Gold nanoparticles in metallic or plasmonic state have been widely used to catalyze the homogeneous and heterogeneous reactions. However, the catalytic behaviours of gold catalysts in non-metallic or excitonic state remain elusive. Atomically precise Aun clusters (n = number of gold atoms) bridge the gap between non-metallic and metallic catalysts. Different from metallic catalysts with the collective excitation behavior, the atomically precise metal clusters can be classified into three distinct states: metallic, transition regime, and non-metallic. Non-metallic or molecular-like clusters possess discrete electron energy levels. With the evolution of electronic structures from metallic to non-metallic state, these clusters can reveal a hidden mystery in the catalytic field, that is, the non-metallic cluster catalysts may have similar or even superior catalytic abilities compared to the metallic ones.
Yan Zhu’s groupreport that the non-metallic gold clusters, Au9, Au11 and Au36, exhibit atomicity-dependent catalytic performances in the hydrogenation processes of CO2, where they can selectively determine the reaction pathways towards C1 or C2 products. Specially, Au11 can give >80% selectivity for ethanol as high-added value chemicals and Au36 can achieve >85% selectivity for formic acid. They reveal the molecular-level mechanisms of CO2 reaction with H2 over the three clusters, which are governed by their distinct binding capabilities and electronic structures. The exceptional properties of the non-metallic gold clusters highlight the importance of pursuing non-metallic metal clusters for extensively catalytic applications and thus they will open an avenue for a new type of metal catalysts with high efficiency for a series of challenging chemical reactions.
The work entitled “Controllable Conversion of CO2 on Non-metallic Gold Clusters” has been published in Angewandte Chemie (2020, 59, 1919-1924)。
Figure. (a) Crystal structure of Au9, Au11, and Au36 clusters; (b) Catalytic performances of CO2 hydrogenation over the three catalysts; (c) Energy diagrams of CO2 hydrogenation on the three clusters by DFT calculations.