Cs Modified Cu–Al Catalysts for Selective Synthesis of Secondary Amines from Ammonia in Flow

Secondary amines are valuable compounds widely used in pharmaceutical and environmental applications. Direct synthesis of secondary amines from ammonia via reductive amination represents a cost-effective and atom-economical strategy, offering an attractive alternative to conventional multistep methods. However, previous methods rely on noble metals to enhance secondary imine activation and achieve high selectivity. Compared to noble metal catalysts, catalysts based on earth-abundant elements are more accessible, cost-effective, and environmentally friendly. In this study, we developed Cu–Al catalysts enabling the direct and selective synthesis of secondary amines from ammonia and aldehydes. A 93% yield of dibenzylamine was achieved at 50 °C and 2 MPa H 2 within a short residence time of 7 min. Mechanistic studies reveal that the catalysts possess a core–shell structure, in which Cu 0 in the core facilitates hydrogen activation and promotes hydrogenation, Cu + species in the shell assist C═N bond activation and suppress alcohol formation, and oxygen vacancies enhance secondary imine adsorption and improve selectivity toward secondary amines.