Synthesis and Catalytic Activity of Cu(II), Fe(III) and Bi(III) Complexes of Thio-Schiff Base Encapsulated in Zeolite-Y for Hydroxylation of Phenol

Coordination of 4-{[(1E)-(2-hydroxyphenyl)methylene]amino}-2,4-dihydro-3H-1,2,4-triazole-3-thione, [sal(thiotriazol)], with M-exchanged zeolite-Y (M = Cu(II), Fe(III) and Bi(III)) leads to the encapsulation of the metal complexes in the supercages of zeolite-Y by flexible ligand method. The prepared encapsulated metal complexes have been characterized by physico-chemical techniques, which indicated that the complexes were effectively encapsulated inside the supercages of Na–Y, without any modification of the morphology and structure of the zeolite. 3D model structure generated for these complexes suggests that zeolite-Y can accommodate these complexes in the FAU supercages without any strain. The catalytic activity of all the catalysts towards the hydroxylation of phenol was evaluated under heterogeneous conditions using hydrogen peroxide as an oxidant. Under the optimized conditions, these catalysts show moderate activity with excellent selectivity (>95%) towards catechol. These catalysts were stable in hydroxylation of phenol and have been reused a further three times after recovering. The results reflect the reusability of the catalysts, as no significant loss in their catalytic activity was noticed.