Core–Shell Bio-Z5@NiFe Catalyst Derived from Biogenic Silica for Selective Hydrodeoxygenation of Fatty Acids to Linear Alkanes

A sustainable one-pot hydrothermal strategy is reported for the synthesis of a core–shell Bio-Z5@NiFe catalyst utilizing rice husk derived biogenic silica. Ethylenediamine and EDTA-2Na function as chelating ligands to confine Ni and Fe species at the zeolite crystallization front, yielding a uniform, approximately 20 nm thick bimetallic coating intimately wrapped around the siliceous framework. This architectural precision circumvents the metal agglomeration endemic to conventional impregnation methods, while simultaneously providing a larger external surface area, enhanced metal dispersion, and intimate metal-acid proximity. In the hydrodeoxygenation of stearic acid, the optimized Bio-Z5@5Ni2Fe achieves complete conversion with exceptional selectivity exceeding 96% for n-octadecane under mild conditions. The catalyst exhibits remarkable substrate generality across C12–C18 fatty acids, consistently delivering >94% selectivity to linear alkanes, and retains >90% of its initial activity over four consecutive cycles. In situ DRIFTS and kinetic profiling elucidate a spatially concerted metal-acid relay mechanism. Spectroscopic evidence confirms that the bimetallic interface synergistically stabilizes bidentate and monodentate carboxylate intermediates, polarizing the C═O bond to facilitate hydrogen transfer. The proximity between the NiFe shell and Brønsted acid sites ensures the instantaneous rehydrogenation of transient α-olefin intermediates immediately following alcohol dehydration, thereby quenching decarbonylation and decarboxylation pathways. This work establishes a robust paradigm converging biomass valorization with atomic-level control over adsorption geometry and reaction trajectories for advanced biofuel production.