Avaliação de catalisadores a base de ferro suportados em nióbia na Síntese de Fischer-Tropsch

Abstract

Currently, the Fischer-Tropsch Synthesis comes up with a new rule, to contribute to the socio/economic/environmental, meeting the expectations of today\'s global world. Aiming at the production of alternative fuels and clean, arising mainly from biomass, in response to the current global requirements. In this work, we chose to study the catalyst Fe/Nb2O5 due to little research related to this system reactions/processes, and be more commercially interesting for large scale production. The parameters evaluated were the influence of temperature reduction, the Fe content present in the catalyst, GHSV and temperature reaction, under reaction conditions 225-275 °C and 20 bar in a fixed bed reactor. Catalysts were prepared with concentrations of 5, 10 and 20% Fe supported on niobia. The characterization by Temperature Programmed Reduction, showed that the reduction to Fe° catalysts obey these 2 steps. The interaction of species oxides (iron oxide and niobia) present in the catalysts was checked by infrared spectroscopy, confirming that the change in displacement or intensity of the bands is closely linked to their interaction, which grows with increasing content Fe in the catalyst. The evolution of species in the process of reduction of the catalysts was initially accompanied by diffuse reflectance spectroscopy Uv-Vis, noting that the interactions between species FexOy with Nb2O5, undergo a continuous decrease with temperature reduction, being more intense in iron content and higher temperatures decrease, and this result confirmed after analysis of x-ray diffraction. Subsequently, we used a qualitative analysis by Temperature Programmed Surface Reaction for proving the existence of the SMSI effect (interaction with the metal support) in these catalysts, noting that the increase in temperature caused a reduction in peak broadening consumption of the load reactive H2/CO = 2, or product formation, decreasing its intensity to the shift to higher temperatures, this drop in activity was most evident in catalyst content of 20% Fe. Through the catalytic tests, it was found that the growth of catalytic activity with increasing temperature reduction is probably due to higher amount of active sites which do not suffer significant SMSI effect. Assigning to the catalysts 5 and 10% Fe/Nb2O5, the best results in producing gasoline, diesel and C20+, due to the higher scattering sites present in the surface layer thereof, where maximizing selectivity of these becomes smaller at higher temperatures and GHSV. Comparing the results obtained in this work to others described in the literature with the iron-based catalysts supported on reducible oxides, there was a significant increase in the production of selectivities in the range of gasoline and diesel.