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

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 degrees 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 H-2 at 180-250 degrees 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.