J. Li et al.
catalytic performance with its T10, T50, and T90 of 142, 185
and 221 °C, respectively. As summarized in SM Table S5,
these values are much lower than (red labels in SM
Table S5) or at least comparable with (blue labels in SM
Table S5) those reported for other Pd-based catalysts
associated with benzene oxidation [38–42], although low
catalyst loading and high space velocity were adopted in
our studies. As indicated by the green labeled in SM
Table S5, the bimetallic Au–Pd catalysts supported on the
Fe-modified ceria contributed by Tabakova and coworkers
[43] have lower T90 (ca. 150–170 °C) than that of Pd/
Co3O4-PP-350 in this work. However, a very low space
velocity (4000 h-1) and high catalyst loading (0.5 cm3)
were used to catalyze the benzene oxidation, which lead to
long time contact between benzene and catalysts, favorable
for reducing the temperature for benzene conversion.
The sequence of the catalytic activity is highly related to
the structural properties and the reducibility of the cata-
lysts. Furthermore, the influence of porous structure and
bulk structure on the catalytic performance is shown in
Fig. 6b and d. The catalytic activity of Pd/Co3O4-PP-350
(T90 = 221 °C) is superior to that of Pd/Co3O4-NP-350
(T90 = 243 °C). Furthermore, both the Pd/Co3O4-PP-350
and Pd/Co3O4-NP-350 catalysts exhibit high catalytic sta-
bility for the benzene oxidation. As evinced by SM Fig. S4,
no deactivation is observed for these two catalysts after
performing the catalytic reaction for 50 h at 236 °C (for
Pd/Co3O4-PP-350) and 265 °C (for Pd/Co3O4-NP-350),
respectively.
controlled by adjusting calcination temperature, proved by
SEM and TEM. It is of interest to note that the order of
catalytic activity is the same as the order of binding energy
for Oads, suggesting that the Oads plays a crucial role in the
complete oxidation of benzene. The H2-TPR profile
demonstrates that the Oads correlates with the PdOx species.
The porous structure may expose more PdOx species on the
surface of catalyst, and the electron transfer from Pd to O
for Pd/Co3O4-PP-350, may make the Oads more active.
These two primary factors render the Pd/Co3O4-PP-350 the
best catalyst for the complete oxidation of benzene.
Acknowledgments The authors gratefully acknowledge the support
from the National Natural Science Foundation of China (NSFC) (Nos.
51272253, 21376246, and 21573240), the National High Technology
Research and Development Program of China (Grant No.
2012AA062702), the Strategic Priority Research Program of the
Chinese Academy of Sciences (Grant No. XDB05050300), the
Knowledge Innovation Project of CAS (No.KZCX2-EW-403), and
the Hundred Talents Program of the Chinese Academy of Sciences
(No. MPCS-2014-C-01).
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4 Conclusions
In summary, porous polyhedron Pd/Co3O4 catalysts are
synthesized by pyrolysis of Co-based ZIF-67. The proper
porosity and nanoparticle size of the catalyst could be
123