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

Abstract

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.