Advances in the development of novel cobalt Fischer-Tropsch catalysts for synthesis of long-chain hydrocarbons and clean fuels.

We report on the synthesis of phase-pure TiO2 nanoparticles in anatase, rutile and brookite structures, using amorphous titania as a common starting material. Phase formation was achieved by hydrothermal treatment at elevated temperatures with the appropriate reactants. Anatase nanoparticles were obtained using acetic acid, while phase-pure rutile and brookite nanoparticles were obtained with hydrochloric acid at a different concentration. The nanomaterials were characterized using x-ray diffraction, UV–visible reflectance spectroscopy, dynamic light scattering, and transmission electron microscopy. We propose that anatase formation is dominated by surface energy effects, and that rutile and brookite formation follows a dissolution–precipitation mechanism, where chains of sixfold-coordinated titanium complexes arrange into different crystal structures depending on the reactant chemistry. The particle growth kinetics under hydrothermal conditions are determined by coarsening and aggregation–recrystallization processes, allowing control over the average nanoparticle size.

http://iopscience.iop.org/article/10.1088/0957-4484/19/14/145605/pdf

Phase-pure TiO 2 nanoparticles: anatase, brookite and rutile

Brookite is the least studied TiO2 photocatalyst due to the difficulties usually encountered in order to obtain it as a pure phase. In this review, a comprehensive survey of the different methods available for preparing brookite powders and films is reported. Attention has been paid both to the most traditional methods, such as hydrothermal processes at high temperatures and pressures, and to environmentally benign syntheses using water soluble compounds and water as the solvent. Papers reporting the photocatalytic activity of pure and brookite-based samples have been reviewed.

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Brookite, the Least Known TiO2 Photocatalyst

This review paper deals with proven and potential applications of mesoporous molecular sieves in catalysis. In addition to introduction and conclusion, the text is divided into two parts, respectively, dedicated to the design of solid catalysts and catalyst supports and to some relevant examples of catalytic processes.

/pdf/perspectives-in-catalytic-applications-of-mesostructured-4jgvbmynn3.pdf

Perspectives in catalytic applications of mesostructured materials

The adsorption behavior of cesium on pure minerals is reviewed. Although this field has been investigated intensively, the data are extremely variable in scope and interpretation with detailed information being available for only a few minerals. In current investigations in this field, the emphasis is on the nature of the adsorption sites and identification of these sites using spectroscopic techniques. In the first section of this review, the general mechanism of cesium adsorption is discussed and this is followed by consideration of the effect of parameters such as cesium concentration, the properties of the mineral and the characteristics of the solution phase, on cesium adsorption. Finally, interaction of cesium with some different minerals is described in some detail.

Adsorption of cesium on minerals: A review

Hydrothermal synthesis of potassium hexatitanate was carried out under various subcritical and supercritical water conditions using potassium hydroxide and titanium tetraisopropoxide as starting materials. Characterization of these hydrothermally synthesized potassium hexatitanates by XRD, SEM, TEM, and thermal analysis showed that long, felted-like fibers of potassium hexatitanates were formed and these fibers are thermally stable up to 1273 K. The use of these fibers as photocatalysts in water decomposition was investigated using ruthenium oxide as the catalytic active phase. Photocatalytic activitiy in the water decomposition reaction was found to be much higher in comparison with the solid state synthesized photocatalyst. Activites of more than 13-fold were obtained for the photocatalysts synthesized under subcritical water conditions and between 27- and 59-fold for those synthesized under supercritical water conditions for water decomposition.

Hydrothermal Synthesis of Potassium Hexatitanates under Subcritical and Supercritical Water Conditions and Its Application in Photocatalysis

A series of mesoporous vanadosilicate V−MCM-41 molecular sieves with variable Si/V ratios have been synthesized at room temperature using a minimum amount of template. The chemical environment of the vanadium centers in V−MCM-41 was investigated by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, diffuse reflectance UV−visible (UV−vis) spectroscopy, electron spin resonance (ESR), and 29Si and 51V nuclear magnetic resonance (NMR), and the optimal synthesis condition have been established. The increase of the unit cell parameter and decrease of Q3/Q4 ratio of 29Si NMR spectra with vanadium content suggest the incorporation of vanadium in the framework of the MCM-41 structure. UV−vis and 51V NMR studies confirm the presence of V5+ ion in the tetrahedral position. In the case of a freshly synthesized sample, VO2+ in a square pyramidal arrangement was detected by ESR. After calcination, V5+ species remain in the tetrahedral arrangement, con...

Characterization of tetrahedral vanadium-containing MCM-41 molecular sieves synthesized at room temperature

Hydrothermal synthesis of brookite was performed at 110-200 °C within 24 h using amorphous TiO2 and sodium salts as the starting material. Brookite was obtained as an almost single phase at 200 °C and TiO2 / NaOH mole ratio ≅ 1. By the results of XPS and UV-vis measurements, brookite was considered to be formed from sodium titanate by releasing Na+ and H+ of the surface accompanied by oxidation of Ti in the structure.

Hiromichi Hayashi

Papers

Hydrothermal Synthesis of Potassium Hexatitanates under Subcritical and Supercritical Water Conditions and Its Application in Photocatalysis

Characterization of tetrahedral vanadium-containing MCM-41 molecular sieves synthesized at room temperature

Hydrothermal Synthesis of Brookite.

Effect of layer charge on fixation of cesium ions in smectites

Quantum chemical calculation on clay-water interface