RESUMO
Recently, CO2 hydrogenation had a new breakthrough resulting from the design of catalysts to effectively activate linear CO2 with symmetry-breaking sites. However, understanding the relationship between symmetry-breaking sites and catalytic activity at the atomic level is still a great challenge. In this study, a set of gold-copper alloy Au13 Cux (x=0-4) nanoclusters were used as research objects to show the symmetry-controlled breaking structure on the surface of nanoclusters with the help of manipulability of the Cu atoms. Among them, Au13 Cu3 nanocluster displays the highest degree of symmetry-breaking on its crystal structure compared with the other nanoclusters in the family. Where the three copper atoms occupying the surface of the icosahedral kernel unevenly with one copper atom is coordinately unsaturated (CuS2 motif relative to CuS3 motif). As expected, Au13 Cu3 has an excellent hydrogenation activity of CO2 , in which the current density is as high as 70â mA cm-2 (-0.97â V) and the maximum FECO reaches 99 % at -0.58â V. Through the combination of crystal structures and theoretical calculations, the excellent catalytic activity of Au13 Cu3 is revealed to be indeed closely related to its asymmetric structure.
RESUMO
Unraveling the evolution mechanism of metal nanoclusters is of great importance in understanding the formation and evolution of metallic condensed matters. In this work, the specific evolution process between a pair of gold nanocluster (Au NC) isomers is completely revealed by introducing hydride ligands to simplify the research system. A hydride-containing Au NC, Au22(SR)15H, was synthesized by kinetic control, and the positions of the hydrides were then confirmed by combining X-ray diffraction, neutron diffraction, and DFT calculations. Importantly, a reversible structural isomerization was found to occur on this Au22(SR)15H. By combining the crystal structures and theoretical calculations, the focus was placed on the hydride-binding site, and a [Au-H] migration mechanism of this isomerization process is clearly shown. Furthermore, this [Au-H] migration mechanism is confirmed by the subsequent capture and structural determination of theoretically predicted intermediates. This work provides insight into the dynamic behavior of hydride ligands in nanoclusters and a strategy to study the evolution mechanism of nanoclusters by taking the hydride ligand as the breakthrough point.
RESUMO
"Core sliding" in metal nanoclusters drives the reconstruction of external structural units and provides an ideal platform for mapping their precise transformation mechanism and evolution pathway. However, observing the movement behavior of metal atoms in experiments is still challenging because of the uncertain stability of intermediates. In this work, a series of Au-Cd alloy nanoclusters with continuously assembled kernels (one icosahedral building block assembled with 0 to 3 tetrahedral units) were constructed. As the assembly continued, it eventually led to the Cd atom doping into the inner positions of the clusters. Importantly, the Cd doped into the interior of the cluster exhibits a different behavior than the surface or external Cd atoms (dispersion doping vs localized occupy), which provides experimental evidence of the sliding behavior in the nanocluster kernel. Furthermore, density functional theory (DFT) calculations reveal that this sliding behavior in the inner sites of nanoclusters is an energetically favorable process. In addition, these Au-Cd nanoclusters exhibit tunable optical properties with different assembly patterns in their kernels.
RESUMO
Structural transformation in nanoclusters is important not only in obtaining functional nanoclusters controllably but also in understanding their structural evolution. This study investigated the role of Cu2+ ions in structural transformation. It was revealed that Cu2+ exhibits two different functions, doping and oxidation, in determining the final products. Starting with a new silver nanocluster, [Ag25(2,5-DMBT)16(DPPF)3]+ (Ag25), a doping process would occur when no more than 0.5 equiv of Cu2+ was added, resulting in the formation of [Ag25-xCux(2,5-DMBT)16(DPPF)3]+ (Ag25-xCux). When 1 equiv of Cu2+ was introduced to Ag25, a structural transformation process would occur instead, forming [Ag22-xCux(2,5-DMBT)12(DPPF)4Cl4]2+ (Ag22-xCux). Considering the similar Cu doping amounts in Ag25-xCux and Ag22-xCux, an oxidation process induced by Cu2+ in the solution can account for this transformation process, which was further demonstrated by the addition of other oxidant substitutions. On the other hand, the role of other valence states of copper in the transformation of the Ag25 cluster was explored. It was found that copper powder can hardly change Ag25 and Cu+ can only proceed the doping process, both of which are different from the role of Cu2+. Overall, this work explores the role of copper in the transformation of the Ag25 cluster in detail, including its concentrations and valence states.
RESUMO
The change in the valence state of nanocluster can induce remarkable changes in the properties and structure. However, achieving the valence state changes in nanoclusters is still a challenge. In this work, we use Cu2+ as dopant to "oxidize" [Ag62 S12 (SBut )32 ]2+ (4 free electrons) to obtain the new nanocluster: [Ag62-x Cux S12 (SBut )32 ]4+ with 2 free electrons. As revealed by its structure, the [Ag62-x Cux S12 (SBut )32 ]4+ (x=10â¼21) has a similar structure to that of [Ag62 S12 (SBut )32 ]2+ precursor and all the Cu atoms occupy the surface site of nanocluster. It's worth noting that with the Cu atoms doping, the [Ag62-x Cux S12 (SBut )32 ]4+ nanocluster is more stable than [Ag62 S12 (SBut )32 ]2+ at higher temperature and in electrochemical cycle. This result has laid a foundation for the subsequent application and exploration. Overall, this work reveals crystals structure of a new Ag-Cu nanocluster and offers a new insight into the electron reduction/oxidation of nanocluster.
