Stabilizing Pt-Fe dual-metal single atoms in ZIFs: a pathway to form heterogeneous catalysts

Dual-atom catalysts (DACs) show promise for enhanced catalytic performance through synergistic metal interactions, yet their formation and stability during high-temperature pyrolysis remain poorly understood. In this study, we report the atomic-scale structural evolution and stabilization of Pt-Fe hetero-pairs anchored on N-doped carbon derived from zeolitic imidazolate framework-8 (ZIF-8) using in situ high-resolution high-angle annular dark-field scanning transmission electron microscopy (HR HAADF-STEM) during pyrolysis up to 900 °C. Post-pyrolysis analysis of Pt(acac)₂/Fe(acac)₃-encapsulated ZIF (denoted as PF-ZIF) at 900 °C confirms the formation of stable Pt-Fe hetero-pairs, driven by enhanced electronic coupling with the N-doped carbon matrix. In contrast, the Fe atoms in Fe(acac)₃-encapsulated ZIF (denoted as F-ZIF), tend to aggregate into Fe₃C nanoparticles (NPs) under electron beam exposure at 500 °C, rather than remaining as Fe single atoms (SAs). Additionally, increasing Pt and Fe precursor concentrations in PF-ZIF (denoted as HPF-ZIF) drives a transition from SAs to amorphous nanoclusters (NCs), culminating in crystalline Pt-doped α-Fe NPs, highlighting robust Pt-Fe bonding and temperature-dependent phase transitions. Our findings empower the precise tailoring of synthesis strategies, offer insights into atomic-scale structural evolution mechanisms, and establish fundamental design principles for advancing dual-metal materials.