Spin-State Engineering in Ni-Doped Co3O4 Hollow Prisms for Enhanced Toluene Oxidation

Abstract

Although the spin state of active centers is crucial to catalytic activity, its role in VOC deep oxidation remains unclear. Here, we report a spin-state engineering strategy to construct Ni-doped Co3O4 hollow prisms (Ni-Co3O4-HP) via sacrificial-template etching. The mesoporous hollow architecture improves reactant diffusion and suppresses water accumulation, while Ni selectively substitutes octahedral Co3+ sites without forming segregated NiO. This local coordination perturbation induces a low-spin to high-spin transition of adjacent Co3+ centers, upshifts the d-band center, weakens Co-O bonding, and lowers the formation energy of oxygen vacancies. As a result, the optimized Ni-Co3O4-HP(2:1) catalyst achieves 90% toluene conversion at 239 °C, 28 °C lower than pristine Co3O4, with high stability. In situ DRIFTS, combined with XAS and DFT calculations, reveals that high-spin Co3+ sites and oxygen vacancies act as dual active centers in a Mars-van Krevelen pathway, accelerating methyl C-H activation and intermediate mineralization via rapid lattice oxygen replenishment.