Host (nano cage of zeolite Y)/guest transition metal complexes of N,N-bis (salicylidene)4,5-dimethyl-1,2-phenylenediamine: synthesis, characterization, catalytic activity for oxidation of phenol and kinetic study

Abstract

In this work, transition metal (M = Cu(II), Mn(II), Co(II), Ni(II)) complexes of tetradentate Schiff base ligand H2L: (C22H20N2O2) have been introduced to cavity of zeolite-Y by flexible ligand method. These host–guest materials were characterized by several techniques: chemical analysis, diffuse reflectance spectroscopy, Fourier transfer infrared, X-ray diffraction, thermo gravimetric analysis and Burner–Emmet–Taller. The catalytic activity of [M(L)]/NaY (M = Mn, Co, Ni, Cu) was investigated with oxidation of phenol to catechol and hydroquinone with hydrogen peroxide (H2O2) as oxidant in different solvents. The reactivity of these heterogeneous catalysts was compared with corresponding homogeneous catalysts. The activity of phenol oxidation decreases in the series [Cu(L)]/NaY > [Mn(L)]/NaY > [Co(L)]/NaY > [Ni(L)]/NaY at mild conditions. We considered the effect of different factors on percent of products in oxidation of phenol such as: amount of catalyst, temperature, type of oxidant and solvent. Finally, the kinetic of phenol oxidation with excess H2O2 over [M(L)]/NaY catalysts at several temperatures of 40, 60 and 80 °C was studied. These catalysts were very stable and can be reused for more than three times. Results show that a pseudo-first order with respect to phenol and the catalytic reaction occurred via a radical mechanism.