Switchable reductive amination of aldehydes over metal-encapsulated S-1 zeolites with tunable acid-base properties

Catalytic reductive amination of aldehydes is a valuable strategy to synthesize nitrogen-containing compounds but often suffers from low selectivity and complex reaction mechanisms. This study aims to develop a selective control method for the syntheses of primary amines and secondary imines, which are widely used in fine and bulk chemicals, materials, and pharmaceuticals. Metal-encapsulated zeolite is a special type of catalyst that combines the advantages of metal nanoparticles and zeolites, such as high activity and selectivity. Herein, metal-encapsulated zeolites (Pd-M@S-1, M=Ni, Mn, Co) were applied as catalysts for the reductive amination of aromatic aldehydes. Results showed that the reductive amination of aldehydes over Pd-M@S-1 catalysts can be selectively switched between primary amines over Pd0.6@S-1 and secondary imines over Pd0.6Ni@S-1 by tuning the acid-base properties of the catalysts. The effect of acid-base properties of catalysts on selectivity control was claimed by conducting control experiments, time-dependent curves, and detailed characterizations.