Insights into structure-activity relationships in efficient silica-supported Ni catalysts for selective hydrogenation of levulinic acid

Upgrading biomass-derived levulinic acid (LA) with greater carbonyl (C=O) group activation is crucial in converting biomass and its derivatives into valuable biochemicals and biofuels. In the present investigation, highly dispersed Ni nanoparticle catalysts supported on various supports (HZSM-5, SiO2, SBA-15, and COK-12) were developed for the selective catalytic hydrogenation of LA to ?-valerolactone (GVL) under vapor-phase conditions. The pyridine adsorbed-FTIR profiles revealed the existence of Bronsted and Lewis acid sites. The Bronsted acidic sites are crucial for forming angelica lactones as intermediates and dehydration of 4-hydroxy valeric acid to ?-valerolactone, whereas the Lewis acidic sites are useful for the production of 4-hydroxy valeric acid as an intermediate. Electron microscopy images reveal that the NiCOK-12 catalyst exhibits a smaller particle size (TEM average particle size = 6.8 nm) than the remaining catalysts. H-2-TPR and pulse chemisorption results showed the highly dispersed metallic Ni on the support and strong metal-support interaction between the metallic Ni and support matrix. Among all the synthesized catalysts, the Ni-supported COK-12 catalyst exhibited higher catalytic performance in the selective hydrogenation of LA to GVL products. The best performance of the NiCOK-12 catalyst corresponded to greater Ni dispersion, superior AMSA, ample Lewis acidic sites, smaller Ni particle size, and strong metal-support interactions. The NiCOK-12 catalyst showed more stability in the constant conversion of LA and GVL formation until 30 h of reaction time. The rationally designed earth-abundant and inexpensive catalysts in this work show controllable catalytic activity and robust stability to upgrade biomass-derived platform molecules into valuable chemicals and biofuels.