Rh Cluster Catalysts with Enhanced Catalytic Activity: The ‘Goldilocks Rh Size’ for Olefin Hydroformylation

This study investigated the performances of Rh single-atom catalysts (SACs), cluster catalysts, and nanoparticle (NP) catalysts in olefin hydroformylation. Using in situ characterization techniques, we elucidated the distinct chemical and electronic properties of each catalyst type. Our findings revealed that Rh cluster catalysts exhibit distinctive characteristics between those of SACs and NPs, significantly influencing their catalytic performance. Notably, Rh cluster catalysts achieved a 5-fold increase in turnover frequency (∼25,589 h–1) compared to SACs (∼5,430 h–1) and a 9-fold increase relative to NP catalysts (∼2,838 h–1) in the propylene hydroformylation. Theoretical calculations revealed that the Rh cluster catalysts possess optimal CO adsorption energies, allowing them to efficiently overcome the energy barrier for CO insertion during the rate-determining step of propylene hydroformylation. Additionally, density of states and crystalline orbital Hamilton population analyses confirmed that the Rh cluster catalyst exhibited adjusted electronic properties, positioned between those of Rh SAC and NP catalysts. This study highlights the unique properties of the Rh cluster catalysts and offers valuable insights into the design of high-performance catalysts for hydroformylation and other catalytic processes.