Preparação e caracterização de materiais híbridos ferro-carbono e avaliação de suas propriedades catalíticas

Abstract

The one pot hydrothermal carbonization method was used to prepare hybrid materials based on carbon and iron species. The as - prepared solids were appliedin glycerol acetylation with acetic acid reaction at 180 °C for 24 h. The glucose was used as carbon source whereas ferrous iron sulfate salt was the iron species precursor. The synthetized samples were labelled as xFe@C, being x the nominal iron (II) content in weight percentage (0, 1, 5, 10, 15 and 30 %wt). The hybrid materials were characterized through chemical composition, structure, morphology and texture, as well. X - ray diffraction (XRD) and Fourier transform infrared spectra (FTIR) techniques showed that the solids mostly amorphous had carboxylic acids and hydroxyls superficial functional groups. FTIR spectra exhibited band sassigned to be from carboxylic acids /carboxylate functional groups interacting with Fe2+/Fe3+species. SEM images indicated the formation of dense spheres possessing smooth surfaces with sizes varying from 1 to 7 μm. X-ray photoelectron spectroscopy confirmed the existence of the ionic Fe2+and Fe3+ species on the surface of the solids. The catalytic properties of the as - synthesized solids towards glycerol acetylation reaction with acetic acid were carried out using the following parameters: catalyst mass (25, 50, 75 and 100 mg), temperature (80, 100 and 120 °C) and the acetic acid/glycerol molar ratio (3:1, 6:1, 9:1). The solids possessing low iron content such as from 1Fe@C to 15Fe@C samples showed very low activity. On the other hand, increased iron contents as for 30Fe@C sample had a glycerol conversion of 20%. The main products o btained in the reaction were monoacetylglycerol (MAG), diacetylglycerol (DA G) and triacetylglycerol (TAG), being the byproducts formation negligible. The results obtained using the several parameters indicates that the catalyst performance depend ed on the amount of iron species, catalyst mass as well as the glycerol to acetic acid molar ratio.