ABSTRACT

This chapter summarizes the systematic density functional theory

studies on the adsorptions and decompositions of water and ethanol

on PtnM (n = 2, 3, 6, and 9; M = Pt, Sn, Ru, Rh, Pd, Cu, and Re). The results show that from both kinetic and thermodynamic viewpoints

Sn is more active to water decomposition than pure Pt and all of

the other investigated PtM except for PtRe, which well supports the

assumption of the bifunctional mechanism that Sn site accelerates

the dissociation of H2O. However, although the energy barrier for water decomposition on the Re site of the PtRe is only slightly lower the that on Sn site, the adsorption energy and dissociation energy on the Re site are considerably more favorable than those on the Sn site of PtS. Although the α-hydrogen adsorption is weaker than the hydroxyl of ethanol, the adsorptions of ethanol on Pt and M

sites of PtM via the α-hydrogen were well established, and the

potential energy profiles show that the dehydrogenation via the α-

H path has much lower energy barrier than that via the hydroxyl

path. Generally for the α-hydrogen path the adsorption is a rate-

determining step because of rather low dehydrogenation barrier for

the α-hydrogen adsorption complex (thermodynamic control), while the hydroxyl path is determined by its dehydrogenation step (kinetic control). Alloying of Sn enhances the adsorption of ethanol on Pt site through the α-H, as well as those on both Pt and Sn sites through

the hydroxyl. However, the Re alloying does not enhance the former

adsorption although it enhances the latter one on both Pt and Re

sites.