Novel core–shell nanocomposite as an effective heterogeneous catalyst for the synthesis of benzimidazoles

Core–shell nanocomposites with a catalytic metal-organic framework (MOF) shell are more effective and stable than bare MOF. We have successfully designed an effective heterogeneous catalyst for the synthesis of benzimidazole by integrating acidic catalytic activity, and promoted the aerobic oxidation and magnetic recyclability of core–shell nanocomposite Fe₃O₄@SiO₂@UiO-66. The Fe₃O₄@SiO₂ core is encapsulated by the in situ-grown UiO-66 shell, and the UiO-66 shell retains the porous structure and crystallinity of UiO-66 with abundant exposed Lewis acid sites. It shows high catalytic ability for the synthesis of various benzimidazoles through the acid-catalyzed condensation and aerobic oxidation with in situ oxygen. The Fe₃O₄@SiO₂ core provides magnetic recyclability of Fe₃O₄@SiO₂@UiO-66, and maintains high catalytic ability and stability over six cycles. (paper)