Solvothermal synthesis of inorganic materials and their performance as catalysts

The synthesis of inorganic materials was investigated in organic solvents at temperatures (200-300 degrees C) higher than their boiling points (solvothermal method), and various inorganic materials were directly obtained. The solvothermal products had high surface areas, superior thermal stabilities, and characteristic morphologies as well as unique surface properties with high potential for catalytic applications. Here, two recent studies on catalytic applications of nanocrystalline mixed oxides synthesized by the solvothermal method are reviewed. First, the solvothermal synthesis of gamma-type Ga2O3-A1(2)O(3) solid solutions and their activities for selective catalytic reduction of NO using methane as a reducing agent are described. Ga2O3-Al2O3 catalyst prepared in diethylenetriamine exhibited quite high activity for this reaction. The physicochemical properties of the catalysts as well as the active sites for this reaction are discussed. Second, the synthesis of nanocrystalline silica-modified titanias with large surface areas and high thermal stabilities by the glycothermal treatment of the mixture of titanium tetra-isopropoxide and tetraethyl orthosilicate in 1,4-butanediol is described. The products were characterized by several techniques and the origin of the thermal stability of the products is discussed. The recovery of silica-modified titania particles as xerogels by flash evaporation of the reaction medium after the glycothermal reaction is described. Photocatalytic activities of the products under UV light irradiation and the visible light responsive photocatalytic activity of N-doped silica-modified titanias are also discussed.