Zeolite-Encapsulated Ir Single Atom Catalysts Toward Efficient and Stable Propane Dehydrogenation

Single-atom precious metal catalysts with maximized metal utilization and versatile electronic-state engineering have shown great potential in heterogeneous catalysis. However, the applications of single-atom precious metal catalysts under harsh reaction conditions are significantly restricted due to their thermodynamic instability from sintering-driven degradation. We report herein the construction of thermally stable Ir single atoms encapsulated in Ge-substituted S-1 zeolite, namely, IrGe@S-1 catalysts, for direct propane dehydrogenation. The optimized IrGe@S-1 catalyst exhibits unprecedented propane dehydrogenation activity with a state-of-the-art propylene formation rate of 1249.2 mol_C3H6 g_Ir^-1 h^-1 at 600 °C. IrGe@S-1 also shows excellent stability for over 800 h under a high weight hourly space velocity of 20 h^-1 (pure propane feeding at 580 °C), indicating its potential to produce 9000 tons of propylene with 1 ton of IrGe@S-1 catalyst without regeneration. The introduction of Ge species promotes the overlap between the Ir 5d and the O 2p orbitals and thereby enhances their interaction via Ir-O-Ge bonds to derive Ir single-atom catalysts. Under propane dehydrogenation conditions, propane molecules can induce the dissociation of framework oxygen atoms and the formation of Ir single atoms in low oxidation state. The specific electron-rich Ir single atoms significantly lower the energy barrier of the rate-determining step of propane dehydrogenation, and the isolated nature of Ir sites efficiently inhibits the side reaction of overdehydrogenation, together contributing to the remarkable performance in propane dehydrogenation. This work provides a successful example of stable single-atom precious metal catalysts for working under harsh reaction conditions.