Pyridylimine Cobalt(II) and Nickel(II) Complex Functionalized Multiwalled Carbon Nanotubes and Their Catalytic Activities for Ethylene Oligomerization

Abstract

ABSTRACTMultiwalled carbon nanotubes (MWCNTs) were covalently functionalized with pyridylimine and its metal complexes. The synthesized compounds were characterized by several analytical techniques. The pyridylimine metal complex–functionalized multiwalled carbon nanotubes [Pyr‐M(II)‐MWCNTs] were evaluated as catalyst precursors for ethylene oligomerization with methylaluminoxane (MAO) used as an activator at different Al/M [M(II) = Co(II) and Ni(II)] ratios and at two different ethylene pressures. [Pyr‐Co(II)‐MWCNTs] (C1) and (Pyr‐Ni(II)‐MWCNTs] (C2) were isolated as solid materials in good yield. Complex C2 was found to be a more effective precatalyst than C1 in the presence of MAO. Thus, C2 exhibited a maximum catalytic activity of 1.89 × 106 g mol−1(Ni) h−1 bar−1 with an Al/Ni ratio of 2000:1 at room temperature with a 5‐atm pressure of ethylene, whereas C1 exhibited a maximum activity of 1.87 × 106 g mol−1(Co) h−1 bar−1 in a similar condition. When the Al/Co ratio was increased at a 1‐atm pressure of ethylene, the catalytic activity of the precatalyst increased and the process became more selective toward higher oligomers. The catalytic activity and selectivity with 1‐decene using C1 were 3.02 × 105 g mol−1(Co) h1 bar−1 and 72%, respectively, with 5 atm ethylene and an Al/Co ratio of 200:1.