Development of Room-Temperature Synthesis Method of Mesoporous Silicates and Their Application to Catalysts and Adsorbents

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Synthesis and Application to catalysts and adsorbents of various mesoporous metallosilicates have been investigated, and some important results are summarized below.1. As a convenient and low-cost surfactant-mediated method, we developed a rapid room temperature (RRT) process, which gave hexagonal mesoporous silica (MPS) in a few hours from aqueous solutions (0<pH<11) of cationic surfactants and inorganic Si sources like sodium silicate. By the simple modification, mesoporous metallosilicates (MPMSs) such as aluminosilicate (MPAS), ferrosilicats (MPFS) and titanosilicate (MPTS) were successfully synthesized by the RRT method. The structural properties of MPMSs were dependent on the pH and the charged Si/M ratio of synthetic solutions. High quality MPMSs were successfully synthesized at 6<pH<11 and Si/Al>20 for MPAS, at 8<pH<12 and Si/Fe>30 for MPFS, and at pH<1 and Si/Ti>10 for MPTS.2. Modification of MPS with SnO_2, ZrO_2 or TiO_2 was investigated by the repeated post-grafting method, … More which consisted of the repetition of the cycle of hydroxylation of the surface, grafting of metal chloride or alkoxides through the reaction with surface hydroxyl groups and calcination in air. The resulting SnO_2- and ZrO_2-coated MPSs were quite resistant, as compared with the host MPS, against treatments at high temperature (>800 ℃) and aqueous NaOH (<70 ℃).3. MPASs showed the ion-exchange property and Cu ions introduced in MPASs by the ion-exchange method were reduced by H_2 in two steps, Cu^<2+> → Cu^+→ Cu^0. Cu^+-MPAS, which was obtained by the partial reduction of Cu^<2+>-MPAS, was found to be an excellent adsorbent for CO with high oxidation-resistance and CO/CO_2 selectivity.4. MPS and MPMSs were investigated as adsorbents and photo-catalysts for bleaching of aqueous methylene blue (MB) with or without photo-illumination. The introduction of Al and Fe in the silicate framework of MPS was effective in enhancing the adsorption of MB (dark reaction). Under illumination, MPFS and MPTS showed photocatalytic decomposition activity of MB and MPFS was more photocatalytically active than MPTS.5. In addition to the above-mentioned researches, also investigated were SO_2 adsorption property of MPS and MPMSs, alginic acid-aided preparation of adsorbent beads containing mesoporous materials, and so on. Less