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The modification of ruthenium species supported on ceria in the presence of suitable phosphines under H2 at 100 °C was found to generate catalytically active Ru species that were effective for the regio- and stereoselective addition of carboxylic acids to terminal alkynes. The reactions in the presence of a catalytic amount of Ru/CeO2 modified with 1,4-bis(diphenylphosphino)butane gave the anti-Markovnikov adducts in high yields with excellent (Z)-isomer selectivities. On the other hand, the reactions with the trioctylphosphine-modified catalyst gave the Markovnikov adducts as major products. Among the catalysts examined, only ceria- or zirconia-supported catalysts were effective, and hot filtration tests using the phosphine-modified Ru/CeO2 catalyst suggested that soluble ruthenium species showed quite a high catalytic activity. Very small amounts of ruthenium species were detected in the solution. The solid Ru/CeO2 could be repeatedly used as a reservoir of active catalysts without a significant loss of...

The gamma-Ga(2)O(3)-Al(2)O(3) mixed oxides with a spinel structure were prepared by the solvothermal reaction of gallium acetylacetonate and aluminum isopropoxide in diethylenetriamine. In the crystal structures of the catalysts obtained by the calcination of these mixed oxides, Ga(3+) and Al(3+) ions preferentially occupied tetrahedral and octahedral sites, respectively. The catalysts with low Ga contents had a unique structure with high surface areas and a concentration gradient of decreasing Ga content from the surface to the bulk. In methane-selective catalytic reduction (SCR) of NO, higher NO conversion to N(2) was attained on the catalyst with high occupation of Ga(3+) ions at tetrahedral sites and Al(3+) ions at octahedral sites. For the gamma-Ga(2)O(3)-Al(2)O(3) mixed oxide with a charged Ga molar content of 0.3 (ST(0.3)), tetrahedral and octahedral sites were solely occupied by Ga(3+) and Al(3+) ions, respectively, and the catalyst exhibited the highest NO conversion to N(2). Therefore, it was concluded that the active site for methane-SCR of NO is tetrahedral Ga(3+) ion and octahedral Al(3+) ion, which are linked to each other. Nitrogen monoxide is adsorbed on the isolated hydroxyl group attached to Al(3+) ions and then oxidized by O(2) yielding surface nitrate species. Tetrahedral Ga(3+) ions work as Lewis acid sites for the activation of methane because of their coordinative unsaturation. The Ga(3+) ions in the gamma-Ga(2)O(3)-Al(2)O(3) catalyst have a redox property, which plays important roles in both the oxidation of NO to surface nitrate species and the activation of methane. The most important factor for this catalyst is that the sites for the formation of surface nitrate species reside next to the methane activation sites, which facilitates the reaction between surface nitrate species and the activated species derived from methane, thus mitigating the consumption of methane by simple combustion with O(2). Therefore, ST(0.3), which has the largest number of ensembles of the tetrahedral Ga(3+) ions and octahedral Al(3+) ions, shows the highest activity for methane-SCR of NO.

Silicon-modified titanias prepared by thermal reactions of mixtures of titanium tetraisopropoxide and tetraethyl orthosilicate with various ratios in 1,4-butanediol at 300 °C (glycothermal reaction) were calcined at 500 °C in air, treated in an NH3 flow at 600 °C for 1 h, and then annealed in air at different temperatures. The properties of the thus-obtained nitrified Si-modified titanias were characterized by UV−vis diffuse reflectance spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, nitrogen adsorption, and electron spin resonance. The products had absorptions in the visible-light region and exhibited photocatalytic activities for decomposition of acetaldehyde under visible-light irradiation. It was found that the amount of Si modification significantly affected the amount of doped nitrogen and the visible-light-induced photocatalytic activity. Higher annealing temperature (500 °C) decreased the population of oxygen vacancies and increased photocatalytic activity in spite of the fact t...

Spinel-type Ga2O3−Al2O3−ZnO mixed oxides were prepared by the glycothermal reaction of zinc acetylacetonate hydrate, gallium acetylacetonate, and aluminum isopropoxide. With increasing Zn content, the crystallinity of the spinel structure of the glycothermal product increased, although excess Zn content resulted in the formation of zinc oxide as a byproduct. To optimize the Ga/Al/Zn ratio, the activities of catalysts prepared from various starting compositions and calcined at 700 °C were tested for the methane-SCR of NO under wet conditions. For this reaction, catalysts with compositions in a narrow range exhibited high activity. An increase in crystallinity of the catalyst decreased the amount of adsorbed water on the surface of the catalyst and improved the tolerance for water present in the feed gas, which inhibited the catalytic activity for the methane-SCR of NO. The optimal ratio for the spinel-type Ga2O3−Al2O3−ZnO catalyst was Ga/Al/Zn = 1/5/0.75. This catalyst exhibited a higher activity than γ-Ga...

Nanosized titanium(IV) oxide in the anatase form was synthesized by hydrolysis of titanium(IV) alkoxide in toluene with water that was dissolved from the gas phase at high temperatures (150−300 °C). With elevation of the reaction temperature and an increase of the reaction time, the crystallite size of the anatase was gradually increased from several to ca. 20 nm in the present reaction medium. Corresponding to the crystal growth, surface areas of the products were decreased while the rutile-transformation temperature became higher and the thermal stability was improved. For example, the product obtained by the reaction at 300 °C for 24 h possessed a surface area of 54 m2 g-1 even after calcination at 900 °C and began to transform to the rutile phase at around 1000 °C.

The reaction of gibbsite (a modification of Al(OH)3) in glycol at elevated temperatures yielded the glycol derivative of boehmite together with a small amount of well-crystallized boehmite and a re...

Mixtures of aluminum isopropoxide and tetraethoxysilane in 1,4-butanediol were autoclaved at 300 °C for 2 h. The products were then calcined in air to yield silica-modified aluminas. These silica-modified aluminas had high α-alumina-transformation temperatures and maintained significantly large surface areas at elevated temperatures (1000−1300 °C). For example, the product prepared from a mixture of Al/Si ratio 8 transformed into α-alumina at around 1500 °C, and it possessed a surface area of 55 m2/g, even after calcination at 1300 °C for 30 min.

La reaction de la gibbsite avec l'ethyleneglycol donne AlO(OCH 2 CH 2 OH) 0,31 (OH) 0,69 , qui aurait une structure boehmite. Etude de la calcination

On compare les vitesses d'hydrolyse de cyano-2 dimethyl-3,3 butyrates d'alkyle et d'aryle avec celles des cyanoacetates correspondants