Ligand-tailored Co-O bond strength in MOF-derived Co₃O₄ for boosting NO oxidation

Recent intensive research has established that modulating oxygen species activity in transition metal oxide (TMO) catalysts is pivotal for catalytic NO oxidation, which is regarded as a key step that governs NO_x abatement technologies. Despite this recognition, the fundamental relationship between metal–oxygen bond strength and the intrinsic catalytic properties of TMOs remains poorly understood. To address this gap, we fabricated dodecahedral-, rod-, and sphere-like Co₃O₄ catalysts (Co₃O₄-D, Co₃O₄-R, Co₃O₄-S) with tunable Co-O bond covalency using a MOF-templating strategy. Systematic evaluation revealed a distinct activity trend, wherein Co₃O₄-D displays the best activity, for which a maximal NO conversion (82.0 %) could be attained at 250 °C under a WHSV of 150, 000 mL·g⁻¹·h⁻¹, followed by Co₃O₄-R (75.0 % at 275 °C) and Co₃O₄-S (66.0 % at 300 °C). Mechanistic studies demonstrate that weakened Co-O bond strength enhances catalytic function through dual pathways: (1) lowering the energy barrier for oxygen vacancy formation, which accelerates surface lattice oxygen activation and improves the intrinsic redox capability; (2) preferentially exposing undercoordinated Co-O sites that serve as main active sites for NO adsorption and subsequent conversion to NO₂. This work provides a theoretical foundation for designing high-efficiency NO oxidation catalysts by leveraging MOF-templated structural and electronic regulation.