Synthesis and catalytic behavior of nickel heterogenized in covalent organic frameworks as precatalysts in ethylene oligomerization

Two covalent organic frameworks (COFs), as the supports of transition metal catalysts, were prepared and coordinated with nickel to synthesize two precatalysts for ethylene oligomerization. The chemical structure of sub-constructing unit had a significant influence on the specific surface area and the catalytic performance of covalent organic frameworks supported nickel(Ⅱ) catalysts. Two COFs were stacked in lamellae, and the specific surface area and the pore volume of COF with p-phthalaldehyde as sub-constructing unit were far larger than those of COF with butanedione as sub-constructing unit. The catalyst with a larger specific surface area had a higher catalytic activity and a higher selectivity of low carbon olefins in ethylene oligomerization because of a higher specific surface areas and larger pore structure for ethylene diffusion and mass transfer. Two catalysts can be reused at least three times without considerable loss in the catalytic activity and the selectivity toward short-chain α-olefins.