Design, Synthesis, and Mechanistic Evaluation of Iron-Based Catalysis for Synthesis Gas Conversion to Fuels and Chemicals
This project extends previously discovered Fe-based catalysts to hydrogen-poor synthesis gas streams derived from coal and biomass sources. These catalysts have shown unprecedented Fischer-Tropsch synthesis rate, selectivity for feedstocks consisting of synthesis gas derived from methane. During the first reporting period, we certified a microreactor, installed required analytical equipment, and reproduced synthetic protocols and catalytic results 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 the third reporting period, we improved the catalysts preparation method, which led to Fe-based FT catalysts with the highest FTS reaction rates and selectivities so far reported, a finding that allowed their operation at lower temperatures and pressures with high selectivity to desired products (C{sub 5+}, olefins). During this fourth reporting period, we have determined the effects of different promoters on catalytic performance. More specifically, we have found that the sequence in which promoters are introduced has a marked positive impact on rates and selectivities. Cu or Ru chemical promoters should be impregnated before K to achieve higher Fischer-Tropsch synthesis rates. The catalyst prepared in this way was evaluated for 240 h, showing a high catalytic activity and stability after an initial period of time necessary for the formation of the active phases. Concurrently, we are studying optimal activation procedures, which involve the reduction and carburization of oxide precursors during the early stages of contact with synthesis gas. Activation at low temperatures (523 K), made possible by optimal introduction of Cu or Ru, leads to lower catalyst surface area than higher activation temperatures, but to higher reaction rates, because such low temperatures avoid concurrent deactivation during the reduction-carburization processes. In this reporting period, we have measured the evolution of oxide, carbide, and metal phases of the active iron components using advanced synchrotron techniques based on X-ray absorption spectroscopy. These studies have revealed that Zn inhibits the isothermal reduction and carburization of iron oxide precursors. The concurrent presence of Cu or Ru compensates for these inhibitory effects and lead to the formation of active carbide phases at the low temperatures required to avoid deactivation via carbon deposition or sintering. Finally, we have also examined the kinetic behavior of these materials, specifically the effects of H{sub 2}, CO, and CO{sub 2} on the rates and selectivities of Fischer-Tropsch synthesis reactions. This has led to a rigorous rate expressions that allows the incorporation of these novel materials into larger scale reactors and to predictions of performance based on the coupling of hydrodynamic and kinetic effects ubiquitous in such reactors.
- Research Organization:
- Univ. of California (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FC26-03NT41964
- OSTI ID:
- 861888
- Country of Publication:
- United States
- Language:
- English
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DESIGN, SYNTHESIS, AND MECHANISTIC EVALUATION OF IRON-BASED CATALYSIS FOR SYNTHESIS GAS CONVERSION TO FUELS AND CHEMICALS
Design, Synthesis, and Mechanistic Evaluation of Iron-Based Catalysis for Synthesis Gas Conversion to Fuels and Chemicals