Vapor phase hydrogenation of aqueous levulinic acid over hydroxyapatite supported metal (M = Pd, Pt, Ru, Cu, Ni) catalysts.

• Ca5(PO4)3(OH) a suitable support for Ru in hydrogenation of aqueous levulinic acid
• Enhanced gamma-valerolactone yields with H2O as solvent
• Weak Bronsted acid sites on Ru/hydroxyapatite led to gamma-valerolactone
• Pyridine adsorbed IR spectra revealed weak Bronsted acid sites on Ru/hydroxyapatite
• High TOF of γ-valerolactone over Ru/Ca5(PO4)3(OH) compared to Pt and Pd.

Ca5(PO4)3(OH) (HAP) supported metal (Ru, Pt, Pd, Cu and Ni) catalysts were examined for vapour phase hydrogenation of aqueous levulinic acid (LA). Ru/HAP demonstrated higher TOF of γ-valerolactone (gVL) over the other metal catalysts. The LA dehydration products such as angelica lactones (both α- and β-AL) were formed significantly over Pt, Pd, Ni and Cu/HAP catalysts. Influence of Bronsted and Lewis acid sites was exemplified by pyridine adsorbed FT-IR studies on Ru/HAP that exhibited very weak band due to Bronsted sites at 1552 cm−1 and a strong band at 1450 cm−1 attributed to Lewis acid sites. Ru supported on SO42−_HAP demonstrated selective dehydration of LA to α-angelica lactone. Hydrogenation activity of Ru was diminished while supported on SO42− -HAP, quite contrast to this the fresh HAP behaved as a selective support for Ru towards GVL formation. Thus, HAP has been identified as suitable support for Ru in the conversion of LA at ambient pressure.

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