γ-Valerolactone Production from Furfural Residue with Formic Acid as the Sole Hydrogen Resource via an Integrated Strategy on Au-Ni/ZrO2

The integrated conversion of raw lignocellulosic biomass selectively to gamma-valerolactone (GVL), using formic acid as the sole hydrogen resource, is of great importance from economic and engineering viewpoints. In this work, we developed an integrated strategy for GVL production from furfural residue. Wherein, levulinic acid and formic acid were produced from furfural residue using SnCl4 as a catalyst in the first step, which were subsequently employed as feedstock for GVL production by the catalysis of a developed bimetallic Au-Ni/ZrO2 catalyst in the second step. It was revealed that an appropriate amount of Ni loading could promote the reduction of Au delta+ to Au-0, and facilitated Au-0 dispersion with less aggregation, when compared to the Au/ZrO2 catalyst. Ni loading also slightly enhanced the amount of Lewis acid on the catalyst. These contributions enabled the high activity of 1Au-2Ni//ZrO2 catalyst with a very small amount of Au loading for the hydrogenation of levulinic acid with formic acid as hydrogen resource, and the subsequent dehydration reaction. 2-Methyltetrahydrofuran extraction before the second step effectively removed the byproducts, possibly polymer/humins, formed simultaneously with levulinic acid, thereby significantly alleviating catalyst poison. With the addition of extra formic acid, overall yields of GVL as high as 51.5 mol % were achieved, based on the total C6 sugar in furfural residue. This work gives a potential strategy for the production of GVL directly from raw lignocellulosic biomass, using formic acid as the sole hydrogen resource.