Role of Brønsted and Lewis acid sites on Ni/TiO2 catalyst for vapour phase hydrogenation of levulinic acid: Kinetic and mechanistic study

The TiO2 supported Ni catalysts were investigated for vapour phase hydrogenation of aqueous levulinic acid at ambient pressure. Ni/TiO2 demonstrated high selectivity of γ-valerolactone (GVL) compared to noble metal (Pt, Pd, Ru) catalysts. The surface acid sites played an important role on the product distribution. Pyridine adsorbed DRIFT spectra revealed that the Lewis acid sites on Ni/TiO2 were responsible for high selectivity of γ-valerolactone. In contrast, the Brønsted acid sites are prone to ring opening of γ-valerolactone to produce valeric acid and hydrocarbons. The physicochemical characteristics of Ni/TiO2 were correlated with γ-valerolactone rates. Based on the kinetic study a mechanism has been proposed.