Zeolite-Y Encapsulated Copper (II) and Cobalt (II) Species as Hybrid Nano-catalysts: Structural and Catalytic Aspects

Abstract

Special properties inherent to zeolites in facilitating the construction of novel supramolecular assemblies by encapsulation of guest molecules (metal complexes) into their large cages can be utilized to use these assembled materials as novel catalysts. These modified solids have the advantages of both behaving as the homogeneous and the heterogeneous catalytic system. In the present work, copper (II) and cobalt (II) complexes of 2-amino ethanoic acid (2-AEA) encapsulated in the cages of zeolite-Y have been prepared utilizing Flexible Ligand Synthesis technique. Both these solids (catalysts) including their precursors NaY, CuY and CoY are characterized for their analytical, textural, spectral and morphological behaviour. Based on the physicochemical measurements, it is established that the successful encapsulation of Cu(2-AEA) and Co(2-AEA) complexes inside the cages of zeolite-Y has taken place. This is also confirmed by BET studies of the encapsulated species whose surface area and pore volume are found to decreased by the uptake of Cu(2-AEA) and Co(2-AEA) complexes. All these observations confirm the location of the complexes in the cages of zeolite-Y. These encapsulated species can be used as catalysts because of the free coordination site available in the cages. Both the catalysts including all their precursors have also been screened for catalyzing the oxidation of phenol using 30% H₂O₂ as an oxidant. Performing several sets of experiments, reaction parameters, such as oxidant-substrate ratio, temperature, type of solvents and concentration of catalysts have been optimized to obtain the maximum conversion of phenol to p-CAT (p-Catechol) and HQ (Hydroquinone). Blank reaction was also carried out under the similar optimized conditions. The catalytic activity followed the order: [Co-2-AEA]Y (28.70%) > [Cu-2-AEA]Y (25.20) > Cu-Y (20.60)> Co-Y (13.60) >Na-Y (4.90) > Blank (0.60) after 12 h of reaction time at 80°C in acetonitrile medium. It is concluded that the encapsulated catalysts [Co-2-AEA]Y (28.70%) > [Cu-2-AEA]Y (25.20) are highly active in comparison to their simple ion exchanged precursors.