Caracterização de cerâmicas magnéticas NiFe2O4 e dopada com Zn2+, Co2+ e Cu2+ para avaliação na obtenção de ésteres alquílicos de ácidos graxos

Abstract

Biofuels stand out as an alternative to stop the current process of climate change caused by high greenhouse gas emissions. Biodiesel is figure as a renewable source of expansion in Brazil, which an important parameter is the type of applied catalysis, a key point for both kinetic and economic aspects regarding production costs. The aim of this study is the application of magnetic ceramics with catalytic potential for biodiesel production. The magnetic ceramics tested were: NiFe2O4, Ni0,5Zn0,5Fe2O4, Ni0,5Cu0,5Fe2O4 and Ni0,5Co0,5Fe2O4 which were characterized regard the morphology, texture, thermal and magnetic structure. The results pointed that the ceramic showed the characteristic inverse spinel phase, with a crystallite size of 20-93 nm and the chemical composition of the oxides in agreement with the expected stoichiometry. It was observed that doping with Zn2+ and Cu2+ in the NiFe2O4 sample did not change the morphology, and it consists of large agglomerates in the form of irregular blocks, non-porous and fragile aspect except the sample doped with Co2+ which showed dense blocks with formation of irregular pre-sintered particles. All samples showed the characteristic behavior of soft ferromagnetic materials, however, the ferrite containing Zn2+ and containing Cu2+ showed an increase in 5 times in saturation magnetization and a decrease in coercivity about 72 and 61% respectively, when compared to the NiFe2O4. The samples had surface area values of 32.6 to 83.7 m2.g-1, the classification of pores in the mesoporous range, exhibit good thermal stability and indicated by low weight loss during thermogravimetric analysis. The catalytic tests showed catalytic activity around 10% in the transesterification reaction conditions proposed. In the esterification samples showed promising results, the highest conversion was observed for obtaining ceramic Ni0,5Zn0,5Fe2O4 about 15% within 1 hour of reaction. The catalytic activity both in transesterification as for esterification may be related to the low acidity of lewis sites in these materials, in addition to the restrictions on conversion of the products by the reactants diffusion hindrance in the internal structure. However, it was found that ceramics doped with Zn2+ ions had larger diameter portion (12.06 nm), which probably contributed to the satisfaction of fames of obtaining methyl estes of fatty acids (FAMEs).