a 32,88% extent of burn-off with CO2 gasification exhibited a BET surface area ranging from 574 to 3101 m2/g, with the pore volume significantly increased from 0.29 to 2.08 cm3/g. The pore size and its distribution could be tailored by the selection of suitable conditions, including the gasification time, temperature, and flow rate of the gasifying agents. The experimental results of this analysis revealed that ACSs obtained under different conditions were mainly microporous. The development of the surface morphology of ACSs was also studied with scanning electron microscopy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Study of the preparation and composition of the metallic function for the selective hydrogenation of CO2 to gasoline over bifunctional catalysts,JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2-3 2003Javier Ereña Abstract Bifunctional catalysts for the transformation of carbon dioxide and hydrogen into gasoline have been prepared by conventional and novel processes and characterized by measurement of BET surface area and volume and distribution of pores, and by X-ray diffraction, FTIR spectroscopy and X-ray fluorescence. The effects of the preparation conditions and of the atomic ratios between the metals on the structure and on the properties of the catalysts were studied. © 2003 Society of Chemical Industry [source] Preparation, characterisation and modification of carbon-based monolithic rods for chromatographic applicationsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 9 2010Ali H. Eltmimi Abstract A range of porous carbon-based monolithic (PCM) rods with flow-through pore sizes of 1, 2, 5 and 10,,m, were produced using a silica particle template method. The rods were characterised using SEM and energy-dispersive X-ray spectroscopy, BET surface area and porous structure analysis, dilatometry and thermal gravimetry. SEM evaluation of the carbon monolithic structures revealed an interconnected rigid bimodal porous structure and energy-dispersive X-ray spectroscopy analysis verified the quantitative removal of the embedded silica beads. The specific surface areas of the 1, 2, 5 and 10,,m rods were 178, 154, 84 and 125,m2/g after pyrolysis and silica removal, respectively. Shrinkage of the monolithic rods during pyrolysis is proportional to the particle size of the silica used and ranged from 9 to 12%. Mercury porosimetry showed a narrow distribution of pore sizes, with an average of ,700,nm for the 1,,m carbon monolith. The suitability of bare and surface oxidised PCM rods for the use as a stationary phase for reversed and normal phase LC was explored. The additional modification of PCM rods with gold micro-particles followed by 6-mercaptohexanoic acid was performed and ion-exchange properties were evaluated. [source] Preparation, Characterization, and Photocatalytic Properties of CaNb2O6 NanoparticlesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2009In-Sun Cho CaNb2O6 nanoparticles with a size range of 30,50 nm were synthesized by heat treatment at 600°C after a solvothermal process and their optical and photocatalytic properties were investigated. The prepared powders were characterized by X-ray powder diffractometer, field-emission scanning electron microscope, transmission electron microscope, UV-Vis diffuse reflectance spectroscopy, Fluorescence spectroscopy, and Raman spectroscopy. Compared with a powder of the same material prepared by a solid-state reaction (SS) method, the nanoparticles exhibited a higher Brunauer,Emmett,Teller (BET) surface area, more efficient light absorption, and enhanced photocatalytic activity for producing H2 from pure water under UV irradiation. The photoluminescence spectra revealed that a radiative recombination process is dominant in the powder prepared by the SS method (strong blue emission at 300 K) under UV light irradiation, while no obvious emission was observed in the nanoparticles. This decrease of the radiative recombination as well as the higher optical absorption ability and higher BET surface area resulting from the reduced dimensionality led to enhanced photocatalytic activity of the nanoparticles. [source] Factors influencing the adsorption of stabilizers onto carbon black: Flow microcalorimetry studiesJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 2 2000J. M. Peñta The surface activity of various kinds of carbon black toward phenolic antioxidants and hindered amine light stabilizers (HALS) was examined by using flow microcalorimetry (FMC). Phenolic hydroxyl and ester groups were found to be the moieties responsible for the adsorption activity of primary phenolic antioxidants onto the carbon black surfaces. Furthermore, a difference in the degree of phenolic hydroxyl hindrance by alkyl groups was found to be the main factor affecting the adsorption activity of the phenol group. A difference in the degree of substitution of the piperidine amine, as well as the number and type of functionality per molecule, are important factors that were found to influence the adsorption activity of HALS. Data from adsorption studies using model compounds, some of which represented functional portions of the stabilizer molecules, reflected behavior sin ilar to that observed with the stabilizers. In addition, these latter results showed that FMC analysis can yield potentially useful information beyond that given by the usual parameters such as BET surface area, I2, DBP, and CTAB adsorption values. Differences in the behavior between types of carbon black were evident and showed that the specific surface area is not the most important factor in the adsorption/desorption activity, but also the chemical nature of the surface. From the activity observed for model compounds, it was deduced that the presence of secondary and tertiary amine in the backbone and branch structures also has an important role in the adsorption activity of polymeric HALS. In general, the observed quantities can be related to the values of adsorption/desorption energy and to the molar mass of the probe. [source] Mechano-Chemical Changes of Nano Sized ,-Al2O3 During Wet Dispersion in Stirred Ball MillsPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 1 2004Frank Stenger Abstract The mechano-chemical changes in synthetic ,-Al2O3 during wet dispersion in a stirred ball mill, are studied. It is shown that a second phase is generated which can be identified as an aluminum hydroxide (Bayerite) by use of dynamic scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetry (TG), Fourier transformed infrared (FTIR) spectroscopy and transmission electron microscopy (TEM). The amount of the Bayerite phase produced increases with milling time. A comparison of the evaluated amounts from TG- and DSC-measurements are in reasonable agreement. Furthermore, the measured BET surface area shows a strong dependence on the temperature of sample preparation. Depending on the temperature, the bayerite phase is seen to convert to the ,-phase again and also forms meso- and possibly micro-pores, leading to a high BET surface area. In this paper, we highlight the necessity for using different methods to characterize the dispersion process, and for a correct interpretation of the measurement results. [source] Sm3+ -Doped Bi2O3 Photocatalyst Prepared by Hydrothermal SynthesisCHEMCATCHEM, Issue 4 2009Jakkidi Krishna, Reddy Abstract Bi2O3 and Sm3+ -doped Bi2O3 visible-light-active photocatalysts with different Sm3+ loadings (0.5, 1.0, and 2.0,wt,%) were synthesized by a hydrothermal method. The structural properties of the prepared catalysts were studied by X-ray diffraction (XRD), BET surface area, UV/Vis diffuse reflectance (DRS), FTIR, and X-ray photoelectron (XPS) spectroscopic techniques. The XRD spectra of the Sm-doped Bi2O3 catalysts calcined at 550,°C show only the characteristic peaks of Bi2O3. A high red shift in the range 450,600,nm was detected in the DRS band, leading to a large decrease in the band-gap energy from 2.82 to 2.0,eV. This red shift increased with increasing Sm content. XPS results revealed that Sm interacted with Bi2O3, wherein both Bi and Sm were in the +3 oxidation state. The photocatalytic activities of the catalysts were evaluated for the degradation of methylene blue and phenol under solar irradiation. Of all of the catalysts prepared, the Sm3+ -doped Bi2O3 with a Sm loading of 1,wt,% gave the best photocatalytic activity. [source] Highly Dispersed Ruthenium Hydroxide Supported on Titanium Oxide Effective for Liquid-Phase Hydrogen-Transfer ReactionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 36 2008Kazuya Yamaguchi Dr. Abstract Supported ruthenium hydroxide catalysts (Ru(OH)x/support) were prepared with three different TiO2 supports (anatase TiO2 (TiO2(A), BET surface area: 316,m2,g,1), anatase TiO2 (TiO2(B), 73,m2,g,1), and rutile TiO2 (TiO2(C), 3.2,m2,g,1)), as well as an Al2O3 support (160,m2,g,1). Characterizations with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and X-ray absorption fine structure (XAFS) showed the presence of monomeric ruthenium(III) hydroxide and polymeric ruthenium(III) hydroxide species. Judging from the coordination numbers of the nearest-neighbor Ru atoms and the intensities of the ESR signals, the amount of monomeric hydroxide species increased in the order of Ru(OH)x Effects of TiO2 Film on the Performance of Dye-sensitized Solar Cells Based on Ionic Liquid ElectrolyteCHINESE JOURNAL OF CHEMISTRY, Issue 12 2005Xu Pan Abstract Photo correlation spectroscopy was used to measure the particle size distribution of TiO2 films. Other parameters, such as porosity, BET surface area, average pore size, crystallite size D101, distribution of pore size etc. were also measured. The effects of these parameters on the ionic liquid based dye-sensitized solar cells (DSC) were studied. It was concluded that the particle size distribution of nanocrystalline TiO2 played an important role on the performance of DSC. The narrow particle size distribution of nanocrystalline TiO2 increased the efficiency of DSC, while the wide distribution decreased the efficiency of DSC. From the result above, it was also concluded that the photo correlation spectroscopy was a good method to identify the performance of TiO2 films. Based on electrochemical impedance spectroscopy, we found that the particle size distribution could affect the electronic contact between the TiO2 layers as well. The narrow particle size distribution made the electronic contact between TiO2 layers better than the wide particle size distribution of the TiO2 films, and then better the electronic contact, higher the efficiency of the DSC. [source] Characterization of biochar from fast pyrolysis and gasification systemsENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 3 2009Catherine E. Brewer Abstract Thermochemical processing of biomass produces a solid product containing char (mostly carbon) and ash. This char can be combusted for heat and power, gasified, activated for adsorption applications, or applied to soils as a soil amendment and carbon sequestration agent. The most advantageous use of a given char depends on its physical and chemical characteristics, although the relationship of char properties to these applications is not well understood. Chars from fast pyrolysis and gasification of switchgrass and corn stover were characterized by proximate analysis, CHNS elemental analysis, Brunauer-Emmet-Teller (BET) surface area, particle density, higher heating value (HHV), scanning electron microscopy, X-ray fluorescence ash content analysis, Fourier transform infrared spectroscopy using a photo-acoustic detector (FTIR-PAS), and quantitative 13C nuclear magnetic resonance spectroscopy (NMR) using direct polarization and magic angle spinning. Chars from the same feedstocks produced under slow pyrolysis conditions, and a commercial hardwood charcoal, were also characterized. Switchgrass and corn stover chars were found to have high ash content (32,55 wt %), much of which was silica. BET surface areas were low (7,50 m2/g) and HHVs ranged from 13 to 21 kJ/kg. The aromaticities from NMR, ranging between 81 and 94%, appeared to increase with reaction time. A pronounced decrease in aromatic CH functionality between slow pyrolysis and gasification chars was observed in NMR and FTIR-PAS spectra. NMR estimates of fused aromatic ring cluster size showed fast and slow pyrolysis chars to be similar (,7,8 rings per cluster), while higher-temperature gasification char was much more condensed (,17 rings per cluster). © 2009 American Institute of Chemical Engineers Environ Prog, 2009 [source] A comparative in situ Rietveld refinement study: thermal decomposition and transformation of CoAl and CoZnAl layered double hydroxidesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2008Rune E. Johnsen Rietveld refinement based on in situ X-ray powder diffraction (XRPD) data was combined with thermogravimetric analysis (TGA) and mass spectrometry (MS) to study and compare the phase transformations, thermal stability, microstructural and structural changes of two cobalt-containing nitrate-based layered double hydroxides (LDHs) upon heating in a controlled inert atmosphere of nitrogen. The XRPD data were collected, using synchrotron X-ray radiation, with a time resolution of 107,s, which made it possible to carry out detailed structural studies of the initial layered double hydroxides as well as their decomposition products: spinel for a CoAl,NO3 LDH and spinel/zincite for a CoZnAl,NO3 LDH. Correlating these data with those from the TGA,MS analyses gives us information about the transformation mechanisms. Rietveld refinements of the two spinel phases reveal remarkable differences. The a axis of the spinel formed by decomposition of the CoAl,NO3 LDH increases almost linearly from approximately 598 to 1163,K, mainly due to the dominating thermal expansion, whereas the a axis of the spinel formed by decomposition of the CoZnAl,NO3 shows a more complex temperature dependency. Between approximately 698 and 1073,K, the a axis is almost constant due to pronounced chemical interaction with an additional amorphous phase and the zincite phase, whereas from 1073 up to 1163,K it increases linearly. Calculations, based on the results of the Rietveld refinements, of the size of the octahedral and tetrahedral coordination polyhedra in the spinel show that the octahedra shrink and the tetrahedra expand with increasing temperature. The unusual thermal behaviour of the octahedra is discussed and attributed to the low formation temperature of the cobalt aluminium spinel phase. Finally, the intensity of a low-angle scattering (LAS) signal observed in the XRPD patterns was correlated with the decomposition of the LDH, and determination of the specific surface areas gave the temperature-dependent BET surface areas. [source] Porosity and surface characteristics of activated carbons produced from waste tyre rubberJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 1 2002Guillermo San Miguel Abstract Waste tyre rubber has proven to be a suitable precursor for the production of high quality activated carbons. The performance of these carbons in commercial applications such as water treatment or gas purification is highly dependent on their surface characteristics. This paper presents an in-depth investigation on how production conditions may affect the yield and characteristics of activated carbons produced from tyre rubber. For this purpose, three tyre rubbers of different particle sizes were consecutively pyrolysed and then activated in a steam atmosphere at 925,°C using a laboratory-scale rotary furnace. Activation was conducted at different intervals over 80,640,min to achieve different degrees of carbon burn-off. The resulting carbons were analysed for their elemental composition, ash content and nitrogen gas adsorption characteristics. The BET and t -plot models were used to investigate various aspects of their porosity and surface area characteristics. SEM analyses were also conducted for visual examination of the carbon surface. Results show that pyrolytic chars, essentially mesoporous materials, developed a very narrow microporosity during the initial stages of the activation process (up to 15,25,wt% burn-off). Further activation resulted in the progressive enlargement of the average micropore width and a gradual development of the mesoporous structure. Total micropore volumes and BET surface areas increased continuously with the degree of activation to reach values up to 0.498,cm3g,1 and 1070,m2g,1 respectively, while external surface areas developed more rapidly at degrees of activation above 45,wt% burn-off. Results presented in this work also illustrate that carbons produced from powdered rubber developed a narrower and more extensive porosity, both in the micropore and mesopore range, than those produced from rubber of a larger particle size. © 2001 Society of Chemical Industry [source] Oligomeric Alkoxysilanes with Cagelike Hybrids as Cores: Designed Precursors of Nanohybrid MaterialsCHEMISTRY - AN ASIAN JOURNAL, Issue 3 2008Hideki Kuge Abstract Well-defined alkoxysilane oligomers containing a cagelike carbosiloxane core were synthesized and used as novel building blocks for the formation of siloxane-based hybrid networks. These oligomers were synthesized from the cagelike trimer derived from bis(triethoxysilyl)methane by silylation with mono-, di-, and triethoxychlorosilanes ((EtO)nMe3,nSiCl, n=1, 2, and 3). Hybrid xerogels were prepared by hydrolysis and polycondensation of these oligomers under acidic conditions. The structures of the products varied depending on the number of alkoxy groups (n). When n=2 and 3, microporous xerogels (BET surface areas of 820 and 510,m2,g,1, respectively) were obtained, whereas a nonporous xerogel was obtained when n=1. 29Si,NMR spectroscopic analysis suggested that partial rearrangement of the siloxane networks, which accompanied the cleavage of the Si,O,Si linkages, occurred during the polycondensation processes. By using an amphiphilic triblock copolymer surfactant as a structure-directing agent, hybrid thin films with a 2D hexagonal mesostructure were obtained when n=2 and 3. These results provide important insight into the rational synthesis of molecularly designed hybrid materials by sol,gel chemistry. [source]
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