Caracterização e avaliação de catalisadores de Fe suportado em zeólita HZSM-5 para a síntese de Fishcer-Tropsch

Abstract

The increasing of energy demand and the concerns about the climate change make the development of synthetic fuels of utmost importance. The Fischer-Tropsch synthesis (FTS), a step in the gas-to-liquid processes, is a catalytic reaction that converts synthesis gas (CO and H2) into a wide range of hydrocarbons and is as a promising technology to produce synthetic fuels. This process occurs by a polymerization mechanism and its results are dependent on the operating conditions, and mainly on the catalyst used. Iron (Fe)/zeolite catalysts have been extensively studied for FTS due to their cost-effectiveness and bifunctional activity. However, little research has been reported addressing a complete understanding of physical-chemical properties of Fe/H-ZSM5 and the effects of varied reaction condition on FTS, as well as the kinetic assessment of CO conversion over this type of catalyst. This work focused on studying the synthesis, characterization, catalytic and kinetic assessments of Fe/H-ZSM5 for Fischer-Tropsch synthesis. The characterization results showed zeolite and iron oxide structures with crystallinity, high surface area of the support, and presence of mesopores. Fe particles were heterogeneously distributed on the support in different sizes, presenting multiple reduction stages. The catalysts were active for the Fischer-Tropsch synthesis, showing a maximum CO conversion of 86% at 350°C and an average conversion greater than 50% at 300°C. In general, the catalysts exhibited greater formation of short-chain, C2-C4, and medium chain, C5-C8, hydrocarbons. Temperature, pressure, space velocity and feed composition showed a considerable influence on CO conversion. The catalyst exhibited a stable activity over time without structural changes or coke deposition. Finally, the proposed kinetic model for the best performing catalyst followed the carbide route, considering a double site mechanism with dissociative adsorption of CO and H2, and participation of CO2, which was further confirmed by in situ characterization.