Abstract
Carbon nanotubes (CNTs) have excellent catalytic activity in liquid
phase reaction, especially in aerobic oxidation of cumene. In previous
work, the conversion of cumene was 41.8% and the selectivity of cumene
hydroperoxide was 71.5%, which was catalyzed by CNTs. But a small
amount of impurity Zn2+ totally blocked up the aerobic oxidation of
cumene that catalyzed by CNTs, which is an unexpected discovery. By
analyzing the catalytic mechanism of CNTs, the inhibition effect of Zn2+
is locked on the abstraction of H atom from cumene. The inhibition of
Zn2+ is confirmed in two effects by density functional theory (DFT)
calculations. Firstly, due to the strongly coordination of active oxygen
species (ROS) by Zn2+, the energy barrier of initial reaction increases
to 1.90 eV, which is nearly 4 times higher than that of the only ROS
promoted-process. Secondly, the interaction of Zn2+ and RO· or ROO· to
inhibits the chain propagation reaction of free radicals. This work
precisely demonstrates that the inhibition effect of Zn2+ on initial
reaction of cumene. The most significant thing is that the effect of
metallic heteroatoms is not negligible in organic oxidation reaction.