Showing papers on "Mixed oxide published in 1994"

Zirconium/cerium mixed oxide catalyst/catalyst support compositions having high/stable specific surfaces

Abstract: Zirconium/cerium mixed oxides (optionally including thermally stabilizing dopant values), comprising solid solutions thereof, having contents of zirconium of up to 99% by weight, and having high specific surface areas, are well suited as catalysts and/or catalyst supports, notably for the treatment/conversion of vehicular exhaust gases; such ZrO 2 /CeO 2 mixed oxides are conveniently prepared by (i) intimately admixing a zirconium sol with a cerium sol, the ratio r of the mean diameter r 1 of the particles of the zirconium sol to the diameter r 2 of the particles of the cerium sol being at least 5, (ii) adding a precipitating amount of a base thereto, (iii) recovering the precipitate thus formed, and (iv) calcining the recovered precipitate.

Raman spectroscopic study of the Pt–CeO2 interaction in the Pt/Al2O3–CeO2 catalyst

Abstract: Raman spectra have been obtained from a series of Pt/Al2O3 catalysts containing from 0 to 20% CeO2, and a Pt/CeO2 catalyst, prepared by sol–gel processing. Spectra were recorded following calcination of the catalyst precursors at various temperatures up to 600 °C and compared with thermogravimetric data. The results clearly present evidence for a strong interaction between Pt and CeO2. The surface mixed oxide species persists in an oxidising environment up to 600 °C and in a reducing environment up to 170 °C.

A highly active and highly selective oxide catalyst for the conversion of ethanol to acetone in the presence of water vapour

Abstract: In the presence of water vapour and a suitable catalyst, ethanol is converted to acetone rather than to ethylene and acetaldehyde. In order to develop an appropriate catalyst for this reaction, steady-state catalytic activities and selectivities were studied for 24 oxide catalysts. It was found that the acetone selectivity is high on a catalyst having both surface acidity and basicity, suggesting that the acetone formation is an acid-base bifunctional catalytic reaction. Iron oxide is superior to the other oxides studied here in both conversion and acetone selectivity. The superiority is greatly enhanced by mixing iron oxide with zinc oxide. The preparation method for the iron–zinc mixed oxide catalyst was also studied and it was found that the optimal composition is Zn/(Fe + Zn)= 0.1–0.4 and that the optimal condition for calcination is 773 K for 3 h. The catalyst gave 100% ethanol conversion and 94% acetone selectivity at a reaction temperature of 713 K. It is initially a mixture of Fe2O3 and ZnO but is converted to a spinel type compound, ZnFe2O4, during the reaction. The optimal reaction temperature was determined to be 713 K, and at this temperature, the acetone yield decreased by 34% after a time of 24 h.

Thermal behaviour and reactivity of manganese cobaltites MnxCo3 –xO4(0.0 ⩽x⩽1.0) obtained at low temperature

Abstract: The thermal behaviour and reactivity in air, N2 and vacuum of manganese cobaltites MnxCo3 –xO4(0 ⩽x⩽1.0) with a cubic spinel-type structure obtained at low temperature have been studied by thermal analysis, X-ray powder diffraction, IR spectroscopy, transmission electron microscopy and X-ray energy-dispersive spectroscopy. In air, the formation of mixed Co–Mn oxides with rock-salt-type structure as a single phase is attained between 1100–1300 °C, depending on x. In a vacuum, the rock-salt-type mixed oxide is formed at ca. 700 ° C; Co metal and MnO are the products obtained at 800 °C. The change with temperature of the lattice constant in the cubic spinel-type phase MnCo2O4, has been also determined. It increases from a= 8.167(2)A at 450 °C to 8.2626(3)A at 950 °C. These results are interpreted with regard to the progressive reduction of manganese in the cubic spinel lattice.

Use of catalytic reactions to probe Mg-Al mixed oxide surfaces

Abstract: In this work, we investigated the effect of catalyst composition on the surface reactivity of magnesium-aluminum mixed oxides using three probe reactions: dehydrogenation of 2-propanol to propanone, dehydration of 2-propanol to propene, and isomerization of 1-butene. Turnover rates were calculated from the total CO2 adsorption capacity of the mixed oxides, assuming one adsorption site corresponds to one active site. Turnover rates for the dehydrogenation of 2-propanol were independent of the catalyst composition, which is consistent with the structure insensitivity of dehydrogenation reactions. The other two probe reactions followed opposite trends with the Mg:Al ratio: as the Al content of the mixed oxides increased, the turnover rate for 2-propanol dehydration increased while that for 1-butene isomerization decreased. The magnitude of these changes confirms that the mixed oxides are truly interdispersed and not present as separate phases.

Selective ammoxidation of propane over multicomponent oxide catalysts

Abstract: The ammoxidation of propane to acrylonitrile was investigated over various multicomponent mixed oxidecatalysts. Bi3GaMo2 oxide, Bi0.85V0.55Mo0.45 oxide and Bi2TiMo oxide showed a good selectivity to acrylonitrile. The catalytic performance was strongly dependent on the components constituting the oxides due to the concentration of defects, the nature of the component and the mixed oxide phases. The effect of support type on the catalytic performance of Bi0.85V0.55Mo0.45 oxide showed that selectivity to acrylonitrile decreased in the order silica > alumina > magnesia. The catalytic performance of Bio0.85V0.55Mo0.45 oxide was improved by the addition of a small amount of a component such as magnesium, calcium and tellurium. The catalytic performance of Bi3GaMo2, oxide catalyst, however, decreased significantly with the addition of a smallamount of alkali metal (Li, Na, K, Cs).

Titanium sites of titania-silica mixed oxides for epoxidation activity and Lewis acidity

Abstract: Titania-silica was synthesized by rapid hydrolysis of Ti(OPri)4 and Si(OEt)4, and the state of titanium and epoxidation activity of this mixed oxide were investigated. XANES analysis showed that the amount of tetrahedrally coordinated titanium increased with a decrease in the titanium content. The epoxidation activity increased in accordance with the decreased amount of tetrahedral titanium sites. The amount of Lewis acid sites also increased with the decrease in titanium content. Thus the tetrahedral titanium was responsible both for the epoxidation acitivity and the Lewis acidity due to its coordinatively unsaturated nature.

Reactor Trap To Remove Hydrocarbons from Engine Exhaust during Cold Start

Abstract: The concept and the performance of a device to remove hydrocarbons from engine exhaust during cold start were described. The device consisted of a hydrocarbon adsorbent and a metal oxide that could react with the hydrocarbon by oxidation to form carbon oxide and water. The metal oxide could then be regenerated later in the drive cycle by reaction with oxygen. Using a mixed oxide containing Cr, Co, Fe, and Al; ZSM-5 zeolite as the adsorbent; and propene, propane, or toluene as the hydrocarbon, the efficiency of hydrocarbon removal was measured in the laboratory during the 2 min when the unit was heated from room temperature at a rate of 150 o C/min.

Basic characteristics of spinel type manganese mixed oxide/titanium composite anodes for electroorganic redox catalysis†

Abstract: Manganese mixed oxide composite layers of about 1 μm thickness on titanium sheet as substrate were fabricated by firing of the corresponding nitrates at a typical temperature of 400°C in air. The activity of these anodes was evaluated by cyclic voltammetry (10 mV/s) and the stability was determined by chronopotentiometry (2.5 mA/cm 2 ) in 1M H 2 SO 4 . The oxidation of 2-propanol was examined as a simple electroorganic model reaction. The quality of a first category of mixed oxides with general composition MnMe 2 O 4 decreased in the order Me = Co, Ni, Fe. In a second group with the general formula MeMn 2 O 4 a decrease in the order Me = Co, Cu, Fe, Ni, Ti, Zn, Cd, Ca, Mg, (Zn, Ge), Li was observed. The corresponding candidates of the second group were superior to those of the first. The anode service life τ of the optimum spinel anode CoMn 2 O 4 /Ti is dependent on the current density, according to j λ τ = const. (λ=1.7). Thus high current densities are precluded. The mechanism has been discussed in terms of a heterogeneous redox catalysis: surface Mn(VII) states are formed in a slow electrochemical step. In a subsequent fast chemical oxidation of the organic molecule the original reduced state is regenerated. This also explains the comparatively good service life of these anodes

Study of The Microstructure and Oxidation of NbSi2 Base Alloys

Abstract: The microstructures of arc melted ingots and melt spun ribbons of NbSi2 and NbSi2-(8,20 at%)Cr alloys are discussed. Rapid quenching from the melt refined the grain size of the alloys by two orders of magnitude and suppressed the formation of Nb5Si3 in Zone A of the binary alloy ribbons. In the ternary alloy ingots and ribbons formation of the Nb5Si3 was suppressed, and the C40 NbSi2 and CrSi2 and orthorhombic Nb2Si6Cr3 phases were formed. Zone A was not formed in the ribbons of the ternary alloys. The microhardness of these phases and the oxidation behaviour of the alloys up to 1350°C in air and an Ar atmosphere are discussed. NbSi2 did not form a protective silica layer on oxidation. Instead a mixed oxide scale of silica and α-Nb2O5 formed which cracked during growth of the oxide and hindered protection of the alloy. It is shown that the addition of Cr modifies the oxide to a duplex oxide of SiO2 and Cr2O3 and that the underlying matrix becomes depleted in Cr. Pest oxidation at 750°C was suppressed in Nb-60Si-20Cr.

Characterization of RuO2-based film electrodes by secondary ion mass spectrometry

Abstract: Concentration depth profiles of Ti-supported RuO2–TiO2 films, prepared by pyrolysis of ruthenium(III) chloride hydrate and titanium diisopropoxide bis-pentane-2,4-dionate, have been studied by secondary ion mass spectrometry (SIMS). The 102Ru : 48Ti ion intensity ratio vs. the nominal concentration of ruthenium oxide was followed for samples obtained from precursors dissolved in different solvents. The dependence on bombarding time of ion intensity profiles for other species, such as O –(m/z= 16), OH–(m/z= 17), 46TiO+(m/z= 62), 50TiOH+(m/z= 63) was also studied. The mixed oxide films were characterized by cyclic voltammetry. The results of the combined research support the idea that microstructural and chemical impurities are concentrated in the outermost part of the film. This phenomenon seems to depend on the composition of the solvent used for the precursor salts.

Non-toxic gas-generating mixt. with thermal-mechanical stability

Abstract: A gas-generating mixt. consists of a fuel which is rich in N and low in C, selected from nitro-guanidine (NIGU), triaminoguanidine nitrate (TAGN), di-guanidinium-5,5'-azotetrazolate (GZT) and 3-nitro-1,2,3-triazol-5-one (NTO), catalyst, oxidant and opt. coolant. The oxidant comprises Cu(NH3)2(NO3)2 (I) and the catalyst is V2O5/MoO3 mixed oxide and/or oxide mixt..

Synthesis and Characterization of Ta2o5-sio2 Mixed Oxides

Abstract: Mixed oxides, especially silica containing multicomponent oxides, have recently found many applications in the production of glasses, ceramics and catalysts. This paper reports for the first time the synthesis of SiO2-Ta2O5 mixed oxide by the sol-gel method. The advantage of the sol-gel method is that a relatively large concentration of tantalum can be incorporated in the mixed oxide structure. Physicochemical characterization shows that tantalum atoms are incorporated into the silica matrix producing Si-O-Ta bonds.

Mixed oxide effect in an ion-exchanged glass

Abstract: Samples of flat glass (content of Na2O 14.4 wt%) were ion-exchanged in different mixed silver nitrate/sodium nitrate melts. The concentration dependence of the ac conductivity shows the typical mixed oxide effect. The results are qualitatively in agreement with the theory of Bunde and co-workers.

Composition precursor and cerium and zirconium mixed oxide based composition, method for its preparation and use thereof

Abstract: Method for the preparation of a cerium and zirconium mixed oxide based composition. The method is characterized by the following stages: a liquid mixture is prepared comprising cerium and zirconium compounds; said mixture is placed in contact with a carbonate or bicarbonate and a reactive medium is formed having, during the reaction, a neutral or basic pH, the resulting precipitate is then recovered. A cerium and zirconium mixed oxide based composition is obtained by calcining this precursor. The composition is characterized by having a total porous volume of at least 0.6 cm3/g and in that at least 40 %, and more particularly 50 %, of the total porous volume is provided by pores having a diameter of a maximum of 1 νm.

Alumina-titania oxides: Synthesis and characterization

Abstract: Alumina-titania mixed oxides with nominal atomic ratios Al/Ti=25 and 2 have been synthesized by cohydrolysis of Al(OsecBu)3 and Ti(OBu)4. The oxides were amorphous at 500°C, showing only short range order. Ti was incorporated in alumina in a well dispersed way creating a true Al/Ti mixed oxide. The strength of surface acid sites and specific surface areas were increased at the higher Ti content. The TiO2 anatase phase was avoided and rutile was formed directly at 900°C.

Modified mixed oxide perovskites 0.7Sr(Al1/2B1/2) O3·0.3LaAlO3 and 0.7Sr(Al1/2B1/2) O3·0.3NdGaO3 (B=Ta5+ or Nb5+) for high-Tc superconductor substrate applications

Abstract: Single-crystal fibres of modified strontium aluminium tantalum oxide (1-x)Sr(Al1/2Ta1/2) O3·xLaAlO3(SAT-LA) and (1-x)Sr(Al1/2Ta1/2)O3·xNdGaO3 (SAT·NG), and modified strontium aluminum niobium oxide (1-x)Sr(Al1/2Nb1/2)O3·xNdGaO3(SAT·NG) and (1-x)Sr (Al1/2Nb1/2)O3·xLaAlO3 (SAN·LA) were grown using a laser-heated pedestal growth technique. 0.7SAT·0.3LA grows congruently and retains a twin free simple cubic perovskite structure (as the SAT) when cooled down to room temperature. 0.7SAT·0.3LA crystals have a moderate dielectric constant (κ = 21.7) and low dielectric loss (tan δ = 7.5 × 10−5) at 10 kHz and 90 K. The reduction problem of Ta5+ is eliminated (which is common in the case of SAT growth). 0.7SAT·0.3NG and 0.7SAN·0.3NG have lower melting temperatures and crystal growth is easier. NdGaO3 addition to the SAT and SAN enhances the potential of SAT and SAN as large-area substrates for high-Tc superconductor growth. However, the dielectric constants increased from κ∼-12 to κ∼-16(0.7SAT·0.3NG) and from κ∼18 to κ∼23 (0.7SAN·0.3NG) as a result of NdGaO3 incorporation.

Sable coating solutions for coating valve metal anodes

Abstract: Stable catalytic coating solutions are prepared using soluble compounds of at least two platinum group metals or at least one platinum group metal and at least one soluble compound of a valve metal. Valve metal anode bases coated with mixed oxide catalytic coating layers of a valve metal oxide and a platinum group metal oxide can be prepared with longer useful life by incorporation of a second platinum group metal. A mixed oxide coating of ruthenium, iridium, and titanium oxides is preferred for the coating layers in order to provide longer useful anode life.

Transformation of Isopropanol Over Pt/hxvmoo5.5 Hydrogen Bronze

Abstract: The transformation of isopropanol was studied at 423 K over a mixed molybdenum-vanadium oxide, with and without platinum as well as over the corresponding hydrogen bronze prepared via hydrogen spillover. In the absence of platinum, dehydration is the main reaction. However, propane and acetone are produced in small amounts, which points to the acid-base character of the oxide and to the existence of distinct hydrogenation sites. For the Pt/oxide system, higher conversions and acetone selectivities over 90% are obtained. A marked deactivation with time is noted, which is probably due to the continuous modification of the oxide surface and of the metal oxide contact. The hydrogen bronze of the mixed oxide exhibits a much improved activity and stability. Without platinum, switching from helium to hydrogen as carrier gas has a slight influence on the selectivity whereas for Pt/oxide, both activity and acetone selectivity are affected. The influence of temperature on the reaction was studied over the hydrogen bronze. The effect is different below and above 373 K and is related to the hydrogen stoichiometry of the bronze, the bronze with the lower stoichiometry (lacunar bronze) being the most active catalyst.

Growth and Characterization of Oxide Films on Zirconium-Niobium Alloys

Abstract: Pressure tubes for CANDU reactors are made from extruded and cold-drawn Zr-2.5Nb alloy. Their microstructure consists of elongated {alpha}-Zr grains containing about 1 atom % Nb, surrounded by a thin network of metastable {beta}-Zr phase, containing about 20 atom % Nb. Alloys of Zr-1Nb an Zr-20Nb were prepared, heat treated, and oxidized in 573 K water to produce bulk microstructures and oxides that would simulate those normally found on a much finer scale in pressure tubes. Oxidation of Zr-20Nb ({beta}-Zr phase) was more rapid than that for the Zr-1Nb (predominantly {alpha}-Zr phase) but, despite this, the hydrogen absorption was considerably lower. During corrosion testing, the metastable {beta}-Zr undergoes partial decomposition to omega phase. The oxides show contrasting morphologies in terms of crystallite size (20 to 60 nm for oxides on {alpha}-Zr versus about 15 nm for oxides on {beta}-Zr). In addition to monoclinic ZrO{sub 2}, there is evidence for either tetragonal ZrO{sub 2} or the mixed oxide, 6ZrO{sub 2}Nb{sub 2}O{sub 5} in the {beta}-Zr oxide. Scanning transmission electron microscopy (STEM) imaging shows niobium associated with the oxide formed over the {beta}-Zr phase in oxidized pressure tube material. Hydrogen depth profiling by {sup 15}N nuclear reaction analyses has been used tomore » investigate the diffusion of hydrogen in these oxides. The oxide films were implanted with hydrogen and the progressive dispersion of the implanted hydrogen, as a result of annealing, was used to investigate hydrogen diffusion as a function of temperature. The nondispersive nature of the implanted hydrogen peaks in the Zr-1Nb oxide after annealing was suggestive of the presence of interconnected porosity in those oxides. The broadened peaks in the Zr-20Nb oxide after annealing are indicative of a normal diffusion process in a nonporous medium. The implications of these observations will be discussed in terms of corrosion and hydrogen uptake in Zr-2.5Nb pressure tubes.« less

Characterisation of a thin-film/thick-film strain gauge sensor on stainless steel

Abstract: Thin-film strain gauges of the mixed oxide Bi2O3-V2O5 have been deposited on insulated stainless steel substrates. The thin-film gauges are insulated from the steel by application of dielectric layers printed using thick-film techniques. Various strain gauge parameters are analysed, including linearity, hysteresis, repeatability and temperature effects. Comparisons have also been made with similar gauges deposited on glass. It has been observed that the thin-film strain sensor deposited on steel performs much better than the one deposited on glass in terms of maximum applicable strain, hysteresis and linearity. However, the film on glass is much more sensitive than the one deposited on steel. The lower-sensitivity of the sensor on steel is attributed to the increased thickness of the deposited resistor and the poorer surface characteristics of the thick-film dielectric layers. The d.c. conductivity variation at high temperatures has also been studied and it has been observed that freeband conduction takes place at these temperatures.

Hard-coat film

Abstract: PURPOSE: To obtain a hard-coat film having a high refractive index, excellent in wear resistance and capable of being cured by cross-linking in a short time by forming the film with a composition contg. a specified component. CONSTITUTION: The composition contg. a component A as a multifunctional acrylate and a component B as >=1 kind of inorg. oxide fine grain selected from among antimony oxide, tin oxide, indium-tin mixed oxide, cerium oxide, titania and zirconia, is cured to constitute the hard-coat film. An acrylate having >=2 functional groups in one molecule can be used as the multifunctional acrylate of the component A. The functional group curable with photopolymerization, an active energy beam such as electron beam and radiation and heat are used, and especially the photopolymerizable functional group is preferably used. Although the inorg. oxide fine grain used in the component B can be dispersed in the coating film on condition that the transparency of the film is maintained, a sol wherein the grains are dispersed in the form of colloid is most preferably used from the standpoint of operability, etc.