Bimetallic AuCu/TiO2 with cooperative oxygen activation pathway for selective aerobic oxidation of vanillin to vanillic acid

A bimetallic AuCu/TiO 2 catalyst was synthesized via photo deposition for the selective oxidation of lignin-derived vanillin to vanillic acid. To compensate for Cu loss arising from galvanic replacement during sequential deposition, the precursor input ratio was optimized to Au:Cu = 2:2 to achieve a target molar composition of 3:1. TEM analysis revealed uniformly dispersed bimetallic nanoparticles with a mean diameter of 7.0 nm ± 2.1 nm, and XPS confirmed zerovalent deposition of both metals on TiO 2 surface. Also, ESR analysis detected Ti 3+ and additionally detected interfacial Cu 2+ paramagnetic species that were undetectable by XPS, supporting the electronic metal-support interaction between the metal nanoparticles and TiO 2 . O 2 -TPD measurements demonstrated a synergistic downshift in the atomic oxygen radical anion (O − ) desorption temperature from 434.8 °C (Au/TiO 2 ) to 391.4 °C in AuCu/TiO 2 , attributed to a sequential cooperative mechanism in which Cu facilitates primary O 2 activation to superoxide (O 2 − ), followed by further conversion to reactive O − at Au–TiO 2 interfaces. Finally, HPLC analysis of the vanillin oxidation confirmed that the bimetallic AuCu/TiO 2 catalyst exhibited the highest catalytic performance, achieving a vanillin conversion of 81.34 %, vanillic acid yield of 74.01 %, reaction rate of 2.77 mol · g −1 · h −1 , and the effects of various reaction conditions on the vanillin oxidation behavior were further investigated.