Silicalite-1 zeolite encapsulated Pt nanoparticles via ligand-protected in-situ construction for boosting auto-exhaust carbon particle oxidation

The enhancement of activity and stability of noble metal-based catalysts for purification of auto-exhaust carbon particle (soot) oxidation remains a grand challenge under harsh reaction conditions. Herein, the encapsulated catalysts of platinum nanoparticles (NPs) confined in silicalite-1 (S-1) zeolite were prepared by the ligand-protected in-situ synthesis method. The Pt NPs (4 nm) are located within the intersectional channels between the straight and the sinusoidal 10-ring channels of rigid S-1 zeolite and well stabilize inside the S-1 via Pt–O–Si bonds. The Pt@S-1 catalyst (0.38 wt.% of Pt loading) exhibits excellent performance (T₅₀ = 368 °C, T₅₀ corresponds to the temperatures at which 50% of soot conversion occurs) compared with the conventional Pt/S-1 catalyst during soot oxidation. The Pt@S-1 catalyst displays high long-term catalytic stability after the hydrothermal aging at 800 °C for 10 h, and the deactivation rate of the Pt@S-1 catalyst is one-tenth that of the Pt/S-1 catalyst. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations corroborated that the encapsulated Pt NPs in Pt@S-1 catalyst display a higher d-band center than the isolated Pt NPs, which enhances bonding strength for co-adsorption of NO and O₂ molecules. The steric hindrance effect promotes the desorption of the critical intermediate of NO₂, which is the key step to the NO₂-assistant catalytic mechanism for soot oxidation. The ligand-protected in-situ confinement synthesis of metal nanoparticle catalysts not only ensures high activity and stability but also paves the way for the development of effective catalysts for soot oxidation in practical applications.