Vapour phase hydrocyclisation of levulinic acid to γ-valerolactone over supported Ni catalysts

Abstract

Various Ni catalysts with 30 wt% Ni content were prepared by a conventional wet impregnation method using different supports such as Al₂O₃, SiO₂, ZnO, ZrO₂, TiO₂ and MgO. The prepared catalysts have been characterised by XRD, N₂ physisorption, H₂ pulse chemisorption, pyridine adsorbed FTIR, ammonia-TPD, TPR, XPS and TEM techniques. Pyridine adsorbed IR patterns reveal the presence of both Lewis as well as Brønsted acid sites which are responsible for the dehydration of the intermediate 4-hydroxy valeric acid to yield γ-valerolactone. Ammonia-TPD profiles also showed the presence of acidic sites in all catalytic systems, which explains the formation of the targeted product. The better activity shown by the 30 wt% Ni/SiO₂ catalyst (signifying maximum productivity, i.e., 0.8506 kg_GVL kg_catalyst⁻¹ h⁻¹ at 250 °C) is due to the presence of a greater number of surface Ni species. The present work aims to provide a continuous down flow process for the hydrocyclization of one of the biomass derived platform molecules such as levulinic acid over non-noble metal (nickel) based catalysts. The Ni/SiO₂ catalyst is tested for 25 h and found to be stable during the time on stream which reveals its robustness.