Effects of Nuclearity and Microenvironment of Pt Clusters in MFI Zeolite for Propane Dehydrogenation: Insights from AIMD and Microkinetic Simulations

Propane dehydrogenation (PDH) over zeolite-confined metal clusters has emerged as a promising strategy for propene production. Nevertheless, the underlying structure–activity relationship remains elusive, not least owing to the intrinsic structural dynamics of subnanometric clusters under reaction conditions. Herein, by combining machine-learning-accelerated ab initio molecular dynamics simulations with density functional theory calculations, we systematically investigate the dynamic evolution and structural characteristics of four typical subnanometric Ptn clusters (n = 4, 7, 9, 15) confined in pure-silica (Si-MFI) and framework Al-substituted (Al-MFI) zeolites. Stronger interactions between Pt clusters and the Al-MFI matrix sustain Pt–O linkages and induce distinct structural rearrangements compared to those in Si-MFI. In Si-MFI with weak interaction, most Pt clusters (except larger Pt15 cluster) retain local geometries close to their gas phase counterparts. Spatially accessible two- and three-coordinated Pt atoms constitute the dominant active sites for the PDH reaction in zeolites. Microkinetic simulations demonstrate that the PDH activity is synergistically governed by cluster nuclearity, zeolite microenvironment, and reaction conditions. A volcano-like activity trend with cluster nuclearity is observed at typical reaction condition of 853 K and 0.1 MPa, in which Pt7 cluster achieves the highest activity. Under elevated temperatures and reduced pressures, small Pt4 cluster delivers higher PDH activity over other larger clusters. Framework Al-substitution however reduces the activity of larger Pt clusters. Propene desorption acts as the rate-determining step for Pt4 cluster, leading to the strong temperature dependence of PDH activity. In contrast, the PDH activities of other three larger clusters are more sensitive to pressure. Moving beyond prior static analyses of zeolite-confined metal clusters, this work reveals how cluster nuclearity and zeolite microenvironment collectively influence PDH catalytic behavior.