Abstract
Multiwalled 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 x 10(6) 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 x 10(6) 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 x 10(5) g mol(-1)(Co) h(1) bar(-1) and 72%, respectively, with 5 atm ethylene and an Al/Co ratio of 200:1.