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

The depolymerization of lignin to bioaromatics usually requires a hydrodeoxygenation (HDO) step to lower the oxygen content. A mixed Cu-Mg-Al oxide (CuMgAlO ) is an effective catalyst for the depolymerization of lignin in supercritical ethanol. We explored the use of Ni-based cocatalysts, i.e. Ni/SiO, NiP/SiO, 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 . A drawback of using an acidic support is extensive dehydration of the ethanol solvent. Instead, combining CuMgAlO with Ni/SiO and especially NiP/SiO proved to be effective in increasing the lignin monomer yield, while at the same time reducing the oxygen content of the products. With NiP/SiO, the lignin monomer yield was 53 wt %, leading to nearly complete deoxygenation of the aromatic products.