12
W. Wu et al. / Journal of Catalysis 286 (2012) 6–12
posed by Takaki and coworkers [39] and supported by the experi-
mental facts above described; of course, another minor pathway
via CyOO abstracting one H atom of cyclohexane to yield a CyOOH
and another cyclohexyl radical (i.e., an auto-oxidation pathway)
may exist. Finally, the CyOOH can be converted to form the corre-
sponding alcohol and ketone (Eq. (3)), as described by Hermans
and coworkers [45]. The precipitate Cu2(OH)3Cl is easily converted
into CuCl2 in an aqueous HCl medium (see Eq. (4)). Of course, an-
other cycling pathway of CuCl2 is achieved through O2 directly oxi-
dizing CuICl in the presence of HCl (Eq. (5)). Undoubtedly, the
formation of chlorocyclohexane should be due to the combination
of Clꢀ with cyclohexyl radicals, and the product, as supported by
the above experiment (see entry 22 in Table 1), can be further con-
verted to cyclohexene via a complex and an unverified photoreac-
tion pathway (Eq. (6)). This mechanism shown in Scheme 1 may
explain the difference among the photocatalytic performance of
other metal salts. It is evident that the Eq. (1) hardly occurs upon
the metal salts containing non-halogen anions (CuAc2 and Cu(-
NO3)2ꢀ3H2O) or metal cations of low oxidizability such as AlCl3,
LaCl3ꢀxH2O, SnCl2ꢀ2H2O, CoCl2ꢀ6H2O, ZnCl2, MnCl2, and NiCl2(see
their standard redox potential listed Table 1). CuBr2 should be eas-
ily converted to CuBr and Br atom through Eq. (1), but the Br atom
formed is no easy to capture H atom of cyclohexane due to its low
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
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Acknowledgments
We acknowledge the financial support for this work by the Na-
tional Natural Science Foundation of China (20873040, 21073057,
and 20573035) and the Natural Science Foundation of Hunan Prov-
ince (10JJ2007).
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