Abstract
Three tridentate or bidentate Schiff-base ligands inclusive of salicylaldehyde benzoylhydrazone (L1), vanillic aldehyde benzoylhydrazone (L2) and 4-methyl benzaldehyde benzoylhydrazone (L3), have been designed, synthesized and employed to coordinate with Co2+ ions and ion-exchanged Co-ZSM-5 forming several Co-L complexes and Co-ZSM-5(L) composite catalysts. The catalytic epoxidation of several alkenes with dry air has been carried out at 90°C under atmospheric pressure using Co-L complexes and Co-ZSM-5(L) catalysts (using TBHP in small amounts as the initiator). In contrast, the catalysts Co-ZSM-5(L) shows higher catalytic activity than Co-ZSM-5 itself and Co-L complexes. Among three Co-ZSM-5(L) catalysts, Co-ZSM-5(L1) exhibits the highest activity for the selective epoxidation of alkenes. Recycling studies show the recyclability of Co-ZSM-5(L1) as a heterogeneous catalyst, which does not lose the catalytic activity after even eight reuses appreciably. Based on the experiments, one possible reaction mechanism is proposed.
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