Catalytic hydrogenation of waste-derived lipids: A route to producing sustainable drop-in biofuels by using Re/TiO2 catalysts

The urgent threat of climate change compels modern society to transition to alternative energy sources swiftly. The production of sustainable liquid biofuels capable of substituting fossil-derived fuels is a topic of great interest. This study explores the effectiveness of Re/TiO2 catalysts in producing drop-in biofuels from waste-derived feedstock. Specifically, four Re-based catalysts supported on different TiO2 materials, namely TiO2 P25, TiO2 FSP, TiO2 M, TiO2 COTIOX were synthesized using the wet impregnation method, characterized and tested in the hydrodeoxygenation reaction of fatty acids, to uncover fundamental insight into this process. These catalysts exhibited varying levels of effectiveness. Apart from Re/TiO2 COTIOX, which showed the lowest conversion of fatty acids (30 %), the other three catalysts allowed over 98 % conversion of fatty acids into hydrocarbons after 6 h reaction, at 35 bar of H2, under solvent-free conditions and without pre-reduction of the catalyst. Notably, Re/TiO2 P25 was the most effective, attaining this remarkable result at 300 °C. The remaining catalysts, Re/TiO2 FSP and Re/TiO2 M, required higher temperatures (350 °C) to achieve complete hydrogenation of fatty acids into hydrocarbons. These effective catalysts also demonstrated great recoverability, reusability, and robustness, successfully converting waste-derived lipids, such as grease recovered from urban sewage sludge and waste cooking oil, into hydrocarbons. These findings underscore Re/TiO2 as a promising robust catalyst for waste-derived lipids hydrogenation, enabling the efficient production of drop-in biofuels and paving the way for innovative solutions in the renewable energy landscape.