Room-Temperature Formaldehyde Oxidation over ZIF-Derived Co-Based Catalysts: Morphology-Dependent Co-N ₄ 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.