Tailoring Acidity and Structure of ZSM-5 and NaY Zeolites via Ion Exchange and Nb2O5 Impregnation for Enhanced Hydrocracking of Crude Soybean Oil

Abstract The catalytic hydrocracking of crude soybean oil was investigated using ZSM-5 and NaY zeolites modified by ammonium ion exchange and wet impregnation with 5 wt % niobium pentoxide (Nb2O5). The aim was to correlate changes in acidity, structural properties, and product selectivity for biofuel production. Catalysts were characterized by XRD, FTIR, SEM, N2 physisorption, NH3-TPD, and atomic absorption spectroscopy. Ion exchange significantly increased total acidity, particularly for HY (241% increase) and HZSM-5 (59% increase), while Nb2O5 impregnation modified the acidity profiles and influenced the distribution of acid sites without affecting the zeolites’ framework stability. The observed changes in acidity following Nb2O5 impregnation were not uniform, suggesting a redistribution of acid site strength rather than simple neutralization. Hydrocracking reactions were carried out at 450 °C under hydrogen flow in a fixed-bed reactor. ZSM-5-based catalysts exhibited higher selectivity toward gaseous hydrocarbons (C1–C5), whereas NaY-based catalysts favored light liquid hydrocarbons (C6–C8), reflecting their weaker acid sites and larger pores. Proton-exchanged HZSM-5 enhanced gasoline-range product formation and improved deoxygenation efficiency. Niobium-impregnated catalysts promoted aromatization and shifted the deoxygenation pathway from hydrodeoxygenation toward decarboxylation over time. The results demonstrate that acidity tuning through ion exchange and Nb2O5 addition effectively controls cracking pathways and hydrocarbon distribution, offering a viable strategy for biofuel production from vegetable oils.