Selective production of γ-valerolactone or 1,4-pentanediol from levulinic acid/esters over Co-based catalyst: Importance of the synergy of hydrogenation sites and acidic sites

Abstract

γ-Valerolactone (GVL) or 1,4-pentanediol (1,4-PDO) are the value-added chemicals, selectivities of which from conversion of levulinic acid/ester depend on balanced distribution of metallic sites and other active sites of the catalysts. In this study, Co-based catalysts with various precursors of LDH structures were synthesized to investigate the roles of hydrogenation, acidic and basic sites in the formation of GVL and 1,4-PDO from ethyl levulinate (EL). The results indicated that Al in Co-Mg-Al or Co-Al created acidic sites and facilitated cobalt dispersion by developing porous structures and strong interaction with Co species. Kinetic study indicated that the conversion of GVL controlled the formation rate of 1,4-PDO from EL. The superior catalytic activity and recyclability were observed over Co-Mg-Al and Co-Al catalysts, with the selectivity of both of GVL and 1,4-PDO reaching 98%, which was equivalent or superior to noble-metal based catalysts. Brønsted acidic sites in catalyst could facilitate the lactonization of ethyl 4-hydroxyvalerate to GVL and the ring-opening of GVL to 1,4-PDO, by cooperating with hydrogenation sites. Lewis acidic sites improved the adsorption of substrates and reaction intermediates, accelerating the ring-opening of GVL. The synergy between acidic sites together with hydrogenation sites was the key for achieving the excellent catalytic performance.