Well-Defined RhO4 Species Confined in Self-Pillared Pentasil Zeolite as Efficient Nano Reactors for Hydroformylation of Higher Olefins.

Heterogeneous catalytic hydroformylation of higher olefins often suffers from substrate diffusion limitations and unclear active species. We overcame both challenges using a self-pillared MFI zeolite anchoring Rh single atoms. By controlling reaction and calcination conditions, we synthesized catalyst Rh1@SPP-MFI (Rh1@SPP-S-1, Rh1@SPP-ZSM-5, Rh1@SPP-TS-1) using a one-pot method. Extended x-ray absorption analysis combined with cs-corrected high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) confirmed each Rh atom coordinated with four O atoms as a well-defined Rh1.5+-O4 structure confined in zeolite cages. The thickness of the zeolite nanosheets was approximately 1.5 b-axis unit cells, interlayer spacing ∼ 3.0 nm, making them ideal as nanoreactors. At 353 K and 2.5 MPa, the catalyst achieved a turnover frequency (TOF) of 7074 h-1 for 1-octene to nonanal, outperforming most homogeneous/heterogeneous catalysts under comparable conditions. Over five cycles (36 h), each Rh atom processed ∼6881 olefin molecules per hour. Density functional theory (DFT) revealed evident electron transfer from O to Rh in the RhO4 unit, and the flexible Rh-O bonds mitigated steric hindrance during hydroformylation. This work reveals the microstructure and working mechanism of supported Rh catalysts, and correlates them with the classical homogeneous catalytic mechanism.