Metal Precursor Composition Is Key in the Synthesis of Pd Single Atom Catalysts

Single-atom catalysts (SACs) with atomically dispersed platinum-group metals (PGMs), such as Pd on γ-Al₂O₃, offer high metal utilization and distinct catalytic behavior. However, achieving atomic dispersion remains challenging due to metal aggregation during deposition or post-treatment, even at low PGM loadings (≪1 wt %). Developing reliable SACs thus requires clear guiding principles for promoting atomic dispersion. This study demonstrates the influence of metal precursor characteristics (nature of counterions and coordinating ligands) on the resulting structure of deposited Pd domains on γ-Al₂O₃ during scalable impregnation synthesis. It is shown that Pd-nitrate, a commonly used precursor, forms polynuclear hydroxo complexes in aqueous solution, resulting in Pd cluster deposition on γ-Al₂O₃. In contrast, Pd-ammonia precursors, such as tetraammine Pd nitrate, inhibit aggregation via NH₃ ligand stabilization, leading to improved atomic dispersion. This study underscores the necessity of optimizing precursor characteristics to maximize the atomic dispersion of metals, enabling more reproducible development of SACs.