Development of Nobel Catalytic Process Aimed at Green Chemistry by Functionalization of Solid Surface

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This research demonstrated that the design of highly-functionalized heterogeneous catalysts contributes to developing environmentally-acceptable chemical processes such as selective oxidations of hydrocarbons using molecular oxygen and hydrogen peroxide, fixation of carbon dioxide, and C-C bond formation reactions. The results are summarized as below.Selective OxidationsFor preparation of high performance oxidation catalysts, we extensively utilized unique characters of crystalline metal hydroxides, i.e, hydrotalcite and hydroxyapatite, and metal clusters.Ruthenium cation could be immobilized in the Brucite layer of the hydrotalcite as monomeric species based on the cation-exchange ability. The oxidation catalysis was greatly enhanced by introducing Co cation in the Brucite layer through Redox interactions between Ru and Co cations. These functionalized materials efficiently catalyzed oxidations of various alcohols and aromatic hydrocarbons to the corresponding carbonyl compounds in th … More e presence of molecular oxygen.The isolated Ru species are also created on the surface of hydroxyapatite by a simple ion-exchange procedure, which acted as an effective heterogeneous catalyst for aerobic oxidation of alcohols and amines. A nobel oxidation mechanism was proposed in relation to the monomeric structure of the Ru cations.It was also found that base sites of hydrotalcites promotes monooxygenation type reactions of olefins and pyridines using hydrogen peroxide as an oxidant.Further, we developed preparation method of the giant palladium cluster as a highly active catalyst for the acetoxylation of aromatic hydrocarbons in the presence of molecular oxygen. The prominent catalysis of the above Pd cluster is ascribed to specific ensemble sites composed of metallic Pd and neighboring Pd cations on its surface.Fixation of Carbon DioxideThe surface of Mg-Al mixed oxides obtained by calcination of hydrotalcites showed acid-base bifunctional properties and unique catalysis for the cycloaddition of carbon dioxide to various epoxides under mild reaction conditions. The generation of acid-base sites on the surface of the Mg-Al mixed oxide was discussed on the basis of XAFS measurements.(iii) C-C Bond Formation ReactionsTitanium cation-exchanged montmorillonite acted as a strong solid acid catalyst for aromatic alkylations with carbonyl compounds to synthesize valuable raw materials for speciality polymers. We found hydrotalcite-catalyzed the condensation of various aldehydes to the corresponding aldol compounds.The above solid catalysts were easily separated from the reaction mixture and recyclable keeping their high activities and selectivities. Less