Synthesis and Photocatalytic Properties of HTaWO<Subscript>6</Subscript> Intercalated with Oxide Materials

Transition metal oxides (TiO₂, MnO₂, Cr₂O₃, Fe₂O₃, NiO, CuO) were intercalated into the interlayer of HTaWO₆ by (1) hydrothermal reaction on HTaWO₆ with 1 M soluble metal nitrate aqueous solution at 130C for 12 h followed by calcination at 250C for 3 h and (2) sol reaction on HTaWO₆/n-C₃H₇NH₂ precursor with metal oxide sol, followed by UV irradiation. The gallery height of transition metal oxide in the interlayer of HTaWO₆ is changed from 0.42 to 0.71 nm, the band gap energies of intercalated materials are less than 3 eV. HTaWO₆/Cr₂O₃, HTaWO₆/MnO, HTaWO₆/Fe₂O₃, HTaWO₆/NiO and HTaWO₆/CuO porous materials are capable of photocatalytic decomposing methyl orange, and the photocatalytic activity of HTaWO₆/TiO₂ is superior to that of unsupported TiO₂.     

Nb2O5 as efficient and recyclable photocatalyst for indigo carmine degradation

Heterogeneous photocatalysis is a significant green technology for application in water purification. The application of Nb₂O₅ catalyst for the photodegradation of contaminants is few reported in the literature. Thus, the Nb₂O₅ catalyst was characterized by SEM, FTIR, surface area and charge surface density. This catalyst was applied to degrade indigo carmine dye, which was compared with degradation catalyzed by TiO₂ and ZnO. Almost 100% of dye degradation occurred at 20, 45 and 90 min for TiO₂, ZnO and Nb₂O₅, respectively. The effect of Nb₂O₅ catalyst concentration, pH and ionic strength (μ) was investigated. The Nb₂O₅ activity increased at 0.7 g/L and for higher catalyst concentrations the degradation was kept constant. Degradation of indigo carmine dye catalyzed by Nb₂O₅ was improved at pH < 4.0 and μ = 0.05 mol/L. TiO₂, ZnO and Nb₂O₅ were recovered and re-applied in other nine reaction cycles. While TiO₂ and ZnO have an abrupt loss of their catalytic activity, Nb₂O₅ maintained 85% of catalytic activity after 10 reaction cycles.     

Rates of reaction of SO2 with metal oxides

Rates of sorption of SO₂ from synthetic flue gas by 14 metal oxides were determined. These oxides had been selected for their potential applicability to processes for removing SO₂ from flue gas using thermal regeneration of sorbent. Measurements were performed using thermogravimetric analysis, and rates were fitted to semi-empirical expressions; CeO₂, Co₃O₄, Cr₂O₃, CuO, Fe₂O₃, and NiO displayed measurable rates in the range 200° to 500°C, and were converted to sulphates. Rates were immeasurably small at 25° to 800°C for Al₂O₃, Sb₂O₅, SnO₂, TiO₂, V₂O₅, WO₃, ZnO, and ZrO₂, CuO and CeO₂ showed the highest rates     

Anatase–rutile transformation in doped titania under argon and hydrogen atmospheres

Abstract

Pure titania pulp containing amorphous titania was heated at different temperatures and times. Above 650°C anatase phase was evolved and between 900 and 1000°C, anatase–rutile transformation occurred. The anatase–rutile transformation in TiO₂ in the presence of different transition metal oxides, namely Fe₂O₃, Cr₂O₃, NiO, CuO and MnO₂ under argon and hydrogen atmospheres was investigated. The different phases of TiO₂ were determined using powder X-ray diffraction (XRD). The anatase–rutile transformation temperature was found to be lowered in the presence of transition metal oxides. The transformation temperature was found to vary much in argon and hydrogen atmospheres compared to air in the presence of the metal oxides. Also the method of preparation of metal oxide doped TiO₂ influences rutilation. Other methods such as chemical analysis, surface area measurements and crystallite size calculation were used for the characterisation of the samples. The surface area of heated samples was found to be decreased while crystallite size increased due to rutilation on heating. The samples were also observed under a scanning electron microscope to characterise the microstructural changes associated with each thermal treatment and atmosphere. The morphology of doped titania changes much on heating due to phase modification. The atmosphere of heating also has important effect on deciding the morphology of rutilated titania.     

Dehydration of 2,3-butanediol into 3-buten-2-ol catalyzed by ZrO2

Vapor-phase catalytic dehydration of 2,3-butanediol was investigated over metal oxides such as CeO₂, La₂O₃, Yb₂O₃, ZrO₂, Al₂O₃, TiO₂, ZnO, Fe₂O₃, NiO, and Cr₂O₃. In the dehydration of 2,3-butanediol, 3-buten-2-ol was preferentially produced over monoclinic ZrO₂ along with major by-products such as butanone and 3-hydroxy-2-butanone. Over ZrO₂ calcined at 900 °C, 3-buten-2-ol was produced with a maximum selectivity of 59.0% at 300 °C without producing 1,3-butadiene.     

The effect of foreign ions on the reactivity of the CaO-SiO2-Al2O3-Fe2O3 system: Part II: Cations

The subject of this paper is the effect of foreign cations on the reactivity of the CaO-SiO₂-Al₂O₃-Fe₂O₃ system. One reference mixture and eighteen modified mixtures, prepared by mixing the reference sample with 1% w/w of chemical grade MnO₂, CuO, V₂O₅, PbO, CdO, ZrO₂, Li₂O, MoO₃, Co₂O₃, NiO, WO₃, ZnO, Nb₂O₅, CrO₃, Ta₂O₅, TiO₂, BaO₂ and H₃BO₃ were studied. The effect on the reactivity is evaluated on the basis of the free lime content in samples sintered at 1200 and 1450 °C. At 1200 °C, the reactivity of the mixture is greatly increased in the presence of Cu and Li oxides. Based on their effect at 1450 °C, the added elements can be divided into three groups. W, Ta, Cu, Ti and Mo show the most positive effect, decreasing the free CaO (fCaO) content by 30-60%, compared with the pure sample. Cr and B cause an increase of fCaO content, while the rest of the elements exhibit a marginal positive effect. According to their volatility at 1450 °C, the added compounds can be subdivided into three groups of low (Ti⁴⁺, Cu²⁺, Mo⁶⁺, W⁺⁶, V⁵⁺, Zn²⁺, Zr⁴⁺), moderate (Cr⁶⁺, Co³⁺, Ni²⁺, Mn⁴⁺) and high volatility (Cd²⁺, Pb²⁺). All burned samples, analyzed by means of X-ray diffraction, have a final mineralogical composition, which corresponds to the structure of a typical clinker.     

Effects of metal oxides on electrochemical hydrogen storage of nanocrystalline LaMg12-Ni composites

Nanocrystalline LaMg₁₂-Ni composites were prepared by ball-milling a LaMg₁₂ alloy and Ni powders with additions of small amounts of metal oxides (TiO₂, Fe₃O₄, La₂O₃ and CuO). The composites with additions of small amounts of metal oxides were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the effects of the addition of the metal oxides on the electrochemical hydrogen storage were investigated. It is demonstrated that the initial discharge capacities of the composites with additions of small amounts of metal oxides were significantly higher than that of the original composite. The additions of TiO₂ and Fe₃O₄ as catalysts improved the electrochemical hydrogen storage properties more effective than additions of La₂O₃ and CuO. Analysis of the electrochemical impedance spectra (EIS) showed that the function of the metal oxides was considered to reduce the electrochemical reaction resistance as catalysts and to increase the specific surface area as impurities. However, more extensive investigation is still necessary in order to improve the cyclic stability of these materials for practical application in Ni/MH batteries.     

Ordered Crystalline Mesoporous Oxides as Catalysts for CO Oxidation

Crystalline mesoporous metal oxides have attracted considerable attention recently, but their catalytic applications have rarely been studied. In this work, a series of crystalline three-dimensional mesoporous metal oxides (i.e., CeO₂, Co₃O₄, Cr₂O₃, CuO, Fe₂O₃, β-MnO₂, Mn₂O₃, Mn₃O₄, NiO, and NiCoMnO₄) were prepared using the mesoporous silica KIT-6 as a hard template. These ordered mesoporous metal oxides with highly crystalline walls were characterized by PXRD, TEM, N₂ adsorption and evaluated as CO oxidation catalysts. These mesoporous materials, except for mesoporous Fe₂O₃, exhibit much higher catalytic activities than their bulk counterparts. In particular, mesoporous Co₃O₄, β-MnO₂, and NiO show appreciable CO oxidation activity below 0 °C, and the catalytic activities of mesoporous β-MnO₂, and NiO are even higher than those of their nanoparticulate counterparts with large surface areas. β-MnO₂ is particularly interesting because it combines low cost and low toxicity with high activity (T ₅₀ = 39 °C).     

Effect of metallic oxides on thermal stability of ethylene–propylene terpolymer

Thermal stability of ethylene–propylene terpolymer (EPDM) loaded with various metallic oxides (PbO, CuO, NiO, Fe₂O₃, Cr₂O₃, TiO₂, ZrO₂) was assessed by the oxygen uptake method. The effects of 5 phr oxide of thermal aging of elastomer were investigated under isothermal (180°C) and isobaric (air at normal pressure) conditions. The influence of this was pointed out. Some mechanistic considerations on the oxidative degradation of EPDM are presented. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2155–2158, 2001     

Amorphous Ru1−yCryO2 loaded on TiO2 nanotubes for electrochemical capacitors

Amorphous Ru_1−yCr_yO₂/TiO₂ nanotube composites were synthesized by loading different amount of Ru_1−yCr_yO₂ on TiO₂ nanotubes via a reduction reaction of K₂Cr₂O₇ with RuCl₃·nH₂O at pH 8, followed by drying in air at 150 °C. Cyclic voltammetry and galvanostatic charge/discharge tests were applied to investigate the performance of the Ru_1−yCr_yO₂/TiO₂ nanotube composite electrodes. For comparison, the performance of amorphous Ru_1−yCr_yO₂ was also studied. The results demonstrated that the three dimensional nanotube network of TiO₂ offered a solid support structure for active materials Ru_1−yCr_yO₂, allowed the active material to be readily available for electrochemical reactions, and increased the utilization of active materials. A maximum specific capacitance 1272.5 F/g was obtained with the proper amount of Ru_1−yCr_yO₂ loaded on the TiO₂ nanotubes.     

The Effects of Al2O3 Addition and WO3 Modification on Catalytic Activities of NiO/TiO2 for Acid Catalysis

NiO/Al₂O₃–TiO₂/WO₃ catalysts for acid catalysis were prepared by the addition of Al₂O₃ and the modification with WO₃. The strong acid sites were formed through the bonding between dispersed WO₃ and TiO₂. The larger the dispersed WO₃ amount, the higher both the acidity and catalytic activity. The addition of Al₂O₃ up to 5 mol% enhanced acidity and catalytic activity of NiO/Al₂O₃–TiO₂/WO₃ gradually due to the interaction between Al₂O₃ and TiO₂ and consequent formation of Al–O–Ti bond. The presence of NiO may attract reactants and enhance the local concentration of reactants near acid sites and consequently increase catalytic activity.     

Thin metal oxide films on transparent substrates for Li-insertion devices

Lithium insertion in metal oxides is a process of interest in many electrochemical applications, including rechargeable batteries and electrochromic displays. In this work we have examined the characteristics of this process in a series of oxides prepared in the thin-film configuration. The lithium insertion process has been examined in WO₃, NiO, V2O₅, Nb₂O₅ and tin-doped indium oxide (ITO) thin film electrodes deposited on transparent substrates. We have considered various aspects of the insertion process in these oxides with particular attention to charge capacity, reversibility, kinetics, structural and optical changes. The results suggest that the process may induce irreversible modifications in some of the host structures. However, under certain well defined conditions, the process occurs reversibly and thus some of the studied oxides may find successful application in electrochemical devices of prime technological interest.     

Role of support in reforming of CH4 with CO2 over Rh catalysts

The reforming of CH₄ with CO₂ over supported Rh catalysts has been studied over a range of temperatures (550–1000 K). A significant effect of the support on the catalytic activity was observed, where the order was Rh/Al₂O₃>Rh/TiO₂>Rh/SiO₂. The catalytic activity of Rh/SiO₂ was promoted markedly by physical mixing of Rh/SiO₂ with metal oxides such as Al₂O₃, TiO₂, and MgO, indicating a synergetic effect. The role of the metal oxides used as the support and the physical mixture may be ascribed to the promotion in dissociation of CO₂ on the surface of Rh, since the CH₄ + CO₂ reaction is first order in the pressure of CO₂, suggesting that CO₂ dissociation is the rate-determining step. The possible model of the synergetic effect was proposed.     

Microwave dielectric characteristics of Nb2O5-added 0.9Al2O3–0.1TiO2 ceramics

The sintering characteristics, phase composition, and microwave dielectric properties of Nb₂O₅-added 0.9Al₂O₃–0.1TiO₂ ceramics sintered at 1300–1500 °C have been investigated. Results show that Nb⁵⁺ and Al³⁺ can co-substitute for Ti⁴⁺ and form Ti_0.8Al_0.1Nb_0.1O₂, which can lower effectively the sintering temperature, and improve the quality factor of 0.9Al₂O₃–0.1TiO₂ ceramics.     

On the development of metallic inert anode for molten CaCl2–CaO System

Some fundamental aspects related to inert anode development in molten CaCl₂–CaO were investigated based on thermodynamic analysis, electrochemistry of metals and solubility of oxide measurements. The Gibbs free energy change of several key anodic reactions including electro-stripping of metals, electro-formation of metallic oxides, electro-dissolution of metallic oxides as well as oxygen and chlorine evolution was calculated and documented, for the first time, as a reference to develop metallic inert anode in chloride based melts. The anodic behaviors of typical metals (Ni, Fe, Co, Mo, Cu, Ag, and Pt) in the melt were investigated. The results confirmed the thermodynamic stability order of metals in the melts and revealed that surface oxide formation can increase the stability of the electrodes in CaO containing melt. Furthermore, solubility of several oxides (NiO, Fe₂O₃, Cr₂O₃, Co₃O₄, NiFe₂O₄) in pure CaCl₂ or CaCl₂–CaO melts was measured to evaluate the stability of oxide coating or a cermet inert anode in the melt. It was found that the solubility of NiO decreased with increasing CaO concentration, while that of Fe₂O₃ increased. Ni coated with NiO film had much higher stability during anodic polarization.     

Raman investigations of NH3 adsorption on TiO2, Nb2O5, and Nb2O5/TiO2

A study has been carried out of the interactions of NH₃ with TiO₂, Nb₂O₅, and Nb₂O₅/TiO₂. Raman spectroscopy was used to characterize the structure of the adsorbed NH₃ and perturbations of species present at the surface of the adsorbent. On each oxide, NH₃ adsorbs predominantly at Lewis acid sites. Hydrogen-bonding occurs between the adsorbed NH₃ and OH groups present on the surface of TiO₂. A small concentration of NH ₄ ⁺ is observed, consistent with the relatively low concentration of Brønsted acid sites compared to Lewis acid sites on each of the samples investigated. Exposure of Nb₂O₅/TiO₂ to NH₃ at temperatures up to 500°C does not result in partial reduction of the supported niobia.     

Influence of refractory oxide additives on the stability of alumium titanate

Conclusions Batch additives incorporated in the form of various oxides as a means of improving the physicochemical properties of aluminum titanate can be divided into two groups. The first consists of additives which prevent the decomposition of the titanate at temperatures below 1200°C, and stabilize its high-temperature modification. In terms of the degree of activity these oxides are arranged in the series: MgO, TiO₂, SiO₂, Cr₂O₃, La₂O₃. It is possible to assume that their influence is due mainly to the formation of limited solid solutions, and also the development during sintering of impurity grain boundary phases. The second group of oxides (SnO₂, NiO, excess Al₂O₃, etc.) contributes to the sintering of aluminum titanate by forming secondary crystalline phase on the grain boundaries of the ceramic. In this connection in obtaining sintered ceramic materials based on aluminum titanate it is preferable to consider additives of the first group or their combinations with additives of the second group.Translated from Ogneupory, No. 4, pp. 29–31, April, 1987.     

Influences of oxide chemical modified on microstructure and electrical properties of PbTiO3-Bi(Ni1/2Ti1/2)O3

The piezoelectric ceramics 0.45PbTiO₃-0.55Bi(Ni_1/2Ti_1/2)O₃ doped with PbO, Bi₂O₃, NiO and TiO₂ were synthesized by conventional solid state reaction method. Thereafter, the structural, ferroelectric and piezoelectric properties of modified ceramics were investigated systematically. By adding Bi₂O₃, NiO and TiO₂, the leakage current of ceramics was found to diminish pronouncedly. Moreover, the coercive field was observed to decrease by modification with TiO₂ in these ceramics. It was also proven that NiO can only be added in the B-site in PT-55BNT from the results of X-ray photoelectron spectroscopy analysis. Therefore, the modification with oxides can inhibit the volatilization of Pb during the sintering process that eventually improves the performance of materials.     

Development of Catalyst-Sorbents for Simultaneous Removal of SO2 From Flue Gas by Low Temperature Ozone Oxidation

One technological process employing ozone and heterogeneous catalyst-sorbents was proposed for removal of SO₂ from flue gas. The catalyst-sorbents were developed and tested especially for adsorption and oxidation of SO₂. Alternative catalyst-supporters including γ-Al₂O₃, permutite, silica gel, activated carbon and diatomite combined with different metal oxides (MnO₂, Cr₂O₃, Fe₂O₃, CuO, CoO and NiO) were evaluated and tested. It was found that γ-Al₂O₃ doped with MnO₂ can be considered as removal-effective sorbent for adsorption and oxidation of SO₂. The synergetic effect between ozone and catalyst was found to be dominated. Effects of catalyst preparation parameters like calcination temperature, metal loaded and reaction temperature, etc. were investigated based on the MnO₂/Al₂O₃ catalyst-sorbents. Results show that γ-Al₂O₃ combined with 8% Mn, calcinated under 573 K and reacted at 413 K are the optimal parameters for removal of SO₂. Extra NO in flue gas can slightly enhance the capture efficiency of SO₂.     

The catalytic performance in oxidative coupling of methane and the surface basicity of La2O3, Nd2O3, ZrO2 and Nb2O5

The catalytic performance in oxidative coupling of methane (OCM) of unmodified pure La₂O₃, Nd₂O₃, ZrO₂ and Nb₂O₅ has been investigated under various conditions. The results confirmed that the activity of La₂O₃ and Nd₂O₃ was always much higher than that of the remaining two. The surface basicity/base strength distribution of pure La₂O₃, Nd₂O₃, ZrO₂ and Nb₂O₅ was measured using a test reaction of transformation of 2-butanol and a temperature-programmed desorption of CO₂. Both methods showed that La₂O₃ and Nd₂O₃ had high basicity and contained medium and strong basic sites (lanthanum oxide more and neodymium oxide somewhat less). ZrO₂ had only negligible amount of weak basic sites and Nb₂O₅ was rather acidic. The confrontation of the basicity and catalytic performance indicated that in the case of investigated oxides, the basicity (especially strong basic sites) could be a decisive factor in determination of the catalytic activity in OCM. Only in the case of ZrO₂ it was observed a moderate catalytic performance in spite of negligible basicity. The influence of a gas atmosphere used in the calcination of oxides (flowing oxygen, helium and nitrogen) on their basicity and catalytic activity in OCM had been also investigated. Contrary to earlier observations with MgO, no effect of calcination atmosphere on the catalytic performance of investigated oxides in OCM and on their basicity was observed.