Synergy in Lignin Upgrading by a Combination of Cu-Based Mixed Oxide and Ni-Phosphide Catalysts in Supercritical Ethanol

[Image: see text] The depolymerization of lignin to bioaromatics usually requires a hydrodeoxygenation (HDO) step to lower the oxygen content. A mixed Cu–Mg–Al oxide (CuMgAlO(x)) is an effective catalyst for the depolymerization of lignin in supercritical ethanol. We explored the use of Ni-based cocatalysts, i.e. Ni/SiO(2), Ni(2)P/SiO(2), and Ni/ASA (ASA = amorphous silica alumina), with the aim of combining lignin depolymerization and HDO in a single reaction step. While the silica-supported catalysts were themselves hardly active in lignin upgrading, Ni/ASA displayed comparable lignin monomer yield as CuMgAlO(x). A drawback of using an acidic support is extensive dehydration of the ethanol solvent. Instead, combining CuMgAlO(x) with Ni/SiO(2) and especially Ni(2)P/SiO(2) proved to be effective in increasing the lignin monomer yield, while at the same time reducing the oxygen content of the products. With Ni(2)P/SiO(2), the lignin monomer yield was 53 wt %, leading to nearly complete deoxygenation of the aromatic products.