Reduced Titanium Dioxide Research Articles

Mapping chemical and bonding information using multivariate analysis of electron energy-loss spectrum images

Electron energy-loss spectroscopy (EELS) in the transmission electron microscope (TEM) is used to obtain high-resolution information on the composition and the type of chemical bonding of materials. Spectrum imaging, where a full EEL spectrum is acquired and stored at each pixel in the image, gives an exact correlation of spatial and spectral features. However, determining and extracting the important spectral components from the large amount of information contained in a spectrum image (SI) can be difficult. This paper demonstrates that principal component analysis of EEL SIs can be used to extract chemically relevant components. With weighted or two-way scaled principal component analysis, both compositional and bonding information can be extracted. Mapping of the chemical variations in a partially reduced titanium dioxide sample and the orientation-dependent bonding in boron nitride and carbon nanotubes are given as examples.

Effects of Sr/Ti-ratio in SrTiO 3-based SOFC anodes investigated by the use of cone-shaped electrodes

In this work the A-site deficiency limit for undoped SrTiO 3, calcined in air or reducing atmosphere, was investigated. XRD and SEM analyses showed that when using the solid-state synthesis route it was difficult to achieve any A-site deficiency. Even very small deviations from unity in the Sr/Ti-ratio resulted in impurity phases. The effects of Sr/Ti-ratio on the performance of SrTiO 3 anodes for solid oxide fuel cells (SOFCs) was investigated by impedance spectroscopy with cone-shaped electrodes. The electrocatalytic activity of the SrTiO 3 cone samples, with various amount of reduced titanium dioxide phases (Magnéli phases), was investigated for oxidation of H 2 at 700 °C. High temperature treatment at 1000 °C, between the measurements at 700 °C, showed that high content of Magnéli phases leads to faster degradation of the activity. The suitability for using cone-shaped electrodes as a tool for investigating electrode materials is discussed.

Study of oxygen adsorption and reoxidation of reduced titanium dioxide by thermal desorption mass spectrometry

The adsorbed oxygen species formed upon the reoxidation of reduced titanium dioxide (Degussa P-25) and oxygen adsorption on the reduced and reoxidized titanium dioxide are studied by thermal desorption mass spectrometry. The reoxidation of the oxide in the presence of O2 at P ≥ 2 × 10–3 Pa and T ≥ 500 K is shown to result in the appearance of a peak with a maximum at ∼700 K in the thermal desorption spectrum. The desorption of oxygen corresponding to this peak occurs via the recombination mechanism with the activation energy Edes = 1.4 eV. The dynamic model of reoxidation occurring through the adsorption and desorption of oxygen is suggested for the explanation of the temperature dependences of the concentration of surface oxygen that were obtained earlier for the process of reoxidation of rutile single crystal.

N2O Adsorption and Photochemistry on High Area TiO2 Powder

The adsorption and photochemistry of N2O chemisorbed on TiO2 powder has been investigated. At 157 K, nitrous oxide is molecularly adsorbed on the reduced titanium dioxide. Adsorption on the TiO2 surface takes place through both the N and O ends of the nitrous oxide molecule. The photochemistry of the adsorbed N2O molecules was studied at 157 K by use of UV irradiation in the range 2.1−5.0 eV. The photoactivity of the adsorbed molecule is dependent on the N2O coverage. At low coverages, the adsorbed N2O is photodepleted to produce adsorbed nitrogen. Larger coverages of N2O are not photodepleted to N2 due to the site blocking in the adsorption process. N-bonded species show a higher photoreactivity than the O-bonded species. Photoformation of NO was not observed at any N2O coverage.

Electronic structure of reduced titanium dioxide

We use the local spin-density approximation in density-functional theory to study the electronic structure of ${\mathrm{TiO}}_{2}$ and its (110) stoichiometric surface, as well as ${\mathrm{Ti}}_{2}{\mathrm{O}}_{3}$ and the reduced (110) surface, which are examples of reduced ${\mathrm{TiO}}_{2},$ in order to address the question of how donated electrons are distributed among the previously unoccupied Ti $3d$ states. We conclude that, whereas a split-off band in ${\mathrm{Ti}}_{2}{\mathrm{O}}_{3}$ probably leads to Mott-Hubbard insulating behavior, a picture of itinerant electrons in approximately one-electron states with Stoner exchange splitting is an appropriate description in the case of the reduced surface. Our calculations will be useful in interpreting photoemission experiments as well as measurements of core-level shifts at surfaces.

Reduced titanium dioxide as support for Ziegler–Natta catalysts

AbstractTitanium tetrachloride heterogenized on reduced TiO2 has been studied as a catalyst for ethylene polymerization. The catalyst has good storage stability and exhibits good activity for ethylene polymerization. The polymer chains grow linearly during ca. 1 h, giving an average molecular weight of up to 2.5 × 106 which indicates that practically no β‐elimination occurs. The activity of the catalyst at 50°C, based on Ti(III), is 7.6 × 106 PE/mol Ti h bar and based on the quantity of polyethylene formed it is 1.25 × 106 g PE/mol Ti h bar. The molecular weight of the polymer can be controlled with the addition of hydrogen, under 0.5 bar hydrogen, polyethylene with a molecular weight of 411,000 and a relatively low polydispersity index of 2.2 is obtained. The catalyst shows good thermal stability; the Arrhenius activation energy is 31.8 kJ/mol for the polymerization. The catalyst is also active for propylene polymerization, giving 3 × 106 g PP/mol Ti h bar with the high isotacticity of 93%. © 1994 John Wiley & Sons, Inc.

Kinetics of Solid-State Reduction of Ilmenite Ore

Abstract Solid-state reduction of ilmenite ore by carbon under nitrogen was studied at temperatures up to 1200°C. The rate of reduction was followed by determination of oxygen loss and by chemical analysis for metallic and ferrous iron. The reduction process proceeds through different stages with formation of structures intermediate between iron and reduced forms of titanium oxides. The results show that the reduction of titanium dioxide to its lower oxides takes place in parallel with the reduction of iron oxides. The oxygen deficiency in reduced titanium dioxide increases with increases in reduction temperature and time. Iron oxides are not reduced completely owing to the presence of some residual ferrous oxide combined in a structure which resists reduction. The mechanism and kinetics of the reduction process are discussed. The reduction data under isothermal conditions are consistent with a mixed model with phase-boundary reaction and diffusion processes controlling the reduction rate up to about 80% ...

Identification of oxygen species adsorbed on reduced titanium dioxide

The nature of oxygen adsorbed on slightly reduced TiO2 has been investigated using oxygen enriched with 17O2. On anatase, the oxygen adsorbs as O–2 with a hyperfine splitting Axx about g3 of 77 G; no structure could be resolved for Ayy and Azz. On rutile, oxygen adsorbs as O–2 on two sites of different thermal stability; (I) with g1= 2.030, g2= 2.008, g3= 2.004 and Axx= 76 G, and (II) with g1= 2.020, g2= 2.009, g3= 2.003 and Axx= 72 G. The evidence indicates that O–2 exists in a largely ionic form on TiO2 and other oxides. A symmetrical line at g= 2.003 which appears on some anatase samples after oxygen adsorption is attributed to the localization of a conduction electron by the adsorbed oxygen.

Surface reactivity of reduced titanium dioxide

Download options Please wait... Article information DOI https://doi.org/10.1039/DF9715200140 Article type Paper Download Citation Discuss. Faraday Soc., 1971,52, 140-148 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Surface reactivity of reduced titanium dioxide P. C. Gravelle, F. Juillet, P. Meriaudeau and S. J. Teichner, Discuss. Faraday Soc., 1971, 52, 140 DOI: 10.1039/DF9715200140 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author P. C. Gravelle F. Juillet P. Meriaudeau S. J. Teichner

Electrical Resistivity and Defect Energy Levels in Reduced Titanium Dioxide at Low Temperatures

The resistivity of reduced rutile was measured from 80°K down to about 2°K. Activation energies derived from the slopes of resistivity curve are 0.01∼0.02 eV above about 20°K and 0.0005∼0.005 eV below about 20°K. It is proposed that the electronic conduction in this substance below about 20°K is due to the “defect level conduction” Conduction mechanisms at higher temperatures are also discussed.