Activity of Rh-containing catalysts in naphthalene hydrogenation under pressure

Sol-gel method was used for the preparation of titania. A series of sulfated titania catalysts with different sulfate loadings were prepared and characterized by X-ray diffraction, FTIR, UV-VIS DRS, TGA, BET surface area and pore volume. The acidity of these systems was determined by TPD of ammonia. Sulfate ion impregnation decreases the crystallite size and stabilizes the anatase phase of TiO₂. Surface area was found to increase with the sulfate loading. FTIR results show strong bidentate bridge of sulfate species. The catalytic performance of TiO₂/SO₄ ^2- for liquid phase benzylation of toluene was studied. It was found that the conversion increases with sulfate loading. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis of Spherical Titanium Dioxide Particles by Homogeneous Precipitation in Acetone Solution

Titania powders were synthesized by thermal hydrolysis of titanium tetrachloride in a mixed solvent was studied. The dielectric constant was tuned by regulating the acetone/water volume ratio (R/H ratio) and temperature of the solvent. Hydroxypropyl cellulose (HPC) was used as a steric dispersant. The synthesis were carried out at R/H ratios of 0–4, temperatures of 70–90°C, TiCl₄ concentrations of 0.05–0.2 M, HPC concentrations of 0–5 × 10^–3 g/cm³, and synthesis times of 15–60 min. The TiO₂ particles obtained at an R/H ratio of 0, i.e., pure water system, were fine and agglomerated. In contrast, the TiO₂ particles prepared at an R/H ratio of 3 were uniform and spherical. The TiO₂ particle size increased with increasing TiCl₄ concentration. The synthesis temperature did not influence the particle size, but greatly influenced the morphologyof the TiO₂. Adding HPC to the solution yielded more uniform and spherical particles. In addition, the synthesis time should be longer than 30 min to obtain the most uniform and spherical particles. The dielectric constant of the acetone-water mixed solvent at 28 gave the most uniform and spherical TiO₂ particles. The powders prepared at the condition of 0.1 M TiCl₄, R/H ratio of 3, HPC concentration of 0.001 g/cm³, temperature of 70°C, and synthesis time of 1 h exhibited the most uniform and spherical morphology. The as-synthesized powder was anatase and retained the phase below 400°C. It transformed to the rutile phase after calcination at 700°C.     

Enhanced Adsorption Capacity and Photo-Catalytic Oxidative Activity of Dyes in Aqueous Medium by Hydrothermally Treated Titania Pillared Clay

Titania pillared montmorillonite clay was prepared by two different routes viz. 1) conventional ion exchange method and 2) modified method wherein the post hydrothermal treatment after ion-exchange was employed. The influence of the post hydrothermal treatment on the textural properties of titania-pillared clays was studied. The calcined clay was characterized by different physico-chemical techniques such as XRD, EDX, low temperature (77 K) nitrogen adsorption and UV-Vis diffuse reflectance spectroscopy. The content of pillared titania remained unchanged irrespective of the method of preparation. The method of preparation and severity of the conditions employed for the hydrothermal treatment resulted in alteration of the crystallinity and crystallite size of the anatase. The changes in the average pore diameter was found to comensurate with the changes in crystallite size of anatase phase. The increase in total pore volume as a function of the severity of the post hydrothermal treatment resulted in the decrease in micropore volume. The severity of the post hydrothermal treatment governed the extent of the blue shift in UV-Vis DRS spectra.The behaviour of titania pillared clays in adsorptive capacity and in photo-catalytic oxidation of methylene blue and victoria pure blue in aqueous medium was studied as a function of their physico-chemical characteristics. The titania pillared clays prepared by post hydrothermal route has shown enhanced adsorption capacity and photo-catalytic oxidation.     

Temperatures and kinetics of anatase to rutile transformation in doped TiO<Subscript>2</Subscript> heated in microwave field

The influence of aliovalent ions such as Mn, Cr, Fe, Mo, and V on the temperature and kinetics of anatase to rutile phase transformation in TiO₂ heated in microwave field was studied in this work. The results indicated that heat treatment method and dopants considerably affected the anatase-to-rutile phase transition temperature and kinetics of transformation. The activation energy for anatase to rutile transformation of TiO₂ derived from the isothermal data was found to be 328.4 kJ mol^–1, which was considerably reduced by the addition of dopants in TiO₂ matrix. The activation energy for Mo, Mn and V doped samples was 252.0, 101.3 and 96.4 kJ mol^–1, respectively.