Hierarchical Zeolite-Based Catalysts for Tandem One-Step Renewable Diesel Production via Fischer-Tropsch Synthesis

The demand for low carbon biofuels such as renewable diesel (RD) and sustainable aviation fuel (SAF) is increasing drastically worldwide as driven by the shift towards cleaner energy and the imperative need to reduce carbon footprint while maintain the balance of transportational energy landscape toward the decarbonization goal 2050. Fischer-Tropsch synthesis (FTS), converting biomass-derived syngas into long-chain hydrocarbons, is a promising route for sustainable RD and SAF production. However, the liquid hydrocarbons obtained from FTS usually require additional refinements and upgrade treatments, such as hydro-processing, distillation, and fractionation, prior to further application. Here, through rational materials design and manipulation, we have formulated a multi-layer hierarchical monolithic catalyst which can integrate the syngas-to-wax hydrocarbons and wax hydrocarbons-to-diesel fuel conversions in a tandem one-step catalysis process for sustainable drop-in RD production via FTS. The multi-layer hierarchical catalyst comprises of a bottom layer of cobalt oxide (Co₃O₄) dispersed on γ-alumina (γ-Al₂O₃) support, covered by a top zeolite layer. The influence of zeolite type (ZSM-5 and Zeolite Y), ion-exchange cations (H, Na, K, La, and Ce), and reaction parameters on FTS performance have been investigated. Results show that multilayer catalysts exhibit high diesel selectivity under 220 °C at 20 bar conditions. The produced RD possesses high cetane number and low aromatic content with drop-in fuel potential. For the catalyst formulation, the ion-exchange cations and their dispersion extent play an important role in product selectivity and carbon number distribution. This work provides an energy efficient and cost-effective strategy for sustainable drop-in diesel fuel production with easy catalyst scalability and high market demand.