oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Preparation and Catalytic Properties of Various Oxides and Mesoporous Materials Containing Niobium and Sulfate Ions, in the Etherification Reaction of 2-Naphtol  [PDF]
Alaa H. Hussein, Hiba Nahas, Mohamad Jahjah, Mourtada Srour, Rabih Jahjah, Nicolas Duget, Marc Lemaire, Daoud Naoufal
International Journal of Organic Chemistry (IJOC) , 2018, DOI: 10.4236/ijoc.2018.81002
Abstract: Several types of solid acid catalysts were prepared based on oxides like (ZrO2, TiO2, HfO2, MCM-41 and SBA-15), using two main preparation methods: the precipitation and the sol-gel methods. Each catalyst was subjected to two types of impregnations: sulfate ions using sulfuric acid as precursor and niobium using niobium oxalate as precursor. These prepared catalysts were tested in the etherification reaction of 2-naphtol, where the catalysts showed both acidic and redox properties. The acidic character was manifested through the formation of 2-butoxynaphtalene (with moderate yields) when oxide is sulfated, and the redox character (when impregnated with niobium) manifested through the formation of the interesting product 2-ethylnaphtofuran (with low yields) and other products that were a result of oxidative coupling of two 2-naphtol molecules (binol and acetal of binol). However despite the effort, several attempts to increase the yield of 2-ethylnaphtofuran did not work. All products prepared were obtained in pure form and characterized by 1H and 13C NMR, GC and MS.
Catalytic Properties of Various Oxides and Mesoporous Materials Containing Niobium and Sulfate Ions, in the Oxidation Reaction of 1-Octanol  [PDF]
Alaa H. Hussein, Ahmad Khalil, Mohamad Jahjah, Mourtada Srour, Rabih Jahjah, Nicolas Duget, Marc Lemaire, Daoud Naoufal
International Journal of Organic Chemistry (IJOC) , 2018, DOI: 10.4236/ijoc.2018.81003
Abstract: Several types of solid acid catalysts were prepared based on oxides like (ZrO2, TiO2, HfO2, MCM-41 and SBA-15). Each catalyst was subjected separately to two types of impregnations: sulfate ions and niobium. The catalytic activity of these solids was tested in the oxidation reaction of 1-octanol. These catalysts showed acidic and redox characters. MCM-41 and SBA-15 materials showed higher redox catalytic activities through the formation of (octyl octanoate, peroxyacetal and octanal). Our interest was focused on obtaining the ester (octyl octanoate) with high yields.
THE INFLUENCE OF NIOBIUM ON THE ACIDITY AND STRUCTURE OF GAMMA-ALUMINA-SUPPORTED VANADIUM OXIDES
Sathler, M.N.B.;Eon, J.G.;
Brazilian Journal of Chemical Engineering , 1998, DOI: 10.1590/S0104-66321998000200012
Abstract: gamma-alumina-supported niobium oxide was used as a support for vanadium oxides. the influence of the addition of niobium oxide was studied by looking for changes in the structure and acid-base character of superficial species. vanadium oxide was deposited using the continuous adsorption method; niobium oxide was impregnated using the incipient wetness method. the catalysts were characterized by xps, uv-visible and ir spectroscopy. catalytic tests were performed using propane oxidation reaction at 400oc. for coverage below the monolayer, both vanadium and niobium oxides were observed in slightly condensed superficial species. the presence of vanadium oxide on the support was found to increase the lewis acidity and create some bronsted acidity. higher catalytic activity and selectivity for propene were associated with vanadium oxides. the presence of niobium did not contribute to the modification of the chemical properties of superficial vanadium but did decrease the adsorption of vanadium on the alumina.
THE INFLUENCE OF NIOBIUM ON THE ACIDITY AND STRUCTURE OF GAMMA-ALUMINA-SUPPORTED VANADIUM OXIDES  [cached]
Sathler M.N.B.,Eon J.G.
Brazilian Journal of Chemical Engineering , 1998,
Abstract: Gamma-alumina-supported niobium oxide was used as a support for vanadium oxides. The influence of the addition of niobium oxide was studied by looking for changes in the structure and acid-base character of superficial species. Vanadium oxide was deposited using the continuous adsorption method; niobium oxide was impregnated using the incipient wetness method. The catalysts were characterized by XPS, UV-visible and IR spectroscopy. Catalytic tests were performed using propane oxidation reaction at 400oC. For coverage below the monolayer, both vanadium and niobium oxides were observed in slightly condensed superficial species. The presence of vanadium oxide on the support was found to increase the Lewis acidity and create some Bronsted acidity. Higher catalytic activity and selectivity for propene were associated with vanadium oxides. The presence of niobium did not contribute to the modification of the chemical properties of superficial vanadium but did decrease the adsorption of vanadium on the alumina.
Electrochemical and Photoelectrochemical Properties of Nano-Islands of Zinc and Niobium Oxides Deposited on Aluminum Thin Film by RF Magnetron Reactive Sputtering  [PDF]
Go Sajiki, Yasuhiko Benino, Tokuro Nanba, Hiroshi Okano
Materials Sciences and Applications (MSA) , 2015, DOI: 10.4236/msa.2015.64035
Abstract: Zinc oxide (ZnO) and niobium oxide (NbOx) with a nano-island structure were deposited by a sputtering method on Al-coated glass substrates. Cells with a (ZnO or NbOx)/Al/glass|KNO3aq.|Al/ glass structure were assembled, and electrochemical and photoelectrochemical properties were evaluated. The ZnO and NbOx electrodes had higher electrode potentials than the counter Al/glass electrode, and electron flows from the counter electrode to the ZnO and NbOx electrodes through the external circuit were commonly confirmed. In the ZnO-based cell, only faint photocurrent generation was seen, where Zn and Al elution from the ZnO electrode was found. In the NbOxbased cell, however, stable generation of electricity was successfully achieved, and electrode corrosion was not recognized even in microscopic observations. A photoelectrochemical conversion model was proposed based on potential-pH diagrams. In the case of nano-island structures formed at shorter NbOx deposition time, it was concluded that the photoelectrochemical reactions, which were proceeded in the immediate vicinity of the boundary among nano-islands, substrate, and electrolyte solution, were predominant for the photoelectrochemical conversion, and in the case of film structures with longer deposition time, the predominant reactions took place at the film surface.
Studies on the stability of anodic oxides on zirconium biocompatible alloys
Oliveira, Nilson T. C.;Biaggio, Sonia R.;Rocha-Filho, Romeu C.;Bocchi, Nerilso;
Journal of the Brazilian Chemical Society , 2002, DOI: 10.1590/S0103-50532002000400009
Abstract: studies on the stability of anodic oxides grown on zirconium and its biocompatible alloys ti-50zr at.% and zr-2.5nb wt.%, in aerated ringer physiological solution, at 25 and 37 °c, were carried out by comparing their formation charge and their reconstruction charge after dissolution at open circuit in the physiological solution. the stability of oxides grown in the ringer solution and in a 0.15 mol l-1 na2so4 solution was compared. the obtained results show that the stability of these oxides is increased by aging under potentiostatic conditions and can be decreased by the presence of chloride ions in the electrolyte during the anodization process.
Studies on the stability of anodic oxides on zirconium biocompatible alloys  [cached]
Oliveira Nilson T. C.,Biaggio Sonia R.,Rocha-Filho Romeu C.,Bocchi Nerilso
Journal of the Brazilian Chemical Society , 2002,
Abstract: Studies on the stability of anodic oxides grown on zirconium and its biocompatible alloys Ti-50Zr at.% and Zr-2.5Nb wt.%, in aerated Ringer physiological solution, at 25 and 37 °C, were carried out by comparing their formation charge and their reconstruction charge after dissolution at open circuit in the physiological solution. The stability of oxides grown in the Ringer solution and in a 0.15 mol L-1 Na2SO4 solution was compared. The obtained results show that the stability of these oxides is increased by aging under potentiostatic conditions and can be decreased by the presence of chloride ions in the electrolyte during the anodization process.
Thin Oxide Films on Copper Single Crystals: Anodic Formation and Photoelectrochemical Properties  [cached]
Vvedenskii A.V.,Eliseev D.S.,Grushevskaya S.N.,Ganzha S.V.
Proceedings of the International Conference Nanomaterials : Applications and Properties , 2012,
Abstract: Thin oxide films were grown anodically on polycrystalline copper and single crystals Cu(100), Cu(110) and Cu(111). Semiconductor properties of copper oxides were obtained by photocurrent measurements. The morphology of the anodic oxides was monitored by SEM. A p-type conductivity was established for Cu2O and СuO formed on Cu during the anodic polarization. The main semicon-ductor properties do not depend on the crystal face; the band gap in thin Cu2O is equal to 2.2 eV.
Superconducting DC and RF Properties of Ingot Niobium  [PDF]
Pashupati Dhakal,Gianluigi Ciovati,Peter Kneisel,Ganapati Rao Myneni
Physics , 2012,
Abstract: The thermal conductivity, DC magnetization and penetration depth of large-grain niobium hollow cylindrical rods fabricated from ingots, manufactured by CBMM subjected to chemical and heat treatment were measured. The results confirm the influence of chemical and heat-treatment processes on the superconducting properties, with no significant dependence on the impurity concentrations in the original ingots. Furthermore, RF properties, such as the surface resistance and quench field of the niobium rods were measured using a TE011 cavity. The hollow niobium rod is the center conductor of this cavity, converting it to a coaxial cavity. The quench field is limited by the critical heat flux through the rods' cooling channel.
Novel Technology for Chlorination of Niobium and Tantalum Oxides and Their Low-Grade Ore Concentrates  [PDF]
B. A. Shainyan, Yu. S. Danilevich, Yu. L. Garmazov, A. L. Finkelstein, T. S. Aisueva, V. K. Turchaninov
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2008, DOI: 10.4236/jmmce.2008.72013
Abstract: A novel energy-economic and environmentally benign technological procedure for chlorination of niobium and tantalum oxides as well as their low-grade ore concentrates was elaborated. The process is based on using carbon tetrachloride or silicon tetrachloride as a chlorinating agent under pressure. It proceeds at moderate temperatures and is free from the shortcomings of conventional carbochlorination processes such as the use of chlorine gas at very high temperatures and formation of toxic products and ozone depleting agents (phosgene, carbon monoxide, chlorohydrocarbons).
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.