Design of Solid Catalysts by Sol-gel Method Using Organic Polydentate Ligands and Their Catalytic Performance

Abstract

Advantages and effectiveness of using an organic polydentate ligand in the sol-gel process were discussed. The sol-gel method using the ligand was presented herein for preparation of metal oxides including mixed oxides. Design of metal oxide particles using organic polydentate ligands, i.e., control of specific surface area, particle size, pore size, and structure, was examined for silica, alumina, iron oxides, and some mixed oxides. Furthermore, regarding the mixed oxides, the dispersibility of constituent particles and homogeneity of the composition were compared among the sol-gel, coprecipitation, and kneading methods. The mixed oxides prepared using the sol-gel method showed the highest dispersibility and homogeneity. Reflecting this, the sol-gel silica/alumina was much more acidic and effective for alkylation of aromatics than the coprecipitation and kneading ones. The sol-gel method also yielded thermostable alumina and alumina mixed oxides that were useful as combustion catalyst supports; platinum-loaded or palladium-loaded sol-gel alumina, and alumina mixed oxides showed high performance for model purification reactions of exhaust gas. Regarding the supported metal catalysts prepared using the sol-gel method, ruthenium/silica and palladium/silica catalysts activated in hydrogen without calcination, respectively showed high performance for partial hydrogenation of benzene to cyclohexene and for conversion of acid chlorides to the corresponding aldehydes. Furthermore, ruthenium/tin/alumina catalysts activated in a similar manner converted unsaturated fatty acids to corresponding alcohols through hydrogenation while maintaining carbon-carbon double bonds. This type of ruthenium/tin/alumina catalyst was also effective for conversions of aromatic acids and dibasic acids, respectively, to the corresponding alcohols and diols via hydroxycarboxylic acids.