Metalloporphyrin/dendrimer-decorated MCM-41 biomimetic hybrid catalysts: high stability combined with facile catalyst recyclability

Abstract

In this work, a series of biomimetic catalysts consisting of iron(III)/porphyrin complexes and biocompatible polyamidoamine dendrimers incorporated on mesoporous silica MCM-41 has been successfully synthesized. The structural and surface characteristics of catalysts were characterized by transmission electron microscopy (TEM), Field-emission scanning electron microscopy, N-2 adsorption-desorptionisotherm (BET specific surface area), Fourier transform infrared spectroscopy, X-ray diffraction, diffuse reflectance DR UV-vis spectroscopy, thermal gravimetric and elemental analyses. Furthermore, the catalytic performance of the prepared catalysts was evaluated in the oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethyl-p-benzoquinone, an important precursor for the production of vitamin E, with hydrogen peroxide by varying several parameters such as the structure of catalysts, generation numbers of dendrimers, temperature, solvent and reaction time. Gas chromatography and GC-mass spectrometry analyses confirmed the selective formation of 2,3,5-trimethyl-p-benzoquinone as final product which is presumably due to the presence of dendritic functionality at the peripheral positions of a metalloporphyrin and resulting in regioselective catalytic performance of the hybrid catalysts. In addition, these biocompatible hybrid catalysts were found to act as highly-stable catalysts with excellent selectivity combined with considerable recyclability.