A. A. Shutilov

Effect of silicon dioxide on the formation of the phase composition and pore structure of titanium dioxide with the anatase structure

The formation of the structure of titanium dioxide modified with silicon dioxide, which was introduced as tetraethyl orthosilicate, was studied. It was found that the formation of the nanocrystalline structure of TiO2 occurred upon the modification of titanium dioxide with silicon dioxide. This nanocrystalline structure of TiO2 was formed by highly dispersed anatase particles of size 6–10 nm stabilized by silicon oxide layers, which were formed upon the decomposition of tetraethyl orthosilicate. An increase in the modifier concentration resulted in a deceleration of the growth of anatase particles and an increase in the temperature of the phase transition of anatase to rutile. It was found that the anatase phase in the samples containing 5–15 wt % SiO2 was stable up to 1000°C. The stabilization of highly dispersed anatase particles facilitated the retention of the developed fine-pore structure of xerogels with a pore diameter of 4 nm up to 900°C.

Formation of the Structure of Cerium Oxide-Modified Titanium Dioxide

The formation of the structure of titanium dioxide containing 3–15 wt % CeO2 in a wide temperature range (300–850°C) has been investigated by X-ray powder diffraction, electron microscopy, and adsorption methods. Modification of titanium dioxide with cerium oxide causes the formation of nanostructured Ce-Ti-O compounds consisting of incoherently intergrown fine anatase crystallites. The crystallites are separated by interblock boundaries in which cerium ions are stabilized. The nanostructure formed in the Ce-TiO2 oxide system stabilizes the anatase phase, prevents the sintering of anatase particles at high temperatures, and allows modified anatase to retain a larger specific surface area and a higher porosity upon heat treatment than pure titanium dioxide does.

Effect of silica on the stability of the nanostructure and texture of fine-particle alumina

The effect of the modification of aluminum oxide with silicon oxide on the stability of fine-particle Γ- and δ-Al2O3 phases upon heat treatment in the wide temperature range of 550–1500°C was studied. It was found that the Γ- and δ-Al2O3 phases modified with silica are thermally stable up to higher temperatures than pure aluminum oxide. This is due to changes in the real structure of the modified samples, specifically, an increase in the concentration of extensive defects stabilized by hydroxyl groups bound to not only aluminum atoms but also silicon atoms. It is likely that Si-OH groups, which are thermally more stable than Al-OH groups, stabilize the microstructure of Γ- and δ-Al2O3 to higher temperatures, as compared with aluminum oxide containing no additives. Simultaneously, an increase in the thermal stability of the modified samples is accompanied by the retention of a high specific surface area and a developed pore structure at higher treatment temperatures.

Phase composition and catalytic properties of ZrO2 and CeO2-ZrO2 in the ketonization of pentanoic acid to 5-nonanone

The phase composition, microstructure, and catalytic properties of the samples of ZrO2 and CeO2-ZrO2 calcined in air at 450–500°C in the ketonization reaction of pentanoic acid were studied. It was found that ZrO2 of tetragonal and monoclinic modifications is characterized by sufficiently high activity and selectivity for 5-nonanone; the yield of 5-nonanone was 66.3–64.9%. The modification of zirconium dioxide with cerium oxide leads to the formation of a substitutional solid solution based on tetragonal ZrO2. Upon the addition of CeO2 in an optimum amount of 10 wt % to zirconium dioxide, an increase in the conversion of pentanoic acid was observed with the retention of high selectivity for the target product, which led to an increase in the yield of 5-nonanone to 73.3%. Based on the results of physicochemical studies performed by high-resolution transmission electron microscopy, X-ray diffraction analysis, and X-ray photoelectron spectroscopy, the physicochemical and catalytic properties of the test catalysts were compared.

Effect of the microstructure of Pt/CeO2-TiO2 catalysts on their catalytic properties in CO oxidation

The microstructure of 2% Pt/CeO2-TiO2 catalysts has an effect on their catalytic properties in CO oxidation. The nanostructured catalysts as platinum clusters 0.3–0.5 nm in size are the most active. These clusters are stabilized at crystal boundaries formed by irregularly intergrown anatase particles. The catalyst containing platinum particles 2–5 nm in size is less active because of the decrease in the extent of dispersion of platinum and the change of its electron state.

Effect of the microstructure of the supported catalysts CuO/TiO2 and CuO/(CeO2-TiO2) on their catalytic properties in carbon monoxide oxidation

The effect of the microstructure of titanium dioxide on the structure, thermal stability, and catalytic properties of supported CuO/TiO2 and CuO/(CeO2-TiO2) catalysts in CO oxidation was studied. The formation of a nanocrystalline structure was found in the CuO/TiO2 catalysts calcined at 500°C. This nanocrystalline structure consisted of aggregated fine anatase particles about 10 nm in size and interblock boundaries between them, in which Cu2+ ions were stabilized. Heat treatment of this catalyst at 700°C led to a change in its microstructure with the formation of fine CuO particles 2.5–3 nm in size, which were strongly bound to the surface of TiO2 (anatase) with a regular well-ordered crystal structure. In the CuO/(CeO2-TiO2) catalysts, the nanocrystalline structure of anatase was thermally more stable than in the CuO/TiO2 catalyst, and it persisted up to 700°C. The study of the catalytic properties of the resulting catalysts showed that the CuO/(CeO2-TiO2) catalysts with the nanocrystalline structure of anatase were characterized by the high-est activity in CO oxidation to CO2.

Influence of CeO2 addition on the physicochemical and catalytic properties of Pd/TiO2 catalysts in CO oxidation

The influence of CeO2 addition on the formation of the microstructure, electronic state, and catalytic properties of Pd/TiO2 supported catalysts in CO oxidation were investigated. It was shown that, when Pd is supported on titanium dioxide modified with cerium dioxide, annealing at 500°C results in the formation of Pd/(CeO2-TiO2) catalysts with a nanocrystalline structure composed of incoherently intergrown fine anatase crystals and interblock boundaries in which palladium and cerium are stabilized. The higher catalytic activity of Pd/(CeO2-TiO2) catalysts compared to Pd/TiO2 catalysts is explained by the smaller size of Pd particles and the higher proportion of palladium in the Pdδ+ state.

Effect of yttrium oxide on the formation of the phase composition and porous structure of titanium dioxide

The formation of the structure of TiO2 (anatase) doped with 1–5 mol % Y2O3 is reported. The dopant changes the anatase structure from regular to nanocrystalline. The nanocruystalline structure consists of incoherently intergrown 5- to 7-nm anatase crystallites (500°C) separated by interblock boundaries accommodating yttrium ions. The formation of the nanocrystalline anatase structure stabilizes small anatase crystallites and raises the anatase-to-rutile phase transition temperature above 900°C. Owing to this structure, the developed specific surface area and fine porous texture of yttrium oxide-doped titanium dioxide survive up to higher temperatures than those of undoped titanium dioxide.

Physicochemical properties of TiO2 (anatase) prepared by the centrifugal thermal activation of hydrated titanium dioxide

The physicochemical properties of titania (anatase) prepared from hydrated titanium dioxide by centrifugal thermal activation (CTA) at 140–700°C were studied. It was found that the microstructure and the texture parameters of anatase prepared by the above method were considerably different from those of the samples prepared by the traditional thermal decomposition of titanium hydroxide. The conditions of centrifugal activation exerted a considerable effect on the structure and the texture parameters of the resulting anatase. The crystal structure of anatase prepared at a temperature lower than 650°C was imperfect, and it approached a regular structure only at a temperature of >650°C. At temperatures higher than 300°C, the samples of TiO2 prepared using CTA were characterized by higher specific surface areas, fine pore structures, and comparable mesopore volumes, as compared with the samples prepared by commonly used synthetic methods.

Effect of iron oxide additives on the physicochemical and catalytic properties of the supported Pt/TiO2 catalysts in the oxidation of carbon monoxide

The effect of iron oxide additives on the formation of the microstructure, the electronic state, and the catalytic properties of supported Pt/TiO2 catalysts in the reaction of CO oxidation was studied. It was established that the microstructure of the catalyst changed upon the introduction of iron additives and activity in the oxidation of CO increased. The increase in the catalytic activity was explained by a decrease in the particle size of supported platinum and by an increased contribution from the Ptδ+ state. The optimum chemical composition of the catalyst, which ensured the highest catalyst activity in the reaction of CO oxidation, was determined.