Propane Dehydrogenation on PtxSny (x, y ≤ 4) Clusters on Al2O3(110)

With increasing interest in atomically dispersed and sub-nanometer Pt and Pt–Sn cluster catalysts for propane dehydrogenation (PDH), understanding structure–property relationships is of great importance. In this work, we present density functional theory calculations and microkinetic modeling of PDH on eight alumina-supported Pt x ( x = 1–4) and Pt x Sn y ( x = 1–3, y = 1 and x = 2, y = 2) model catalysts and elucidate the effects of Pt nuclearity and Sn heteroatoms. Pt x clusters are prone to sintering, and their stability is improved with the addition of Sn. The Pt x activity changes nonmonotonically with cluster size. Pt 1 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 Pt 2 being the most active cluster. An increase in Pt nuclearity beyond x = 2 leads to lower rates due to increased dehydrogenation barriers. Moderate addition of Sn somewhat depresses the Pt activity, whereas Pt x Sn y clusters with a Pt/Sn ratio of 1:1 become inactive. The Pt 3 Sn 1 cluster exhibits good activity with improved stability compared to Pt 3 and Pt 2 and could be an experimental target. While Sn promotes propylene desorption, propane hydrogenolysis to C1 and C2 species on single atoms and small Pt x and Pt x Sn y clusters is unfavorable. Low selectivity to propylene seen experimentally should instead stem from other routes.