Controlling Reaction Pathways of Ethylene Hydroformylation Using Isolated Bimetallic Rhodium-Cobalt Sites

Designing efficient ligand-free heterogeneous catalysts for ethylene hydroformylation to produce C₃ oxygenates is of importance for both fundamental research and practical applications, but it is often hindered by insufficient catalytic activity and selectivity. This work designs isolated rhodium-cobalt (Rh-Co) sites confined within a ZSM-5 zeolite to enhance ethylene hydroformylation rates and selectivity while maintaining catalyst stability. By adjusting the Co/Al ratio in Co-ZSM-5, different sizes of Co are formed; subsequent Rh introduction produces isolated Rh₁Co clusters with different Rh-Co coordination numbers (CNs). In-situ characterizations and density functional theory calculations reveal that a Rh-Co CN of 3, corresponding to an isolated Rh₁Co₃ site, provides optimal bindings to reaction intermediates and thus achieves the highest hydroformylation rates among supported Rh-based catalysts. This study demonstrates the role of coordination-tuning via a secondary metal in effectively controlling the reaction pathway over single Rh atom catalysts.