Hydrogenation of Furfural with Nickel Nanoparticles Stabilized on Nitrogen-Rich Carbon Core-Shell and Its Transformations for the Synthesis of γ-Valerolactone in Aqueous Conditions

In this article, we report the synthesis of nitrogen-rich carbon layer-encapsulated Ni(0) nanoparticles as a core-shell structure (Ni@N/C-g-800) for the catalytic hydrogenation of furfural to furfuryl alcohol. The nickel nanoparticles were stabilized by the nitrogen-rich graphitic framework, which formed during the agitation of nickel acetate-impregnated cucurbit[6]uril surface in a reducing atmosphere. Furthermore, the catalyst was characterized using various physicochemical methods such as powder X-ray diffraction, Raman, field emission-scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller surface area, CO₂-temperature-programmed desorption, inductive coupled plasma, and CHN analyses. The nitrogen-rich environment of the solid support with metallic Ni nanoparticles was found to be active and selective for the catalytic hydrogenation of furfural with molecular H₂ in an aqueous medium at 100 °C. To understand the reaction mechanism, the diffuse reflectance infrared Fourier transform study was performed, which revealed that the C=O bond is activated in the presence of a catalyst. In addition, we have extended our methodology toward the synthesis of "levulinic acid" and " γ-valerolactone", by successive hydrolysis and hydrogenation of furfuryl alcohol and levulinic acid, respectively, in an aqueous medium. Moreover, the heterogeneous catalysts used in all of the three consecutive steps help in recovery and recycling of the catalyst and easy separation of products.