Role of Coordination Environment in Synergistic Catalysis: A Molecular Orbital Perspective on M ₁ M ₂ N ₆ Catalysts

High Resolution Image Download MS PowerPoint Slide Visualizing the coordination environment-dependent synergistic mechanisms that govern the structural stability and adsorption behavior of dual-atom catalysts (DACs) is pivotal for precise catalyst design. However, insights into these mechanisms at the molecular orbital level remain elusive. Herein, we present large-scale density functional theory calculations to elucidate how synergistic effects arise from the combination of d atomic orbitals into molecular orbitals between M 1 and M 2 sites, with notable variations observed from M 1 –N 3 –M 2 –N 3 –C to M 1 –N 4 –M 2 –N 4 –C. We identify an average weakening of M 1 /M 2 –N bond strength in M 1 –N 3 –M 2 –N 3 –C relative to M 1 –N 4 –M 2 –N 4 –C, which is attributed to a shift from direct d x 2 –y 2 orbital overlap to nitrogen-mediated interactions involving the hybridization of bridge nitrogen 2 p orbitals. Using hydrogen as a model adsorbate, we demonstrate that hydrogen adsorption on M 1 –N 3 –M 2 –N 3 –C shifts from wild modulation via a bridge configuration to mild modulation through an end-on configuration, signifying a selective orbital coupling from d x 2 –y 2 to d z 2 orbitals. In contrast, hydrogen adsorption on M 1 –N 4 –M 2 –N 4 –C exhibits only mild modulation via an end-on configuration. This behavior is ascribed to the symmetry constraints of antibonding ( d - d / d *)- p * molecular orbitals near the Fermi level, mediated by nitrogen-mediated d z 2 - d z 2 * molecular orbitals. Furthermore, machine learning analyses corroborate these coordination environment-dependent synergistic mechanisms. Our findings provide a comprehensive molecular orbital-level understanding of how the interplay between coordination environments and electronic structures influences the properties of M 1 M 2 N 6 catalysts, thereby establishing a theoretical framework for enhanced DACs design.