Hierarchically porous single catalyst Ru/HPW/UiO-66 with synergistic acid/metal sites for one-pot catalytic synthesis of γ-valerolactone

Abstract

γ-Valerolactone (GVL) is an important lignocellulosic platform molecule with huge potential for various industrial and chemical applications, which is usually produced using levulinic acid (LA) or its esters as raw materials. However, a two-step reaction process in which hydrogenation of the carbonyl groups on metal sites and subsequent lactonization catalyzed by acidic sites over multiple catalysts has generally been needed to realize this synthesis. In this work, a hierarchically multifunctional single catalyst of Ru/phosphotungstic acid/hierarchically porous UiO-66 (Ru/HPW/HP-UiO-66), simultaneously integrated with acidic and metal sites, has been fabricated via a simple strategy and successfully applied in the one-pot synthesis of GVL using methyl levulinate (ML) as the raw material. The hierarchically porous and nanosized (∼15 nm) HP-UiO-66 can not only provide sufficient space for the mass transfer of substrates but also favors the loading of bulk HPW molecules, which can effectively mediate the catalytic activities and stability of Ru NPs using the confined pore effect of UiO-66 and the strong interaction between HPW and Ru. When applied in the one-pot synthesis of GVL, the hierarchical Ru/HPW/HP-UiO-66 catalyst showed excellent catalytic activity (>97% yield) and stability (maintained after 7 successive cycles) for GVL. More importantly, the hierarchical catalyst also exhibited an extraordinary performance in the hydrogenation of different unsaturated hydrocarbons in aqueous solution. It is expected that our study offers a novel route to biomass upgrades involving metal/acid bifunctional synergistic catalysts.