Convergent Active Site Evolution in Platinum Single Atom Catalysts for Acetylene Hydrochlorination and Implications for Toxicity Minimization

Platinum single atoms anchored onto activated carbon enable highly stable Hg-free synthesis of vinyl chloride (VCM) via acetylene hydrochlorination. Compared to gold-based alternatives, platinum catalysts are in initial phases of development. Most synthetic approaches rely on chloroplatinic acid, presenting opportunities to explore other precursors and their impact on catalyst structure, reactivity, and toxicity aspects. Here, we synthesize platinum single atom catalysts (Pt SACs, 0.2-0.8 wt % Pt) employing diverse Pt²⁺ and Pt⁴⁺ complexes with ammine, hydroxyl, nitrate, and chloride ligands, following a scalable impregnation protocol on activated carbon extrudates. X-ray absorption spectroscopy (XAS) reveals that Pt⁴⁺ species reduce to Pt²⁺ upon deposition onto the support. Despite similar oxidation states, the initial activity is precursor dependent, with tetraammine-derived Pt SACs displaying 2-fold higher VCM yield than chlorinated counterparts, linked to superior hydrogen chloride binding abilities by density functional theory (DFT) simulations. Their activity gradually converges due to dynamic active site restructuring, delivering remarkable precursor-independent stability over 150 h. <i>Operando</i> XAS and DFT studies uncover reaction-induced ligand exchange, generating common active and stable Pt-Cl <i>_x</i> (<i>x</i> = 2-3) species. Convergent active site evolution enables flexibility in metal precursor selection and thus toxicity minimization through multiparameter assessment. This study advances safe-by-design catalysts for VCM synthesis, highlighting the importance of toxicity analyses in early-stage catalyst development programs.