Convergent Active\nSite Evolution in Platinum Single\nAtom Catalysts for Acetylene Hydrochlorination and Implications for\nToxicity Minimization

Platinum single atoms anchored onto activated carbon\nenable highly\nstable Hg-free synthesis of vinyl chloride (VCM) via acetylene hydrochlorination.\nCompared to gold-based alternatives, platinum catalysts are in initial\nphases of development. Most synthetic approaches rely on chloroplatinic\nacid, presenting opportunities to explore other precursors and their\nimpact on catalyst structure, reactivity, and toxicity aspects. Here,\nwe synthesize platinum single atom catalysts (Pt SACs, 0.2–0.8\nwt % Pt) employing diverse Pt<sup>2+</sup> and Pt<sup>4+</sup> complexes\nwith ammine, hydroxyl, nitrate, and chloride ligands, following a\nscalable impregnation protocol on activated carbon extrudates. X-ray\nabsorption spectroscopy (XAS) reveals that Pt<sup>4+</sup> species\nreduce to Pt<sup>2+</sup> upon deposition onto the support. Despite\nsimilar oxidation states, the initial activity is precursor dependent,\nwith tetraammine-derived Pt SACs displaying 2-fold higher VCM yield\nthan chlorinated counterparts, linked to superior hydrogen chloride\nbinding abilities by density functional theory (DFT) simulations.\nTheir activity gradually converges due to dynamic active site restructuring,\ndelivering remarkable precursor-independent stability over 150 h. <i>Operando</i> XAS and DFT studies uncover reaction-induced ligand\nexchange, generating common active and stable Pt–Cl<i><sub>x</sub></i> (<i>x</i> = 2–3) species.\nConvergent active site evolution enables flexibility in metal precursor\nselection and thus toxicity minimization through multiparameter assessment.\nThis study advances safe-by-design catalysts for VCM synthesis, highlighting\nthe importance of toxicity analyses in early-stage catalyst development\n programs.