(569ae) Highly Dispersed Bimetallic Ir-Co on Leaf-Shaped Carbon Catalysts Derived from Zeolitic Imidazolate Framework for Fischer-Tropsch Synthesis

Fischer-Tropsch synthesis (FTS) has attracted significant interest because it enables the production of platform chemicals and fuels using synthesis gas produced from various alternative resources. In conventional Co-based catalysts, the optimal Co fractions (~20 wt.%) have been reported. Surpassing the fraction can induce Co particle aggregation, leading to reduced FTS activity. Zeolitic Imidazolate Framework (ZIF) can provide high surface area with unique pore structure, and chemical and thermal stabilities. Especially, in Co-based ZIF catalysts (ZIF-67), the strong Co-N interaction between the imidazolate-based organic linker and Co²⁺ allows high weight loading of metals, giving high productivity per unit mass of catalysts. However, the mass-transfer limit attributed to the micro-porous structure of ZIF cuases an imbalance in CO/H₂ ratio on the catalytic surface, resulting in a high selectivity for the undesired methane. Additionally, there remains a need for enhancing hydrocarbon productivity and controlling selectivity in Co-based catalysts in FTS.

Herein, we synthesized leaf-shaped bimetallic Co-Ir ZIF catalysts to overcome mass-transfer limitations due to the microporous structure, leading to a high hydrocarbon formation rate. The leaf-shaped Co-ZIF-based catalyst exhibits highly dispersed Co-Ir species throughout the supports, even with a high portion of Co (~35wt.%). The structurally improved leaf-shaped monometallic Co-ZIF catalyst exhibits a three-fold increase in CO consumption rate in the FTS reaction with a significant decrease in methane selectivity from 9% to 5%. Furthermore, bimetallic Co-Ir catalysts show a lower apparent activation energy (ΔE_a,app=~20 kJ/mol) than that of monometallic Co catalysts (Figure 1), indicating a promotional effect of Ir species. Steady-state measurements with characterizations support the structural advantages and the enhanced catalytic activity of leaf-shaped bimetallic Ir-Co ZIF catalysts.

This work was supported by “Carbon Upcycling Project for Platform Chemicals” (Project No. 2022M3J3A1050076, 2022M3J3A1039377) through the National Research Foundation (NRF) funded by the Ministry of Science and ICT, Republic of Korea.