Acidic-basic-redox trifunctional Cu/P2W17V/{001}-TiO2 promotes photocatalytic lignin model conversion via tunable C-C/C-O cleavage

Abstract

Developing multifunctional photocatalysts is promising for selective and tunable lignin conversion to valuable chemicals. Herein, recyclable TCP photocatalysts with acidic, basic, and redox sites were developed by integrating {001} facet-containing TiO₂, Cu, and polyoxometalates P₂W₁₇V together. Lignin model compound with β-O-4 structure was effectively and adjustably transformed to aromatic aldehydes and phenol in photocatalysis, involving C_β-centered radical-mediated C_α-C_β bond cleavage and elimination-hydrolysis-induced C_β-O bond cleavage. C_α-C_β bond scission selectivity exceeded 90 % by prolonging reaction time, whereas C_β-O bond breakage was pronounced at short reaction time. Cu interacted with reacting species, improved charge transfer, and promoted C_β-O bond scission. P₂W₁₇V acted as acidic-basic-redox components, accelerated electron acceptance, and facilitated C_α-C_β bond cleavage. Additionally, alkaline lignin could also be photocatalyzed to vanillin. This work presents the first instance of C_α-C_β/C_β-O bond breakage modulation by varying reaction time. The design of trifunctional photocatalyst provides a new way for deriving valuable products from lignin.