Catalisadores heterogêneos de cobalto e nióbio suportados em carvão hidrotermal para obtenção de bio-hidrocarbonetos a partir do hidroprocessamento catalítico do ácido oleico

Abstract

Drop-in biofuels are bio-hydrocarbons, like green diesel and bio-jet fuel, which have the same chemical composition as fuels derived from petroleum. As a result, they can be used without changes in structure that already exists to fossils fuels, like motors, turbines, and tanks. That is why drop-in biofuels appear as a more effective alternative to conventional biofuels. In this thesis, it was proposed the synthesis, characterization, and evaluation of novel carbon-supported cobalt and cobalt-niobium catalysts to produce bio-hydrocarbons from a model compound, the oleic acid. The catalysts were synthesized by different methods, including a one-pot hydrothermal method, in which both carbonization and impregnation of metals occurred simultaneously. The niobium phosphate in-situ synthesis was also studied, comparing the utilization of phosphoric acid and ammonium dihydrogen phosphate as phosphorous precursors. The catalysts characterization was made by different techniques, such as X-ray diffraction, infrared spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalytic performance was studied by several batch reactions, at 350 °C, 30 bar of H2 during 3h, using 10 %wt of catalyst. The characterization and reaction results showed that the hydrothermal one-pot synthesis is efficient to produce very active cobalt-based catalysts, with 100 %wt conversion resulting in a liquid product composed only by hydrocarbons. On the other hand, the one-pot synthesis of cobalt-niobium catalysts resulted in catalysts with low conversion rates, since the niobium species presence seems to reduce the availability of active cobalt sites. Furthermore, the treatment with H3PO4 e (NH4)2HPO4 resulted in the leaching of cobalt and in the production of cobalt phosphate, respectively. However, the previous synthesis of niobium phosphate over the carbon support followed by the incipient impregnation of cobalt resulted in a bifunctional catalyst, also with 100 %wt conversion and yield in hydrocarbons. Insights into the acidity of these catalysts were made and discussed, and it was concluded that the amount of Bronsted sites produced in the cobalt-niobium catalyst, produced by H3PO4 treatment, were capable to promote, even that in low extent, cracking and isomerization reactions, resulting in a product with about 3.5 %wt of branched alkanes.