(681c) Insights of Structure-Property Relationships of Pt-Sn and Pt-Zn Bimetallic Catalysts for Propane Dehydrogenation

Pt-based bimetallic catalysts with doping metals such as Sn and Zn and tuned particle sizes have been synthesized on various supports to improve the selectivity and stability for propane (C₃H₈) dehydrogenation (PDH) to propylene (C₃H₆). Among them, Pt subnanometer clusters recently emerged to exhibit superior PDH performance, including high activity and selectivity, and good stability. Considering the tremendous interest in atomically dispersed and sub-nanometer metallic catalysts on oxide supports, our work aims to develop structure-property relationships. Here, the roles of Pt nuclearity and doping metals, Sn and Zn, on activity and selectivity are elucidated, based on the investigation of PDH mechanism on Pt_x and Pt_xSn_y clusters on γ-alumina (Al₂O₃) Pt_xZn_y clusters on silicalite-1 zeolite, and on extended surfaces using density functional theory (DFT) calculations and microkinetic modeling (MKM).

The Pt_x clusters are prone to sintering, and their stability is improved with the addition of Sn and Zn. On Al₂O₃(110), the Pt_x activity changes non-monotonically with cluster size. Pt₁ presents the most favorable dehydrogenation barriers, but its PDH rate is highly limited by the blocking of sites by hydrogen. A volcano-like activity-nuclearity relation is found, with Pt₂ being the most active cluster. Increased Pt nuclearity beyond x=2 leads to lower rates due to increased dehydrogenation barriers. Moderate addition of Sn depresses the Pt activity, whereas Pt_xSn_y clusters with a Pt:Sn ratio of 1:1 become inactive. As a result of an activity-stability tradeoff, the Pt₃Sn₁ cluster exhibits good activity with improved stability compared to Pt₃ and Pt₂. While Sn promotes propylene desorption, propane hydrogenolysis to C1 and C2 species on single Pt atoms and small Pt_x and Pt_xSn_y clusters is unfavorable. Like Sn, Zn improves Pt stability and inhibits Pt activity. Finally, Zn and Sn are compared, and the differences are elucidated.