Thermally stable metal-organic framework based iron 2,6-naphthalenedicarboxylic catalyst (Fe-NDC) for syngas conversion to olefin

Abstract

Olefins are the backbone of the petrochemical conversion industries, like polymers, plastic, lubricating oil, surfactants, and synthetic fuels. It is a wide but challenging process to customize. Metal-organic frameworks (MOFs) are highly regarded for their potential in Fischer-Tropsch synthesis (FTS), yet they often have inadequate thermal stability. This study demonstrated the remarkable potential of the Fe-NDC MOF. It maintains its initial structure until it reaches a temperature of 500 °C (Fe@C-500), which is efficient for syngas conversion to olefin. The Fe@C-500 catalyst exceeded a twofold increase in the ratio of olefin to paraffin compared to Fe@C-600 (2 vs. 0.8). The maintained structure of Fe@C-500 enhances the transport of reactants and restricts the hydrogenation of olefins. The Fe@C-500 catalyst showed ~ 50% and 27% selectivity to total olefin and light olefin, respectively, with a Fe-time yield (FTY) for light olefins of 180 mmol_CO g^-1_Fe h^-1. In contrast, Fe@C-600 exhibits a shift in product selectivity towards paraffin (~ 70%) at a lower FTY for light olefins of 130 mmol_CO g^-1_Fe h^-1. The performance of the Fe@C-500 catalyst is particularly intriguing and warrants further investigation. Retaining the porous structure of MOF-derived catalysts might greatly enhance olefin production.

Keywords: Iron catalyst; Olefin production; Syngas conversion; Thermally stable MOF.

Fig. 1

Process scheme of the Power-to-X system.

Fig. 2

TGA and DTG of Fe-NDC (a), XRD patterns (b), and FTIR spectra (c) of Fe-NDC MOF and derived catalysts. MOF under nitrogen flow.

Fig. 3

XPS spectra of (a–c) Fe@C-500 and (d–f) Fe@C-600.

Fig. 4

SEM, TEM, HRTEM, STEM, and iron elemental mapping (red) images of (A) Fe-NDC, (B) Fe@C-500, and (C) Fe@C-600. (D) PSD of derived catalysts. (E) Schematic of the structural change at different pyrolysis temperatures.

Fig. 5

(a) Nitrogen adsorption isotherms of Fe-NDC and derived catalysts. (b) H₂-TPR. (c) H₂ and (d) CO chemisorption of derived catalysts.

Fig. 6

FTS activity of (a) Fe@C-500, (b) Fe@C-600 as a function of TOS, (c) Hydrocarbon distribution and FTY, and (d–f) olefin product distribution, at P = 20 bar, GHSV = 20,000 mL g⁻¹_cat h⁻¹, and H₂/CO ratio of 1.

Fig. 7

(a) Carbon number product distribution and ASF distribution of (b) Fe@C-500 and (c) Fe@C-600 at T = 340 °C, P = 20 bar, GHSV of 20,000 mL g⁻¹_cat h⁻¹, and H₂/CO of 1.

Fig. 8

(a) Catalytic performance stability of catalysts at T = 340 °C, P = 20 bar, GHSV = 20,000 mL g⁻¹_cat h⁻¹, and H₂/CO ratio of 1. (b) XRD of spent catalysts.

Fig. 9

Product distribution comparison of Fe@C-500 at different temperatures and GHSV at P = 20 bar and H₂/CO = 1.

Fig. 10

(a) Product distribution comparison and (b) olefin selectivity and FTY of Fe@C-500, Fe@C-600, and Fe/Al₂O₃, at T = 340 °C, P = 20 bar, GHSV = 20,000 mL g⁻¹_cat h⁻¹, and H₂/CO = 1.

Fig. 11

Olefin indicators produced in this work compared to state-of-the-art Fe-MOF-based catalysts.