Jet Fuel Range Hydrocarbon Production from Propanal: Mechanistic Insights into Active Site Requirement of a Dual-Bed Catalyst

Utilization of sustainable biomass to produce jet fuel range hydrocarbons is imperatively needed to mitigate CO₂ emissions and to liberate the over-reliance on fossil resources. Using propanal as the feedstock, an excellent jet fuel range hydrocarbon yield (81.7%), high conversion (ca. 100%), and purity (85%) were achieved over a novel dual-bed Cu/SiO₂–TiO₂||Ni/ZSM-5 catalyst at low temperature and pressure in only one reactor. The intrinsic active site requirement was further investigated by multitechniques including density functional theory calculation, quantitative CO₂/NH₃-temperature-programmed desorption/diffuse reflectance infrared Fourier-transform spectroscopy, high-resolution transmission electron microscopy, and thermogravimetric analysis–mass spectrometry. Results showed that for the upstream bed catalyst (Cu/SiO₂–TiO₂), the Ti–O site pair and Ti Lewis acid site were crucial for enolate formation, carbon-chain growth, and ring closure reactions, which can be altered by the calcination temperature. The synergy between the site strength and number led to a volcanic relationship between acidity/basicity and the intermediate yield. In addition, the downstream bed Ni/HZSM-5 catalyst promoted the hydrodeoxygenation reaction toward hydrocarbon formation.