Propriedades catalíticas de oxidos mistos a base de ferro contendo promotores aplicados na oxidação seletiva de hidrocarbonetos

Abstract

Iron oxides containing metals were synthesized with the objective to obtain efficient solids to catalyze the styrene oxidative reaction in the presence of H2O2, one of the reaction routes for the production of benzaldehyde. Styrene is a high-value commercial monomer used in the manufacture of polymers and resins, among other applications, and its products have high commercial value. Due to the low efficiency of the commercial catalysts, solids were synthesized from the hydrotalcites. The iron-based samples containing the MeFe metals (Me = Ce, Co, Mg, Mn and Ni) were prepared by the co-precipitation method, and a MnFeSi composite was obtained by the mechanosynthesis method. The catalysts were evaluated in a batch reactor at 1 atm and 50 ºC using a molar ratio H2O2/styrene of 1 in the presence of acetone. After the reaction, the catalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, chemical and textural analysis, electron paramagnetic resonance (EPR) and scanning electron microscopy coupled to X-ray spectroscopy (SEM-EDX). In all cases, hematite (α-Fe2O3) and maghemite (γ-Fe2O3) spinel phases were found, and MnFeSi proved to be the most active solid also due to the stability of α-Fe2SiO4 and α-MnO2, performing an important role in the styrene oxidation. The increased performance of the MnFeSi-based hydrotalcite catalyst was also attributed to the action of the Mn promoter, acting on the structural and textural properties of the mixed oxide. With these conclusions, tests with different solvent ratios and catalyst masses can be carried out using MnFeSi in the same reaction, the oxidation of styrene, in concomitance with the oxidative reaction of ethylbenzene and benzyl alcohol, in order to find addictional routes for the production of compounds of high industrial value. Elevated conversions were obtained when 100 mg of catalyst was used, analyzing each reaction alone. As for the selectivity, the reaction with ethylbenzene had the lowest values for benzaldehyde production, which can be explained by the high deposition of coke.