Effect of TiO2 crystal form on the denitration performance of Ce–W–Ti catalyst

Titanium dioxide supports, which were prepared by roasting metatitanic acid under different conditions, were used to prepare a series of Ce–W–Ti catalysts. The structure and denitration properties of the catalyst were studied. The results showed that TiO2 had different crystal types (mixed crystal phases with different proportions of anatase and rutile) under different roasting conditions, and the denitration efficiency of mixed crystal was better than that of pure phase TiO2. Ce–W/200 °C-1 hTiO2 catalyst exhibited a prominent NO conversion rate, and it can reach higher than 90% at a temperature range from 250 to 500°C. The large specific surface area, low content of rutile TiO2 in the support, high content of chemical adsorbed oxygen and high surface acidity were favorable to denitration performance of Ce–W–Ti catalyst.

TITANIUM OXIDE-OXIFLUORIDE SYNTHESIS AND STUDY OF ITS PHOTOCATALYTIC PROPERTIES

The research article discusses a new method for the photocatalyst synthesis based on a mixture of titanium oxide - titanium oxyfluoride. The synthesis was performed by dissolving titanium metal in an acidified solution of ammonium bifluoride, followed by oxidation to the highest oxidation state and hydrolysis with ammonia to obtain metatitanic acid. The decomposition of metatitanic acid was carried out in a muffle furnace at a temperature of 380°C. It was found that during the precipitation of metatitanic acid, the titanium compound with the fluoride ion also passes into the precipitate, which, after calcination, transforms into titanium oxyfluoride. Photocatalytic activity was determined by the oxidation reaction of the methyl orange dye upon irradiation with ultraviolet radiation. The source of ultraviolet radiation was a DRT-125 lamp with a wavelength in the range of 200-400 nm. Suspensions containing 60 mg/L of the dye and various contents of the photocatalyst in the concentration range of 1-7 g/L were subjected to oxidation. The construction of the calibration graph and the determination of the concentrations were carried out on an SF-2000 spectrophotometer at a wavelength of 466.4 nm. The operating wavelength was determined by scanning the solution in the wavelength range of 200-800 nm. It was found that as a result of oxidation, the solution pH shifts to the acidic side to 3.5, which leads to a shift in the wavelength of the maximum absorption; in this regard, the solutions pH was adjusted to the same values.

Microstructure of metatitanic acid and its transformation to rutile titanium dioxide

The microstructure of metatitanic acid and its transformations to titanium dioxide during calcination have been investigated previously. However, the detailed microstructure of metatitanic acid has not been elucidated. Herein, we report the high-resolution scanning electron microscopy and X-ray powder diffraction determinations of the microstructure of metatitanic acid and its transformation to titanium dioxide during calcination. It is the first time that the detailed microstructure of metatitanic acid and its transformation to rutile titanium dioxide during calcination have been observed and elucidated. A mechanism of the transformation from metatitanic acid to crystalline titanium dioxide during calcination is described. The basic building blocks of metatitanic acid are the ultrafine crystals with an averaged diameter of a few nanometres, and these ultrafine crystals aggregate to form the porous primary particles. The primary particles further agglomerate to form the porous secondary particle. During the calcination, metatitanic acid undergoes size enlargement of ultrafine crystals, anatase–rutile transformation, merge of primary particles, and the crystal growth of titanium dioxide.