It
has been a long-standing challenge to create and identify the
active sites of heterogeneous catalysts, because it is difficult to
precisely control the interfacial chemistry at the molecular level.
Here we report the synthesis and catalysis of a heteroleptic gold
trihydride nanocluster, [Au22H3(dppe)3(PPh3)8]3+ [dppe = 1,2-bis(diphenylphosphino)ethane,
PPh3 = triphenylphosphine]. The Au22H3 core consists of two Au11 units bonded via six
uncoordinated Au sites. The three H atoms bridge the six uncoordinated
Au atoms and are found to play a key role in catalyzing electrochemical
reduction of CO2 to CO with a 92.7% Faradaic efficiency
(FE) at −0.6 V (vs RHE) and high reaction activity (134 A/gAu mass activity). The CO current density and FECO remained nearly constant for the CO2 reduction reaction
for more than 10 h, indicating remarkable stability of the Au22H3 catalyst. The Au22H3 catalytic
performance is among the best Au-based catalysts reported thus far
for electrochemical reduction of CO2. Density functional
theory (DFT) calculations suggest that the hydride coordinated Au
sites are the active centers, which facilitate the formation of the
key *COOH intermediate.
Gold does not react with H2 to form bulk hydrides. Here we report the synthesis and characterization of a gold nanohydride protected by diphosphine ligands, [Au22H4(dppo)6]2+ [dppo=1,8‐bis(diphenylphosphino)octane]. The Au22 core consists of two Au11 units bonded by eight Au atoms not coordinated by the diphosphine ligands. The four H atoms are found to bridge the eight uncoordinated Au atoms at the interface. Each Au11 unit can be viewed as a tetravalent superatom forming four delocalized Au‐H‐Au bonds, similar to the quadruple bond first discovered in the [Re2Cl8]2− inorganic cluster. The [Au22H4(dppo)6]2+ nanohydride is found to lose H atoms over an extended time via H evolution (H2), proton (H+) and hydride (H−) releases. This complete repertoire of H‐related transformations suggests that the [Au22H4(dppo)6]2+ nanohydride is a versatile model catalyst for understanding the mechanisms of chemical reactions involving hydrogen on the surface of gold nanoparticles.
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