Preparation, structural characterization of a novel egg-shell palladium sulfide catalyst and its application in selective reductive alkylation reaction

Article abstract of DOI:10.1016/j.cclet.2012.07.016

A novel egg-shell Pd-S catalyst with palladium metal as the core and a membrane of palladium sulfide as the surface has been prepared by sulphidizing Pd/C with H₂S. This catalyst is effective for the reductive alkylation of p-amino diphenylamine (PADPA) and methylisobutyl ketone (MIBK) to afford N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenedianine (DBPPD) with conversion up to 99.42% and selectivity to 97.46%. Comparing with the other common palladium sulfide catalysts, the membrane of palladium sulfide on the surface and the core of palladium metal cause the Pd on the surface of the new catalyst in a lower sulfur coordination, which improves its activity. Our result indicates that this new egg-shell Pd-S/C is an efficient hydrogenation catalyst.

Full text of DOI:10.1016/j.cclet.2012.07.016

Available online at www.sciencedirect.com
Chinese Chemical Letters 23 (2012) 1111–1114
www.elsevier.com/locate/cclet
Preparation, structural characterization of a novel egg-shell
palladium sulfide catalyst and its application in selective
reductive alkylation reaction
Qun Feng Zhang, Jia Chun Wu, Chang Su, Feng Feng, Qiao Ling Ding,
*
Zhao Lian Yuan, Hong Wang, Lei Ma, Chun Shan Lu, Xiao Nian Li
Industrial Catalysis Institute, State Key Laboratory Breeding Base of Green Chemistry Synthesis Technology,
Zhejiang University of Technology, Hangzhou 310032, China
Received 2 May 2012
Available online 23 September 2012
Abstract
A novel egg-shell Pd–S catalyst with palladium metal as the core and a membrane of palladium sulfide as the surface has been
prepared by sulphidizing Pd/C with H S. This catalyst is effective for the reductive alkylation of p-amino diphenylamine (PADPA)
2
0
and methylisobutyl ketone (MIBK) to afford N-(1,3-dimethylbutyl)-N -phenyl-p-phenylenedianine (DBPPD) with conversion up to
9
9.42% and selectivity to 97.46%. Comparing with the other common palladium sulfide catalysts, the membrane of palladium
sulfide on the surface and the core of palladium metal cause the Pd on the surface of the new catalyst in a lower sulfur coordination,
which improves its activity. Our result indicates that this new egg-shell Pd–S/C is an efficient hydrogenation catalyst.
#
2012 Xiao Nian Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: H S; Palladium sulfide; Egg-shell; Reductive alkylation
2
Precious metal catalysts are widely used in the various reductive reactions for their high activity, easy separation
and reusability. But the high activity of these catalysts always brings poor selectivity for the organic compounds with
multiple reducible functionalities. In recent years, precious metal sulfides have attracted much attention as an
excellent catalyst for the reductive reaction due to their high catalytic selectivity [1–6]. For example, platinum sulfide
and ruthenium sulfide are applied to hydrogenation of halogen-containing nitro compounds to amines with high
selectivity and no dehalogenation [2,3] and reductive alkylation [1,7]. However, the application of palladium sulfide
catalyst is limited for its lower activity leading to harsh reaction conditions and poor conversion during the
hydrogenation reactions [1,7]. It is desirable to design new structure of precious metals sulfides catalysts with high
reactivity and selectivity. Here we report the preparation and structural characterization of a novel egg-shell Pd–S
catalyst with palladium metal as the core and a membrane of palladium sulfide as the surface. This catalyst can
catalyze the reductive alkylation of p-amino diphenylamine (PADPA) and methylisobutyl ketone (MIBK) to afford
*
Corresponding author.
E-mail address: xnli@zjut.edu.cn (X.N. Li).
1001-8417/$ – see front matter # 2012 Xiao Nian Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2012.07.016

1112
Q.F. Zhang et al. / Chinese Chemical Letters 23 (2012) 1111–1114
0
N-(1,3-dimethylbutyl)-N -phenyl-p-phenylenedianine (DBPPD) with high selectivity and higher activity. Our result
suggests that the special catalyst can efficiently promote chemoselective hydrogenations.
1
. Experimental
Preparation of egg-shell Pd–S/C catalyst: 10% Pd/C and water were mixed in the weight ratio of 1 to 20, then an
excess of H S was passed into the slurry solution at 40 8C. The resulting catalyst was washed with water until the pH to
2
7
solution with the nominal Pd loading of 10 wt% was added into an aqueous suspension of activated carbon in a weight
and then dried in the vacuum at 110 8C for 10 h. Preparation of PdS/C catalyst: a desired volume of H PdCl aqueous
2
4
ratio of activated carbon to water at 1:20, then an excess of H S was passed into the slurry solution at 40 8C. The
2
resulting catalyst was washed with water until the pH is 7. The obtained product was dried in the vacuum at 110 8C for
1
0 h and then treated with 10% H S in hydrogen at 200 8C for 2 h.
2
Reductive alkylation was carried out at 3 MPa of hydrogen for 4 h in a 75 mL stainless steel autoclave (Parr
Instruments), which contained PADPA (3.7g, 0.02 mol) and MIBK (10 mL, 0.08 mol) and 0.037 g catalyst. The final
products were analyzed by a gas chromatography (Shimadzu GC-14B) equipped with an SE-30 capillary column and
an FID.
2
. Results and discussion
The novel egg-shell Pd–S/C catalyst has been characterized by EDS. The structure of the catalyst has been
determined by XRD and XPS. The EDS data (Table 1) showed that the catalyst contained a certain amount of S.
According to our preparation method, we induced that the S of the egg-shell Pd–S/C catalyst should be combined with
Pd strongly, and not be just a physical adsorption on the activated carbon.
The egg-shell Pd–S/C catalyst was further examined by XRD and XPS to determine its structure. The XRD patterns
Fig. 1) showed that there were only diffraction peaks of Pd, and no peaks of palladium sulfides or other sulfides were
(
observed. This result indicated that S did not enter the bulk to form palladium sulfide as a crystal. Considering the
content of S in the egg-shell Pd–S/C catalyst was 1.43%, we suggested that S should just covered Pd particles as a
membrane. Our conjecture was further confirmed by XPS spectra of the egg-shell Pd–S/C catalyst (Fig. 2). The peaks
Table 1
Elemental composition of egg-shell Pd–S/C catalyst.
Element
C
O
S
Pd
Content (%)
81.64
7.31
1.43
9.62
a: PdS/C
b: eggshell Pd-S/C
c: Pd/C
∗
∗
∗
a
b
c
0
10
20
30
40
50
60
70
80
90
Fig. 1. XRD pattern of catalysts.

Q.F. Zhang et al. / Chinese Chemical Letters 23 (2012) 1111–1114
1113
337.33 eV
342.55 eV
344.00 eV
338.54 eV
348 346 344 342 340 338 336 334
Binding energy(eV)
Fig. 2. Pd 3d XPS spectra of the egg-shell Pd–S/C.
Table 2
Properties of Pd/C, PdS/C and egg-shell Pd–S/C catalysts.
2
Surface area (m /g)
Catalyst
CO chemisorption uptake (ml/g)
Average pore radius (nm)
Pd/C
3.5
0
1517
1460
1476
0.94
0.93
0.94
PdS/C
Egg-shell Pd–S/C
0
of Pd 3d5/2 spectra at 338.84 eVand 337.33 eVof the XPS spectra showed that there was interaction between S and Pd,
and the states of Pd should be +4 and +2, which indicated that Pd existed as palladium sulfide complex on the surface
of the egg-shell Pd–S/C catalyst. Furthermore, no binding energy peak of Pd(0) was found at 3d5/2 spectra, which
indicated that there was no Pd(0) on the surface of the catalyst. The result was also proved by the CO chemisorption
uptake (Table 2). The CO chemisorption uptake showed that the egg-shell Pd–S/C catalyst could not absorb CO
anymore, suggesting that there was no Pd(0) on the surface as well. The surface area and average pore radius of Pd/C,
PS/C and egg-shell Pd–S/C are similar. All these results demonstrated that egg-shell Pd–S/C catalyst had such a
structure with palladium metal as the core and a membrane of palladium sulfide as the surface.
In order to investigate the reactivity of the novel egg-shell Pd–S catalyst, it was applied to reductive alkylation
reaction of PADPA and MIBK. The reaction started from a condensation reaction between PADPA and MIBK,
affording imine as an intermediate, and then imine was hydrogenated in the presence of catalyst to form DBPPD
(
Scheme 1). PADPA, imine and DBPPD were easy to undergo hydrogenolysis to some small molecule by-products,
such as aniline, using ordinary Pd catalysts. And a part of imine remained and could not be hydrogenated completely in
the case of lowly active hydrogenation catalyst.
CH3
CH3
-H O
2
NH
NH2 + O
C
NH
2
N
C
CH CHCH3
2
1
CH CHCH
2
3
CH3
CH3
H2
Imine
MIBK
PADPA
CH3
NH
NH CH
CH CHCH
2
3
CH3
DBPPD
Scheme 1. Reaction pathways.

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Q.F. Zhang et al. / Chinese Chemical Letters 23 (2012) 1111–1114
Table 3
Reductive alkylation over Pd/C, PdS/C and egg-shell Pd–S/C catalysts.
a
Conversion (%)
Catalysts
Reaction temperature (8C)
Selectivity (%)
DBPPD
Imine
Others
Pd/C
160
100
100
62.81
36.53
0
0
37.19
63.47
2
00
160
00
160
00
PdS/C
54.33
90.17
60.87
97.03
37.54
0.87
1.59
2.10
2
Egg-shell Pd–S/C
65.27
99.42
72.43
97.64
25.95
0.32
1.62
2.04
2
a
The reaction time is 4 h.
The catalytic performance of the egg-shell Pd–S/C catalyst was tested comparing with the traditional Pd/C and PdS/
C catalysts in reductive alkylation to DBPPD. The results were summarized in Table 3. We can see that the egg-shell
Pd–S/C showed both high activity and high selectivity. The novel catalyst not only kept the high selectivity as the
normal palladium sulfide catalyst but also improved the activity in chemoselective reductive reaction.
3
. Conclusion
An egg-shell Pd–S/C catalyst with palladium metal as the core and a membrane of palladium sulfide as the surface
was prepared by sulphidizing Pd/C with H S. The palladium sulfide on the surface of the new kind of Pd–S/C catalyst
2
provides high selectivity as common palladium sulfide catalysts, and its core of palladium metal causes the Pd on the
surface in a lower sulfur coordination than common palladium sulfide catalysts, which improves its activity. The egg-
shell Pd–S/C is expected to be an excellent hydrogenation catalyst with combination of high selectivity and good
activity.
Acknowledgments
This work was financially supported by Zhejiang Provincial Natural Science Foundation of China (No.
LY12B03009) and Program from Science and Technology Department of Zhejiang Province (No. 2011R09020-03).
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