Highly Selective Conversion of CO₂or CO into Precursors for Kerosene-Based Aviation Fuel via an Aldol-Aromatic Mechanism

The extensive emission of CO2 into the atmosphere due to the burning of fossil fuels has urged many countries to move toward decarbonized energy. Based on the concept of carbon neutrality, the European Union Emissions Trading System implemented the aviation carbon tax (ACT), which stimulated the rapid transformation in aviation fuels. To cope with the ACT and mitigate the CO2 emissions from the aviation industry, here, we present a promising route for the synthesis of precursors such as aromatics, alkyl benzenes, and naphthenes, which account for 40-50 vol % fraction of the kerosene-based aviation fuel, from waste CO2 or biomass-derived syngas. The ultra-high selectivity of single-ring aromatics (precursors for the kerosene-based aviation fuel) with a selective range of carbon chain numbers (C8-C12) was achieved (>80% in hydrocarbons at a reaction temperature of 275 °C) via the catalytic hydrogenation of CO2 or CO over a bifunctional catalyst (nano-sized ZnCr2O4/Sbx-H-ZSM-5). In situ diffuse reflectance infrared Fourier transform spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, gas chromatography-mass spectrometry, and reaction analysis revealed that the product distribution was controlled by thermodynamics and the formation of the aromatics followed an "aldol-Aromatic"mechanism. The high selectivity of aromatics at the low reaction temperature (i.e., 275 °C) was attributed to the catalyst topology, the closed carbon chain aromatization reaction, and the presence of highly active oxygenated species in the hydrocarbon pool. For the first time, an asymmetric desorption behavior between the active oxygenate species and aromatic hydrocarbons over the ZnCr2O4/Sbx-H-ZSM-5 catalyst is reported with the help of integrated differential phase contrast scanning transmission electron microscopy, which made the reaction highly selective toward aromatics. This strategy gives a carbon-neutral route for the synthesis of kerosene-based aviation fuel precursors and will reduce the burden of the carbon tax on the aviation industry.