Ultrathin Nickel-Based Metal–Organic Framework Nanosheets as Reusable Heterogeneous Catalyst for Ethylene Dimerization

Ultrathin nickel-based metal–organic framework nanosheets (Ni-UMOFNs) were formed from NiCl2·6H2O and benzene-1,4-dicarboxylate through a sonication exfoliation method. In Ni-UMOFNs, the Ni atoms are octahedrally coordinated by six O atoms to form pseudo-octahedra which are further edge/corner connected with each other to form 2D layers separated by benzene-1,4-dicarboxylate linkers. On the Ni-UMOFN surfaces, Ni centers are partially five coordinated owing to the termination of benzene-1,4-dicarboxylate ligands, and these coordinated unsaturated metal sites can be used as catalytic active sites. In this work, Ni-UMOFNs were utilized as ethylene dimerization catalysts in the presence of an alkylaluminum cocatalyst for the first time. The Ni-UMOFN catalytic system showed moderate catalytic activity but high selectivity to 1-butene up to 92.8% under optimal conditions. The optimal Ni-UMOFN catalyst can be reused at least four times without considerable loss in the catalytic activity and selectivity to 1-butene. Extraordinarily, the outstanding level of reusable property is due to continuous exposure of fresh unsaturated metal active sites when the original metal centers on the catalyst surface are used and exfoliated, just like a snake’s molting.