Effective, stable, durable, and tunable Ir-ligand single-atom catalysts for ethylene hydrogenation, studied in situ for structural evolution of Ir single-atoms under a reducing atmosphere.

Heterogeneous single‐site catalysts (SSCs), widely regarded as promising next‐generation catalysts, blend the easy recovery of traditional heterogeneous catalysts with desired features of homogeneous catalysts: high fraction of active sites and uniform metal centers. We previously reported the synthesis of Pt‐ligand SSCs through a novel metal‐ligand self‐assembly method on MgO, CeO2, and Al2O3 supports (J. Catal. 2018, 365, 303–312). Here, we present their applications in the industrially‐relevant alkene hydrosilylation reaction, with 95 % yield achieved under mild conditions. As expected, they exhibit better metal utilization efficiency than traditional heterogeneous Pt catalysts. The comparison with commercial catalysts (Karstedt and Speier) reveals several advantages of these SSCs: higher selectivity, less colloidal Pt formation, less alkene isomerization/hydrogenation, and better tolerance towards functional groups in substrates. Despite some leaching, our catalysts exhibit satisfactory recyclability and the single‐site structure remains intact on oxide supports after reaction. Pt single‐sites were proved to be the main active sites rather than colloidal Pt formed during the reaction. An induction period is observed in which Pt sites are activated by Cl detachment and replacement by reactant alkenes. The most active species likely involves temporary detachment of Pt from ligand or support. Catalytic performance of Pt SSCs is sensitive to the ligand and support choices, enabling fine tuning of Pt sites. This work highlights the application of heterogeneous SSCs created by the novel metal‐ligand self‐assembly strategy in an industrially‐relevant reaction. It also offers a potential catalyst for future industrial hydrosilylation applications with several improvements over current commercial catalysts.

A significant challenge in designing supported metal-ligand catalysts for solution-phase reactions is the stabilization of the metal active sites against leaching into solution. Here, we examine alkene hydrosilylation reactions as model systems to improve the stability of highly dispersed Pt using a metal-ligand coordination strategy on high surface area oxide supports. By evaluating a series of bidentate N-based ligands, we demonstrate several design strategies to improve stability of the highly dispersed Pt 2+ centers against leaching, while maintaining a high level of catalytic activity, selectivity, and recyclability for alkene hydrosilylation batch reactions under mild conditions. These involve a bi-functional approach to ligand design, which considers interaction to the support and a well-defined coordination environment for the metal active site.Three strategies are reported: modifying ligands for stronger interaction with oxide surfaces, mixing ligands, and pre-depositing an "anchoring ligand" to the support before loading the metal-ligand catalyst. Each of these is successful in enhancing Pt recyclability. Particularly, two Pt-phenanthroline catalysts exhibit excellent reusability for multiple batch reaction cycles, due to high stability of the active Pt species. Addressing the active site leaching problem significantly enhances the utility of ligand-coordinated supported metal catalysts as highly stable and selective catalysts for solution-phase reactions.