Catalyst-Free Lignin Photothermal Valorization via Promoted Aromatic C-H Cleavage

Abstract

Chemical conversion offers a promising way to native lignin valorization, which serves as a sustainable alternative to petroleum-derived carbon and hydrogen sources. However, selective transformation of lignin using conventional thermochemical approaches remains challenging, since it is difficult to control the site for C-H/C/O bond activation and cleavage. While catalyst can significantly improve reaction selectivity, they prone to gradual deactivation. Herein, we introduce a light-driven selective lignin valorization to hydrogen and carbon under catalyst-free conditions. Broad-spectrum sunlight photons are absorbed by lignin’s conjugated chromophores and then trigger promoted aromatic C-H bond activation and dissociation, assisted by an excited-state conformation transition of lignin’s multi-aromatic building blocks. This results in the production of solid carbon and hydrogen-rich gas (63.3%) at a yield up to 190 mL H₂/g_Lignin, 112 times that of the conventional thermochemical rate. The solar thermal approach potentially offers a green solution to sustainable lignin valorization.