Direct Conversion of Syngas to Light Olefins through Fischer–Tropsch Synthesis over Fe–Zr Catalysts Modified with Sodium

Abstract

Fe−Zr−Na catalysts synthesized by coprecipitation and impregnation methods were implemented to investigate the promoting effects of Na and Zr on the iron-based catalyst for hightemperature Fischer−Tropsch synthesis (HTFT). The catalysts were characterized by Ar adsorption− desorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, CO temperature-programmed desorption, H 2 temperature-programmed desorption, X-ray photoelectron spectroscopy, and Mossbauer spectroscopy (MES). The results indicated that Na changed the active sites on the catalyst surface for the CO and hydrogen adsorption, owing to the electron migration from Na to Fe atoms, which resulted in an enhanced CO dissociative adsorption and a decrease in hydrogen adsorption on the metallic Fe surface. The decreased H/C ratio on the catalyst surface accounted for the increased chain propagation and weakened hydrogenation of light olefins. Besides, Na could also facilitate the carbonization of catalysts and protect the iron carbide against oxidation, which provides more active sites for HTFT reaction and is beneficial to the C−C coupling. Zr could decrease the hematite crystallite size and stabilize the active phase to improve the HTFT activity. At an optimal Na loading of 1.0 wt %, the Fe−Zr−1.0Na catalyst exhibited the highest light olefin selectivity of 35.8% in the hydrocarbon distribution at a CO conversion of 95.2%.

Production of Light Olefins via Fischer-Tropsch Process Using Iron-Based Catalysts: A Review

“…A series of Na impregnated Fe-Zr catalysts (Fe/Zr molar ratio = 100/15), prepared using the coprecipitation method, were used to evaluate the effect of Zr and Na on the physico-chemical properties of the catalysts and their catalytic performance in the hightemperature FT reaction [57]. The catalytic performances of the catalysts in FT reaction at 320 °C, 1.5 MPa, and H2/CO = 2, are shown in Table 2.…”

Effect of the Zr promoter on precipitated iron-based catalysts for high-temperature Fischer–Tropsch synthesis of light olefins

“…The introduction of zirconium shifts the hydrocarbon distribution to light hydrocarbons on FeMnxZr catalysts, so we hope that the molar ratio of alkenes to alkanes in the C 2 -C 4 hydrocarbons can be increased. According to previous research, [19][20][21] catalysts impregnated with an appropriate amount of Na increased the molar ratio of alkenes to alkanes in the C 2 -C 4 hydrocarbons and suppressed the CH 4 formation.…”

“…Zhang et al 18 proposed that the addition of zirconium reduced the size of iron oxide particles, resulting in better FT activity and poorer chain growth capacity to form a C–C bond compared to Zr-free catalysts. Interestingly, Ma et al 19 found that Na increased CO dissociation adsorption and suppressed hydrogen adsorption, whereas Zr reduced the iron oxide crystallite size and stabilized the active phase. The introduction of Zr and Na resulted in higher FT activity and light olefin selectivity.…”

Selective Conversion of Syngas to Olefins via Novel Cu-Promoted Fe/RGO and Fe–Mn/RGO Fischer–Tropsch Catalysts: Fixed-Bed Reactor vs Slurry-Bed Reactor

“…They are utilized as vital building blocks to produce many essential end products in our daily lives (e.g., plastics, synthetic textiles, coatings, and solvents). 1,2 This crucial role of olefins rendered ethylene as the most produced hydrocarbon product worldwide. 3 As a result, enormous interest is oriented towards the production of olefins through a variety of petrochemical processes.…”

“…Light olefins, especially ethylene, are economically valuable. They are utilized as vital building blocks to produce many essential end products in our daily lives (e.g., plastics, synthetic textiles, coatings, and solvents). , This crucial role of olefins rendered ethylene as the most produced hydrocarbon product worldwide . As a result, enormous interest is oriented towards the production of olefins through a variety of petrochemical processes. − Most of these processes are petroleum-based, and with the rapid depletion of oil resources, the growing demand of light olefins has become a real challenge.…”