Sustainable processing of geothermal waste into a functional catalyst for green diesel from hydrocracking castor oil

Valorizing silica-rich geothermal sludge as a catalyst precursor provides a route to integrate industrial waste management with renewable fuel production. Silica-rich geothermal sludge from the Dieng geothermal power plant was converted into sulfated silica (SO 4 /SiO 2 ) and subsequently impregnated with Ni and Mo to form a bifunctional NiMo/SO 4 /SiO 2 catalyst for the hydrocracking of non-edible castor oil. Physicochemical properties were analyzed using XRF, FTIR, SEM–EDX, BET, and XRD to evaluate elemental composition, structure, and textural characteristics. Sulfated mesoporous silica was obtained with a surface area of 218.26 m 2 g −1 and a pore volume of 0.8886 cm 3 g −1 , providing a suitable support for metal dispersion. Catalytic performance was assessed via castor oil hydrocracking at 225–375 °C under 30 bar H 2 for 120 min, with product distribution analyzed by GC–MS. The NiMo/SO 4 /SiO 2 catalyst achieved 63.93 % conversion with 42.57 % selectivity toward gasoil-range hydrocarbons at 375 °C. The catalyst promotes hydrogenation, deoxygenation, and cracking reactions in triglyceride-derived feedstocks. These results highlight the potential of geothermal sludge–derived silica as a sustainable catalyst support for renewable hydrocarbon fuel production within a circular materials framework.