Oxidative conversion of palm kernel shell waste biomass over Co–Cu/Al-doped HY and Co–Cu/desilicated HY catalysts

Abstract

The valorization of biomass represents a promising alternative to the use of fossil fuels. Palm kernel shell (PKS) lignin was effectively fractionated and oxidatively depolymerized into valuable phenolic monomers using bimetallic Co–Cu catalysts supported on modified zeolite HY. The catalyst support was optimized by modifying zeolite HY through aluminum doping (Al-HY) and desilication (D_S-HY) to fine-tune its acidity and pore structure. The bimetallic catalysts were synthesized using these modified supports with 10 wt% total metal loading at a Co:Cu ratio of 4:1. Characterization techniques, including BET, XRF, NH₃-TPD, H₂-TPR, XPS, and TEM, confirmed successful metal incorporation and preserved crystallinity, hierarchical porosity, and redox-active metal states. Catalytic oxidative cracking was conducted in a 9:1 isopropanol/water medium with hydrogen peroxide as the oxidant at atmospheric pressure. The implementation of the desilicated zeolite-supported bimetallic catalyst (10 %Co₄-Cu₁/D_S-HY) substantially improved the catalytic reaction, achieving a lignin-derived monomer yield of 37.62 % and 86.75 % biomass conversion. This represents a 9.83 % improvement over the conventional zeolite HY-supported bimetallic catalyst. The enhanced activity is attributed to the synergistic interaction between the Co–Cu redox sites and the tailored acidity and mesoporosity of the modified zeolite support. Furthermore, catalyst reusability tests demonstrated that the optimized catalyst retained over 90 % of its initial activity after four reaction cycles, confirming its stability and potential for industrial applications. The insights from this study are expected to drive progress in lignin-based biorefinery technologies.