A Study of Porous and Surface Properties of Nickel-Molybdenum Catalyst Incorporated on Alumina Modified with Sodium and Magnesium Ions

A series of nickel-molybdenum samples supported on alumina modified with sodium or magnesium ions was studied by the BET method, differential thermal analysis (DTA) and IR spectroscopy to determine their surface properties, pore volume and distribution. Modification with sodium and magnesium ions causes a decrease of the surface area of the nickel-molybdenum catalysts. The decrease proceeds with increasing concentration of the modifying ions. Incorporation of these ions does not change the type of catalyst pores (the ink-bottle or bottle types), yet it affects the size and distribution of pores. It was found that sodium ions prevent from the formation of aluminum molybdate, while magnesium ions increase the thermal stability of the catalyst.     

Structure and Texture of Nickel-Molybdenum Catalysts on Alumina Support Modified with Fluoride or Chloride Ions

The performed study involves measurements of a specific surface area via a BET method, of the pore volume, FT-IR, and a derivatographic study of a series of Al₂O_3-supported nickel-molybdenum catalysts modified with fluoride and chloride ions. It was found that fluoride ions lead to a decrease in the specific surface area of catalysts, whereas chloride ions have a small effect on this parameter. Modification does not change the type of pores of the catalysts, yet it affects their size and increases concentration of OH groups adsorbed on the surface of the catalysts relative to the carrier and the unmodified catalyst. Addition of fluoride ions decreases the thermal stability of the catalyst, whereas chloride ions does not cause any change.     

Texture and structure of nickel-molybdenum catalysts supported on alumina modified with sulfate and phosphate ions

A series of nickel-molibdenum catalysts supported on alumina modified with sulfate and phosphate ions was studied. The studies involved texture evaluation measurements through N₂ adsorption isotherms. Besides, IR spectroscopic and derivatographic studies were carried out. Results of the studies enable us to conclude that modification of the alumina support with the above ions leads to a significant decrease in its surface area and pore volume. Modification does not result in a change of the type of pores of the support, but in the change of their size dimention. The pores present on the surface of the catalyst have the shape of “ink-bottles”. Modification with phosphate ions improves the thermal stability of the catalyst, whereas sulfate ions present on the surface of the catalyst undergo decomposition upon heating of the sample. Phosphate ions inhibit formation of aluminum molybdate, and instead form polymeric layer structures of phosphate on the surface of catalysts. Sulfate ions occur in the form of surface aluminum sulfate.     

The Effect of Sequence Incorporation of Sodium Ions on Structural and Thermal Properties of CoMo/Al2O3

The alumina supported cobalt-molybdena catalysts containing sodium ions were subjected to X-ray diffraction studies, IR spctroscopy and thermal analysis. Sodium ions were introduced onto Al₂O₃ either simultaneously with the other components, or prior to them or after them. Di- and polymolybdates phases were found to be formed on the support in all samples. In samples obtained in a two-stage process the interaction of Na⁺ ions with the support ions was detected which did not occur in samples obtained in a single-stage process. Nitrate ions introduced simultaneously with the other components undergo a relatively strong thermal decomposition while in the samples synthesised in two stages they are strongly bounded. The greatest number of strongly bound nitrates was found in the sample into which sodium ions were introduced in the second stage of the preparation procedure.     

Characterization of nickel–alumina aerogels with high thermal stability

The characterization of NiO–Al₂O₃ aerogels prepared from nickel nitrate and aluminum iso-propoxide through a sol–gel processing and subsequent supercritical drying was performed. The UV–visible, XPS and FT–IR investigations revealed that nickel ions were incorporated into alumina spinel structure as nickel aluminate form, not as nickel oxide, after calcination. TEM observations after the subsequent reduction exhibited uniform and fine nickel particles less than 6 nm diameter throughout the alumina aerogel support with high dispersion, by which not only high thermal stability of the metal at elevated temperatures but also high reforming activity and stability should be brought about. The large surface area and pore volume also provided the catalyst stability through the improvement of the thermal stability of alumina support.     

The Effect of Fluoride Concentration and Catalyst Preparation Method on Structural and Thermal Properties of CoMo/Al2O3 Catalysts

The effect of the sequence of incorporation of F⁻ ions on the properties of fluorinated CoMo/Al₂O₃ catalysts was investigated by the methods of X-ray diffraction, infrared spectroscopy and thermal analysis. Three kinds of samples were prepared into which the F⁻ ions were introduced either simultaneously with Co and Mo (sample labelled as CoMoF), or prior to them (F/CoMo) or after them (CoMo/F). The samples contained fixed amounts of Mo (15 wt.% MqO₃) and Co (3 wt.% CoO). Formation of surface di- and polymolybdate species as well as Al–F was evidenced in all samples. The concentration of molybdenum containing species was the highest in CoMoF sample, while that of fluoride containing species was the highest in CoMo/F samples.     

Magnetic resonance of the B2O3Na2OMoO3 vitreous system

The structure and properties of molybdenum-doped soda-borate glasses were studied by means of electron paramagnetic resonance as functions of the molybdenum oxide concentration in the range 1–25 mol% MoO₃, the keeping time of the samples at the preparation temperature in the range of 15–180 min, the preparation temperature in the range of 900–1300°C, and the soda-borate matrix composition in the range 0–34 mol% Na₂O.The EPR measurements gave evidence of the existence of three types of site for the Mo⁵⁺ ions, their relative fraction as well as the paramagnetic center density and the EPR lineshape symmetry being dependent on the above-mentioned factors. The evolution of the ¹¹B NMR lineshape in the studied samples also showed that the fourfold-coordinated boron atoms fraction is greatly influenced by the modification of these factors. The good agreement between the structural information obtained by ¹¹B NMR and Mo⁵⁺ EPR studies recommends the EPR spectra of Mo⁵⁺ ions as an excellent sensor for the structure of the borate glasses.     

离子液体改性白炭黑及性能表征

采用离子液体1-烯丙基-3-甲基氯化咪唑(AMI)改性白炭黑(SiO2).通过傅里叶红外光谱(FT-IR),X射线衍射(XRD),X射线光电子能谱(XPS),热失重分析仪(TGA),扫描电镜(SEM),接触角仪,BET比表面积和孔径分析仪,对改性前后白炭黑的微观结构以及性能进行表征.结果表明,经AMI改性后,白炭黑粒子间的相互作用明显减小,团聚倾向减弱,在橡胶复合材料基体中的分散性提高.AMI改性白炭黑疏水性增强,接触角由12.7°增加到80.5°,比表面积由67.84cm2/g增加到124.28cm2/g.改性前后,白炭黑晶型结构变化不大,仍为无定形态.     

A characterization study of xerogel silicapropylaniline powders

Silicapropylaniline nanometric materials with varying organic content were obtained using a sol-gel synthesis. By increasing the organic load, the scanning electron microscopy technique shows a slight increase in the average size of aggregated particles. N₂ isotherms and positron annihilation lifetime spectroscopy measurements show that the average pore size decreases accompanied by a surface area reduction. FTIR thermal analysis was used to estimate the thermal stability of the organic phase and also to detect the presence of trapped organic groups in closed pores. From the organic coverage and surface area measurements the surface density of the immobilized organic molecules as well as the average intermolecular distance between them could be estimated.     

Preparation and characterization of monolithic alumina aerogels

Alumina aerogels were prepared by a sol-gel method combined with the ethanol supercritical drying technique using aluminum tri-sec butoxide and nitric acid as the precursor and catalyzer respectively. This method affords high-surface-area alumina aerogel monoliths without the use of complexing agents. The structure and morphology of the aerogels were investigated by TEM, XRD, FTIR and BET techniques. The results confirmed that the as-prepared alumina aerogel possessed a network microstructure made up of pseudoboehmite fibers and a surface area of 690 m²/g. It was transformed to γ-Al₂O₃ after heat treatment at 800 °C without a significant loss in surface area. DMA analysis and hotdisk thermal analysis were performed to characterize the mechanical and thermal properties of the samples. The results indicated that the alumina aerogel was robust and exhibited excellent thermal insulating properties. The elastic modulus was up to 11.4 MPa after drying, which is the one of the highest modulus of alumina aerogels ever reported. The thermal conductivities at 30 °C and 400 °C were 0.028 W/mK and 0.065 W/mK respectively.     

Effects of metal precursor in the sol–gel synthesis on the physicochemical properties of Pd/Al2O3–CeO2 catalyst: CO oxidation

The object of this research was to investigate the effects of various precursors and different fabricating procedures of Pd/Al₂O₃–CeO₂ catalysts by the sol–gel method. The physicochemical properties and structures of catalyst were characterized with BET surface area, X-ray powder diffraction (XRPD), and scanning electron microscopy (SEM). The performance of the Pd/Al₂O₃–CeO₂ catalyst was also evaluated by CO oxidation tests with a continuous quartz reactor. The results indicated that the catalyst prepared with inorganometallic precursors showed a high dispersion of Pd, large surface area and pore volume, and a high activity in CO oxidation. The higher redox interaction between Pd and Ce of the support starting with inorganometallic precursors, as determined from X-ray powder diffraction, is suggested as being responsible for such a catalytic behavior.     

Nano‐sized silver crystals and their dispersion over α‐alumina for ethylene epoxidation

Ethylene oxide catalyst is a high metal loading catalyst, in which silver crystals is impregnated on α‐Al₂O₃ support. In this type of catalyst, metal dispersion plays an important role on catalyst selectivity for desired products. In this work, silver nitrate and silver oxide together with oxalic and lactic acid as the raw materials were used with different impregnation techniques to make catalysts with high silver content and dispersion. It is also known that the use of promoters affect the metal dispersion on the catalyst support and for that cesium was used as the promoter to improve the silver crystal dispersion. Physical and chemical characteristics of the prepared catalysts, i.e., surface area, pore volume, silver content, nano‐sized silver crystals and their dispersion were measured using BET method, Atomic Absorption Spectroscopy, X‐ray diffraction and TEM. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

硬脂酸/插层高岭石复合相变材料的制备和热性能研究

高岭石(K)是一种常见的黏土矿物,具有低成本、阻燃、多层结构等固有优点。本文采用真空浸渍法将硬脂酸(SA)吸附到插层高岭石(IKL)和二甲基亚砜(DMSO)复合物的孔隙中来制备用于储热的复合相变材料。通过X射线衍射(XRD)、红外光谱(FT-IR)、热重分析(TG)、差示扫描量热法(DSC)、扫描电子显微镜(SEM)和比表面积分析仪(BET)表征了复合材料的热性能、结构和主要组分。由于插层复合物形成后高岭石层间距增大,对SA的吸附率达到32.3%,熔化和凝固潜热值分别为43.36 J/g和43.16 J/g,熔化和凝固温度分别为51.9 ℃和51.7 ℃。此外,该复合相变材料具有较好的热稳定性。由于SA/IKL复合相变材料具有高吸附量、高潜热、良好的热稳定和低成本等优点,因此,其在实际的应用中具有潜在的价值。     

On the crystallochemical origin of the disordered form of Ba7(EuII)F12Cl2 and the structural changes induced at high temperature

The crystal structure of the disordered modification of Ba₇F₁₂Cl₂ has been carefully re‐examined on several new crystals prepared under different conditions of synthesis. All single crystal structure refinements reveal a residual electron density of ∼3 e^–/ų in the 0,0,0 position which is explained by the introduction of a small amount of sodium ions in the crystal. The title compound transforms from a disordered to an ordered modification at ∼800 °C. New structural data show a change in space group from P6₃/m to P6. During this process, a slight chemical change and the formation of nano‐channels in the crystals is observed by electron microscopy. These changes were further studied by electron microprobe analysis, by spectroscopic methods and thermal analysis. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of surface and porous properties of synthetic hybrid lamellar silica

Synthetic lamellar silica and hybrid lamellar silicas have been prepared by liquid crystal templating, template extraction and silanization. The samples have been characterized by thermogravimetric analysis (TGA), carbon analysis, spectroscopy, X-ray diffraction (XRD) and nitrogen adsorption. The XRD analyses have shown that the lamellar periodic stacking is preserved for all samples. The quantity and type of organic molecules at the silica surface have been evaluated by carbon analysis, TGA and spectroscopy. The covalent grafting of the solvent used for extraction of the initial surfactant has been highlighted by these analyses. The nitrogen adsorption analyses have revealed three categories of pores and two types of samples. The initial lamellar silica exhibits a very low specific surface area and plate-like type of pores. The second type of samples is made up of the hybrid samples and the initial substrate from whom the surfactant has been extracted. These samples show a significantly higher specific surface area with interlamellar spaces corresponding to narrow-slit like mesopores around 4 nm. The nitrogen adsorption data analysis has highlighted the presence of micropores within the silica sheets. The difference of the specific surface is due to pore blocking by the surfactant impeding the access to nitrogen into interlamellar spaces and by the silanes covering the pores once the surface modified. The presence of micro and mesopores combined to a high BET specific surface of 612 m²/g makes these lamellar silicas interesting materials for catalysis applications.     

The effect of Si/Al ratio of ZSM‐5 zeolite on its morphology,acidity and crystal size

ZSM‐5 zeolite crystal with different Si/Al molar ratios in the range of 10‐50 was synthesized using sodium silicate, aluminum sulfate and tetrapropylammonium bromide (TPA‐Br) as the organic template. The produced samples were characterized using XRD, FT‐IR, SEM and EDX techniques. All synthesized samples were found to be ZSM‐5 zeolite as confirmed by XRD and supported by FT‐IR. SEM results showed that ZSM‐5 synthesized with different Si/Al molar ratios had different morphologies and particle sizes. It was found that the average ZSM‐5 crystal size increased as Si/Al molar ratio increased. Thermogravimetric‐difference thermal analysis (TG‐DTA) technique was also used to measure the amount of template occluded inside the crystal pore. The synthesized Na‐ZSM‐5 was transformed into its acidic form, i.e., H‐ZSM‐5 using ion exchange method with ammonium nitrate solution. The H‐ZSM‐5 acidity was determined by NH₃‐TPD. These results showed that different Si/Al molar ratios have effect on surface acidity of samples. The surface areas of the H‐ZSM‐5 were measured using BET method and the results showed that, decrease in Si/Al ratio, decreased the surface area. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of acidity on the structural and textural evolution of titania in the presence of primary amine and inorganic precursor

Titania was synthesized from laurylamine hydrochloride (LAHC) and Ti(SO₄)₂ under different acidic conditions. The effect of acidity on the structural and textural evolution of titania has been investigated by X-ray diffraction (XRD), nitrogen adsorption–desorption, transmission electron micrographs (TEM), FTIR spectroscopy and thermogravimetric analysis (TGA). With increasing the pH value in the initial mixture, the obtained samples transformed from nanoparticles with intra-particle mesostructures (pH 0.6 and 2.0) to nanoparticles with nonporous structure (pH 3.7), and finally to worm-like porous materials with inter-particle mesostructures (pH 4.2) resulted from the aggregates of nanoparticles. The obtained mesoporous nanoparticles (pH 0.6 and 2.0) have mean diameter of ca. 25 nm, and the pore size distributions are bimodal with fine intra-particle pores and larger inter-particle pores. The intra-particle mesostructure not only retard the growth of nanocrystallites, but also prevent phase transition of anatase to rutile at high temperature. The BET surface area of the TiO₂ calcined at 300 °C decreased from 212 to 74 m²/g with pH increasing from 0.6 to 4.2.     

Zr‐doped CeO2 Hollow slightly‐truncated nano‐octahedrons: One‐pot synthesis,characterization and their application in catalysis of CO oxidation

Zirconium‐doped ceria hollow slightly‐truncated nano‐octahedrons (HTNOs) (Ce_1‐xZr_xO₂) were synthesized by a one‐pot, facile hydrothermal method. The morphology and crystalline structure were characterized with powder X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and the high resolution transmission electron microscopy (HRTEM). The composition and chemical valence on the surface of the as‐prepared Ce_1‐xZr_xO₂ powders were detected by X‐ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry (EDS). The surface area and pore size distribution of as‐obtained Zr‐doped ceria HTNOs were measured by N₂ adsorption‐desorption measurement. Mechanisms for the growth of Zr‐doped ceria HTNOs are proposed as both oriented attachment and Ostwald ripening process and the formation of the hollow structure is strongly dependent on the addition of Zr⁴⁺ ions. Furthermore, the as‐obtained Zr‐doped ceria HTNOs revealed superior catalytic activity and thermal stability toward CO oxidation compared to pure ceria. It may provide a new path for the fabrication of inorganic hollow structures on introducing alien metal ions.     

Optical and FTIR studies of CuO-doped lead borate glasses and effect of gamma irradiation

CuO doped lead borate glasses of the composition PbO 70%–B₂O₃ 30% with varying CuO contents were prepared. UV–visible and infrared spectroscopic studies were measured before and after successive gamma irradiation with two different doses namely 2 and 8 Mrad. The experimental results indicate that the undoped sample reveals strong UV–near visible absorption while copper doped samples show additional broad visible band due to (Cu^2 +) ions.FT infrared absorption spectrum reveals vibrational bands due to triangular and tetrahedral borate groups together with the sharing of Pb–O vibrations.CuO-doped glasses have been found to show a shielding behavior towards the effects of progressive gamma irradiation causing the maintenance of the spectral curves. The changes in the UV–visible and infrared spectral data are discussed in relation to the states of copper ions and structural evolution caused by the change in glass composition including the CuO.     

Crystal growth of tin oxide nano-sheets in aqueous solutions and time variation of N2 adsorption characteristics

Nucleation and crystal growth of tin oxide were realized in aqueous solutions. Nano-sheet structures grew in the solutions containing SnF₂ at 90 °C to develop in-plane size and thickness gradually. Their color, size, morphology, crystal structure and N₂ adsorption property varied with progress of crystal growth. Color of powder changed from white to light yellow, light blown to light green particles with growth. XRD analyses clarified that single phase of SnO₂ was synthesized in the aqueous solutions without high temperature annealing. It is an advantage to conventional ceramic firing process. Growth curves of crystallite size were consistent with morphological observations using Field Emission Scanning Electron Microscopy FE-SEM. Development of sheet structure was caused by crystal growth of SnO₂. Large crystallite size perpendicular to (200) planes indicated that growth along c-axis was suppressed compared to a-axis. Anisotropic crystal growth resulted anisotropic shape of nano-sheets. Chemical composition of fluorine-doped SnO₂ nano-sheets was estimated to Sn : F = 1 : 0.06–0.12. BET surface area increased with crystal growth and reached to 85 m²/g. It gradually decreased with synthesis period. Growth of sheet structure along in-plane direction related to increase of surface area. Further growth in thickness increased volume of the sheets to cause decrease of surface area per weight. N₂ adsorption property strongly related to crystal growth and shape change of the nano-structures. The system has the advantage of morphology controllability of tin oxide nano-structure and low environmental load.