Sustainable Green Diesel Production via Hydrotreating of Biodiesel over Fe–Ni Catalysts Supported on Natural Mordenite

Monometallic Ni catalysts supported on zeolites may undergo deactivation through carbon deposition and particle growth during hydrotreating. In this study, FeNi catalysts supported on modified natural mordenite (MO), with total metal loadings of 20–40 wt.%, were prepared by co-deposition–precipitation and evaluated for biodiesel conversion to green diesel. XRD and TEM analyses showed that Fe incorporation was associated with smaller Ni crystallites and a narrower particle size distribution compared with the monometallic 30Ni/MO reference. NH3-TPD measurements indicated changes in ammonia desorption behavior, particularly a reduced high-temperature contribution, while CO chemisorption revealed the highest uptake (137.5 μmol g−1) for 30FeNi/MO. Under the investigated conditions (310 °C, 40 bar H2, 9 h), this catalyst achieved approximately 99% biodiesel conversion and a 97 wt.% diesel-range hydrocarbon fraction. The product carbon-number distribution suggested a greater relative contribution of carbon-removing deoxygenation pathways following Fe incorporation, although definitive mechanistic assignments require additional evidence. Reusability tests revealed substantial deterioration in hydrocarbon production upon direct reuse. Washing and re-activation restored nearly complete biodiesel conversion but only partially recovered hydrocarbon production (66 wt.%). These findings demonstrate promising initial catalytic performance while highlighting limitations in catalyst stability and regeneration.