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

Abstract

We have synthesized Pt 1 Zn 3 /ZnO, also termed 0.01 wt %Pt/ZnO-O 2 − H 2 , 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-N 2 −H 2 . Selectivity for H 2 on Pt 1 Zn 3 /ZnO reaches 96%−100% at 290−330 °C, arising from the uniform coordination environment of single-atom Pt 1 in singly dispersed single-atom bimetallic sites, Pt 1 Zn 3 on 0.01 wt %Pt/ZnO-O 2 −H 2 , which is sharply different from various coordination environments of Pt atoms in coexisting Pt x Zn y (x ≥ 0, y ≥ 0) sites on Pt− Zn bimetallic nanoparticles. Computational simulations attribute the extraordinary catalytic performance of Pt 1 Zn 3 /ZnO to the stronger adsorption of methanol and the lower activation barriers in O−H dissociation of CH 3 OH, C−H dissociations of CH 2 O to CO, and coupling of intermediate CO with atomic oxygen to form CO 2 on Pt 1 Zn 3 /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 M x A y (x ≥ 0, y ≥ 0). As these singleatom 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.