Hydrodeoxygenation of fatty acids and triglycerides by Pt-loaded Nb2O5 catalysts

Abstract

Platinum nanoparticles loaded onto various supports have been studied for the selective hydrogenation of lauric acid to n-dodecane. The activity depends on the support material and pre-reduction temperature. Pt/Nb₂O₅ reduced at 300 °C gives the highest activity. Pt/Nb₂O₅ shows higher activity than various Nb₂O₅-supported transition metals (Ir, Re, Ru, Pd, Cu, Ni). Under solvent-free conditions Pt/Nb₂O₅ is effective for the hydrodeoxygenation of lauric, capric, palmitic, myristic, oleic, and stearic acids under 8 bar H₂ at 180–250 °C, which gives high yields (88–100%) of linear alkanes with the same chain length as the starting compound. Tristearin is also converted to give 93% yield of n-octadecane. Pt/Nb₂O₅ shows more than 60 times higher turnover number (TON) than the previously reported catalysts for the hydrogenation of stearic acid to n-octadecane. Mechanistic study shows a consecutive reaction pathway in which lauric acid is hydrogenated to 1-dodecanol, which undergoes esterification with lauric acid as well as hydrogenation to n-dodecane. The ester undergoes hydrogenolysis to give the alcohol, which is hydrogenated to the alkane. Infrared (IR) study of acetic acid adsorption on Nb₂O₅ indicates that Lewis acid–base interaction of Nb cation and carbonyl oxygen, which suggests a possible role of Nb₂O₅ as an activation site of carbonyl groups during hydrodeoxygenation.