カリキサレン-Ti (IV) 複合体によって触媒化されたアルケンのエポキシド化における外球表面酸性の役割
Justin M Notestein1, Andrew Solovyov, Leandro R Andrini
1Department of Chemical Engineering, University of California at Berkeley, Berkeley, California 94720, USA.
Journal of the American Chemical Society
|November 23, 2007
まとめ
表面酸度とチタニウム (Ti) ルイス酸の部位は,共作用してエポキシデーション触媒を制御する. SiO2は,ヒドロペロキシド結合と酸素転送のバランスをとって,Ti触媒における外界圏の相互作用を強調することによって,増強速度をサポートします.
科学分野:
- 異質なカタリシスである.
- 表面化学について
- オーガノメタリック化学
背景:
- エポキシデーション触媒は,貴重な化学物質の合成に不可欠です.
- 表面酸性や金属部位などの触媒の特性を調節することは,反応効率を向上させるための鍵です.
- 支持材料と活性部位の相互作用を理解することは,触媒設計に不可欠です.
研究 の 目的:
- エポキシデーション触媒における酸化表面に対するブロンステッド酸性サイトとルイス酸性カリキサレン-Ti (IV) 複合体の協力効果を調査する.
- 媒介物質 (SiO2,Al2O3,TiO2) と表面酸度が触媒活性調節における役割を明らかにする.
- エポキシデーション反応におけるヒドロペロキシド活性化と酸素伝達のメカニズムを決定する.
主な方法:
- 様々な酸化基 (SiO2,Al2O3,TiO2) に接ぎ木されたカリキサレン-Ti(IV) 複合体の合成.
- 紫外線可視光譜法とTi-KエッジX線吸収近縁構造 (XANES) 光譜法を用いた特徴付け.
- tert-ブチル水酸化物を用いたサイクロヘキセンのエポキシデーションにおける触媒性能の評価.
- ブロンステッド酸性 (pKa) とH結合相互作用を含む表面特性の分析.
主要な成果:
- 材料は,異なるサポーターとカリキサレン置換剤の間で,類似のTi調整環境を示した.
- 同型システムと比較して,SiO2のTiサイトあたりのエポキシデーション率は20倍増加しました.
- Al2O3とTiO2の表面酸性の低下は,SiO2.2と比較して50倍減少した触媒速度をサポートしています.
- 触媒の性能は,Tiの調整から独立して,サポート酸化物に対して非常に敏感でした.
結論:
- SiO2は,外界圏のH結合相互作用を通じて,ヒドロペロキシド結合と酸素転送を最適化することによって,エポキシデーションの速度を高めることをサポートします.
- サポートのブロンステッド酸度が重要な役割を果たし,より強い酸度 (より低いpKa) は触媒速度を低下させます.
- この発見は,効率的なチタン基エポキシデーション触媒の設計において,サポート効果と外界の相互作用の重要性を強調しています.
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