Table 2 Reusability of Pt/g-ZrP catalyst for the selective hydrogena-
tion of P-CNBa
in the aromatic ring would favor the hydrogenolysis of the
carbon–halogen bond in aromatic haloamines, but acid–base
interaction between the OH groups of g-ZrP and NH2 groups
of produced CAN molecules decreases the electron-donating
ability of NH2 groups, so the hydrodechlorination of CAN is
suppressed. (2) A strong metal–support interaction (SMSI)
between the g-ZrP support and the Pt particles weakens the
extent of electron feedback from the Pt atom to the aromatic
ring in CAN, which would further suppress the hydrodechlor-
ination of CAN. It is well known that adsorption of substrate
molecules to the surface of the catalyst is the main factor
determining catalytic activity.18 Based on the XPS data, Pt is
electron-enriched while the nitro group of CNB is a strong
electron-withdrawing group. As a result, the electropositive
nitrogen atom of the nitro group is absorbed on the surface of
electron-enriched Pt atom, therefore, the NQO bond of CNB,
which is activated by electronic interaction between the nitro-
gen atom of the nitro group and Pt atoms, becomes more
susceptible to hydrogen attack, thereby promoting the hydro-
genation of CNB. From Table 1 (entry 7), we can observe that
the conversion and the selectivity can reach 100% even when
the turnover number is 426 000. To the best of our knowl-
edge, this excellent catalytic performance for the hydrogena-
tion of p-CNB over Pt-based catalysts has rarely been reported
up to now.
Product selectivityd (%)
Cycle
Conv.c (%)
Dechlor.
CAN
Othersb
1
2
3
4
a
99.9
97.3
95.8
92.9
1.0
0.03
0
97.2
92.4
91.1
90.3
1.9
7.5
8.9
9.7
0
Reaction conditions: 3 mmol substrate in 8 ml methanol, 10 mg Pt/g-
b
c
ZrP, 2 MPa H2, 40 1C, 20 min. See footnote d in Table 1. The
reproducibility of the conversion results is within the range of
d
Æ(0.1–2.8)%. The reproducibility of the product selectivity results
is within the range of Æ(0.05–2.0)%
(2) other by-products, para-chloronitrosobenzene and
dichloro-azoxybenzene as intermediates, could be further hy-
drogenated to the desired product p-CAN with the extension
of reaction time, which was supported by the results of Table 1
(entries 4–7). A possible reason for 100% p-CAN selectivity
over recovered catalyst could be the aggregation of the Pt
particles. TEM measurements (Fig. 2) showed that the size of
Pt particles of 7 nm in the recovered Pt/g-ZrP sample was
significantly larger than that in the fresh (unreacted) sample (3
nm), which suggested the highest selectivity in p-CAN (100%)
was achieved on larger Pt particles, this conclusion was in
agreement with the result reported in previous literature.12 In
conclusion, we believe it would be possible to achieve a 100%
CAN selectivity at complete CNB conversion by optimizing
the size of Pt particles with g-ZrP as support.
Coq et al. studied the effect of supports on the selective
hydrogenation of para-chloronitrobenzene over Pt-supported
catalysts, among different supported platinum catalysts, a
selectivity of 99.3% for p-CAN was obtained at 99.7% con-
version of p-CNB when platinum was supported on titania
and reduced at high temperature, this unique behaviour is due
to a strong metal–support interaction (SMSI) state for plati-
num. However, the dehalogenation reaction was unavoidable
over the Pt/TiO2 and better selectivity of CAN was not
maintained by longer reaction time.1 Over Pt/g-ZrP catalyst,
dechlorination product was avoidable, even when the reaction
time was extended over 5 h after p-CNB was exhausted, and
we conclude that the suppression of p-CAN hydrodechlorina-
tion is responsible for high selectivity for p-CAN. For the
mechanism in the hydrodehalogenation reaction of aromatic
halides, most researchers agreed that is caused by electrophilic
attack of cleaved hydrogen on the absorbed aromatic ha-
lides.17 According to this mechanism, we believe that the
protection of CAN against dechlorination over Pt/g-ZrP
catalyst can be explained in terms of: (1) the amino group of
produced CAN molecules as an electron-donating substitution
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