Effect of Tin in the Bulk of Platinum–Tin Alloys for Ethane Dehydrogenation

Abstract

Catalytic ethane dehydrogenation was studied with density functional theory (DFT) calculations to investigate the differing role of Sn in the bulk and surface of PtSn alloys on the activity, selectivity, and stability of the catalyst. Pristine Pt(111), a surface alloy of Pt3Sn/Pt(111) and a bulk alloy of Pt3Sn(111) were compared. Binding energies of adsorbates were weakened by Sn on both alloys. With few changes for binding geometries of adsorbates, the change in binding energies was mainly attributed to the changes in the electronic interaction due to the strain effect and/or the ligand effect from d-band theory on the alloys. Especially, the combination of ligand and strain effects on the bulk alloy made the binding energies of adsorbates generally weaker than on Pt but stronger than on the surface alloy. In the successive dehydrogenation of C2Hx species, the activity was expected in the order of Pt > Pt3Sn > Pt3Sn/Pt by comparing the activation energies for ethene formation. The selectivity toward ethene was predicted using two descriptors from which the best selectivity was expected on Pt3Sn/Pt. Sn in the bulk made the gap between the barriers for ethene desorption and further dehydrogenation comparable, whereas ethene desorption was much more favorable on Pt3Sn/Pt. The preference for ethene formation from ethyl was also weakened on Pt3Sn. Therefore, despite the higher Sn composition, worse selectivity was predicted for Sn-rich bulk alloy than the surface alloy, followed by Pt.