Preparation Of ZIF-8 Confining Phosphine Ligand Catalyst For Hydroformylation

Hydroformylation of olefin is the catalytic process for preparation one more carbon aldehydes or alcohol,which owns 100%atom economy and is widely used in high value-added products,such as surfactant,pharmaceutical intermediate and so on.At present,hydroformylation of low olefin has been realized,but high olefin still has the problems from its low activity and poor stability,so it is urgent to explore an efficient and s Tab.catalyst for hydroformylation of high olefin.In order to combine the advantage of homogeneous and heterogeneous catalysts,here we prepared a Rh base catalyst,which confined the phosphine ligands and active component in ZIF-8 materials.The main research contents are summarized as follows:（1）The P-Rh/ZnO@ZIF-8 catalyst was prepared by in-situ growth of ZIF-8 on the surface of ZnO,meanwhile confining phosphine ligands.Characterization results confirm that the ZIF-8 shell layer have been successfully grown on the surface of ZnO.Under mild reaction conditions,the catalyst achieved 69%conversion and 20%selectivity of aldehydes.But cyclic experiments showed that the active species could not be effectively stabilized during the hydroformylation reaction,which might be attributed to phosphine ligands on the surface leaching during the etching process,resulting in little amount of phosphine ligand in the catalyst.The PPh₃-Rh@ZIF-8 catalyst was synthesized by in-situ confining PPh₃ during the growth of ZIF-8 with solvothermal and double solvent method.Characterization results showed that both method could effectively confine PPh₃ ligand.Comparatively speaking,the catalyst obtained by two-solvent method owned a higher content of phosphine ligand.Under mild reaction conditions,the better catalyst achieved 98%conversion and 45%selectivity of aldehydes.However,the catalytic performance decreased slightly after three cycles.Further studies demonstrated that the structure of ZIF-8 in the catalyst reconstructed under hydroformylation reaction condition.In the meantime,the localized ligands were released,which resulted in the gradual degradation of the stability.（3）In order to improve the stability,Rh-P@ZIF-8 catalyst prepared by double solvent method was treated by reduction.The results showed that the structure of ZIF-8 did not change before and after reduction treatment by Na BH₄ or H₂.For 1%Rh-PPh₃@ZIF-8Na BH₄ catalyst,the conversion is more than 98%,the selectivity of aldehydes is above 30%.But the catalytic performance decreased obviously after five cycles.When reduced with H₂,1%Rh-P@ZIF-8 R300 catalyst significantly improved the stability in the hydroformylation reaction.Under the same conditions,the catalyst obtained 98%conversion and 30%selectivity of aldehydes,and the catalytic performance maintained after five cycles.It was noted that the PPh₃ ligand decomposed and combined with Rh metal to form a s Tab.Rh-P species during the H₂ reduction treatment,which acquired a high cyclic stability.