Breaking Continuously Packed Bimetallic Sites to Singly Dispersed on Nonmetallic Support for Efficient Hydrogen Production
Tao Jiang, Yuting Li, Yu Tang, Shiran Zhang, Duy Le, Talat S. Rahman, Franklin Tao
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 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.