Synergistic (Pd₁-Cu₁)₅/ZrO₂ nanoarchitectures: Catalytic valorization of larch tannin into high-antioxidant oligomers

To address the low bioavailability of polymeric proanthocyanidins (PPCs) in larch tannin, we developed a bimetallic catalyst, (Pd₁-Cu₁)₅/ZrO₂, to convert PPCs into bioactive oligomeric proanthocyanidins (OPCs) via catalytic depolymerization. SEM, XRD, and XPS characterization indicate a high specific surface area and Pd-Cu synergistic active sites; combined with ZrO₂ solid acid sites, these features enhance substrate adsorption and CC bond cleavage. Single-factor optimization showed that under 0.05 g catalyst, 4 MPa H₂, 140 °C and 3 h, the average degree of polymerization decreased from 9.5 to 2.48, corresponding to a 74 % degradation rate. The degradation products exhibited markedly improved antioxidant activity in DPPH and ABTS⁺ assays.