Atomic-Scale Structure and Catalysis on Positively Charged Bimetallic Sites for Generation of H₂.

Abstract

Here, we report that a cationic bimetallic site consisting of one Pd and three Zn atoms (Pd₁Zn₃) supported on ZnO (Pd₁Zn₃/ZnO) exhibits an extraordinarily high catalytic activity for the generation of H₂ through methanol partial oxidation (MPO) that is 2-3 orders of magnitude higher than that of a metallic Pd-Zn site on Pd-Zn nanoalloy (Pd-Zn/ZnO). Computational studies uncovered that the positively charged Pd atom of the subnanometer Pd₁Zn₃ bimetallic site largely decreases the activation barrier for dehydrogenation of methanol as compared to a metallic Pd atom of Pd-Zn alloy, thus switching the rate-determining step of MPO from methanol dehydrogenation over a Pd-Zn alloy with high barrier to the O₂ dissociation step on a cationic Pd₁Zn₃ site with a low barrier, which is supported by our kinetics studies. The significantly higher catalytic activity and selectivity for H₂ production over a cationic bimetallic site suggest a new approach to design bimetallic catalysts.