New Insights into Green Protocols for Oxidative Depolymerization of Lignin and Lignin Model Compounds

Abstract

Oxidative depolymerization of lignin is a hot topic in the field of biomass valorization. The most recent and green procedures have been herein detailed. Photochemical and electrochemical approaches are reviewed highlighting the pros and cons of each method. Mechanochemistry activated strategies are able to combine oxidation and depolymerization in the deconstruction of lignin. Homogenous and heterogeneous catalytic systems are exemplified stressing the green aspects associated with both the procedures. Solvent-free approaches as well as those carried out in alternative media are listed. Finally, the few examples of selenium catalyzed lignin valorization reported so far are cited.

Electro-oxidative depolymerization of lignin for production of value-added chemicals

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Selective aerobic oxidative C–C bond cleavage using a high-entropy oxide-derived multimetallic catalyst

“…The obtained products have promising applications in the chemical industry. In past investigations, some homogeneous or heterogeneous catalysts have been used to achieve oxidative cleavage of the C–C bond; 7–10 however, there are the shortcomings of severe reaction conditions, high temperature and low product selectivity. 11 Thus, developing a stable and active heterogeneous catalyst is still a challenge nowadays.…”

Mechanocatalytic Oxidative Cracking of Poly(ethylene) Via a Heterogeneous Fenton Process

“…The collisions can create transient sites on the surface of solid catalysts and hot spots that are characterized by rapid local temperature rises, followed by dissipation of heat throughout the feedstock and catalyst within the vessel . Mechanochemical processes for depolymerization of biomass, most notably cellulose and lignin, − and plastics such as polystyrene (PS) and poly­(ethylene terephthalate) (PET) − have been reported.…”