Direct Conversion of Levulinic Acid into Valeric Biofuels Using Pd Supported Over Zeolites as Catalysts

A series of Pd-based catalysts was prepared by incipient wetness impregnation over different acidic supports: amorphous SiO₂-Al₂O₃, ZSM5 and beta zeolites. In addition to the effect of the support, other variables like the metal loading (0, 1, 2 and 4 wt%) on ZSM5 were tested in the direct conversion of levulinic acid (LA) to valeric biofuels (valeric acid/ester). The best result, a 92% yield of valeric biofuels, was obtained for a 2 wt% Pd supported on ZSM5 catalyst (2PdZSM5) after 8 h of reaction at 240 °C. Characterization techniques such as FTIR spectroscopy (using deuterated acetonitrile and CO as probe molecules), TEM and XPS were employed to explain this catalytic performance. FTIR spectra with deuterated acetonitrile evidenced the moderate acidity (in terms of concentration and strength) of the 2PdZSM5 catalyst, a desirable feature for the proper realization of this reaction. It has been observed that the acidity of the support favors the Pd dispersion, but it is less relevant for its catalytic properties. Finally, the stability of a representative catalyst was demonstrated under flow conditions for over 90 h, obtaining moderate but stable yields for the 2PdZSM5 catalyst.