Introduction
Liquid-phase oxidation of hydrocarbons with molecular oxygen to high
value-added products such as ketone, carboxylic acids, and alcohols is a
very important industrial process.[1-3] The liquid
aerobic oxidation of cumene is a most crucial reaction, which can
produce cumene hydroperoxide (CHP), acetophenone (AP) and
2-phenyl-2-propanol (PP).[4, 5] Those oxidation
products are intermediate platform molecules to produce fine synthetic
chemicals such as phenol, fragrances, and polyesters. For instance, over
95% of world production of
phenol
is produced by the conversion of CHP.[6, 7] To
pursue high performance catalysts, a great deal of research about
catalytic reaction have been done for decades.[8,
9]
The nonmetallic, excellent catalytic performance and high stability of
CNTs made them an excellent catalyst for selective
oxidation.[10-12] Based on our previous research,
we found that CNTs possess excellent catalytic performance for the
oxidation of
cumene.[11,
13-15] The advantage of CNTs is that oxygen can be activated on the
surface of CNTs to generate ROS, which has been
reported.[16, 17] The catalytic performance of
CNTs was further improved by doping nitrogen.[18]Because doping nitrogen would cause the strong interaction between CHP
and CNTs.[15] The main oxidation product of cumene
catalyzed by CNTs is CHP.[11, 13, 19] In that way,
cumene and CHP are able to react continuously on the surface of CNTs.
Moreover, we recently found that the selectivity of the oxidation
products would be changed by mixing different metal cocatalysts
(CuCl2, FeCl3, MnCl2 and
so on) into the system catalyzed by CNTs, especially, the trace amount
of CuCl2 could significantly improve the reactivity and
regulate product selectivity for cumene
oxidation.[14]
Most recently, we added a small amount of ZnCl2 as a
co-catalyst and observed a curious result that the oxidation product
could hardly be detected at the end of the reaction. To our best
knowledge, this is the first time that this inhibition phenomenon has
been found. A reasonable guess is that the key steps about the
production of CHP were blocked by ZnCl2, while the
generation of AP and BP is related to the participation of CHP. Thus,
inhibiting the production of CHP leads to no oxidation products at the
end of the reaction. To find out how ZnCl2 works in the
oxidation reaction of cumene, the interactions between
ZnCl2 and key reactants should be considered by DFT.
This work is of great significance to reveal the influence of impurity
of metal ion on the oxidation of cumene, and to have a deeper
understanding of carbon catalyzed radical oxidation reaction.
Experimental