Steel Slag as a Highly Efficient Catalyst for the Hydrodeoxygenation of Fatty Acids: From a Waste to a Precious Material for Renewable Fuels Production

With no precedent in the literature, steel slag, an inexpensive and plentiful by-product of the steel industry, was discovered to be a highly selective and active catalyst for the hydrodeoxygenation (HDO) of triglycerides and fatty acids. This material, which is not always recyclable, proved to perform in the virgin state (without any chemical pretreatment), actually fostering the conversion, via a hydrothermal reaction, of palmitic and stearic acids into the corresponding (C16 and C18) alkanes with selectivity above 90%. In addition, by moving to a more complex system such as soybean oil, a complete conversion and the possibility of recycling the catalyst were maintained. Catalytic material, which came from an Italian steel industry (Acciaierie d'Italia), was characterized by XRF, XRD, N2 physisorption analyses, TPR, and TPD techniques. Catalytic performance was successfully correlated with the characterization results, and mechanistic proofs were provided on the catalytic role played by the several iron species present in the slag. The results reported in this work represent a significant contribution to the large-scale production of green diesel and, thanks to the possibility of using a catalyst based on steel slag in HDO processes, open the way to decarbonization and climate neutrality processes.