Beneficial Synergistic Intermetallic Effect in ZnCo₂O₄ for Enhancing the Limonene Oxidation Catalysis

Abstract

Utilization of naturally occurring limonene from renewable biomass as a key starting material for the synthesis of valuable chemicals is a promising avenue to reduce both the dependence on nonrenewable fossil fuels and global CO₂ emission. Herein, we report a highly active tremella-like ZnCo₂O₄ catalyst for the selective oxidation of limonene with molecular oxygen under mild reaction conditions. The developed ZnCo₂O₄ catalyst exhibits an appealing reaction performance with a limonene conversion of 93.5% (reaction rate of 0.0823 mmol g_cat^-1 h^-1) and selectivity of 75.8% for 1,2-limonene oxide (LO), far outperforming the monometallic oxides of ZnO and Co₃O₄. Detained experimental characterizations and analyses manifest that the substitution of Zn into the Co₃O₄ framework can facilitate the formation of more unsaturated coordination sites and oxygen vacancies due to the modified chemical environment of Co atoms, inducing a beneficial synergistic intermetallic effect for the limonene oxidation catalysis.