Room-Temperature Formaldehyde Oxidation over ZIF-Derived Co-Based Catalysts: Morphology-Dependent Co-N4 Sites and Enhanced Oxygen Activation

The development of high-efficiency non-noble-metal catalysts for HCHO removal is of great significance in indoor air purification. Zeolitic imidazolate frameworks (ZIFs) are characterized by large specific surface areas, well-defined porous structures, and tunable electronic properties, making them suitable for constructing single-atom catalysts with adjustable coordination environments. In this study, three Co-ZIF materials with distinct morphologies were synthesized and subsequently pyrolyzed, yielding cobalt-based catalysts with varied coordination structures. Among these catalysts, the Co–N–C(F) primarily features atomically dispersed Co species coordinated with four N atoms, forming Co-N4 active sites. Theoretical calculations indicate that the Co-N4 coordination structure exhibits enhanced oxygen activation compared to metallic cobalt sites, which is crucial for the degradation of intermediate products in the oxidation of HCHO. The Co–N–C (F) catalyst demonstrates superior activity in HCHO oxidation to even most noble metal catalysts. During a 710 h continuous test at 15 °C, the catalyst maintained 100% HCHO removal efficiency without observable deactivation. Simulation experiments further confirmed its practical applicability, with the catalyst module able to degrade 1 ppm of HCHO to <0.07 ppm within 2 h at room temperature. This work provides valuable insights for the development of commercial nonprecious metal catalysts for HCHO oxidation.