Inhibitory effect of Zn2+ on the chain-initiation process ofcumene oxidation
Zhicheng Chena, Yuhang Li*c, Yonghai Caob, Qiao Zhanga, Hao Yub and Feng Peng*a
a School of Chemistry and Chemical Engineering, Guangzhou University, Guangzhou 510006, China.
b School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, China
c School of Chemistry, Sun Yat-sen University, Guangzhou 510275, China
* Corresponding author, E-mail: liyh@mail.sysu.edu.cn (Y. Li);
fpeng@gzhu.edu.cn (F. Peng)
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.
Keywords: carbon catalysis; cumene oxidation; inhibition effect; DFT calculations