Synthesis and Applications of Semiconducting Microporous Crystals

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Pillared clay is a new type of microporous solids which have opened a new field of microporous crystals other than zeolies. In this project, a semiconducting layred titanate has been pillared with silica. The adsorption and catalytic properties and their applications are studied.1. Synthesis and adsorption properties of silica pillared manganese titanateA layr structured RbxMnxTi2-XO4 (x=0.75) was pillared with silica. The Rb ions were first exchanged with n-alkylammonium ions (CnH2n+1NH3, n=6-18) to separate the interlayr space of the titanate, and then tetraethoxysilane was hydrolyzed between the layrs. Burning off the organic parts resulted in silica pillared microporous solids with a surface area as large as 500-800m2/g. The porous structure was stable up to 600ﾟC.Adsorption desorption isotherms for various vapors, water, methanol, toluene and mesitylene, were measured, which suggested that the porous structure formed between the layrs was very similar to those of zeolites, and uniform. The pores showed hydrophobic properties. Their size was estimated to be in the order of mesitylene.2. Control of micropore structures in silica pillared titanatesIn an attempt to control the pore structure, the ion exchange capacity of RbxMnxTi2-xO4 (x=0.75) was reduced by the oxidation with KMnO4, and then pillared with silica similarly. It had been expected that the titanate with a reduced ion exchange capacity could give a smaller pore size, however, the experimental results suggested that a larger pore size was obtained. This finding is important and should be further studied in relation with the mechanism of pillar formation.3. Application of silica pillared titanate to catalystsSilica pillared manganese titanates were loaded with various kinds of ions. The sample loaded with Cu ions showed an extremely high catalytic activity to oxidation of CO.This can be explained in terms of the high surface area of the pillared structure and the rebox properties of the micropores.