Selectively catalytic epoxidation of α-pinene with dry air over the composite catalysts of Co–MOR(L) with Schiff-base ligands

•The composite catalysts Co–MOR(L) are prepared by a simple route.•Co–MOR(L) exhibits high activity for the epoxidation of α-pinene with air.•Co–MOR(L8) is highly reusable heterogeneous catalyst.•The electrochemical behaviors of Co species in Co–MOR(L8) are studied.

Twelve bi-/tridentate Schiff-base ligands (L1–L12) have been designed, synthesized and coordinated with ion-exchanged Co–MOR (Mordenite) forming a series of Co–MOR(L) composite catalysts, for which various analyzes and characterizations are conducted. Selectively catalytic epoxidation of α-pinene with dry air over Co–MOR(L) catalysts has been carried out, where uses TBHP in small amounts as the initiator. Among these Co–MOR(L) catalysts, Co–MOR(L8) exhibits the best activity for the titled reaction to obtain 85.8 mol% conversion and 90.8% selectivity of epoxide. Some factors such as the structure of ligands, the oxidants, the solvents, the catalyst amount, the reaction temperature and time play important roles in controlling the epoxidation. The recyclable stability of the Co–MOR(L8) catalyst is confirmed. The studies on the electrochemical behaviors of Co species in Co–MOR(L8) reveal the importance of reversible change between Co oxidation states for the epoxidation.

Graphical abstractCatalytically selective epoxidation of α-pinene with dry air has been effectively carried out at 90 °C over the composite catalysts Co–MOR(L) under atmospheric pressure.Figure optionsDownload full-size imageDownload high-quality image (83 K)Download as PowerPoint slide