Showing papers on "Mixed oxide published in 1990"

Characterization and catalytic activity of cobalt-chromium mixed oxides

Abstract: Three cobalt-chromium mixed oxide samples having Co:Cr atomic ratios 33:67, 50:50, and 75:25 (indicated as Co33, Co50, and Co75, respectively) were prepared by a coprecipitation method and characterized structurally before and after catalytic CO hydrogenation. Before reaction, all the catalysts are monophasic, with normal spinel structures, and are covered by chromate species, with Co{sup 3+} and Cr ions in a relatively high oxidation state (+3 or higher) exposed on the surface. Co33 corresponds to the compound CoCr{sub 2}O{sub 4}, and its bulk structure is substantially unaltered after the catalytic tests, independently from the reduction temperature adopted. The other two catalysts are solid solutions of CoCr{sub 2}O{sub 4} and Co{sub 3}O{sub 4}, which, upon reduction up to 623 K, evolve toward rock salt type structures and segregate crystallized cubic metallic cobalt when activated at higher temperature. All three powders act as catalysts for CO hydrogenation to hydrocarbons, with low catalytic activities when reduced up to 623 K; in these conditions, methanol was also produced in small amount with Co33. After reduction up to 773 K, a strong increase of catalytic activity was observed mainly for Co50 and Co75 catalysts, over which an increase of methane formation is also observed. A correlationmore » between IR and catalytic data is discussed, evidencing the role of the calcination and reduction steps on bulk and surface properties and on catalytic activity.« less

XPS and UPS studies of gas-phase oxidation, electrochemistry and corrosion behaviour of Ti and Ti5Ta

Abstract: Owing to its high corrosion resistance, Ti is used as a containment material for processes in hot nitric acid. The corrosion stability of Ti can be improved still further by alloying with 5% Ta. The oxidation behaviour of Ti and Ti5Ta and the composition and stability of their oxide layers are compared by means of XPS, UPS, electrochemical measurements and corrosion test. Thin oxide layers of up to 2 nm have been formed by gas-phase oxidation. Three regions can be observed due to chemisorption, oxide formation and oxide growth. The average composition of the oxide layer after an oxygen exposure of 1000 L is Ti2O3, with a layer thickness of 1.8 nm. The change of Ti oxidation states during oxidation shows that the metal/oxide interface is a mixed oxide of TiO, Ti2O3 and TiO2, while TiO2 is formed at the oxide/vacuum interface. The change of work function during oxidation is similar for Ti and Ti5Ta. Thicker oxide layers have been built electrochemically, with no differences in capacity measurements between Ti and Ti5Ta, indicating similar electronic properties. No significant Ta enrichment in 1 N H2SO4 and 1 N HNO3 is found up to 10 V. Preferential dissolution of Ti in corrosion tests in hot HNO3 leads to Ta enrichments by factors of >10, which explains the improved corrosion stability of the alloy. The surface is covered by a barrier oxide of ∼10 nm and a porous outer layer with a thickness of >50 nm.

Amorphous V-P mixed oxide with P/V=2.0 as active phase for butane oxidation

Abstract: V–P mixed oxide catalysts prepared by evaporation method was made up of a mixture of an amorphous phase with P/V = 2.0 and a crystalline phase of (VO)2P2O7. The amorphous phase, separated from the (VO)2P2O7 particles by dissolving the precursor in boiled water, was found to show essentially the same selectivity and activity per unit surface area for the maleic anhydride formation from butane as the unseparated catalyst.

Mixed oxide capacitor of BaTiO3-PbO as a new type CO2 gas sensor.

Abstract: Mixed oxide capacitor of BaTiO3–PbO is studied as the sensor for CO2 detection. The oxide gave the large capacitance change on exposure to CO2. The CO2 sensing characteristics strongly depended on the operation temperature as well as the operation frequency. A linear relationship exists between the sensitivity and the concentration of CO2 below 6%.

Investigations on the mixed oxide material TiO2-In2O3 in regard to photoelectrolytic hydrogen production

Abstract: A new photoelectrode system TiO2-In2O3 for photo-assisted electrolysis of water is described. The mixed oxide electrodes have been synthesised by solid-state sintering. These sintered electrode discs exhibited enhanced photovoltage and photocurrent of 0.78 V, 14 mA cm-2 whereas for TiO2 they were 0.8 V, 5 mA cm-2 respectively. X-ray diffraction and scanning electron microscopy investigations of the mixed oxide electrodes have been carried out to monitor their bulk and surface characteristics. EDAX analysis has been done to explore the chemical stoichiometry. These studies indicate microcrystalline-like surface characteristics and a cation doping ('In' up to approximately 2%) for the TiO2-In2O3 electrodes. The Mott-Schottky plots (1/c2-V) in 1 M NaOH solution and temperature variation of electronic conductivity (In sigma -1/T) for TiO2 as well as TiO2-In2O3 have been evaluated. These investigations suggest decrease in band gap and slight shift in the flat-band potential of the mixed oxide electrode compared with TiO2. The relative enhancement in hydrogen evolution under photo-assisted mode of electrolysis of TiO2 and mixed oxide (TiO2-In2O3) electrodes has been found to be from 1.2 to 1.8 ml h-1. The probable causes of the enhancements in photoactivity and hydrogen evolution have been suggested as: (i) 'In' cation doping in TiO2 lattice; (ii) increased surface area with In2O3 inclusion; (iii) decrease in the band gap and enhanced range of absorption of mixed oxide electrode; and (iv) catalytic activity of In2O3.

Oxidative coupling of methane over CaO-MgO mixed oxide

Abstract: Mixed oxide catalyst prepared by co-precipitating magnesium oxide and calcium oxide showed an excellent activity for the oxidative coupling of methane. The high performances were presumed to arise from the high basicity of the mixed oxide.

Iron-tellurium-selenium mixed oxide catalysts for the selective oxidation of propylene to acrolein

Abstract: This paper reports on iron-tellurium-selenium mixed oxide catalysts prepared by coprecipitation from aqueous solution investigated for the propylene to acrolein reaction in the temperature range 543-773 K. Infrared spectroscopy, electron dispersive X-ray analysis, X-ray diffraction, and isotopic tracer techniques have also been employed to characterize this catalytic system. Properties of the Fe-Te-Se mixed oxide catalysts have been compared with Fe-Te mixed oxides in an effort to deduce the functionality of Se. The selenium in the Fe-Te-Se-O catalyst has been found to be the hydrocarbon activating site. The activation energies for the acrolein and carbon dioxide formation are 71 and 54 kJ/mol, respectively. Reactions carried out with {sup 18}O{sub 2} have shown lattice oxygen to be primarily responsible for the formation of both acrolein and carbon dioxide. The initial and rate-determining step for acrolein formation is hydrogen abstraction as determined by an isotope effect associated with the C{sub 3}D{sub 6} reaction. No isotope effect is observed for carbon dioxide formation from C{sub 3}D{sub 6} suggesting that CO{sub 2} is formed by parallel, not consecutive, oxidation of propylene.

Divinylbenzene Synthesis by Dehydrogenation of Diethylbenzene over Iron-based Mixed Oxide Catalysts

Abstract: 酸化鉄を主成分とする種々の触媒を用いてジエチルベンゼンの脱水素反応を試みた。X線回折より, 鉄-カリウム系触媒は複合酸化物KFeO2を形成するが, CO2により分解することが分かった。カリウム以外のアルカリ金属は複合酸化物を形成しにくく高活性が得られない。原子レベルでの混合を促進させるために, 触媒前駆体として鉄とアルカリ金属を含むシュウ酸錯体をアルミナに担持して, 脱水素反応に用いた。鉄-カリウム系で従来の触媒をしのぐ高活性が得られた。さらにカリウム以外のアルカリ金属•アルカリ土類金属でも高活性が得られ, セシウム系で最も高い活性が得られた。しかしエチルベンゼンの脱水素反応では異なった傾向がみられた。

Interfacial Chemistry of Titanium Films Deposited on PMDA-ODA Polyimide:

Abstract: Titanium was evaporated onto PMDA-ODA polyimide surfaces at room temperature up to total thicknesses of about five monolayers. The polyimide backbone is ruptured at both the oxygen ether linkage in the ODA and at the nitrogen imide linkage. The first fraction of a monolayer reacts with oxygen atoms in both the carbonyl and ether functionalities, and forms a mixed oxide with titanium predominantly in the Ti+3 oxidation state. Near one monolayer coverage, a carbide or mixed oxy-carbide species forms. Above one monolayer, nitrogen is strongly attacked and ~50% of the nitrogen reacts with titanium. The deposited titanium begins to take on metallic character only after the coverage has reached several monolayers. Heating at 575 K causes additional reaction. Scanning tunelling microscopy images obtained in air following heating show that the composite surface is substantially roughened.

Modification of thin film gas-sensor to avoid degradation - by adding mixed oxide(s) of alkali metal and tri:valent or higher valency metal to outer layer

Abstract: On a substrate (10), pref. a solid electrolyte, an electrode layer (11) and porous covering layer of a ceramic material are deposited to construct a gas sensor. The feature is that the porous covering layer (12) and/or its pores (13) contain at least a mixed oxide of at least an alkali-element, pref. Li, and a trivalent element with a thermally stable oxide pref. from Groups IIIa, IIIb or IVb of the Periodic System, pref. Al, Ga, B, Y,Sc, Zr or a Lanthanide element. The concn. of each of the constituents is pref. 0.2-99.8 mole %. - Also claimed is the use of an additional layer incorporating the mixed oxide, pref. directly over the electrode and pref. under a covering layer. - The covering layer also pref. contains catalyst. A mfg. process is also claimed.

Interaction of oxygen and CO with Ni3Ti alloy surfaces

Abstract: Clean surfaces of polycrystallineNi3Ti have been prepared and their interaction with oxygen expanding into the oxidation regime has been studied with ultraviolet photoelectron spectroscopy (UPS) and Auger electron spectroscopy(AES) methods at T≥150 K. The elemental surface concentrations of properly prepared alloy surfaces are found close to the bulk values. Low‐temperature oxygen adsorption leads to oxygen bonding to Ni and Ti and in the oxidation regime Ni and Ti oxides are formed simultaneously. Metallic sites which are capable to serve for molecular CO adsorption, presumably Ni sites, are still available at the surface of this mixed oxide. Upon heating to high temperatures, T>700 K, Ni oxide gets reduced to metallic Ni. The resulting surface is covered by TiO which acts as a passivating coating. Interaction of oxygen with clean Ni3Ti surfaces at higher temperatures, T≥300 K initially leads to enhanced Ti–oxygen interaction leaving the Ni constituent unaffected. After annealing to high temperatures a thin TiO layer covers the surface.Adsorption of CO at clean Ni3Ti surfaces is molecular at 150 K and predominantly molecular at 300 K.

Metal electrodes for electrochemical processes

Abstract: Metal electrodes provided with a coating consisting essentially of a mixed oxide compound of (i) a compound of the general formula ABO₄, having a structure of the rutile-type, where A is an element in the trivalent state selected from the group consisting of Al, Rh and Cr, and B is an element in the pentavalent state selected from the group consisting of Sb and Ta, (ii) RuO₂ and (iii) TiO₂; wherein the mole fraction of ABO₄ is between 0.01 and 0.42, the mole fraction of RuO₂ is between 0.03 and 0.42, and the mole fraction of TiO₂ is between 0.55 and 0.96. The electrodes have low precious metal content, provide improved durability and improved current efficiency-anodic overvoltage performance. They are used in the electrolysis of chloride containing liquors in the production of, for example, chlorine and more particularly, chlorate.

Physico-chemical properties and hydrogen reduction reactivity of nickel and cobalt mixed oxides of various stoichiometry

Abstract: Investigations have been made of the effects of the origin and some physico-chemical parameters on the kinetics of reduction with hydrogen of two series of mixed nickel and cobalt oxides differing in the stoichiometry of the two oxides. The first series, consisting of non-stoichiometric mixed oxides NiO-Co3O4 of various compositions, were prepared by calcining the mass of coprecipitated hydroxides in air. High-temperature treatment of the oxides obtained led to the second series, which consisted of stoichiometric NiO and nonstoichiometric CoO. The reactivity of the mixed oxides towards reduction with hydrogen varied with the phase composition and with the amount and ratio of various forms of superstoichiometric oxygen in the systems under study.

Metal oxide powders, their mixtures, metal mixed oxide powders, their mixtures and their use in catalytic dehydrogenation of hydrocarbons

Abstract: Metal oxide powders comprised of Cr(III) oxide, Ti(IV) oxide, V(V) oxide, or mixtures of these, or metal mixed oxides comprised of Cr(III) oxide and Ti(IV) oxide and V(V) oxide, or their mixtures. They have BET surfaces of 5-50m2 /g and mean particle diameters of 25-350 nm and are useful to increase conversion and selectivity in the manufacture of mono-olefins by catalytic dehydrogenation of saturated hydrocarbons. The metal oxide powders are produced from mixtures of the vaporized metal compounds chromyl chloride, titanium tetrachloride, and vanadyl chloride, in the presence of certain gases by laser pyrolysis.

Arsenic-resistant mixed oxide catalyst and process for producing the same

Abstract: In an arsenic resistant mixed oxide catalyst and a process for producing the same, oxides of at least the metals vanadium and molybdenum are provided, especially for reducing nitrogen oxides in flue gases in the presence of a reducing agent such as ammonia and carbon monoxide. A MoO3 phase and at least one oxygen-rich mixed oxide phase such as V9 Mo6 O40 is at least partly converted into a mixed oxide phase being poorer in oxygen such as a V9 Mo4 O25 phase, for increasing arsenic resistance.

Arsenic resistent mixed oxides catalyst

Abstract: 2.1 Mixed oxide catalysts, in particular for decreasing the nitrogen oxides in flue gases in the presence of a reducing agent, have the property of losing their catalytic activity with time as a result of catalyst poisons, such as e.g. arsenic, entrained in the flue gases. Accordingly, an arsenic-resistant mixed oxide catalyst containing oxides at least of the metals vanadium and molybdenum for decreasing the nitrogen oxides in flue gases is to be developed in order to ensure uniform catalytic activities over long periods of operation. 2.2 The invention proposes that in a mixed oxide catalyst containing the phases MoO3 and at least one mixed oxide phase, e.g. V9Mo6O40, the latter, to increase the arsenic resistance, be wholly or partially converted into a mixed oxide phase of lower oxygen content, such as e.g. V9Mo4O25. 2.3 The invention is applicable to mixed oxide catalysts which contain at least the metals vanadium and molybdenum. Such mixed oxide catalysts are used in particular for decreasing the nitrogen oxide content in flue gases in the presence of a reducing agent, such as e.g. ammonia or carbon monoxide.

Process for manufacturing an oxide-ceramic superconductor material with a high conductivity-change temperature.

Abstract: not available for EP0356428Abstract of corresponding document: WO8810010Oxide-ceramic superconducting materials with a superconducting metal oxide phase, having a high conductivity-change temperature, e.g. based on the Me1-Me2-Cu material system (Me1 = rare earth metal or Y; Me2 = alcaline earth metal), can be made by powder metallurgy. In order to achieve the desired superconducting metal oxide phase, a powder containing these components is subjected to compacting and to annealing with the addition of oxygen. For reasons of homogeneity, the processing stages of this process often have to be repeated. In order to reduce the number of process stages, an intermediate powder product is first prepared from a mixed oxide of the components by a grinding process after the manner of mechanical alloying, and then by using the powdery intermediate product at least one compacting and annealing stage is performed, with formation of the desired superconducting metal oxide phase.