Qingtao Niu,Maifen Yang,Xingan Wang,Aihua He,Manman Jin
Immobilization of active site on solid support plays great roles in improving catalyst performance. In this study, a series of solid supported iron precatalysts via the immobilization of iron halides (FeX n , X = Cl, Br or I, n = 2 or 3) on the metal-organic frameworks of UiO type bearing bipyridine moiety (bpy-UiO) were synthesized and used for isoprene polymerization. These bpy-UiO supported iron precatalysts (bpy-UiO-FeX n ) were also well characterized by the powder X-ray diffraction, elemental analysis and N 2 adsorption measurement. Upon activation with trialkylaluminums (AlEt 3 , Al(i-Bu) 3 and AlOct 3 ), bpy-UiO-FeX n exhibited excellent catalytic activity for isoprene polymerization. Interestingly, the iron(III) precatalysts had higher activity than the iron(II) precatalysts, and the highest activity was 1726.4 Kg⋅P/(mol⋅Fe⋅h) for bpy-UiO-FeBr 3 with AlEt 3 . Moreover, the activity gradually increased as the polymerization temperature increased from 0 °C to 50 °C, reflecting the fact that the MOFs supported iron catalysts had excellent thermal stability. Notably, the obtained polyisoprene had the ultrahigh molecular weight ( M w = 1.20×10 6 –3.13×10 6 Daltons), and predominantly consisted of 38.5–54.4 mol % cis -1,4 configuration and 45.6–61.5 mol % 3,4-configuration. This work offers an opportunity to design the high active and stable iron catalyst for conjugated diene polymerization based on the solid support.
While the coordination environment around catalytic metal sites plays a crucial role in catalysis, its precise design and modulation still remain a challenge. Herein, the coordinated N atom number around single Co sites installed on a UiO-type metal–organic framework has been modulated to afford UiO-Co-Nx (x = 2, 3, and 4) for photocatalytic CO2 reduction. Significantly, the photocatalytic performance is affected by the coordinated N atom number around the Co site, in which UiO-Co-N3 exhibits superior activity to the other counterparts. Photo-/electrochemical results support the fastest charge transfer kinetics between the photosensitizer and UiO-Co-N3. Theoretical calculations, together with the results acquired from in situ diffuse reflectance infrared Fourier transform spectra, manifest the lowest energy barriers of the rate-determining step and desorption energy of CO* over UiO-Co-N3 among all UiO-Co-Nx samples.
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