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.

Potential- and Time-Dependent Dynamic Nature of an Oxide-Derived PdIn Nanocatalyst during Electrochemical CO2 Reduction

“…In Figure c, the absorption edge corresponding to the white line of Pd K edge involves a 1s → 4p dipole transition and shifts toward a higher photon energy value in the case of PdIn than in the cases of the Pd foil and PdIn@In 2 O 3 catalyst, indicating the presence of higher-valent Pd species in the PdIn catalyst, which is corroborating the XPS data . The presence of PdO in the PdIn catalyst has also been verified in the Fourier transformed R-space data of the Pd K edge where the characteristic bond at 1.586 Å corresponding to Pd–O has been observed along with the Pd–In bond (at 1.96 Å) as shown in Figure d . The XANES of the In–K edge indicates that In has a higher oxidation state than that of In foil (Figure e) .…”

“…52 The presence of PdO in the PdIn catalyst has also been verified in the Fourier transformed R-space data of the Pd K edge where the characteristic bond at 1.586 Å corresponding to Pd−O has been observed along with the Pd−In bond (at 1.96 Å) as shown in Figure 4d. 53 The XANES of the In−K edge indicates that In has a higher oxidation state than that of In foil (Figure 4e). 54 Fourier transformed R-space data also suggests a proper In−O bond present at around 1.6 Å in the PdIn@In 2 O 3 sample (Figure 4f).…”

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

“…Contrary to a supported monometallic nanoparticle (M) schematically shown in Figure a, atoms of the guest metal (A) of a bimetallic nanoparticle (M-A) in Figure b may tune the catalytic performance of atoms of the host metal, M, through electronic, geometric, bifunctional, or lattice strain effects. − As schematically shown in Figure b, various metallic sites are packed on the surface of a supported bimetallic nanoparticle. Breaking these continuously packed bimetallic sites into separately anchored ones on a nonmetallic support (Figure c) could create a new electronic structure of a bimetallic catalytic site, M x A y ( x ≥ 1 and y ≥ 1) since such isolated bimetallic sites are typically in a nonmetallic state, which could offer a distinctly different catalytic performance compared to the continuously packed bimetallic sites of a bimetallic nanoparticle surface. − …”

“…M 1 A n /A x O y is one of the new types of catalyst reported in literature . A general term for this new type of catalyst is M 1 A n /X-Z (M, A: metal elements, X-Z: a nonmetallic compound). − A comprehensive description of this new type of catalyst reported in literature is a catalyst of singly dispersed single-atom bimetallic sites on a nonmetallic support. Structurally, these single-atom bimetallic sites (M 1 A n ) are isolated from each other on a nonmetallic support, X-Z, avoiding any interadsorbate couplings.…”