Pd/Nb2O5/SiO2 Catalyst for the Direct Hydrodeoxygenation of Biomass-Related Compounds to Liquid Alkanes under Mild Conditions

A simple Pd-loaded Nb2O5/SiO2 catalyst was prepared for the hydrodeoxygenation of biomass-related compounds to alkanes under mild conditions. Niobium oxide dispersed in silica (Nb2O5/SiO2) as the support was prepared by the sol-gel method and characterized by various techniques, including N-2 adsorption, XRD, NH3 temperature-programmed desorption (TPD), TEM, and energy-dispersive X-ray spectroscopy (EDAX) atomic mapping. The characterization results showed that the niobium oxide species were amorphous and well dispersed in silica. Compared to commercial Nb2O5, Nb2O5/SiO2 has significantly more active niobium oxide species exposed on the surface. Under mild conditions (170 degrees C, 2.5 MPa), Pd/10% Nb2O5/SiO2 was effective for the hydrodeoxygenation reactions of 4( 2-furyl)-3-buten-2-one (aldol adduct of furfural with acetone), palmitic acid, tristearin, and diphenyl ether (model compounds of microalgae oils, vegetable oils, and lignin), which gave high yields (> 94%) of alkanes with little C-C bond cleavage. More importantly, owing to the significant promotion effect of NbOx species on C-O bond cleavage and the mild reaction conditions, the C-C cleavage was considerably restrained, and the catalyst showed an excellent activity and stability for the hydrodeoxygenation of palmitic acid with almost no decrease in hexadecane yield (94-95%) in a 150 h time-on-stream test.