Metal-organic framework-based composite Ni@MOF as Heterogenous catalyst for ethylene trimerization

MIL-125(Ti)-NH2 has been post-synthetically modified by reaction of pyridine with the terephthalate amino groups to form pyridine-imine that act as ligands of nickel(II). Ni@MOF showed moderate catalytic activity and high selectivity to low carbon olefins C-4 and C-6. Upon activation with MAO, the catalytic activity could achieve 1.81 x 10(5) g/mol Ni h, and the selectivity toward C-6 was about 76.7 %, of which the 1-C-6(=) occupied 91.5 % under the reaction condition of 50 degrees C, 1.0 MPa, Al/Ni = 800. Compared with homogenous pyridine-imine nickel complex, the selectivity toward C-6 of Ni@MOF composite was greatly enhanced, which could be attributed to confinement effect of pore wall of MOF structure. Moreover, the Ni@MOF could be reused for at least two more catalytic runs without significant loss of activity or selectivity, indicating Ni@MOF had good catalytic stability and recyclability. A possible ethylene oligomerization mechanistic pathway involving reaction intermediates is proposed based on the Cossee mechanism.