Engineering Surface Hydroxyls of Zeolites to Suppress Sintering of Confined PtSn Clusters for Stable Propane Dehydrogenation.

Propane dehydrogenation (PDH) is an attractive on-purpose route for propylene production, yet catalyst deactivation under harsh hydrogen-free conditions remains a major challenge. Although zeolite confinement can stabilize PtSn active sites, gradual sintering during long-term operation at high temperatures persists. Here we developed an HF-free post-synthetic silylation strategy using hexamethyldisilazane (HMDS) to selectively passivate surface silanols in silicalite-1 zeolites to enhance the stability of encapsulated Pt1Sn1 alloy clusters. The resulting catalyst maintains stable PDH performance during a directly measured 2160 h on-stream test under hydrogen-free and pure C3H8 conditions at 550°C. Post-reaction characterizations demonstrate that the enhanced stability originates from the effective suppression of PtSn sintering under reaction conditions, with the PtSn alloy clusters retaining an average size of only 1.0 ± 0.2 nm after 2160 h on stream. This remarkable sintering resistance is attributed to the passivation of external-surface and pore-mouth silanols, which eliminates the hydroxyl anchoring and nucleation sites that would otherwise capture outward-migrating PtSn species and promote their nucleation and coalescence on the external zeolite surface. These findings identify post-synthetic hydroxyl passivation as a practical strategy to reinforce zeolite confinement and stabilize sub-nanometer bimetallic clusters for high-temperature dehydrogenation.