Dual A-B-sites cooperation in AB₂O₄ spinel-type Ni-Co oxides for efficient dual-fuel engine exhaust purification

The natural gas-diesel (dual-fuel) engine is a promising transitional power system for improving energy utilization efficiency and enabling flexible fuel substitution in low-carbon transportation, yet its energy and climate benefits are constrained by the simultaneous emission of soot and CH₄. Herein, we elaborately constructed the single-crystal spinel-type Ni-Co oxides with a pore-rich ultrathin structure, and Ni cations enable dual A-B-sites substitution in Co-based spinel oxides. The pore-rich ultrathin structure in nanosheets enhances the mass transfer of gaseous reactants by shortening diffusion paths and reducing diffusion resistance, and triatomic Ni-O-Co synergistic sites in Ni-Co spinel nanosheets can simultaneously achieve adsorption-activation of NO, O₂ and CH₄. The dual A-B-sites substituted Ni_1.5Co_1.5O₄ catalyst exhibits high catalytic performance and stability during simultaneous soot and CH₄ oxidation, i.e., its temperatures for 90% conversion of soot and CH₄ are 376 and 330 °C, respectively. Based on experimental characterizations and theoretical calculations, the Co site in triatomic Ni-O-Co site facilitates catalytic NO oxidation to NO₂, which is a key step in NO_x-assisted soot oxidation mechanism; while the Ni site activates the C-H bonds, thereby boosting CH₄ oxidation to CO₂. Dual A-B-sites cooperation reconstructs Ni/Co 3d electronic structure and induces a high-spin state, thereby accelerating electron transfer at triatomic Ni-O-Co synergistic sites. It enhances the adsorption-activation capacity of Ni/Co-sites, and activates adjacent lattice oxygen for boosting simultaneous soot and CH₄ purification. This work provides an earth-abundant catalyst for low-carbon and energy-efficient aftertreatment of dual-fuel engine exhaust.