Heterogeneous Hydroformylation Catalysts with Rhodium Nanoparticles Immobilized on Functionalized Porous Aromatic Frameworks

The study investigates the effects of various functional groups contained in porous aromatic frameworks (PAFs) on the properties and performance of a series of rhodium catalysts developed for hydroformylation. Analytical methods such as TEM, FTIR spectroscopy, elemental analysis, XRD, and low-temperature nitrogen adsorption–desorption were used to characterize the catalysts before and after running. The catalysts based on PAFs with sulfo groups (PAF–SO₃H) exceeded those based on PAFs with imidazole substituents (PAF–Im⁺Cl^–) in terms of specific activity in the hydroformylation of 1-hexene. Both catalyst types exhibited high stability over five running cycles. An extra wash with sulfuric acid enhanced the specific activity of the PAF–SO₃H catalysts, although their metal retention capacity declined; the washing had no adverse effect on the stability of the PAF–Im⁺Cl^– catalysts. Rhodium in the catalysts was present as Rh⁰ (nanoparticles) and Rh³⁺, and the reduced Rh was found to most likely act as a precursor of the catalytically active hydridocarbonyl complexes.