DESIGN, SYNTHESIS, AND MECHANISTIC EVALUATION OF IRON-BASED CATALYSIS FOR SYNTHESIS GAS CONVERSION TO FUELS AND CHEMICALS

Abstract

This project explores the extension of previously discovered Fe-based catalysts to hydrogen-poor synthesis gas streams derived from coal and biomass sources. These catalysts have previously shown unprecedented Fischer-Tropsch synthesis rate, selectivity with synthesis gas derived from methane. During the first reporting period, we certified a microreactor, installed required analytical equipment, and reproduced synthetic protocols and catalytic performance previously reported. During the second reporting period, we prepared several Fe-based compositions for Fischer-Tropsch synthesis and tested the effects of product recycle under both subcritical and supercritical conditions. During this third reporting period, we have prepared a large number of Fe-based catalyst compositions using precipitation and impregnations methods with both supercritical and subcritical drying and with the systematic use of surface active agents to prevent pore collapse during drying steps required in synthetic protocols. These samples were characterized during this period using X-ray diffraction, surface area, and temperature-programmed reduction measurements. These studies have shown that these synthesis methods lead to even higher surface areas than in our previous studies and confirm the crystalline structures of these materials and their reactivity in both oxide-carbide interconversions and in Fischer-Tropsch synthesis catalysis. Fischer-Tropsch synthesis reaction rates and selectivities with low H{sub 2}/CO ratio feeds (H{sub 2}/CO = 1) were the highest reported in the literature at the low-temperature and relatively low pressure in our measurements. Current studies are exploring the optimization of the sequence of impregnation of Cu, K, and Ru promoters, of the activation and reaction conditions, and of the co-addition of light hydrocarbons to increase diffusion rates of primary olefin products so as to increase the selectivity to unsaturated products. Finally, we are also addressing the detailed kinetic response of optimized catalysts to reaction conditions (temperature, partial pressures of H{sub 2}, CO, H{sub 2}O, CO{sub 2}, olefins) in an effort to further increase rates and olefin and C{sub 5+} selectivities.