Nanoalloying MgO-Deposited Pt Clusters with Si To Control the Selectivity of Alkane Dehydrogenation

Abstract

Nanoalloying MgO-deposited Pt clusters with eight main-group elements was computationally screened for potential selectivity toward partial dehydrogenation of small alkanes. Si was revealed as a promising dopant for Pt across two cluster sizes, as it appears to favor stopping dehydrogenation of alkanes at alkenes. Pure Pt clusters on MgO(100) tend to strongly adsorb ethane and activate one of the C–H bonds but then bind ethylene in an activated di-σ fashion and even spontaneously dehydrogenate it. They also strongly bind C atoms, as the first step of deactivation by coking. PtSi clusters also bind and activate ethane but, in contrast to pure Pt clusters, bind ethylene preferentially in a weaker π fashion and do not spontaneously dehydrogenate it. Additionally, the affinity of C atoms to PtSi is reduced by ca. 2 eV in comparison to pure Pt clusters of the same size. Finally, Si stabilizes the clusters against dissociating single Pt atoms and thus is predicted to slow down catalyst sintering by Ostwald ripe...