Density Functional Theory Study of Methanol Steam Reforming on Pt 3 Sn(111) and the Promotion Effect of a Surface Hydroxy Group.

Methanol steam reforming (MSR) is studied on a Pt 3 Sn surface using the density functional theory (DFT). An MSR network is mapped out, including several reaction pathways. The main pathway proposed is CH 3 OH + OH → CH 3 O → CH 2 O → CH 2 O + OH → CH 2 OOH → CHOOH → COOH → COOH + OH → CO 2 + H 2 O. The adsorption strengths of CH 3 OH, CH 2 O, CHOOH, H 2 O and CO 2 are relatively weak, while other intermediates are strongly adsorbed on Pt 3 Sn(111). H 2 O decomposition to OH is the rate-determining step on Pt 3 Sn(111). The promotion effect of the OH group is remarkable on the conversions of CH 3 OH, CH 2 O and trans -COOH. In particular, the activation barriers of the O-H bond cleavage (e.g., CH 3 OH → CH 3 O and trans -COOH → CO 2 ) decrease substantially by ~1 eV because of the involvement of OH. Compared with the case of MSR on Pt(111), the generation of OH from H 2 O decomposition is more competitive on Pt 3 Sn(111), and the presence of abundant OH facilitates the combination of CO with OH to generate COOH, which accounts for the improved CO tolerance of the PtSn alloy over pure Pt.