Introductory Remarks

Converting CO₂ from a detrimental greenhouse gas into value-added liquid fuels not only contributes to mitigating CO₂ emissions, but also reduces dependence on petrochemicals. Unfortunately, the activation of CO₂ and its hydrogenation to hydrocarbons or other alcohols are challenging tasks because CO₂ is a fully oxidized, thermodynamically stable and chemically inert molecule. Most research to date, not surprisingly, is focusing on selective hydrogenation of CO₂ to short-chain products, while few studies on long-chain hydrocarbons, such as gasoline-range (C₅–C₁₁) hydrocarbons. The key to this process is to search for a high efficient catalyst.

Herein, we have succeeded in preparing high efficient, stable, and multifunctional Na–Fe₃O₄/Zeolite catalysts for the direct production of gasoline-range (C₅–C₁₁) hydrocarbons from CO₂ hydrogenation. This catalyst displayed record selectivity towards C₅–C₁₁ hydrocarbons (78%) as well as low CH₄ and CO selectivity under industrial relevant conditions, and gasoline fraction are mainly isoparaffins and aromatics thus favouring the octane number. Moreover, the composition of C₅–C₁₁ can be tuned by the choice of zeolite type and the integration manner of multifunctional catalyst. When Na–Fe₃O₄ nanocatalyst was matched with HZSM-5 zeolite and integrated by granule-mixing manner, up to 63% of aromatics in gasoline fraction were produced. While Na–Fe₃O₄ was matched with HMCM-22 zeolite, up to 60% of isoparaffins in gasoline fraction were obtained under the dual-bed configuration. Not only that, the multifunctional catalyst exhibited a remarkable stability for 1,000 h on stream, which definitely has the potential to be a promising industrial catalyst for CO₂ utilization to liquid fuels.

In-depth characterizations indicate that, during CO₂ hydrogenation reaction, this catalyst enables RWGS over Fe₃O₄ sites, olefin synthesis over Fe₅C₂ sites, and oligomerization/aromatization/isomerization over zeolite acid sites. The concerted action of the active sites calls for precise control of their structures and proximity. This study paves a new path for the synthesis of liquid fuels by utilizing CO₂ and H₂. Furthermore, it provides an important approach for dealing with the intermittency of renewable sources (sun, wind and so on) by storing energy in liquid fuels.

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