Development of multifunctional catalysts for fatty acid hydrodeoxygenation as a route towards aviation biofuel production under mild conditions

This study addresses the urgent need for sustainable alternatives to fossil-derived fuels by investigating hydrodeoxygenation (HDO) cascade reactions for upgrading biomass-derived bio-oils into sustainable aviation fuel (SAF). Multifunctional catalysts were designed by combining hierarchical zeolites (ZSM-5 - 40 and USY series) with palladium nanoparticles (Pd NPs) to achieve efficient HDO under mild conditions. Controlled placement of Pd NPs on mesoporous and external surfaces enables partial separation of metal and acid sites, enhancing catalytic activity and selectivity. Catalytic performance was evaluated using lauric acid as a model compound. All catalysts achieved complete conversion within 3 h, except PdNP/USY6DA, which did so due to limited mesoporosity and slower diffusion. PdNP/USY30DA and PdNP/USY40DA exhibited the highest yields of desirable C₁₂ hydrocarbons (86% and 85%, respectively). PdNP/HMZSM5DA showed slightly lower yield (81%) but the highest isododecane fraction (8%), indicating enhanced isomerisation. PdNP/USY15DA demonstrated rapid initial activity and balanced selectivity, attributed to an optimal interplay between acidity and mesoporosity. All catalysts produced similar amounts of the undesired product, undecane (12–15%), via undesirable Pd-driven decarbonylation. Overall, tailoring zeolite structure and metal–acid site proximity provides an effective strategy to optimise HDO performance, offering a viable pathway toward cleaner aviation fuels from renewable carbon sources.