A DFT study of ethanol interaction with the bimetallic clusters of PtSn and its implications on reactivity

The comprehension of the factors affecting the adsorption of ethanol over metals and metal alloys is a crucial step for the rational development of new catalysts for hydrogen production through ethanol reforming. In this work, we analyze the effect of combining Pt and Sn on a metal cluster on the complexation energy and reactivity for OH dehydrogenation of ethanol. Metal clusters of Pt10, Sn10 and Pt5Sn5 had their putative minimum located with the help of the artificial bee colony algorithm. Whereas the isolated Pt cluster shows a high degree of polarization (ESP surface), the Sn cluster shows a quite uniform electron density surface. The PtSn cluster is strongly polarized, with Pt atoms withdrawing electron density of Sn atoms. Complexation occurs with the oxygen atom of ethanol directed towards the point of highest electron potential in the ESP surface. Pt presents the highest complexation energy, -20.90 kcal/mol, against only -7.83 kcal/mol (at the B97-3c level). For the PtSn cluster, the value is intermediate, namely -12.39 kcal/mol. The more malleable electron density of Pt and its electron affinity are responsible for its highest complexation energy. These characteristics are partially transferred to the PtSn cluster. QTAIM results show that, for the PtSn cluster, the O-H bond in ethanol is somewhat weaker than for pure Pt and Sn. As a consequence, the energy barrier for the O-H dehydrogenation has its lowest value for the PtSn cluster, which shows that the alloying of two metals can lead to quite quite unexpected results opening the perspective for a more rational fine tuning of catalysts properties.