Catalytic oxidation of limonene over zeolite-Y entrapped oxovanadium (IV) complexes as heterogeneous catalysts

• The use of zeolite-Y entrapped VO(IV) complexes as heterogeneous catalysts.
• The catalysts were prepared by flexible ligand (FL) technique.
• Oxidation of limonene using t-butyl hydroperoxide and/or 30% H2O2 as oxidants.
• [VO(VTCH)2]-Y showed higher catalytic activity (97.7%) with limonene glycol (45.1%), selectivity.
• The proposed catalytic mechanism explains two possible pathways for limonene oxidation

A series of VO(IV) complexes with Schiff base ligands derived from vanillin thiophene-2-carboxylic hydrazone (VTCH), vanillin furoic-2-carboxylic hydrazone (VFCH), salicylaldehyde thiophene-2-carboxylic hydrazone (H2STCH) and/or salicylaldehyde furoic-2-carboxylic hydrazone (H2SFCH) have been synthesized as neat and their entrapped complexes into the nanopores of zeolite-Y. These materials were characterized by several techniques: chemical analysis (ICP-OES and elemental) and spectroscopic methods (FT-IR, electronic, XRD, SEMs and BET). All the prepared catalysts were tested over the liquid phase limonene oxidation reaction, using t-butyl hydroperoxide (TBHP) and/or 30% H2O2 as oxidants. Limonene glycol, carveol and carvone were the main products obtained. It was observed that zeolite-Y based entrapped complexes exhibited higher catalytic activity than neat VO(IV) complexes. These zeolite-Y based entrapped complexes are stable and recyclable under current reaction conditions. Amongst them, [VO(VTCH)2]-Y showed higher catalytic activity (97.7%) with limonene glycol (45.1%), selectivity.

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