Showing papers on "Mixed oxide published in 1995"

Activity and structure-sensitivity of the water-gas shift reaction over CuZnAl mixed oxide catalysts

Abstract: The activity and structure-sensitivity of the water-gas shift (WGS) reaction over Cu Zn Al mixed oxide catalysts were studied. Three sets of samples with different Cu/Zn and (Cu+Zn)/Al atomic ratios were prepared by coprecipitation. Depending on the cation ratio, the ternary hydroxycarbonate precursors contained hydrotalcite, aurichalcite and/or rosasite phases. The decomposed precursors contained CuO, ZnO, ZnAl 2 O 4 , and Al 2 O 3 . The relative proportion of these phases depended on both the chemical composition of the sample and the calcination temperature employed for decomposing the precursor. After activation with hydrogen, samples were tested for the WGS reaction at 503 K. The turnover frequency of the eighteen samples tested was essentially the same (0.2–0.3 s −1 ) irrespective of changing the copper metal surface area between 3 and 35 m 2 /g Cu and the metallic copper dispersion between 0.5 and 5.0%. This indicated that the WGS reaction is a structure-insensitive reaction, as the specific reaction rate r 0 (mol CO/h/g Cu) is always proportional to the copper metal surface area. Preparation of mixed oxides with a high copper dispersion is therefore required for obtaining more active catalysts. It was found that the value of the metallic copper dispersion is related to the amount of hydrotalcite contained in the hydroxycarbonate precursor: the higher the hydrotalcite content in the precursor, the higher the copper metal dispersion in the resulting catalyst and, as a consequence, the higher the catalyst activity. Ternary Cu/ZnO/Al 2 O 3 catalysts exhibited a substantially faster WGS activity than binary Cu/ZnO catalysts. The addition of aluminium, although inactive for the WGS reaction, is required for improving the catalyst performance.

XANES-TPR Study of Cu-Pd Bimetallic Catalysts: Application of Factor Analysis

Abstract: In this paper we describe the interpretation of X-ray absorption near-edge structure (XANES) data using factor analysis to follow the temperature-programmed reduction (TPR) of CuPd/KL-zeolite catalysts. With this tool it is possible to identify and quantify the chemical compounds in which a metal is present during a reduction treatment. When the method is applied to the Cu K-edge XANES-TPR spectra of two bimetallic catalysts containing (1% Pd + 0.5% Cu), and (1% Pd + 0.25% Cu), it is shown that Cu is initially present in both as two oxidic species, a Cu-Pd mixed oxide and a Cu-exchanged in L-zeolite. Both catalysts show a similar behavior under reduction yielding only one zero valent phase, a Cu-Pd alloy. 25 refs., 6 figs., 3 tabs.

ZnOCr2O3 + ZSM-5 catalyst with very low Zn/Cr ratio for the transformation of synthesis gas to hydrocarbons

Abstract: Three Zn Cr mixed oxide plus ZSM-5 compound catalysts with different compositions covering a wide range of Zn/Cr atomic ratios (0.064 to 1.913), aimed at the direct conversion of synthesis gas into hydrocarbons, were tested under different experimental conditions: temperature ranged from 356 to 410°C, pressure from 3.60 to 4.49 MPa and space velocity from 0.2 to 3.0 mmol reactants/(g cat min). Reaction products included carbon dioxide, water and hydrocarbons with methanol conversion (through which hydrocarbons are formed) being complete. The catalyst with the least content of zinc gave the highest yields of liquid hydrocarbons (up to 74% of total hydrocarbons). Different crystalline phases (ZnO, ZnCr 2 O 4 and Cr 2 O 3 ) were found in the methanol synthesis component as a function of Zn/Cr ratio. The low Zn/Cr catalyst was characterized by X-ray diffraction, differential thermal analysis, nitrogen adsorption, temperature-programmed reduction, Infrared and X-ray photoelectron spectroscopy. The only phases observed in this catalyst were ZnCr 2 O 4 and Cr 2 O 3 . Calcination temperature had an influence in both physical and chemical catalyst properties. After calcination, Cr VI and Cr III species could be seen on the catalyst surface, but only Cr III species were observed after reaction or reduction. The evidences gathered suggest that Cr 2 O 3 is mainly responsible for methanol synthesis, while ZnCr 2 O 4 contributes to increase the specific surface area of the catalyst and influences gas product distributions. Compound catalysts with the mixed oxide (Zn Cr) as the methanol synthesis component showed to be more active than those with the individual (Cr or Zn) oxides.

Raman spectroscopy characterization of molybdena supported on titania-zirconia mixed oxide

Abstract: TiO 2 ZrO 2 support containing 1:1 mole ratio was prepared by the coprecipitation method. TiO 2 and ZrO 2 were also prepared separately. After calcination at 823 K, the mixed oxide was found to be amorphous. These solids were impregnated with molybdenum and examined by laser Raman spectroscopy. Physical mixtures of MoO 3 with the same supports were also studied. It is shown that monolayer structures of the molybdenum oxide overlayers are formed in the presence and absence of water vapour.

Oxidation behavior of titanium-aluminium nitrides

Abstract: Oxidation behavior of titanium-aluminium nitrides of various compositions has been explored to understand the oxidation protection mechanisms and the role of structure and composition in the oxidation behavior. Thin films of (Ti1-x,Alx)N have been sputter deposited on silicon substrates and the nature of oxides resulting from air oxidation at various temperatures has been evaluated using Auger electron spectroscopy. In most of the films, layered oxide structures Al2O3/TiO2 readily form on the nitride surface at about 800 °C and higher temperatures. At about 700 °C and below, the oxidation product is primarily a mixed oxide, such as Al2O3 + TiO2. Oxides forming at elevated temperatures, with a top layer of Al2O3, protect the underlying nitride from further oxidation. Thus, for low and intermediate temperature applications, the titanium-aluminium nitride films may be first treated at an elevated temperature to form a protective oxide. The role of aluminum content in the film oxidation behavior has been explored for x values ranging from 0.25 to 0.67. Despite its higher aluminum content, the (Ti0.33,Al0.67)N film exhibited lower oxidation resistance than other films.

Ion storage properties of CeO2 and mixed CeO2/SnO2 coatings

Abstract: Ion storage CeO2 and CeO2/SnO2 coatings were prepared by the sol-gel dip-coating method using an aqueous-based process. The influence of added SnO2 in the CeO2 oxide coatings on the inserted/extracted charge was determined by chronocoulometric measurements. It was found that for 60 nm thick film, the inserted/extracted charge was twice (Q=10 mC cm−2) as large for films containing 17 mol% SnO2, if compared to pure CeO2. The effect of the addition of SnO2 to the mixed oxide coatings on their optical properties and structural characteristics was studied.

Cerium/zirconium mixed oxide catalysts having high/stable specific surface areas

Abstract: Cerium/zirconium mixed oxides (optionally including yttrium values), comprising solid solutions thereof, having contents of zirconium of up to 60 atom % and having thermally stable, very high specific surface areas at least greater than 80 m 2 /g, preferably at least 100 m 2 /g and more preferably at least 150 m 2 /g, are well suited as catalysts and/or catalyst supports, notably for the treatment/conversion of vehicular exhaust gases; such Ce x Zr 1-x O 2 particulates are conveniently prepared by thermally treating an aqueous solution of soluble compounds of cerium and zirconium (and optionally yttrium), e.g. the nitrates thereof, present in the desired stoichiometric amounts, and thence recovering and, if appropriate, calcining the reaction product thus formed.

Flame-hydrolytically produced titanium dioxide mixed oxide, method of its production and its use

Abstract: Flame-hydrolytically produced titanium dioxide mixed oxide having a BET surface of 10 to 150 m2 /g and 1 to 30% by weight aluminum oxide or 1 to 30% by weight silicon dioxide is produced by evaporating aluminum chloride or silicon tetrachloride, transferring the evaporated aluminum chloride or silicon tetrachloride, together with an inert gas, into the mixing chamber of a burner, mixing them with hydrogen, air and gaseous titanium tetrachloride, burning the resulting 4-component mixture in the reaction chamber of the burner, and separating the titanium dioxide mixed oxide from the gaseous reaction products

Solid propellant based on phase-stabilized ammonium nitrate

Abstract: A solid propellant for rocket propulsion systems or gas generators compri 35 to 80 wt % ammonium nitrate (AN) in pure or nickel oxide, potassium or cesium nitrate phase-stabilized form (PSAN) with an average particle size of 5 to 200 μm, 15 to 50 wt % of a binder system of a binder polymer and an energy-rich plasticizer, as well as 02 to 5 wt % of a burning moderator of vanadium/molybdenum oxide in the form of an oxide mixture or mixed oxide

Preparation of titania–silica aerogels with a double metal alkoxide precursor

Abstract: Diethoxysiloxane–ethyltitanate has been used as a precursor for the preparation of titanic–silica aerogels, the characterization of which shed light on the generation of Bronsted acid sites in a mixed oxide and the IR peak assignments of this mixed oxide pair.

Electrode active material for non-aqueous electrolytic battery and manufacture thereof

Abstract: PROBLEM TO BE SOLVED: To remarkably increase the discharge capacity of a battery in an initial stage and after 50 cycles by coating the surface of a specified lithium- nickel mixed oxide with a lithium-transition metal M mixed oxide. SOLUTION: To produce an electrode active material; compounds of transition metals M (M stands for Co, Mn, and/or Fe including metals partly containing Ni) and a lithium compound are dissolved or suspended in a solvent, a lithium- nickel mixed oxide having a general formula Lix Niy Nz O2 (N stands for elements except Li, Ni, and 0; 0.8

Method of associating precious metals with specific oxides in mixed oxide systems for use as catalysts

Abstract: This invention provides a very low cost effective method to alter the association of precious metal catalysts with specific support oxides in mixed oxide systems. The invention includes two discoveries: 1) that the isoelectric points for the three normally-used gasoline catalyst components are significantly different and the surface charges present have significant magnitude to promote attraction and repulsion of ions or charged radicals; and 2) ammine-chloride or ammine-nitrate salts both dissociate into positively charged precious metal radicals and are stable over a very wide pH range. The pH of the impregnation solution is controlled such that the surface charge of the oxide is opposite to the charge on the precious metal radical if the metal is to be supported on that oxide, and to control the pH such that all charges on the oxide to be avoided are the same as the precious metal radical.

Process for the catalytic conversion of exhaust gases using cerium/zirconium mixed oxide catalyst

Abstract: Cerium/zirconium mixed oxides (optionally including yttrium values), comprising solid solutions thereof, having contents of zirconium of up to 60 atom % and having thermally stable, very high specific surface areas at least greater than 80 m2 /g, preferably at least 100 m2 /g and more preferably at least 150 m2 /g, are well suited as catalysts and/or catalyst supports, notably for the treatment/conversion of vehicular exhaust gases; such Cex Zr1-x O2 particulates are conveniently prepared by thermally treating an aqueous solution of soluble compounds of cerium and zirconium (and optionally yttrium), e.g. the nitrates thereof, present in the desired stoichiometric amounts, and thence recovering and, if appropriate, calcining the reaction product thus formed.

Sol-gel process for obtaining pure and mixed oxide zirconia washcoats, useful as catalysts or catalyst supports

Abstract: A process for obtaining pure or mixed oxide zirconia washcoats consisting of: preparing a zirconium solution in water at a concentration, formally expressed as ZrO2, equal or lower than 400 g/l, starting from a basic zirconium carbonate additioned of glacial acetic acid, and eventually preparing one or more solutions of the other oxides when necessary; preparing a sol of zirconium, eventually mixed to other metals, by a thickening agent; sucking the sol into the honeycomb channels in order to obtain the washcoats, with subsequent gelation with gaseous ammonia; ageing the so obtained gel; drying and calcining.

Vanadium/phosphorus mixed oxide from the precursor to the active phase:Catalyst for the oxidation of n-butane to maleic anhydride

Abstract: This review examines the recent scientific and patent literature dealing with V/P/O-basedcatalysts for the synthesis of maleic anhydride by n-butane oxidation Attention is focused on the different methods of preparation claimed by each company, as well as on the main parameters in precursor preparation and thermal treatment affecting the final catalytic performance The role of the various promoters reported in the literature is also discussed

The Role of Prehydrolysis in the Preparation of Zirconia—Silica Aerogels

Abstract: Prehydrolysis of an 'unreactive' precursor, typically a silicon alkoxide, has long been used to promote homogeneous mixing in sol-gel syntheses of mixed oxides. Studies of single oxide preparations teach that sol-gel parameters, partiularly water concentration, have a profound effect on product properties. However, relatively little attention has been given to the effects of sol gel parameters in the prehydrolysis step of a mixed oxide preparation. In this work, we use a set of 50 mol% zirconia-50 mol% silica aerogels to showthat varying the prehydrolysis ratio over the mixed range 0.00 to 3.22 mols/mol provides a fine degree of control over over the mixed oxides' textural and acidic properties.Furthermore, we demonstrate that the improvements in mixed oxide homogeneity associated with prehydrolysis

Economical continuous oxidative dehydrogenation of propane to propene in high yield

Abstract: In continuous oxidative dehydrogenation of C3H8 to C3H6 with (gas contg.) O2 at 500-600, pref. 530-570 deg C and a C3H8 partial pressure > 0.02 bar, pref. > 0.1 bar and a C3H8/O2 partial pressure ratio of 0.1-10, pref. 0.1-2, the heterogeneous catalysts used are mixed oxides of the type Mel-Bi-Mo-O mixed with a second mixed oxide of the type B-Mell-O; in which Mel = Zn, Mg or Ca; Mell = Al, Zr, Ti and Zn.

Preparation, characterization, and thermal behavior of a new high oxide ion conductor: Bismuth uranium lanthanum oxide

Abstract: This paper describes the structural characterization and crystallization of the mixed oxide Bi{sub 2}U{sub 0.5}La{sub 0.5}O{sub 5.25}. The ionic conductivity was also measured.