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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.
Semiconductive properties of anodic niobium oxides
,A.I. de; Rangel,C.M.; Skeldon,P.; Thompson,G.E.;
Portugaliae Electrochimica Acta , 2006,
Abstract: the semiconductive properties of anodic niobium oxides formed at constant potential and constant current density to different final voltages have been examined by mott-schottky analysis. thin anodic oxides were formed on sputtered niobium specimens at constant potential in the range of 2.5 to 10 vag/agcl in a borate buffer solution. thicker oxides were formed, also on sputtered niobium specimens, at a constant current density of 5 ma cm-2 in 0.1 m ammonium pentaborate solution to final voltages of 10, 50 and 100 v. capacitance measurements were performed in a borate buffer solution of ph 8.8, at a frequency range of 200 to 2000 hz, at a sweep rate of 5 mv s-1 from +2.5 to -1 vag/agcl. the results obtained show n-type semiconductor behaviour with a carrier density in the range of 8 ′ 1018 - 6 ′ 1019 cm-3 on films formed to 10 v. thicker films showed lower carrier densities in the range of 1 ′ 1018 - 2 ′ 1018 cm-3 with a calculated charge depletion layer of 33-36 nm.
Semiconductive properties of anodic niobium oxides  [cached]
A.I. de Sá,C.M. Rangel,P. Skeldon,G.E. Thompson
Portugaliae Electrochimica Acta , 2006,
Abstract: The semiconductive properties of anodic niobium oxides formed at constant potential and constant current density to different final voltages have been examined by Mott-Schottky analysis. Thin anodic oxides were formed on sputtered niobium specimens at constant potential in the range of 2.5 to 10 V Ag/AgCl in a borate buffer solution. Thicker oxides were formed, also on sputtered niobium specimens, at a constant current density of 5 mA cm-2 in 0.1 M ammonium pentaborate solution to final voltages of 10, 50 and 100 V. Capacitance measurements were performed in a borate buffer solution of pH 8.8, at a frequency range of 200 to 2000 Hz, at a sweep rate of 5 mV s-1 from +2.5 to -1 V Ag/AgCl. The results obtained show n-type semiconductor behaviour with a carrier density in the range of 8 ′ 10(18) - 6 ′ 10(19) cm-3 on films formed to 10 V. Thicker films showed lower carrier densities in the range of 1 ′ 10(18) - 2 ′ 10(18) cm-3 with a calculated charge depletion layer of 33-36 nm.
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.
Catalytic Behaviour of Mesoporous Cobalt-Aluminum Oxides for CO Oxidation  [PDF]
Ankur Bordoloi,Miguel Sanchez,Heshmat Noei,Stefan Kaluza,Dennis Gro?mann,Yuemin Wang,Wolfgang Grünert,Martin Muhler
Journal of Catalysts , 2014, DOI: 10.1155/2014/807545
Abstract: Ordered mesoporous materials are promising catalyst supports due to their uniform pore size distribution, high specific surface area and pore volume, tunable pore sizes, and long-range ordering of the pore packing. The evaporation-induced self-assembly (EISA) process was applied to synthesize mesoporous mixed oxides, which consist of cobalt ions highly dispersed in an alumina matrix. The characterization of the mesoporous mixed cobalt-aluminum oxides with cobalt loadings in the range from 5 to 15?wt% and calcination temperatures of 673, 973, and 1073?K indicates that Co2+ is homogeneously distributed in the mesoporous alumina matrix. As a function of the Co loading, different phases are present comprising poorly crystalline alumina and mixed cobalt aluminum oxides of the spinel type. The mixed cobalt-aluminum oxides were applied as catalysts in CO oxidation and turned out to be highly active. 1. Introduction Supported metal oxide catalysts have attracted much attention in recent years due to their widespread applicability in industrially and academically important reactions. The extent and nature of the interaction, dispersion, and reducibility of the metal oxides depend on the synthesis method, loading, calcination temperature, and time. Cobalt supported on alumina is a typical catalyst, which is specially important for Fischer-Tropsch synthesis. Conventionally, the preparation of cobalt catalysts is performed by incipient wetness impregnation using suitable cobalt precursors on commercial alumina at low pH. Weak interaction is normally observed between the positively charged alumina carrier and the cobalt cations resulting in relatively large crystallite sizes [1–4]. Continuous efforts have been made in the last few decades by several groups [5–7] to synthesize porous alumina with high surface area by high-temperature dehydration of bulk powders [8], modified sol-gel synthesis in the presence of organic moieties [9, 10], different surfactants [3], block copolymers [11–14], or evaporation-induced self-assembly (EISA) with colloidal precursors and amine structural agents [15, 16]. These materials represent an active support, which may participate positively or negatively in the formation of the final catalysts. Moreover, the methods of hard templating [17] (carbon template) and microwave irradiation [18] in the presence of surfactants have been applied to synthesize alumina materials with crystalline, ordered, and uniform mesopores. However, this process is very time consuming and hardly scalable for industrial applications. Ordered mesoporous materials
Progress of the Application of Mesoporous Silica-Supported Heteropolyacids in Heterogeneous Catalysis and Preparation of Nanostructured Metal Oxides  [PDF]
Yuanhang Ren,Bin Yue,Min Gu,Heyong He
Materials , 2010, DOI: 10.3390/ma3020764
Abstract: Mesoporous silica molecular sieves are a kind of unique catalyst support due to their large pore size and high surface area. Several methods have been developed to immobilize heteropolyacids (HPAs) inside the channels of these mesoporous silicas. The mesoporous silica-supported HPA materials have been widely used as recyclable catalysts in heterogeneous systems. They have shown high catalytic activities and shape selectivities in some reactions, compared to the parent HPAs in homogeneous systems. This review summarizes recent progress in the field of mesoporous silica-supported HPAs applied in the heterogeneous catalysis area and preparation of nanostructured metal oxides using HPAs as precursors and mesoporous silicas as hard templates.
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).
Preparation and Characterization of Mesoporous Iron-Oxide
XUE Hong-Tao,SHEN Shui-Fa,PAN Hai-Bo,XIE Chang-Huai
无机材料学报 , 2009, DOI: 10.3724/sp.j.1077.2009.00577
Abstract: Transition metal oxides are easy to form insoluble oligomer in reaction because of complicated oxidation states, so it is difficult to obtain the desired mesoporous structure. To resolve the problem, mesoporous iron oxide was synthesized by reacting a micellar phase of sodium dodecyl sulfate (SDS) with iron polymer solution which was prepared by controlling the proportion of sodium hydroxide and ferric chloride. Crystal structure and surface structure of the mesoporous iron oxide was characterized by powder X-ray diffraction (XRD), Fourier transform a2 infrared spectroscopy (FT-IR), thermogravimetric analyse(TGA), Nitrogen adsorptiona2desorption method and so on. The results show that mesoporous | Fe2O3 can be obtained after calcining at 450 ith OH-/Fe3+ ratio of 2.0. Its surface area is 146.5m2 ¤g-1, BJH average diameter is 6.9nm, pore volume is 0.27cm3 ¤g-1. The asa2prepared mesoporous iron oxide has better thermal stability, it still has surface area of 110.2m2 ¤g-1 after calcination at 550
Synthesis of Ordered Mesoporous TiO2 from Industrial Titanyl Sulfate Solution and its Formation Mechanism  [PDF]
TIAN Cong-Xue,ZHANG Zhao
无机材料学报 , 2009, DOI: 10.3724/sp.j.1077.2009.00225
Abstract: Using composite template (CTAB and P123) as structurea2directing agents, industrial titanyl sulfate as Ti source, the precursor of mesoporous TiO2 was prepared via controlling the hydrolysis and condensation rate of industrial TiOSO4, self-assembly rate of template and pH value of solution. The asa2prepared materials were characterized by XRD, HRTEM, SAED and nitrogen adsorptiona2desorption.Ordered mesoporous anatase titania is obtained after template removal, with hexaganol mesopore, SBET of 205.7m2/g£ average pore diameter of 3.28nm. The formatiom process of mesopore belongs to cooperative formation mechanism, i.e. the hydrolysis colloid particles of titanium and composite template interact through static force and hydrogen bond on the interface, cooperating to form mesopore.
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