| Summary: | 碩士 === 國立成功大學 === 化學工程學系 === 107 === This study reports that the Lewis acid-base properties of peroskite-type LaMnO3 and LaFeO3 can be adjusted by immobilizing them on silica. Bulk LaMnO3 and LaFeO3 were strong base catalyst due to unsaturated-coordinated oxygen on the surface, While, after supported them on silica, the basic properties of bulk materials were diluted and simultaneously acidities improved due to the increased amounts of tetravalent B-site cations. Ethanol reactivity was performed to reflect the different acid-base properties of bulk and silica-supported LaMnO3 and LaFeO3. Under differential analysis conditions, bulk perovskites were active in base-catalyzed reactions such as reverse aldolization and Tishchenko reaction, while silica-supported perovskites were active in aldolization and dehydration. We also notice the higher aldolization activity over LaMnO3/SiO2 than that of LaFeO3/SiO2, the different activity was attributed to existence of excess mobile oxygen on the surface of LaMnO3/SiO2, forming aldolization-active Lewis acid (Mn4+)-base (nonstoichiometric oxygen) pair sites while these sites were absent in LaFeO3/SiO2 which was enriched with oxygen vacancies.
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