G Model
CCLET-2848; No. of Pages 4
2
J. Zhao et al. / Chinese Chemical Letters xxx (2014) xxx–xxx
carbon support to obtain a SnO
2
loading of 10 wt%, then the pH
3. Results and discussion
value was adjusted to 8–9 under stirring. Subsequently, the solid
was collected by filtration, washed, dried and then calcined in N
gas stream at 773 K for 4 h. Then an aqueous solution of H PdCl
0.05 gmetal/mL) was added into an aqueous slurry of the SnO
supports to obtain a Pd loading of 2 wt%. After stirring, the solution
pH value of 8–9 was reached, then the precipitated Pd(OH) was
reduced by hydrazine hydrate. Finally, the slurry was washed and
dried under vacuum at 383 K for 10 h, and kept for use. The Pd/C
heterogeneous catalyst with 2 wt% Pd loading was also prepared
2
Fig. 1a showed that the Pd NPs were highly dispersed on the
2
4
SnO
planes that were identified with the NPs, which correspond to the
(1 1 0) plane of SnO and the (2 0 0) plane of Pd. Generally, the
2
NPs. As indicated in Fig. 1b, there were two kinds of lattice
(
2
/C
2
2
activation energy for heterogeneous nucleation is lower than that
0
for homogeneous nucleation [22], which results in Pd atoms
2
depositing on SnO surfaces rather than forming discrete Pd NPs on
carbon support. The size of Pd particles was distributed mainly in
the range of 3–5 nm with an average size of Pd NPs being about
4 nm (Fig. 1a). In the XRD patterns shown in Fig. 2, the obvious
using the same procedures. A classical Pd/SnO
catalyst with 2 wt% Pd loading was also prepared by the traditional
wetness impregnation method using H PdCl and prepared SnO
supports as precursors. The SnO support was prepared by
neutralizing the prepared SnO sol with an aqueous solution of
NaOH and drying the SnO precipitate at 383 K. The catalyst was
calcined at 573 K for 2 h and reduced with hydrogen at 523 K for
h.
TEM study was carried out in a Philips-FEI Tecnai G2 F30 S-Twin
2
heterogeneous
2
4
2
crystal planes of the SnO
SnO /C samples. The peaks corresponding to Pd NPs at 2
and 46.968 relative to the (1 1 1) and (2 2 0) planes, respectively,
could be observed (Fig. 2b). As shown in Fig. 3, the areas of the H
TPD peaks for the Pd/SnO /C catalyst were much larger than those
for the Pd/C and Pd/SnO catalysts, which may be attributed to the
hydrogen spillover effect in Pd/SnO /C. The enhancement in the
2
were observed for both SnO
2
/C and Pd/
2
2
u
= 40.138
2
2
2
2
3
2
2
instrument. XRD measurements of the catalyst samples were
performed on a PANalytical-X’Pert PRO generator. XPS was
amount of chemosorbed hydrogen may be beneficial for improving
catalytic activity [23]. The XPS core level spectra of Pd 3d of the
various catalysts are shown in Fig. 4. The Pd 3d peaks were
detected at a range of binding energy (BE) of 335.1–335.5 eV for
acquired with a Kratos AXIS Ultra DLD spectrometer. H
experiments were performed by first reducing the sample in situ at
00 8C. Then the sample was swept with pure Ar to remove
2
TPD
2
2 2
the Pd/C, Pd/SnO and Pd/SnO /C catalysts, which is typical for
0
physiosorbed and/or weakly bound species. The TPD spectra were
recorded by TCD.
metallic Pd [24]. In addition, the binding energy of Pd 3d5/2
detected at 336.5–337.1 eV was attributed to the presence of
II
II
Liquid phase hydrogenation of DFNB was conducted as follows:
palladium in the form of Pd O. The presence of Pd O on the surface
was ascribed to the easy oxidation of Pd upon contact with air at
1
50 mL of ethanol, 10.0 g of DFNB, and 0.1 g of the catalyst were
mixed in a 500-mL steel autoclave. Air in the autoclave was purged
by hydrogen, and then the reaction proceeded at the required
temperature (363 K) and at 1 MPa of 99.99% pure hydrogen. The
selectivity of the hydrogenation of DFNB was calculated using the
following equations:
room temperature. It was observed that in the Pd/SnO
SnO
slightly shift of 0.3 eV and 0.4 eV, respectively, compared with that
of the Pd/C sample, which presented at a binding energy of
2
and Pd/
2
/C samples, the position of the Pd 3d5/2 signal presented a
0
2
335.1 eV. Upon the addition of the SnO , the electronic structure of
the surface Pd atoms was modified.
When the hydrogenation of nitrobenzene was carried out in
organic solvents, several intermediates were frequently produced
and accumulated during the reaction [25–29]. In the case of
fluoronitrobenzene, a possible side reaction is the nucleophilic
substitution C–N coupling reaction that leads to the formation of
amino- and/or nitro-diphenylamine. Interestingly, the production
of these intermediates was inhibited when hydrogenation of
m
DFAN
%
SelectivityDFAN ¼ m
DFAN% þ m
100%
2
-
FAN% þ m
4
-
FAN% þ mAN% þ mOBP
%
ꢀ
where 2-FAN represents 2-fluoroaniline; 4-FAN represents 4-
fluoroaniline; AN represents aniline; OBP represents the amount of
azoxybenzene (AOB), azobenzene (AB), hydrazobenzene (HAB), N-
phenylhydroxylamine (PHA), nitrosobenzene (NSB), aminodiphe-
nylamine (ADPA) and nitrodiphenylamine (NDPA) in the mixture.
2
nitrobenzene was catalyzed using a Pd/SnO /C catalyst, and the
results can be found in Table 1. Throughout the whole reaction
process, 100% DFAN selectivity was achieved and no undesired
2 2
Fig. 1. (a) TEM image of Pd/SnO /C and the crystallite size distribution and (b) HRTEM image of Pd/SnO /C.
2
Zhao, Jia
