Breaking Continuously Packed Bimetallic Sites to Singly Dispersed on Nonmetallic Support for Efficient Hydrogen...

We have synthesized Pt₁Zn₃/ZnO, also termed 0.01 wt %Pt/ZnO-O₂-H₂, as a catalyst containing singly dispersed single-atom bimetallic sites, also called a catalyst of singly dispersed bimetallic sites or a catalyst of isolated single-atom bimetallic sites. Its catalytic activity in partial oxidation of methanol to hydrogen at 290 °C is found to be 2-3 orders of magnitude higher than that of Pt-Zn bimetallic nanoparticles supported on ZnO, 5.0 wt %Pt/ZnO-N₂-H₂. Selectivity for H₂ on Pt₁Zn₃/ZnO reaches 96%-100% at 290-330 °C, arising from the uniform coordination environment of single-atom Pt₁ in singly dispersed single-atom bimetallic sites, Pt₁Zn₃ on 0.01 wt %Pt/ZnO-O₂-H₂, which is sharply different from various coordination environments of Pt atoms in coexisting PtZn (x ≥ 0, y ≥ 0) sites on Pt-Zn bimetallic nanoparticles. Computational simulations attribute the extraordinary catalytic performance of Pt₁Zn₃/ZnO to the stronger adsorption of methanol and the lower activation barriers in O-H dissociation of CH₃OH, C-H dissociations of CH₂O to CO, and coupling of intermediate CO with atomic oxygen to form CO₂ on Pt₁Zn₃/ZnO as compared to those on Pt-Zn bimetallic nanoparticles. It demonstrates that anchoring uniform, isolated single-atom bimetallic sites, also called singly dispersed bimetallic sites on a nonmetallic support can create new catalysts for certain types of reactions with much higher activity and selectivity in contrast to bimetallic nanoparticle catalysts with coexisting, various metallic sites MA (x ≥ 0, y ≥ 0). As these single-atom bimetallic sites are cationic and anchored on a nonmetallic support, the catalyst of singly dispersed single-atom bimetallic sites is different from a single-atom alloy nanoparticle catalyst. The critical role of the 0.01 wt %Pt in the extraordinary catalytic performance calls on fundamental studies of the profound role of a trace amount of a metal in heterogeneous catalysis.