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

Methanol steam reforming (MSR) is studied on a PtSn surface using the density functional theory (DFT). An MSR network is mapped out, including several reaction pathways. The main pathway proposed is CHOH + OH → CHO → CHO → CHO + OH → CHOOH → CHOOH → COOH → COOH + OH → CO + HO. The adsorption strengths of CHOH, CHO, CHOOH, HO and CO are relatively weak, while other intermediates are strongly adsorbed on PtSn(111). HO decomposition to OH is the rate-determining step on PtSn(111). The promotion effect of the OH group is remarkable on the conversions of CHOH, CHO and -COOH. In particular, the activation barriers of the O-H bond cleavage (e.g., CHOH → CHO and -COOH → CO) 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 HO decomposition is more competitive on PtSn(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.