Is oxidation–reduction a real robust strategy for lignin conversion? A comparative study on lignin and model compounds

Abstract

The enigma of the oxidation–reduction strategy for lignin valorization was disclosed over heterogenous catalysts and was compared with model compound studies.

Catalytic Scissoring of Lignin into Aryl Monomers

“…However, it should be noted that the pretreatment of lignin should be carried out carefully because it may also lead to an undesired change in the lignin structure. In some cases, the conversion of real lignin contrasted with those of model compounds, where the oxidative pretreatment increased the efficiency of the β‐O‐4 cleavage, mostly due to the undesired change in the lignin structure during lignin oxidation …”

Photochemical evolution of hydrogen peroxide on lignins

“…22,23 Electrochemical processes are also of major interest for targeted chemical transformations and lignin valorization to useful chemicals. 20,24,25 Heterogenous ( photo)oxidation of lignins on catalysts is one valorization direction, 26,27 and this raises the idea that such processes maybe can be driven by photochemistry alone. The starting question of this work is: Do lignins themselves also afford photo-redox activity, in particular oxygen reduction to hydrogen peroxide?…”

A Comparison of Phenolic Monomers Produced from Different Types of Lignin by Phosphotungstic Acid Catalysts

“…As shown in Figure c, the G structural units are the whole aromatic region of the pine lignin samples (100 wt %) and signals of S or H are not discovered, indicating that the pine lignin samples appertain to the G types. In Figure e, the amount of H, G and S units observed in the aromatic region are 20.8 wt %, 32.7 wt % and 46.5 wt %, respectively, suggesting straw lignin samples is a typical SGH types grass lignin ,…”