Effective hollow Rh@H-S-1 catalyst for hydroformylation of 1-hexene

A hollow zeolite encapsulated Rh catalyst Rh@H-S-1 with an “eggshell” structure was prepared using the method of organic alkali treatment and recrystallization. Compared with catalysts with directly encapsulated Rh@S-1 and surface impregnated Rh/S-1, this catalyst exhibited both superior activity and a higher TOF value in hydroformylation of 1-hexene due to the high dispersion of Rh and high diffusion. The Rh element did not need to be reduced in the preparation, and it was in situ reduced by the syngas. The content of lower valence Rh^δ+ gradually increased with the reaction procedure and played as an active center. The low oxidized state Rh⁺ or Rh^δ+ in the form of Rh(CO)₂ are proposed as active sites in hydroformylation, which were generated under the synergistic effect between CO and H₂. Importantly, the hollow encapsulated catalyst effectively decreased Rh leaching to 0.1 ppm and showed better stability compared with the impregnated Rh/S-1 catalyst.