Active-Site-Tuned Ni–Fe/HAP Catalysts for Stable Hydrotreatment of Waste Lipids to Diesel-Range Alkanes

Developing low-cost and sulfur-free catalysts is essential for converting waste lipids into green diesel. Herein, hydroxyapatite-supported Ni–Fe catalysts were prepared via a one-step co-precipitation strategy and evaluated for lipid hydrotreatment. The optimized 20Ni–Fe/HAP catalyst delivered 97.1% conversion and 89.1% alkane yield in fatty acid hydrotreatment at 240°C, far outperforming the impregnation-derived counterpart, which gave only 13.1% alkane yield under identical conditions. Characterization results revealed that the superior performance originated from the formation of highly dispersed Ni 3 Fe species, abundant accessible Ni active sites, enlarged surface area, and suitable acidity distribution. Increasing the Ni loading beyond 20 wt.% failed to further improve the activity because of reduced active-site accessibility and pore diffusion efficiency. The catalyst also showed excellent adaptability toward practical feedstocks, affording over 98% alkane yields from used cooking oil and acidified vegetable oil at 260°C. Moreover, 20Ni–Fe/HAP maintained stable performance during five consecutive runs, with negligible changes in conversion and C15–C18 alkane yield. This work provides an efficient Ni–Fe/HAP catalytic system for sustainable production of diesel-range alkanes from waste lipids. Graphical One-step coprecipitation creates a Ni 3 Fe catalyst supported on hydroxyapatite with abundant accessible Ni sites and suitable acidity for efficient lipid hydrotreatment. The optimized 20Ni–Fe/HAP catalyst affords high yields of diesel range alkanes under mild conditions, converts used cooking oil and acidified vegetable oil, and remains stable over five consecutive cycles without noble metals or sulfur.