Selective Oxidation of Benzyl Alcohol in Water With Cobalt-Exchanged Zeolite-NaY Catalyst

Abstract

A low-cost and highly selective benzyl alcohol (BA) oxidation process in water was established through the activation of peroxymonosulfate (PMS) by cobalt-exchanged zeolite-NaY catalyst, Co-NaY. Different physicochemical and spectroscopic analyses confirmed the existence of cobalt(II) species as Co(OH)₂ in zeolite-NaY framework. Zeolite-NaY played a pivotal role in trapping the free radicals, activating the PMS, and stabilizing the active Co(peroxo) species, Co(O–O). The involvement of Co(O–O) species in the reaction mechanism was evidenced by characteristic spectroscopic analyses, including the FTIR band at 926 cm⁻¹ and the Raman band at 983 cm⁻¹, attributed to the ν(O–O) vibration through Fermi resonance. The formation of cobalt(oxo)(hydroxy) complex as the intermediate redox active centre was believed to help the BA oxidation reaction to proceed through a non-free radical pathway. Noninvolvement of the free radical in the course of the reaction was evident from the electron paramagnetic resonance spectroscopic analysis. Benzaldehyde was selectively obtained up to 85% through the benzylic CH bond activation process in water making it a green reaction. Density functional theory calculations further supported the proposed mechanism, indicating that the reaction is thermodynamically favourable at 50°C in water. The catalyst exhibited good recyclability, maintaining product selectivity over three cycles.