Discrete Au1(0) Stabilized by 15-Crown-5 for High-Efficiency Catalytic Reduction of Nitrophenol and Nitroaniline

Single-atom catalysts (SACs) have been synthesized using a variety of methods in recent years, and they have shown excellent catalytic activities. However, metal atoms show a high tendency to agglomerate in liquid media, making the single atom synthesis more difficult in liquid media. The synthesis of such metal single-atom catalysts that do not have strong ligand coordination is rarely reported in the literature. Herein, we report the facile synthesis of monodispersed Au atoms (Au-1) through the reduction in HAuCl4 in 15-crown-5. The complete reduction in HAuCl4 was confirmed through UV-Vis spectroscopy. In addition, the Au was found in a zero valence state after reduction, which was confirmed through XPS and XANES results. Moreover, the dispersion of Au was confirmed as a single atom (Au-1) through transmission electron microscopy and spherical aberration electron microscopy. The possible structure of this catalyst was proposed by matching the EXAFS results with the structure of Au-1@15-crown-5 as -(OC2H4O)-AuCl2H2. The Au-1@15-crown-5 showed high activity (TOF as high as 22,075) in the reduction in nitrophenol and nitroaniline to aminophenol and phenylenediamine by sodium borohydride. Because of the monodispersion of Au atoms, its performance is much better than noble nanoparticles and non-precious metal catalysts.

Automated summary

In recent years, single-atom catalysts (SACs) have been successfully synthesized through various methods, demonstrating excellent catalytic activities. However, the tendency of metal atoms to agglomerate in liquid media complicates the synthesis of SACs in such environments. The synthesis of metal single-atom catalysts without strong ligand coordination is rarely reported. This study presents a straightforward synthesis of monodispersed Au atoms (Au-1) by reducing HAuCl4 in the presence of 15-crown-5. The resulting Au-1@15-crown-5 catalyst exhibits high catalytic activity in the reduction of nitrophenol and nitroaniline, outperforming both noble nanoparticles and non-precious metal catalysts due to the monodispersion of Au atoms.