Toward the Photocatalytic Valorization of Lignin: Conversion of a Model Lignin Hexamer with Multiple Functionalities

The valorization of biomass via photocatalysis is an area of expanding research with advances in new technologies and materials with a view toward enhanced sustainability being reported. A significant challenge within this field, however, is understanding the impact photocatalysis has on more recalcitrant compounds present in biomass, such as lignin. Moreover, the current state of lignin model compound research is still largely focused on the breakdown of small models containing typically only one linkage. Described herein is the use of TiO2-mediated photocatalysis for the degradation of a representative hexameric lignin model compound which contains multiple linkages (e.g., 5-5 ' , beta-5, and beta-O-4). The results revealed that while cleavage of the beta-5 and beta-O-4 occurred, the 5-5 ' appeared to remain intact within the identified reaction intermediates. To understand some of the more fundamental questions, a dimeric compound with a biphenyl linkage was synthesized and studied under photocatalytic conditions. The proposal of intermediates and pathways of degradation based on the studies conducted is presented and discussed herein.

Automated summary

The valorization of biomass via photocatalysis is an expanding research field, but there is a need for further investigation into the impact of photocatalysis on recalcitrant compounds in biomass, such as lignin. Current research on lignin model compounds mainly focuses on the breakdown of small models with few linkages.