Titanium Mixed Oxides Research Articles

Isopropylation of benzene over sulfated ZrO2–TiO2 mixed-oxide catalyst

Zirconia–titania mixed oxide containing 60mol% of zirconium was synthesized by co-precipitation method with and without sodium dodecyl sulfate (SDS) as surfactant. The 110°C dried mixed oxides were loaded with 10wt.% sulfate by wetness impregnation method. Each of the sulfated samples was calcined for 3h at 500, 600 and 800°C, and characterized by surface area and pore size distributions using multipoint BET method. Further, the 600°C calcined sulfated mixed-oxide samples were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption, and ammonia temperature programmed desorption (TPD). The results revealed that amorphous, high surface area materials were obtained possessing both Lewis and Bronsted acid sites. However, the sample prepared with surfactant showed higher total pore volume and average pore diameter and was more acidic than that prepared without surfactant. The catalytic activity of these samples was tested for isopropylation of benzene with isopropanol varying different reaction parameters. The results are correlated to the acidity and textural properties, which show that catalyst prepared in presence of SDS, with improved texture and high acidity, is excellent for this reaction with cumene selectivity more than 97mol%. The deactivation was found to be faster at lower reaction temperature.

Photoelectrochemical Behavior of Heterosystem AIIBVI/TiO2–RuO2 in Electrolysis of Aqueous Electrolytes

Anodic polarization curves for the CdSe/TiO2–RuO2 heterosystem and its components in 0.5 M Na2SO4 with and without illumination are compared. It is shown that the outer film consisting of titanium and ruthenium mixed oxide protects AIIBVI semiconductors from corrosion and promotes the electrocatalytical activity of the heterosystem in the photosplitting of water.

Preparation, physico-chemical characterization and catalytic activity of sulphated ZrO 2–TiO 2 mixed oxides

A series of ZrO 2–TiO 2 mixed oxides was prepared varying mole fraction of titanium from 0 to 1, and characterized by XRD, FT-IR, TG/DTA, UV–VIS–DRS, surface area, surface acidity, and sulphur content. The UV–VIS–DRS and pH of point of zero charge (pH ZPC) data for the mixed oxide samples determined by acid–base titration method revealed that a different surface was formed when zirconium and titanium were co-precipitated. XRD pattern of 700 °C calcined samples showed the formation of ZrTiO 4 phase. The optimum concentration of zirconium in the zirconia–titania mixed oxide in the precipitation solution was 60 mol% for obtaining high surface area and highly acidic mixed oxide system. Sulphur analysis of the sulphate promoted samples showed that the sample containing Ti mole fraction 0.4 retained the highest amount of sulphur. The surface acidity determined by irreversible adsorption of organic bases, such as pyridine, piperidine and 2,6-dimethyl pyridine showed the highest acidity for the above sample. This catalyst also showed the highest catalytic activity towards isopropanol dehydration.

Mesostructured Silica−Titania Mixed Oxide Thin Films

Poly(ethylene glycol) containing surfactant molecules were modified with titanium alkoxides. These surfactants were used in the synthesis of mesostructured silica−titania mixed metal oxide thin films serving two different functions: (a) as a structure-directing agent and (b) as a moderator of the hydrolysis rate of the titanium alkoxide. The resulting amorphous material showed a well-ordered hexagonal mesostructure with titanium species present in a tetrahedral environment. Upon heat treatment above 500 °C, the amorphous structure converted into anatase and finally rutile.

Structural study of lithium titanium mixed oxides prepared by sol-gel process

A structural study, using TGA-DSC analysis, X-ray diffraction, Raman scattering and FT Infrared absorption, is performed on mixed titanium lithium oxide with 20% of lithium prepared by sol-gel process. The structure is investigated as a function of the annealing temperature. At low temperatures the sample is in the anatase phase and transforms to the rutile phase near 500°C. The crystallite size of rutile TiO2 increases from 40 to 100 nm as the temperature increases. However the size increase presents some discontinuity at temperature around 600°C. At thermal treatment temperatures from 500°C to 850°C the presence of LiTi2O4 in the sample is clearly observed. Finally at 1000°C the sample is composed by a mixture of rutile TiO2 and Li2Ti3O7.

Insertion of lithium in vanadium and mixed vanadium–titanium oxide films

Numerous authors have suggested the use of vanadium–titanium mixed oxides as counter-electrodes for lithium conducting electrochromic devices. In this paper insertion of Li in sol–gel made (V 2O 5) x –(TiO 2) 1− x films with x values in the range 0.5–1 were electrochemically studied by coulometric titration, cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Raman spectroscopy was also performed on these films and has shown that the vanadium oxide films are well crystallised. TiO 2 containing films are totally amorphous and consequently the absence of γ-V 2O 5 phase allows the insertion beyond 1 Li per oxide mole in the films. The lithium diffusion in TiO 2 containing films could be explained by the participation of the titanium through the V–O–Ti groups. The decrease of the diffusion rate observed on EIS data is probably due to the difference between the VO and TiO bonds and their respective numbers.

X-ray absorption and XPS study of titanium mixed oxides synthesized by the sol–gel method

The mixed oxides SiO 2 /TiO 2 and SiO 2 /TiO 2 /Sb 2 O 5 were prepared with different Ti and Sb amounts and investigated by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) at the Ti K edge. There is no evidence for structural modification of titanium environment in the samples having between 5.6 and 20.3 wt% of TiO 2 . All the experimental evidence indicates that titanium has a local environment close to that of TiO 2 anatase. XAS show that this similarity is extends up to the next neighbouring Ti shells. XPS analysis shows that Ti and Sb are present as TiO 2 and Sb 2 O 5 .

Redox behaviour of ceria–titania mixed oxides

The reducibility of the supports is one of the properties influencing the catalytic behaviour of platinum catalysts in the selective hydrogenation of α,β-unsaturated aldehydes. Platinum on reducible supports has shown higher selectivities in carbonyl hydrogenation compared to Pt/Al 2O 3 and Pt/SiO 2 catalysts. We report here a study on the redox properties of mixtures of titania and ceria, precursors of Pt/TiO 2–CeO 2 catalysts. Two samples, with atomic compositions Ti/Ce 8/2 and 5/5, were prepared using a sol–gel process. They were treated under hydrogen and air in a wide range of temperatures. Surface compositions and the percentage of reduced ceria were determined by X-ray photoelectron spectroscopy. Temperature programmed reduction (TPR) profiles, and X-ray diffraction patterns were interpreted in terms of the formation and stability of several mixed compounds.

Preparation and properties of antimony (V) oxide adsorbed on silica–titania mixed oxide

SiO 2/TiO 2 binary oxides were initially prepared by the sol–gel process and further reacted with antimony (V) in aqueous solution. Calcined and uncalcined SiO 2/TiO 2/Sb 2O 5 composites with different compositions were characterized by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy techniques. Large ion exchange capacities were determined for alkaline metal ions: Li +, between 0.91 and 1.15 mmol g −1; Na +, between 1.32 and 1.70 mmol g −1; K +, between 1.65 and 1.95 mmol g −1. The proton exchange capacities increased for samples with larger amount of Sb 2O 5 in the composites. The thermal treatment of the samples, i.e., comparing the exchange capacities of uncalcined samples with that of the calcined ones (773 K), did not show significant change.

A Novel Catalyst for CO Oxidation at Low Temperature

Supported catalysts of palladium over ceria–titania mixed oxides (Pd/CeO2–TiO2) were prepared and tested for carbon monoxide oxidation. The catalysts exhibited high catalytic activity at room temperature. The Pd/CeO2–TiO2 catalyst was more active than Pd/CeO2, Pd/SnO2–TiO2, Pd/ZrO2–TiO2, Pd/Al2O2–TiO2 and Pd/TiO2 catalysts under the same conditions examined. The effects of preparation methods of the support, the mole ratio of ceria and titania in mixed supports as well as Pd loading upon the catalytic activity of CO oxidation were investigated. Among the Pd/CeO2–TiO2 catalysts, the best one corresponds to the Pd loading of 1.0 wt% or above, and the mole ratio of ceria and titania ranging from 1 : 7 to 1 : 5. The steady-state catalytic performance of such catalyst was recorded without any deactivation over 8 h time-on-stream in the present study.

Characterization of alumina–titania mixed oxide supports

Abstract Bulk and surface characterization of alumina-rich Al 2 O 3 –TiO 2 mixed oxides with TiO 2 /(Al 2 O 3 +TiO 2 ) molar ratios equal to 0, 0.05 and 0.1, prepared by sol–gel and impregnation procedures have been performed by XRD, DTA, surface area, FTIR, UV–Vis, FT-Raman and TPD of ammonia. The results indicate that in the case of the samples prepared by the sol–gel procedure, an increase in surface area with titania loadings is obtained, in contrast to their impregnation counterparts, where a decrease is observed. The results from XRD, Raman and UV–Vis indicate that better titania dispersions are obtained by the sol–gel procedure and that at the titania loadings used here, no separate titania particles are detected. Additionally, the UV results show that Ti cations are essentially isolated, possibly into an octahedral form and with a lower coordination. In the samples prepared by the sol–gel procedure there is no evidence of titanium oxide species on the surface, suggesting that titania is probably dissolved into the alumina bulk. These results would explain the activity trends observed in alumina-rich Mo/Al 2 O 3 –TiO 2 HDS catalysts.

Isobutane Dehydrogenation on Chromia/Silica−Titania Mixed Oxide and Chromia/γ-Alumina Catalysts

Isobutane dehydrogenation was studied on chromia supported on mixed oxides of silica and titania catalysts. The catalyst supports, silica−titania mixed oxides, were prepared by three different methods: a modified sol−gel method, a mechanical mixing of silica and titania, and a calcination of tetraethyl orthosilicate (TEOS) intercalated crystalline titanate. Chromia supported on the mixed oxide (Si:Ti mole ratio = 0.36) prepared from TEOS intercalated crystalline titanate is the most active among these chromia supported mixed oxide catalysts. The isobutylene yield of this catalyst was about 60% of Girdler G-41 catalyst, comparable to that of the in-house chromia/γ-alumina catalyst, 2 times as much as that of the chromia/titania catalyst, and 6 times as much as that of the chromia/silica catalyst.

Surface modification of titanium alloy implants

Hip replacement stems manufactured from Ti6AI4V titanium alloy were surface treated in one of four ways and tested for dissolution resistance in bovine serum. Those stems treated thermally were found to have significantly lower metal ion release compared with those receiving standard commercial treatments. The improved dissolution behaviour is associated with a change in the surface oxide structure from mixed titanium oxides to a more stable rutile structure.

Acidic and basic properties of zirconia—alumina and zirconia—titania mixed oxides

Two series of mixed oxides ZrO 2Al 2O 3 and ZrO 2TiO 2 were prepared from propylate hydrolysis, followed by drying and calcination. The acidic and basic properties of the various samples were characterized by adsorption of specific probe molecules (carbon dioxide, pyridine, 2,6-di-methylpyridine) studied by FT-IR spectroscopy and activity towards two test reactions (2-propanol dehydration and carbon oxysulfide hydrolysis). Both methods showed that a synergy occurred on ZrO 2TiO 2 samples leading to a maximum of Brønsted acidity and a minimum of basicity for ZrO 2 (23%)TiO 2 (77%). On the other hand, the Lewis acidity of ZrO 2Al 2O 3 samples increased with the alumina content whereas the basicity decreased sharply as soon as alumina was introduced.

Vanadium and titanium oxides prepared by hydrolysis of alkoxides as insertion electrodes in lithium cells with polymeric electrolytes

Single and mixed oxides of titanium and vanadium, prepared by hydrolysis of alkoxides using a sol—gel technique, have been evaluated as positive electrodes in all-solid-state lithium cells. These oxides were shown to have similar gravimetric capacities to, but higher rate capabilities than, the established lithium insertion electrode phase V 6O 13.

Mixed Titanium and Phosphorus Oxides. II. — The Effect of pH Values of Solutions on Surface Acidity

AbstractA series at mixed oxides of titanium and phosphorus were prepared by co‐precipitation method accompanying refluxing treatment. The effect of the pH values of the solutions on the structures, compositions, and surface acidities of the resultants compounds was determined. The samples were characterized by BET surface area measurement, X‐ray powder diffraction (XRD) for structural analysis and amine‐titration for surface acidities. After calcinating the oxides at 773 K, the surface acidities were attributed mainly to Ti(OH)PO4 structure. Elemental analysis revealed that the P/Ti ratios in the samples decreased with increasing the pH value of the preparative solution. When the mixed oxides were used as catalysts for 2‐propanol decomposition reaction, the highest activities were obtained over the samples prepared in the solutions with the pH values being 2 or 3. That result was in agreement with the variation in surface area and acid amount of the catalysts.

Functionalization of alkanes by heterogeneous vapour-phase oxidation.: II. Propane ammoxidation

Propane ammoxidation to acrylonitrile was studied on (VO) 2P2O 7, on vanadium—titanium mixed oxide, on vanadium—antimonate with different Sb:V atomic ratios and on iron—antimonate (Sb:Fe=2.0) catalysts. The results showed a strong deactivation effect of ammonia on propane conversion, interpreted as a competitive adsorption of ammonia on the sites for activation of propane by oxidative dehydrogenation to propylene. Selectivity to acrylonitrile behaves in a complex waywith respect to ammonia concentration showing a maximum value for an NH 3 concent around 15% followed by a decrease with a parallel increase in propylene selectivity. The effect was interpreted considering a double effect of ammonia that (i) transforms total oxidation sites to selective sites for acrylonitrile synthesis and (ii) reduces these sites due to its oxidation to nitrogen oxides. V P O and V Sb O systems show the higher selectivities in acrylonitrile formation from propane.

Characterization of pure titanium oxide and mixed titanium-iron oxide hydrate gels

Characterization of pure titanium oxide and mixed titanium-iron oxide hydrate gels

Mixed oxides of titanium and niobium: Defects in quenched samples

Samples of mixed oxides having the compositions TiO 2.26Nb 2O 5 and TiO 2.7Nb 2O 5 have been quenched from temperatures near the liquidus, in order to freeze in high concentrations of defects. The structure of the quenched materials has been investigated by electron microscopy. Lattice images of suitably oriented fragments contain sufficient information to enable detailed structural models of the defects within them to be derived. These models indicate that the observed defects, which include Wadsley intergrowth defects and several different kinds of displacements of shear planes, are accommodated coherently and without gross misfit of the components of the structure.

Mixed oxides of titanium and niobium: Intergrowth structures and defects

The binary oxides of titanium and niobium, TiNb 2O 7, Ti 2Nb 10O 29, TiNb 24O 62 and TiNb 52O 132, have been examined by electron diffraction and microscopy. The structure of TiNb 52O 132, an ordered intergrowth of TiNb 24O 62 and high temperature Nb 2O 5, is clarified. There are many planar defects in these compounds which can be described in terms of the random intergrowth, at the unit cell level, of very thin fragments of other closely related phases. Similar intergrowths are found in regions of the phase diagram previously referred to as “solid solutions,” and a number of ordered sequences characteristic of new phases are described.