Synthesis of next-generation biofuel additive, γ-valerolactone, via hydrogenation of levulinic acid in the presence of formic acid over nickel-exchanged 12-tungstophosphoric acid supported on neutral Al2O3 and its kinetics study

Abstract

In this study, an innovative approach was developed for the synthesis of γ-valerolactone (GVL), a highly versatile keto-lactone and a promising eco-friendly fuel additive. For that, a sustainable catalyst, nickel-exchanged 12-tungstophosphoric acid supported on neutral Al₂O₃, was synthesized and extensively characterized using EDX, NH₃-TPD, BET, TGA, FT-IR, UV-Vis-NIR, XPS, ³¹P NMR, powder XRD, and TEM analyses. The catalytic activity was studied for the hydrogenation of levulinic acid using formic acid as an internal hydrogen source, which showcased its excellent performance by achieving 76% conversion and a high turnover number of 7451. Compared to existing research, 100% selectivity was demonstrated for GVL, a highly desired product, with an exceptionally high substrate-to-catalyst ratio of 4902. This not only emphasizes the efficiency of the catalyst but also highlights its superior catalytic activity and robust performance under mild reaction conditions, making it a more effective and sustainable option in comparison to previously reported catalysts. To determine the reaction order, detailed kinetic studies were conducted at various temperatures and over different reaction times (in hours). Additionally, this study presents the in situ reduction of Ni(II) to Ni(0), which was confirmed through X-ray photoelectron spectroscopy. The catalyst stability was established via a hot filtration test, and its reusability over multiple catalytic cycles confirmed its robust heterogeneous nature. This work highlights the catalyst potential in advancing sustainable and renewable energy solutions, making significant strides toward green and cost-effective processes.