MoO3 mássico e suportado em argila sintetizado pelo método hidrotermal assistido por micro-ondas aplicados como catalisadores para a obtenção de biodiesel

Abstract

This work aimed to synthesize crystalline nanostructures of molybdenum trioxide (MoO3) using a simple and fast method based on microwave-assisted hydrothermal synthesis (HM), for use in the production of biodiesel from commercial soybean oil. The physical-chemical properties of the materials and the monitoring of the ethanolic transesterification reaction were investigated. The results of X-ray diffraction and Raman spectroscopy indicated the presence of the hexagonal phase (h-MoO3) for hydrothermal reactions at 100oC for 1 min and 150oC for 5 min, while the orthorhombic phase (α-MoO3) was obtained after calcination at 400oC of the hexagonal sample obtained at 150ºC for 5 min. A significant change in morphology was observed by scanning electron microscopy images due to the phase transition, as smooth hexagonal rods change to structures in hexagonal layers, increasing the area from 0.4 to 3.5 (m2 g-1) . The catalytic potential of the clay (montmorillonite (MMT)) used in this work was evaluated, in its natural form and impregnated with MoO3, with hexagonal or orthorhombic structures. The diffraction patterns indicated the formation of peaks characteristic of the clay and α-MoO3 structure, while there was no crystallization of the h-MoO3 phase. By EDX it was determined that an impregnation of about 2% of MoO3 occurred in the clays for the two composites. The products obtained in the syntheses were characterized by gas chromatography; the highest percentage of conversion to esters of the α-MoO3 / clay samples was identified at temperatures of 150º and 200ºC for 1h or 2h, with a synergy in the impregnated material compared to pure materials. In the 1H-NMR spectra it shows the conversion of 91.4% into ethyl ester that was obtained by the orthorhombic catalyst (α-MoO3) at a temperature of 150oC for 0.5 h of reaction, increasing to 94.0% after 2 h . At 200ºC for 2 h of reaction, hexagonal and orthorhombic catalysts lead to similar conversion percentage values. Such behavior indicates that MoO3 is a promising material for the synthesis of biodiesel by transesterification, being the most active orthorhombic phase.