Solvent free hydrogenation of levulinic acid over in-situ generated Ni(0) stabilized by supported phosphomolybdic acid using formic acid as an internal hydrogen source

Abstract

The present work demonstrates, in-situ generation of Ni(0) nanoparticle stabilized by phosphomolybdic acid during the reaction. Nickel exchanged supported phosphomolybdic acid, Zirconia is use as support, (Ni–PMo12/ZrO2) was synthesized, characterized by various physicochemical methods and its catalytic activity was evaluated for the solvent free aqueous phase hydrogenation of lignocellulosic biomass-derived levulinic acid (LA) using formic acid (FA) as internal hydrogen source. FA is promising green hydrogen storage molecule which is selectively hydrogen removed from its chemical structure and utilized it in a variety of catalytic hydrogenation reaction. FA is unique hydrogen source with high hydrogen content (4.4 wt%), low flammability, low toxicity and ease in handling as compared to other hydrogen source. To achieve outstanding performance of the catalyst, a detailed assessment of vital reaction parameters (mole ratio of FA, catalyst amount, temperature and time) were carried out. The catalyst shows outstanding activity (94% conversion) with a very low amount of Ni(0) (0.00247 mmol) and high TON (1092) for LA hydrogenation. The catalyst was found to be sustainable up to three catalytic cycles without any alteration in activity. The hot filtration test shows true heterogeneous nature of the synthesized catalyst as well as stabilizing nature of PMo12. In situ formed Ni(0) was confirmed by thoroughly characterizing the regenerated catalyst by XPS, TEM, HR-TEM and STEM. The catalyst exhibits superior activity against reported catalysts. Also a plausible mechanism was proposed based on control experiments.