The depolymerization
of lignin to bioaromatics usually requires
a hydrodeoxygenation (HDO) step to lower the oxygen content.
A mixed Cu–Mg–Al oxide (CuMgAlOx) is an effective catalyst for the depolymerization of lignin
in supercritical ethanol. We explored the use of Ni-based cocatalysts,
i.e. Ni/SiO2, Ni2P/SiO2, 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 CuMgAlOx. A drawback of using an acidic support is extensive dehydration
of the ethanol solvent. Instead, combining CuMgAlOx with Ni/SiO2 and especially Ni2P/SiO2 proved to be effective in increasing the lignin monomer yield,
while at the same time reducing the oxygen content of the products.
With Ni2P/SiO2, the lignin monomer yield was
53 wt %, leading to nearly complete deoxygenation of the aromatic
products.