(584cw) Structure Property Relationship of Pt Cluster Catalysts for Propane Dehydrogenation

Pt subnanometer cluster catalysts with promoting metals 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, PtZn clusters supported on zeolites 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, our work aims to develop their structure-property relationships. Here, the roles of Pt nuclearity and promoter Zn, on activity and selectivity are elucidated, based on the investigation of PDH mechanism on Pt_xZn_y (x=1-3, y=0-3) clusters on Silicalite-1 zeolite using density functional theory (DFT) calculations, microkinetic modeling (MKM), and experimental measurements.

We find that the coordination of a Pt atom to a nest of grafted Zn atoms increases the stability of the Pt₁Zn_y sites, whose activity is similar for y=0–2 and drops dramatically for y>2. We further demonstrate, via linear scaling relations and MKM, that the turnover frequency obeys a volcano law as a function of propylene binding strength (Figure 1). The Pt₂Zn₁ and Pt₃Zn₁ sites are stable and exhibit activity similar to Pt₁Zn₂, but only Pt₁Zn₂ manifests reaction kinetics consistent with experimental data, strongly suggesting the active site composition in the synthesized catalyst samples. The methodology presented here also suggests a general strategy for deducing active site information such as composition through simple kinetic experiments. In addition, propylene binding strength has been found as a universal descriptor for propane dehydrogenation activity and is used to predict activity for other Pt cluster catalysts.