Recently, scientists of Institute of Solid State Physics, Hefei Institutes of Physical Science developed a facile and efficient laser irradiation in liquid technique to liberate the inaccessible Co-Nx active sites. The research was published in Advanced Materials.

The development of cheap and earth abundant nonprecious metal-based catalysts to realize efficient selective hydrogenation (SH) of quinoline and its derivatives are critically important for the future of pharmaceutical and agrochemical synthetic industries.

The highly dispersed catalysts such as single-atoms (SAs) and atom-clusters (ACs) catalysts have emerged as a new form of catalysts with enormous potentials. However, their potentials as thermal catalysts for organic synthesis have yet been well explored.

The team speculated the presence of rich highly dispersed Co SAs/ACs sites confined inside the acid-leached N-doped carbon nanotubes (N-CNTs) derived from ZIF-67 (Co-SA/AC@N-CNTs, Figure 1), nevertheless, these Co SAs/ACs sites were catalytically inactive. Only few exposed Co SAs/ACs sites were available for the reaction, while the vast majority of Co SAs/ACs sites confined inside N-CNTs were inaccessible to the reactant.

Herein, the group further demonstrated a simple and effective laser irradiation in liquid technique to expose the highly dispersed inaccessible Co SAs/ACs sites confined inside CNTs (Co-SA/AC@N-CNTs-L, Figure 2). The laser irradiation in liquid treatment was capable of not only completely destroying the dodecahedral architecture but also breaking N-CNTs structures.

As a result, N-CNTs consisted of a large number of broken opening structures, which would make them readily accessible by the reactants.

The liberated highly dispersed Co-Nx sites displayed generic catalytic activity toward the selective hydrogenation of quinolone and its hydroxy, methyl and halogen substituted derivatived into corresponding 1,2,3,4-tetrahydroquinolines with almost 100% conversion and selectivity.

The reported approach in this work is widely applicable to unlock the catalytic powers of the inaccessible catalytic active sites confined by other materials.

This work was supported by the Natural Science Foundation of China, the Postdoctoral Science Foundation of China.

Figure 1. (a) Typical SEM images (Inset: high magnification image), (b) TEM image, (c) STEM-EDX mapping and (d) AC HAADF-STEM image of the Co-SA/AC@N-CNTs. The Co clusters and single atoms are marked with yellow and red circles, respectively. (Image by GONG Wanbing) 

Figure 2. (a) Typical SEM image (Inset: TEM image), (b) AC HAADF-STEM image (Inset: HAADF-STEM image) of the Co-SA/AC@N-CNTs-L; (c) Co K-edge XANES spectra and (d) Comparative k3-weighted x(k)-function of EXAFS spectra of Co foil, CoO, Co₂O₃, Co₃O₄, Co-SA/AC@N-CNTs and Co-SA/AC@N-CNTs-L. The Co clusters and single atoms are marked with yellow and red circles, respectively. (Image by GONG Wanbing)