Dalian Institute of Chemical Physics researchers have recently synthesized a gold catalyst for chemoselective hydrogenation of functionalized nitroarenes. By using the Zinc-Aluminum hydrotalcite (ZnAl-HT) supported thiolated Au₂₅ nanoclusters (NCs) as the precursor of the catalyst, they prepared the efficient Au catalyst with high selectivity for the selective hydrogenation of functionalized nitroarenes to the corresponding aromatic amines in wide temperature and time ranges.

Functionalized aromatic amines are important industrial intermediates for pharmaceuticals, agrochemicals, fine chemicals, dyes and polymers. They were generally synthesized by chemoselective hydrogenation of the corresponding functionalized nitroarenes. Generally, the most common problem for traditional noble-metal catalysts was that they were active not only for the reduction of the nitro group but also for the hydrogenation of other unsaturated functional groups existing in the same molecule.

Previoiusly, Prof. Zhang’s group have developed a rationally designed FeO_x supported Pt single-atom and pseudo single-atom catalyst for the hydrogenation of functionalized nitro groups. By precisely controlling the reaction time and temperature, they obtained the good activity and selectivity for this kind of reaction. But the problem was that the nitro group and the other unsaturated groups were competitively adsorbed on the catalyst so that excessive hydrogenation was inevitable while the concentration of the nitro group decreased.

Au catalyst was reported very selective for various oxidation and hydrogenation reactions because of the weak adsorption of reactant and product molecular. Catalysis by Au has been one of the most important research projects in Prof. Zhang’s group in the last decade. They have done a series of important work on this topic. (Nano Today, 2013, 8, 403-416; J. Catal., 2013, 308, 258-271, 50th Anniversary Special Issue). This time they created a gold catalyst with amazingly high selectivity for the hydrogenation of functionalized nitroarenes to the target product.

In comparison with the traditional gold catalysts, the thiolated Au₂₅ NCs supported on the ZnAl-hydrotalcite was highly resistant to sintering, with well controlled size (around 2.0 nm) even after calcination at 500 ^oC. The formation of the Au-S-Zn bond and the epitaxial interaction between gold and the support might contribute to the stabilization of the gold nanoclusters. Besides, the results of the control experiments suggested the catalyst was inert to adsorb other unsaturated groups, thus made it a potential candidate for selective hydrogenation reactions. This is very different from the behavior of the supported platinium-group metals.

This work was published on Angew. Chem. Int. Ed. (http://dx.doi.org/10.1002/anie.201610736). The research work was financially supported by the National Natural Science Foundation of China, the National Key Projects for Fundamental Research and Development of China, the Youth Innovation Promotion Association CAS, and the Strategic Priority Research Program of the Chinese Academy of Sciences. The work was also supported by the BL 14W at the Shanghai Synchrotron Radiation Facility (SSRF) for the XAFS experiments.

(Text and Image by YUAN TAN and XIAO YAN LIU)