Tuning Ligand‐Coordinated Single Metal Atoms on TiO2 and their Dynamic Response during Hydrogenation Catalysis

Ligand‐coordinated supported catalysts (LCSCs) are of growing interest for heterogeneous single‐atom catalysis. Here, the effect of the choice of organic ligand on the activity and stability of TiO2‐supported single‐atom Pt‐ligand catalysts was investigated for ethylene hydrogenation. The activity of these catalysts showed a significant dependence on the choice of ligand and also correlated with coordination number for Pt−ligand and Pt−Cl−. Of the three ligands examined in this study, the one with the lowest Pt coordination number, 1,10‐phenanthroline‐5,6‐dione (PDO), showed the lowest reaction temperature and highest reaction rate, likely due to those metal sites being more accessible to reactant adsorption. In‐situ X‐ray absorption spectroscopy (XAS) experiments showed that the activity also correlated with good heterolytic dissociation of hydrogen, which was supported by OH/OD exchange experiments and was the rate‐determining step of the hydrogenation reaction. In these in‐situ XAS experiments up to 190 °C, the supported Pt‐ligand catalyst showed excellent stability against structural and chemical change. Instead of Pt, the PDO ligand could be coordinated with Ir on TiO2 to form Ir LCSCs that showed slow activation by loss of Ir−Cl bonds, then excellent stability in the hydrogenation of ethylene. These results provide the chance to engineer ligand‐coordinated supported catalysts at the single‐atom catalyst level by the choice of ligand and enable new applications at relatively high temperature. Ligand love: Ligand‐coordinated supported catalysts (LCSCs), consisting of single‐site Pt stabilized on oxide supports by coordination to organic ligands, show good ethylene hydrogenation activity, which correlates with the degree of coordinative saturation and with the efficiency of the heterolytic dissociative adsorption of hydrogen. The Pt‐ligand LCSCs are resistant to reduction and aggregation under reaction conditions.