ZEOLITE-COATED IRON CATALYSTS FOR SINGLE-STEP CONVERSION OF ILLINOIS COAL-DERIVED SYNGAS TO LIQUID FUELS

As a commercially proven technology, indirect coal-to-liquids (CTL) process offers a potentially attractive option to convert Illinois coal into value-added liquid fuels and chemicals. One of the key obstacles that impede wide-spread utilization of CTL resides in its complexity and capital/energy intensity. Therefore, novel catalysts that can intensify state-of-the-art CTL process can play a pivotal role to promote the clean and cost-effective usage of coal in a carbon-constrained world. Through an ICCI funded Exploratory Research (ER) project, a multifunctional core-shell catalyst concept for direct synthesis of gasoline-range iso-paraffins from coal-derived syngas derived in a single-step was successfully validated. The catalyst, with excellent activity for water-gas-shift reaction, Fischer-Tropsch (F-T) synthesis, hydrocracking, and isomerization, has the potential to combine multiple unit operations in conventional CTL into a single step, thereby reducing the capital cost of a CTL plant while increasing its efficiency. The proposed catalyst has a promoted iron core and a zeolite (HZSM-5) shell. The iron-based core has water gas shift (WGS) and F-T activities, while the shell is active toward WGS, isomerization, and hydrocracking reactions. An FeAl-CuK core catalyst resulting from our preliminary studies exhibits extraordinary per-pass CO conversion (up to 89%) when compared to commercial catalysts under identical conditions (<40% conversion). When coated with a HZSM-5 shell using a novel dry-gel method, wax-formation was completely inhibited, leading to high liquid fuel yield without refining steps. The current project aims to further improve the F-T performance of core-shell catalysts by tailoring the mass-transfer resistance of the shell as well as core and shell interactions. Through the proposed project, the effect of zeolite shell on syngas conversion, selectivity of light hydrocarbons, and yield of gasoline-range iso-paraffins will be investigated in detail. The thickness and acidity of the zeolite shell will be tuned by adjusting the mass ratio of shell to core and the Al/Si ratio, repetitively. To facilitate the diffusion of reactants and products through the zeolite, a hierarchical porous shell will be obtained by soft templating or desilication. Through the proposed studies, high-performance multifunctional F-T catalysts that can significantly enhance the technical and economic attractiveness of conventional CTL technologies will be developed.