ZIF-derived spinel CoMn2O4 with hierarchically porous architecture and optimized surface chemistry for efficient low-temperature fast NH3-SCR

Abstract

To address the intrinsic limitations of conventional spinel oxides in low-temperature NH₃-SCR, a hierarchically porous spinel CoMn₂O₄ with optimized surface chemistry was constructed via a ZIF-derived strategy. By leveraging the structural directivity and compositional tunability of the ZIF precursor, CoMn-ZIF displays a sheet-like architecture containing interlinked pores and numerous surface hollows. This effectively mitigates nanoparticle agglomeration, while enhancing gas-phase diffusion and maximizing active site accessibility. Beyond this morphology optimization, this approach simultaneously modulates the key surface chemical properties, characterized by enriched oxygen vacancies, enhanced redox capacity, elevated surface active oxygen species, as well as a high density of Brønsted and Lewis acid sites. Such integrated characteristics enhance NH₃ adsorption and NO oxidation, which in turn accelerate the onset and progression of the fast SCR pathway. As a result, CoMn-ZIF shows exceptional low-temperature NH₃-SCR performance with above 90 % NO conversion at 150 °C, outperforming conventional spinel CoMn. Moreover, CoMn-ZIF also exhibits remarkable catalytic stability under diverse operating conditions, including fluctuating NO concentrations, varying space velocities, and the presence of H₂O and SO₂, underscoring its suitability for operation in variable industrial environments. In situ DRIFTS confirms the formation of NO₂ and -NH₂NO intermediate, providing direct evidence for the dominance of the fast SCR pathway. This study presents a rational strategy for the design of high-performance spinel oxide catalysts targeting efficient low-temperature NH₃-SCR applications.