Integration of Metal Single Atoms on Hierarchical Porous Nitrogen-Doped Carbon for Highly Efficient Hydrogenation of Large-Sized Molecules in the Pharmaceutical Industry.

Single-atom catalysts (SACs) often exhibit superior activity and selectivity in heterogeneous catalysis because of their maximized atom utilization and unique coordination environments. However, most reported studies about SACs in heterogeneous catalysis focus on model reactions with simple molecules. In addition, many reported single atoms are confined in microporous structures, hindering the mass transfer of molecules with large sizes, thus limiting their practical applications in industry. In this study, we report a molten salt-assisted method to synthesize metal single atoms anchored on a hierarchical porous nitrogen-doped carbon support (denoted as M/h-NC, M includes Co, Fe, Ni, Mn, and Cu). Taking Co/h-NC as an example, compared to the control sample which has Co single atoms being encapsulated in a microporous N-doped carbon support (denoted as Co/m-NC), Co/h-NC exhibits significantly higher catalytic activity in the selective hydrogenation of large-sized pharmaceutical molecules, such as nimodipine (calcium channel blocker) and 2-(3',4'-methylenedioxyphenylethyl)quinoline (antispasmodic natural alkaloid intermediate). The superior catalytic performance of Co/h-NC is directly ascribed to the integration of the advantages of single-atom active sites and hierarchical mesoporous structure, which is beneficial for the mass transfer of molecules with large sizes and enables nearly all the Co single atoms to be accessible for catalytic reactions.