Selective Conversion of Carbon Dioxide into Liquid Hydrocarbons and Long-Chain alpha-Olefins over Fe-Amorphous AlOx Bifunctional Catalysts

Abstract

Considerable progress has been made in the conversion of carbon dioxide (CO2), which is highly thermodynamically stable, into liquid hydrocarbons using metal oxide/zeolite composite catalysts. Nevertheless, producing liquid hydrocarbons with a single catalyst without utilizing additional C-C coupling agents remains a formidable challenge. Herein, we report a bifunctional iron aluminum oxide (FeAlOx) catalyst that directly converts CO2 into C5+ hydrocarbons with an overall selectivity of 77.0% and CO2 conversion of 20.2% at a H-2/CO2 ratio of 1:1. Notably, the selectivity for linear alpha-olefins (LAOs) was 52.4%, accounting for 78.4% of the total C4+ olefins. At a high H-2/CO2 ratio of 3:1, the yield of C5+ hydrocarbons was 19.7%. The concept of crystalline-/amorphous-structured active sites in the single FeAlOx catalyst was proposed. The reducible magnetite (Fe3O4) phase, which contains surface oxygen vacancies, facilitated the reverse-water-gas-shift (RWGS) reaction to form CO via CO2 hydrogenation, and subsequent C-C coupling over Hagg iron carbide afforded lower olefins (C2-C4(=)). Long-chain LAOs were then formed on the surface of amorphous aluminum oxide (AlOx) via the readsorption of (C-2-C-4(=)). In addition, the amorphous AlOx phase enhanced CO2 and H-2 adsorption, which facilitated the formation of carbonate, bicarbonate, and formate species via the RWGS reaction and the subsequent formation of long-chain hydrocarbons via the Fischer-Tropsch reaction. The bifunctional FeAlOx catalyst showed excellent stability for up to 450 h onstream, demonstrating its potential as a practical-scale catalyst for the conversion of CO2 into value-added liquid fuels and chemicals.