Synthesis and Development of Nano-structured Organic-Inorganic Cooperative Catalysts

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In this study, we investigated prototypic catalytic systems to demonstrate the advantage of a concept "Organic-inorganic cooperative catalytic system". One is Pd supported on mesoporous alumina with organo-modification to control selectivity for alpha-beta unsaturated aldehyde hydrogenation. Another system is a highly active solid acid catalyst comprising heteropolyacid inorganic molecules and hydrophobic mesoporous silica. In the former system, various organic molecules were grafted on the pore-walls of mesoporous alumina to control selectivity for cinnamaldehyde hydrogenation. It was found that the C=0 bond hydrogenation selectivity was improved by grafting chloropropyl groups on the pore walls of mesoporous alumina. X-ray photoelectron spectroscopy indicated that chloropropyl grafting brought about negative charge shifts of Pd surface. The Pd binding energy and the hydrogenation selectivity showed a good correlation, demonstrating an organic-inorganic cooperative catalysis. Another system investigated in this study, the highly active solid acid catalyst is also a prototype of organic-inorganic cooperative catalyst. We have achieved a solid acid catalyst highly active in aqueous media. The catalyst comprises inorganic active species (H_3PW_<12>0_<40> polyoxometalate molecules) surrounded by hydrophobic alkyl groups in the nanospaces of mesoporous silica. The acidic protons in the hydrophobic environment showed the highest activity for the ester hydrolysis reaction. The mesoporous silica nanostructure afforded paths for the efficient approach of reactant molecules and water to the active sites. The present study indicates that a promising strategy for novel functional materials is to design an organic-inorganic cooperative function on the basis of the mesoporous silica nanostructure.