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

Abstract

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_x 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.