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

Abstract

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.

Advances in porous and nanoscale catalysts for viable biomass conversion

“…An efficient one-pot process by combining both lignin depolymerization and hydrodeoxygenation was developed using a combination of Cu-Mg-Al mixed oxide with various Ni-based catalysts (Ni/SiO 2 , Ni 2 P/SiO 2 , and Ni/amorphous silica-alumina). 380 Results indicated that monomer yield and product selectivity were highly dependent on the nature of Ni catalyst. Chen et al 381 found that oxygen vacancies and Mo 6+ together with Mo 5+ species, formed during the partial pre-reduction treatment, act as the active sites for lignin depolymerization in supercritical ethanol.…”

Preparative Aspects of Supported Ni2P Catalysts for Reductive Upgrading of Technical Lignin to Aromatics

“…We discussed and explained the synergistic and cooperative activation of this optimized two-catalysts system in terms of monomeric product yield and HDO selectivity in more detail in a recent paper [39]. Briefly, the synergy relates to the in situ production of hydrogen by the CuMgAlO x component, maintaining the Ni 2 P surface in its active state.…”

Promising Techniques for Depolymerization of Lignin into Value‐added Chemicals

“…For example, about 55 % and 35 % yields of 4‐n‐propanolsyringol (based on Klason lignin) were obtained via hydrogenolysis of transgenic poplar and birch lignin, respectively . Such high yields of single product were contributed to stabilized pretreatment and effective catalysts which worked not well under harsher conditions ,,. Those results indicate that C3‐phenols are the only phenols that are promising to industrial production.…”