スチレン類二量化に有効な鉄シリカ触媒のXAFS法による構造解析

α-メチルスチレン二量化反応に活性を示す鉄ゾル－ゲル法にて調製した鉄シリカ触媒をX線回折およびX線吸収分光法により評価した．触媒中鉄種の存在状態は仕込みSi /Fe 比に依存し，100 以上では四面体FeOxCl4-x種，50以下ではα-Fe2O3 凝集種が主成分であり，その存在比をXANES解析により求めた．シリカマトリクスに捕捉された孤立FeOxCl4-x が活性種として機能し，固体酸性質を発現する機構について論じた．

　Iron ion-promoted silica solid acid catalysts active for α-methylstyrene dimerization were characterized by XRD and Fe K-edge XANES/EXAFS spectroscopic techniques. The possible active species were proposed. The 1 mol % of iron to Si was incorporated in catalyst samples, which was prepared by sol-gel process using iron chloride and tetraethylorthsilicate (TEOS) as the sources. The incorporated trivalent iron species were characterized as tetrahedral FeOxCl4-x , and excess loaded species were aggregated to form α-Fe2O3 during drying process at 403 K. The fraction of [FeOxCl4-x], [FeCl6] and [FeO6] species in the catalyst samples were determined by the least-squares analysis of XANES.

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