Balanced Rh+-Rh0 Sites over Rh Clusters Enhance Heterogeneous Hydroformylation of Aldehyde

Controlling the metal geometric and electronic structure is of significance in developing efficient catalysts for heterogeneous hydroformylation. This study examines the structural sizes of Rh and Rh⁺-Rh⁰ distribution to construct a highly active catalyst for formaldehyde hydroformylation. The active sites for hydroformylation require several Rh_n atoms, while single-atom Rh can solely catalyze hydrogenation. The highest activity was achieved on Rh nanoclusters (0.95 nm), giving a TOF of 191 h⁻¹ and selectivity of 82% for glycolaldehyde formation. The tunability of the electronic properties of Rh nanoclusters and the synergistic interaction between Rh⁺ and Rh⁰ are essential for enhanced activity. Pseudo-in situ FT-IR analysis elucidated that formaldehyde adsorbed on Rh nanocluster prefers to produce glycolaldehyde via hydroformylation, while formaldehyde adsorbed on isolated Rh^δ+ sites tends to form methanol via hydrogenation. This study provides a new insight into the design of heterogeneous catalysts and guidance for understanding the reaction mechanism for aldehydes/olefins hydroformylation.