Showing papers on "Mixed oxide published in 1984"

A structural investigation of stabilized oxygen evolution catalysts

Abstract: A ternary mixed oxide containing SnO2, RuO2 and IrO2 was shown to exhibit a more stable electrocatalytic behaviour than simpler catalysts consisting of noble metal oxides only. X-ray diffraction and transmission electron microscopy were used to characterize the structure of these oxide catalysts. It was found that precipitation of the fine catalyst powders resulted in the formation of a mixed (Sn, Ru, Ir)O2 rutile phase. This phase was shown to be thermodynamically unstable, decomposing to SnO2 and (Ru, Ir)O2 on annealing at 800° C. X-ray photoelectron spectroscopy revealed that the surface composition of these mixed oxide catalysts varies considerably from the bulk composition. The formation of such metastable, mixed oxides is discussed.

Method of producing monolithic catalyst for purification of exhaust gas

Abstract: A method of producing a monolithic three-way catalyst for the purification of exhaust gases of internal combustion engines. First, a mixed oxide coating is provided to a monolithic carrier by treating the carrier with a coating slip in which an active alumina powder containing cerium in oxide form is dispersed together with a ceria powder and then baking the treated carrier. Next, Pt, Rh and/or Pd are deposited on the oxide coating by a known thermal decomposition process. The addition of the ceria powder to the coating slip is effective in enhancing the CO, HC and NOx conversions and durability of the produced catalyst at high temperatures. Preferably the content of Ce in the active alumina powder is 1-5 wt%, and, in the coating after baking, Ce of the ceria powder amounts to 5-50wt% of the coating. Optionally a zirconia powdertoo may be added to the coating slip such that Zr of the zirconia powder amounts to 1-10 wt% of the coating.

Alkali promoted manganese oxide compositions containing silica and/or alkaline earth oxides

Abstract: A class of mixed oxide catalysts comprising Mn-containing oxides, alkali metals or compounds thereof, and at least one member of the group consisting of oxides of Si, oxides of alkaline earth metals, and mixed oxides of Si and at least one alkaline earth metal. In the more preferred embodiments, the third component serves as a carrier for the Mn and alkali metal components. The composition preferably comprises a major amount of the carrier material and minor amounts of the other components. The compositions are useful for hydrocarbon coversion, methane conversion, and oxidative dehydrogenation processes characterized by formation of coproduct water.

Gas diffusion electrode with a hydrophilic covering layer, and process for its production

Abstract: A gas diffusion electrode for the reduction of oxygen, which contains a hydrophobic electro-catalyst layer, is described. One side of this layer is covered with a hydrophilic layer which is composed of at least one transition metal or an oxide or mixed oxide of transition metals and can also contain a current collector in the form of a mesh. For producing the gas diffusion electrode, a hydrophobic electro-catalyst layer can first be prepared from a pulverulent mixture which contains the electro-catalyst and a hydrophobic polymer, and at least one transition metal or an oxide or mixed oxide of transition metals can be applied in a finely divided form to one side of this layer and bonded to the hydrophobic electro-catalyst layer by the application of pressure.

Phosphorus-vanadium-mixed oxide oxidation catalysts and processes for the preparation and use thereof

Abstract: Maleic anhydride is produced by the oxidation of a non-aromatic hyarocarbon having at least four carbon atoms in a straight chain with molecular oxygen or a molecular oxygen-containing gas in the vapor phase in the presence of a phosphorus-vanadium mixed oxide oxidation catalyst Such catalysts are are prepared by introducing a substantial ly pentavalent vanadium-containing compound and a pentavalent phosphorus-containing compound into an alcohol medium capable of reducing the vanadium to a valence state less than + 5 in the presence of an alcohol-modifying agent to form a phosphorus-vanadium mixed oxide catalyst precursor. The catalyst precursor is recovered, dried, formed into desired structures, and calcined at temperatures from about 250° C to about 600° C. The catalysts are highly effective in that they exhibit a weight weight productivity of at least 70 grams of maleic anhydride per kilogram of catalyst per hour.

Thermal transformations of iron(III)-nickel(II) mixed oxide gels

Abstract: Iron-nickel mixed oxide gels have been prepared by a hydroxide co-precipitation technique and their thermal transformation has been studied by thermal analyses, X-ray diffraction and infra-red spectroscopy. Differential thermal analysis (DTA) of the hydrated ferric oxide gel indicates the presence of three exothermic peaks along with a broad endotherm. Addition of nickel oxide decreases the intensities of the exotherms and the peaks are completely absent in the samples containing more than 10 mol % of NiO. On the other hand these samples show the presence of three endothermic peaks. Thermal analysis of the sample containing 50 mol % of NiO indicates the formation of a precursor at around 185° C which changes to nickel ferrite at around 275° C. This ferrite slowly crystallizes with a broad exotherm in the range 280 to 550° C.

Production of maleic anhydride

Abstract: A process for oxidizing a hydrocarbon to maleic anhydride using a mixed oxide catalyst of vanadium and phosphorous prepared by a procedure including pretreating the dried catalyst precursor of the said mixed oxides in finely divided form with an acid solution.

Low Temperature Plasma Anodization of Silicides

Abstract: In the first time, hundreds nm thick oxide layers were formed by room temperature plasma anodization of some refractory disilicides. Nuclear microanalysis and Rutherford backscattering techniques were used to study the anodic oxidation of various metal silicides (Hf, Ti and Zr) in a multipolar oxygen plasma set-up. We have found that the low temperature (<100 °C) plasma anodization kinetics of Hf or Zr silicides is two orders of magnitude higher than that of Ti silicide although their thermodynamic and physicochemical behaviour are very similar. 200 nm thick Hf (or Zr) and Si mixed oxide layers have been obtained in one hour plasma anodization. Analysis of RBS spectra indicates that the ratio of Si to metal cation concentration in the bulk of oxide grownis the same than the silicide (HfSi2 or ZrSi2), while in the near surface region of oxide (20 to 30 nm) there is an enrichment in metallic oxide leading to a Si to Hf (or Zr) concentration ratio equal to unity. The spectacular difference between the anodization rates in oxygen plasma of Hf (and Zr) silicides comparing to Ti silicides can be related to the catalytic effect on plasma anodization of the Hf and Zr oxides.

Effects of surface fluorination on catalytic activities and surface compositions of TiO2-Al2O3 and TiO2-SiO2-Al2O3

Abstract: Studies showed that the ternary oxide having the atomic ratio of Ti/Si/Al=47.5/47.5/5 exhibited a high catalytic activity for cumene cracking after a surface fluorination using 1 wt% hydrofluoric acid. The catalytic activity for CH3OH conversion into olefins was highly dependent on the preparation method. That is, the ternary mixed oxide promoted olefin formation slightly when the mixed oxide was prepared only by coprecipitation. Surface treatment, using gaseous CF3Cl was effective in enhancing catalytic activity. Although the binary oxide, TiO2–Al2O3, itself, was catalytically inactive for olefin formation, TiO2–Al2O3 prepared by coprecipitation became active after the treatment using CF3Cl. Such an enhancement was found also for the ternary oxide, TiO2–SiO2–Al2O3, and is ascribable to increased acid strength, as determined by NH3 adsorptions at various temperatures. The XPS measurements showed that F atoms introduced into mixed metal oxides by the fluorination using CF3Cl, selectively combined with Al a...

Method of preparing a catalyst for the oxidation and ammoxidation of olefins

Abstract: A method for the preparation of catalysts useful for the oxidation and ammoxidation of olefins contain antimony, uranium, iron, bismuth, and molybdenum in a catalytically active oxidized state. The method comprises preparing a hydrated mixed oxide component containing antimony, uranium iron and bismuth, making an aqueous slurry thereof; adding a molybdate thereto; adjusting the pH, drying and calcining. The catalysts are especially useful for the production of acrylonitrile from propylene, ammonia, and an oxygen-containing gas.

Preparation of mixed vanadium phosphorus oxide catalysts

Abstract: Vanadium phosphorus mixed oxide containing catalysts are prepared by sequentially forming an alpha-VOPO4 catalyst precursor in aqueous media, and thereafter partially reducing a portion of the vanadium to a valence state of +4 in an organic liquid reducing media, in the absence of corrosive reducing agents. The catalysts exhibit excellent activity for the production of maleic anhydride from 4 carbon atom hydrocarbons such as n-butane.

Physico-Chemical Aspects of Intercalation Phenomena

Abstract: Four distinct kinds of intercalation phenomena are discussed involving (i) acceptor guests in graphitic hosts, (ii) inorganic ions and associated organic molecules in sheet silicates, (iii) multiply charged metallic clusters in zeolitic hosts, and (iv) the discovery of a new type of mixed oxide layered catalyst capable of releasing structural oxygen.

Structural mechanism and character of redistribution of tungsten and molybdenum in their reduction from a mixed oxide

Abstract: At temperatures of 600°C and higher the mixed oxide (W0.5Mo0.5)O3 is reduced with the starting uniform distribution of tungsten and molybdenum being retained in the end product, which is due to a single mechanism being operative in the process. As a result, a virtually homogeneous alloy is formed. At 400–600°C the reduction of tungsten and molybdenum from the mixed oxide involves two different structural mechanisms, which brings about a regrouping of the metals, disturbs their uniform starting distribution, and hence lowers the degree of homogeneity of the end product.

Two-dimensional optical element and its production

Abstract: PURPOSE:To obtain a stable element of a fully solid state type which is thin, lightweight and sharp in contrast by constituting a coloring layer of the two- dimensional optical element of an oxide sputtered film contg. W and Li. CONSTITUTION:A coloring layer 21 is formed on a transparent electrode ITO 11 of a substrate 10 by sputter vapor deposition under 3X10 Torr with a mixed oxide of Li and W as a target and Ar as sputtering gas. An ion conductive layer 22 is then formed by using the similar mixed oxide as a target and Ar/O2=1 as sputtering gas. ITO 14 is formed as a counter electrode on the layer 22 and an electric field is applied on the upper and lower electrodes to color and decolor the same. A difference by >=1 digit is observed in the stage of coloring and decoloring at the intensity of the transmitted light of an He-Ne laser with the element formed in such a way, thus the element is substantially usable as an optical element. The memory effect for a several months or above is further confirmed, and the two-dimensional optical element having the thin, lightweight and stable structure is realized.

Reactions on oxide catalysts—kinetics and mechanism of dehydrogenation and decarboxylation

Abstract: Some of the mechanistic studies on dehydrogenation, dehydration and decarboxylation over metal oxide catalysts are reviewed. The type of activity of a catalyst is determined by the nature of the surface-substrate interaction, the same catalyst giving rise to different relative activities depending on the substrate. In addition to dehydrogenation and dehydration reactions many oxide catalysts promote hydrogen transfer reactions too. In the mixed oxide systems the interfaces between the pure oxides as well as interfaces arising from new phases formed by the interaction of component oxides are active regions. In the ketonization of acids the same active sites as those effective for the decomposition of alcohols are involved. The type of the intermediate depends on the conditions of reaction, the most important being the temperature. The technique of competitive reactions has been used to establish that the catalytic ketonization is a bimolecular process on the surface of the catalyst.

Solid-state source to be used for diffusion on semiconductor material

Abstract: Solid-state source for diffusion into semiconductor material, the coefficient of thermal expansion of the source being matched to the semiconductor material. In particular, the solid-state source consists of a mixed oxide of aluminium oxide and the dopant oxide. Alternatively, it is a solution of organic compounds which is to be applied to the semiconductor material, from which compounds the mixed oxide is formed before the diffusion process.