Modification of Metal Complex on the Hydrogenation of Chlorobenzene over Polymer-Stabilized Platinum Colloidal Nanocatalyst

Article abstract of DOI:10.1080/15533174.2014.989610

The metal complex effect on the hydrogenation of chlorobenzene over a poly(N-vinyl-2-pyrrolidone)-stabilized platinum colloidal nanocatalyst (PVP-Pt) has been studied under 298 K and atmospheric pressure. The introduction of metal complexes and ligands exhibited great effect on the activity and the selectivity of the nanocatalyst. It is evidently manifested that the modification of metal complexes is not the simple sum of those of the metal central ions and the corresponding ligands.

Full text of DOI:10.1080/15533174.2014.989610

Synthesis and Reactivity in Inorganic, Metal-Organic, and
Nano-Metal Chemistry
ISSN: 1553-3174 (Print) 1553-3182 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt20
Modification of Metal Complex on the
Hydrogenation of Chlorobenzene Over Polymer-
Stabilized Platinum Colloidal Nanocatalyst
Dan Li, Qiang Bai, Ning Sui, Hailian Xiao, Jun Wan, Shaojie Liu & Manhong Liu
To cite this article: Dan Li, Qiang Bai, Ning Sui, Hailian Xiao, Jun Wan, Shaojie Liu & Manhong
Liu (2016) Modification of Metal Complex on the Hydrogenation of Chlorobenzene Over
Polymer-Stabilized Platinum Colloidal Nanocatalyst, Synthesis and Reactivity in Inorganic,
Metal-Organic, and Nano-Metal Chemistry, 46:6, 902-907, DOI: 10.1080/15533174.2014.989610
To link to this article: http://dx.doi.org/10.1080/15533174.2014.989610
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Date: 13 March 2016, At: 19:01

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry (2016) 46, 902–907
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2014.989610
Modification of Metal Complex on the Hydrogenation of
Chlorobenzene Over Polymer-Stabilized Platinum Colloidal
Nanocatalyst
DAN LI1, QIANG BAI1, NING SUI1, HAILIAN XIAO1, JUN WAN1, SHAOJIE LIU2, and MANHONG LIU1
1College of Materials Science and Engineering, Qingdao University of Science and Technology, Qingdao, P. R. China
2School of Chemistry and Chemical Engineering, Shandong University, Jinan, P. R. China
Received 27 March 2014; accepted 4 November 2014
The metal complex effect on the hydrogenation of chlorobenzene over a poly(N-vinyl-2-pyrrolidone)-stabilized platinum colloidal
nanocatalyst (PVP-Pt) has been studied under 298 K and atmospheric pressure. The introduction of metal complexes and ligands
exhibited great effect on the activity and the selectivity of the nanocatalyst. It is evidently manifested that the modification of metal
complexes is not the simple sum of those of the metal central ions and the corresponding ligands.
Keywords: modification, metal complex, platinum, selective hydrogenation, chlorobenzene
Introduction
The addition of metal complexes to the catalytic system
can considerably modulate both the activity and the selec-
In the field of catalysis, polymer-stabilized metal colloids tivity of the catalyst of PVP-Pt in the hydrogenation of
have shown their particular catalytic performance due to cinnamaldehyde[14] or halonitrobenzene.[15,16] Feng and
their unique chemical and physical properties as compared to Liu[14] reported that the modification of some metal com-
either bulk metal or single metal atoms,[1–3] and the special plexes to the platinum nanocatalysts led to the increase in
catalytic environment modulated by polymer stabilizers.[4,5] both activity and selectivity for hydrogenation of cinna-
It is well known that additives can markedly affect the prop- maldehyde (CAL) to cinnamyl alcohol (COL). When
erties of metal catalysts. The effect of metal ions has been employing Na3FeF6 as the modifier, the conversion was
[6–8]
well studied in the field of heterogeneous
and homoge- promoted from 65.5% to 78.0% and higher selectivity
nous catalytic systems.[9–13] Yu and Liu[9] reviewed their (75.0%) to COL was obtained. While the neat platinum
group efforts on the singular modification effects of metal nanoparticles served as the catalyst, only moderate con-
cations and metal complex ions on the selective catalytic version of CAL and low selectivity (17.7%) to COL were
hydrogenation reactions over noble metal colloidal nanocata- obtained. Otherwise by introducing Ni(bpy)3Cl2 to the
lysts in liquid medium. They declared that metal complex catalytic system, the modification changed the main prod-
ions exhibited more complicate effects in many selective cata- uct to hydrocinnamaldehyde (HCAL) with a selectivity of
lytic hydrogenation reactions. Moreover, the metal com- 97.3%. Yang et al.[15] reported the effect of metal complex
plexes displayed considerable modification effects on the on hydrogenation of o-chloronitrobenzene (CNB) over
catalytic properties of metal colloid nanocatalysts. In recent polyvinylpyrrolidone-stabilized platinum nanocatalysts
years, Liu and colleagues[9–16] prepared a series of polymer- (PVP-Pt). The addition of metal complexes Ni(AcAc)2
stabilized platinum, palladium, and ruthenium monometallic and Na[Co(AcAc)3] showed favorable effect on the selec-
and bimetallic colloidal nanoparticles, and studied the effect tivity to o-chloroaniline (o-CAN; 76.2% and 76.5%,
of metal complexes on metal colloids in the selective hydro- respectively) and the activity (0.72 and 0.83 mol H2/(mol
genation of various reactants.
Pt s), respectively). On the other hand, the highest selec-
tivity to o-CAN (94.0%) was achieved in the complex Ni
(en)3Cl2 modified PVP-Pt catalyst system, though the
activity was lowered to 0.16 mol H2/(mol Pt s). They also
found that Cu(en)2Cl2, Zn(en)2Cl2, and Na3[Fe(SCN)6]
acted as poisons and caused the PVP-Pt catalyst to lose
all the activity. It should be pointed out that the metal
complex modification effect varies greatly with the nano-
catalysts and the substances to be hydrogenated. Tu et
al.[16] disclosed that the same metal complex exhibited
Address correspondence to Shaojie Liu, School of Chemistry
and Chemical Engineering, Shandong University, Jinan 250100,
P. R. China. E-mail: shaojieliu@sdu.edu.cn and Manhong Liu,
College of Materials Science and Engineering, Qingdao Univer-
sity of Science and Technology, Qingdao 266042, P. R. China.
E-mail: liumanhong68@126.com

Hydrogenation of Chlorobenzene
903
different modification effects on the hydrogenation of metal complex effect on the activity and the selectivity of
CNB with different chloro position relative to the nitro the catalyst is investigated.
group. For example, Ni(en)3Cl2 had the most favorable
effect on the selectivity of o-, m-, p-CNB to their corre-
sponding CAN products, while Mn(en)Cl2 had the most Experimental
inferior effect among the metal ethylenediamine com-
plexes. In the PVP-stabilized ruthenium colloid (PVP-Ru) Poly(N-vinyl-2-pyrrolidone) (PVP, average molecular weight
catalyst system,[17] the addition of Zn(II)-diamine com- 10,000) was purchased from Shanghai Chemicals Co., Ltd.,
plexes of led to a significant increase in the activity, while China. Hexachloroplatinic acid (H2PtCl6¢6H2O) of analytical
the selectivity for o-CAN maintained at »100%. Espe- grade was supplied by Beijing Chemicals Co., Ltd. Hydrogen
cially, a rate enhancement more than 30 times over neat (H2) with a purity of 99.999% was supplied by an extra-pure
PVP-Ru was achieved in the presence of Zn(trien)Cl2. It hydrogen generator HA-300. Chlorobenzene was distilled
was verified that the incorporation of Zn(II) complexes of before use. Other reagents of analytical grade were supplied
multi-amines changed the reaction kinetics. It is generally by Qingdao Chemicals Co. and were used directly.
believed that the interaction between the metal complexes
The PVP-Pt was synthesized as reported in a previous
and metal nanoparticles may alter the electronic density paper.[23] Hexachloroplatinic acid (H2PtCl6 6H2O, 0.052 g,
of metal nanoparticle’s active sites, which in turn affects 1.00£10¡4 mol) was dissolved in a mixed solution of 30 mL
its catalytic performances. In conclusion, the mechanism methanol and 30 mL water, PVP (0.222 g, 2.00£10¡3 mol as
of metal complex effect is much more complicated than monomeric unit) was then added to the solution as a stabi-
metal cation effect.
lizer. The vigorous stirring was maintained all the time during
Chlorinated organic compounds are important organic the synthesis. The reaction mixture was refluxed for 3 h and
intermediates and solvents in chemical industry, agricultural led to a homogeneous dark-brown solution of colloidal plati-
chemistry, and medical chemistry.[18] Compared with ali- num nanoparticles. The colloid was evaporated to dryness
phatics, chlorinated aromatic compounds in which the C-Cl with a rotated evaporator under reduced pressure below
bond has a much higher bond strength are generally more 60ꢀC. The resulting solid residues were redispersed in metha-
resistant to dechlorination.[19] In order to modulate the cata- nol with a definite concentration as the catalyst. The particles
lytic hydrodechlorination (HDC) to achieve high yields of in PVP-Pt sol were mostly distributed in the range of 2.3-
the desired products (cyclohexane), many approaches have 5.6 nm with an average diameter of 3.63 nm.[23]
been explored by the preparation of bimetallic or supported
Metal complexes were formed in situ by mixing a metal
catalysts and the use of specific additives (promoters and salt with a corresponding ligand at a proper molar ratio
inhibitors). Liu et al.[20] studied the catalytic HDC of chloro- according to the reported method.[14–16] For example, Ni(en)
benzene over Pd nanoparticles supported on carbon nanofib- (NO3)2 was prepared by mixing Ni(NO3)2¢6H2O (32.6 mg,
ers and found promising HDC performance. Zhu et al.[21] 0.112 mmol) with ethylenediamine (6.75 mg, 0.112 mmol) in
studied HDC of chlorobenzene with 1–3 chlorine atoms on methanol. For the sake of simplicity, only metal complexes
nanoscale Pd/Fe catalysts at room temperature; chlorinated with stepwise stability constant[24,25] k1 higher than ca. 105
benzenes could be completely reduced to benzene. Catalytic were selected for test.
hydrodechlorination of chlorobenzene over supported palla-
Hydrogenation of chlorobenzene was carried out at 298 K
dium catalyst in buffered medium was studied, and it was under 0.1 MPa of hydrogen.[23] The reaction solution typi-
found that aqueous buffer solutions preserved the catalyst cally contained 1.00 mmol chlorobenzene, 10.0 mL PVP-Pt
morphology and the catalytic activity for up to four succes- colloidal dispersion (containing 2.50£10¡5 mol Pt), and
sive HDC reactions.[22]
0.078 g 1-octane (as an internal standard for GC analysis).
Liu et al.[23] recently reported that nearly 100% selectiv- The total reaction solution volume was 30.0 mL with metha-
ity to cyclohexane could be obtained in the HDC of chlo- nol as a solvent. The reaction solution was placed in a three-
robenzene over a PVP-Pt colloidal nanocatalyst; however, neck flask equipped with a magnetic stirrer and the tempera-
the activity was not satisfied. The effect of metal ions on ture was maintained by a thermostatic water bath. After H2
the hydrogenation of chlorobenzene over PVP-Pt colloidal was charged several times to replace the air in the flask, the
catalysts was studied, and it showed that some metal cati- mixture was stirred vigorously and the HDC reaction started.
ons significantly affected the catalytic performances of the The hydrogenation reaction rate was calculated by the uptake
colloidal nanocatalysts.[13] High activity and high selectiv- rate of hydrogen. Chemical analysis of the products was ana-
ity are expected to be obtained by introducing the metal lyzed by GC with an AC-10 column. Reactants and products
complexes as modifiers on the selective hydrogenation of were identified by comparison with authentic samples.
chlorobenzene over PVP-Pt colloidal catalysts. As far as
we know, the effect of metal complexes on metal colloids
in the catalytic HDC of chlorobenzene reaction has rarely Results and Discussion
been studied. To better understand the complex effect and
its relation with reaction substrates, we made further The hydrogenation of chlorobenzene was studied in methanol
investigations. Here we describe the results on the hydro- at 298 K under 0.1 MPa of hydrogen over PVP-Pt colloidal
genation of chlorobenzene over PVP-Pt colloidal nanoca- catalyst. The hydrogenation products determined by GC-MS
talysts modified by metal complexes and ligands; the analysis were benzene and cyclohexane. Benzene was the

904
Li et. al
intermediate product. Thereby, benzene was immediately selectivity. Cation Fe3C (entry 4) hindered the rate of hydro-
found in the beginning of the reaction, and started to convert genation. Moreover, Mn2C (entry 3) and Zn2C (entry 7) acted
to cyclohexane at the same time. No other by-products were as poisons to lose all the activity of PVP-Pt colloidal
detected by GC-MS. Table 1 summarizes the experimental nanocatalysts.
results of the influence of metal complexes, metal ions, and
It is well known that ligands as additives can markedly
ligands on the hydrogenation of chlorobenzene over PVP-Pt affect the properties of metal catalysts. In some reactions,
colloidal catalyst. It can be seen from Table 1 that the com- some ligands as modifiers accelerated the reaction rate by 1–2
plexes composed of the same central metal ion with different orders of magnitude, which was called “ligand-acceleration
ligands (entries 14 and 19; 16 and 25; 21 and 23) and the dif- phenomenon” by Jacobsen et al.[26] Yan et al.[17] found that
ferent central metal ions with the same ligand (entries 14–17; the introduction of some ligands, especially ethylenediamine
19–21; 23–25) exert distinct influences on the catalytic prop- (en), obviously promoted the activity of PVP-Ru without any
erties. It is evidently manifested that the effect of the metal loss in selectivity for o-CAN. In the enantioselective hydro-
complexes is different from both the metal central ions and genation of ethyl pyruvate at low concentration of cinchoni-
the ligands, and it is not the sum of the effects of both.
dine, the addition of achiral tertiary amines (ATA) strongly
From Table 1 it can be seen that an activity of 9.30 mol increased both the rate of the reaction and the enantioselec-
H2/(mol Pt h) was achieved when employing neat PVP-Pt tivity.[27] They all reported that ligand-acceleration reaction
colloids as a catalyst. It also can be observed that the modifi- enhanced the reaction rate and changed the selectivity. In
cation effect of various metal cations on the PVP-Pt catalytic order to obtain high catalytic activity and selectivity, some
system. The addition of metal cations Cr3C (entry 2) and ligands were introduced into the hydrogenation of chloroben-
Ni2C (entry 6) caused subtle loss in activity, while Cr3C had zene reaction. The ligands of bipyridyl (bpy) and diethylene-
an inhibiting effect on the selectivity to cyclohexane. Metal triamine (den) depressed the selectivity of chlorobenzene to
cation Co2C (entry 5) had inferior influence on the hydro- cyclohexane. This indicates that bpy and den can suppress
genation of chlorobenzene in both the activity and the the hydrogenation of benzene but accelerate the
Table 1. The effect of metal complexes on the hydrogenation of chlorobenzene over PVP-Pt nanocatalysta
Selectivity (%)
Entry
Catalytic system
Average rate
Conversation of
Cyclohexane
Benzene
(mol H2/[mol Pt h])
chlorobenzene (%)
1
2
3
4
5
6
7
PVP-Pt
9.30
8.40
0
3.51
4.60
8.64
0
77.5
70.0
0
29.2
38.4
72.0
0
66.0
38.1
—
58.2
33.4
56.4
0
34.0
62.0
—
41.8
66.6
43.6
0
PVP-Pt-Cr3C
PVP-Pt-Mn2C
PVP-Pt-Fe3C
PVP-Pt-Co2C
PVP-Pt-Ni2C
PVP-Pt-Zn2C
8
9
PVP-Pt-bpy
PVP-Pt-den
PVP-Pt-trine
PVP-Pt-tetren
PVP-Pt-Py
PVP-Pt-en
PVP-Pt-Cr(en)3(NO3)3
PVP-Pt-Co(en)(NO3)2
PVP-Pt-Ni(en)(NO3)2
PVP-Pt-Zn(en)2(NO3)2
PVP-Pt-Hacac
PVP-Pt-Cr(acac)3(NO3)3
PVP-Pt-Mn(acac)2Cl2
PVP-Pt-Fe(acac)3(NO3)3
PVP-Pt-8-HQ
10.13
10.57
8.49
7.54
10.30
9.96
7.17
6.03
5.54
0
10.90
9.18
0.32
3.48
6.35
2.83
6.63
8.40
84.4
88.1
70.7
62.8
85.9
83.0
59.7
50.2
46.2
0
90.9
76.5
2.6
29.0
52.9
23.6
55.2
70.0
55.3
54.2
46.1
33.2
62.5
64.8
40.4
41.6
34.7
—
68.4
56.0
100.0
30.8
34.6
14.2
32.3
77.5
44.7
45.8
62.9
66.8
37.5
35.2
59.6
58.4
65.3
—
31.6
44.0
0.0
69.2
65.4
85.8
67.7
22.5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
PVP-Pt-Fe(8-HQ)(NO3)3
PVP-Pt-Co(8-HQ)(NO3)2
PV-Pt-Ni(8-HQ)(NO3)2
en D ethylenediamine; 8-HQ D 8-hydroxylquiline; acac D acetylacetonate; bpy D bipyridyl; den D diethylenetriamine; trine D triethylenetetramine; tetren D
tetraethylenepentamine; Py D pyrrole.
aReaction conditions: PH2 D 0.1 MPa, T D 298 K, V D 30 mL, chlorobenzene: 1 mmol, Pt: 2.5£10¡5 mol, the molar ratio of the modifier to Pt was 1:1, reac-
tion time: 10 h.

Hydrogenation of Chlorobenzene
905
hydrogenation of chlorobenzene at the same time (the aver- in different degrees while remaining high selectivity for o-
age rate of reaction were observed up to 10.13 and 10.57 mol CAN. The activity of PVP-Ru boosted excellently with the
H2/[mol Pt h], respectively). Acetylacetonate (acac) favor- increase of the number of -NH2. In the presence of trine, the
ably raised both the activity and the selectivity greatly (the activity increased by about nineteen times than that of
average reaction rate was improved from 9.30 to 10.90 mol unmodified PVP-Ru and got up to 2.4£10¡3 mol H2/(mol
H2/(mol Pt h), and the selectivity to cyclohexane was Ru s); furthermore, the conversion of o-CNB was increased
increased from 66.0% to 68.4%, respectively). It also can be from 21.6% to 100%.
seen that the ligand of 8-hydroxylquiline (8-HQ) exerted infe-
From the previous discussion, it is obvious that the hydro-
rior influences on the hydrogenation in both activity and genation catalyst PVP-Pt modified by different ligands have
selectivity, while the pyrrole (Py) resulted in an increase in different effects on the catalytic activity and selectivity to
the hydrogenation rate with a decrease of the selectivity to cyclohexane. Most of ligands considerably elevated the activ-
cyclohexane. Further study on the hydrogenation of chloro- ity of PVP-Pt (e.g., en, acac, bpy, den, Py) and some ligands
benzene over PVP-Pt modified by ethylenediamine (en) and increased the selectivity (en, acac, Py). It should be pointed
multiamine ligands showed that the amines ligands had dif- out that the acetylacetonate and pyrrole displayed a more
ferent modification effects compared with the neat PVP-Pt favorable effect comparing with the neat Pt catalyst on both
which indicated evidently in Figure 1.
activity and the selectivity to cyclohexane.
Obviously different results were obtained by the multi-
Metal complexes were formed by mixing a metal salt (usu-
amine ligands (en, den, trine, tetren) with the increase of the ally the nitrate salt) with a corresponding ligand at a proper
number of -NH2 from 2 to 5. The conversions of chloroben- molar ratio. The modification effects of metal ethylenedi-
zene over PVP-Pt-en and PVP-Pt-den catalytic systems were amine, acetylacetonate and 8-HQ complexes on the hydro-
much higher than that of PVP-Pt. When the number of -NH2 genation of chlorobenzene over PVP-Pt colloidal catalyst are
increased to 3, the conversions were evidently decreased and also listed in Table 1. It can be seen that PVP-Pt-en (entry
lower than that of PVP-Pt at 5 h reaction time, which indi- 13) can improve the activity with slight loss in the yield of
cated that the activity of PVP-Pt catalysts modified by multi- cyclohexane. However, the metal ethylenediamine complexes
amine ligands were different with the number of -NH2. After deactivated the PVP-Pt catalyst and resulted in a decrease in
5 h, the conversion of chlorobenzene over PVP-Pt-en system both activity and selectivity. Figure 2 shows the effect of
(containing 2 -NH2) was 76.1%, which was the highest con- metal ethylenediamine complexes on the selective hydrogena-
version, while the conversion of chlorobenzene over PVP-Pt- tion of chlorobenzene over PVP-Pt catalyst. All the metal eth-
tetren system (containing 5 -NH2) was 51.4%. From the pre- ylenediamine complexes hindered the hydrogenation in both
vious results, it is unquestionable that the conversion of chlo- activity and selectivity compared with the neat PVP-Pt and
robenzene decreased obviously with the increase of the PVP-Pt-en catalyst systems. Moreover, the activity and the
number of -NH2. Owing to the interaction of Pt with multi- selectivity declined with the increase of atomic number of
amine ligands, the electronic density of the platinum active metal central ions in the range of 24–30. Cr(en)3(NO3)3 had
site is closely related to the number of -NH2, which in turn higher activity than other metal ethylenediamine complexes
affects the catalytic performance. It was reported that there (Figure 2); however it had some inhibiting effect on the reac-
were different situations about this phenomenon in different tion (the activity was only 7.17 mol H2/[mol Pt h]). It can be
reaction system. However, in Yan et al.’s[17] paper, multi- seen from Table 1 that metal cation Co2C showed bad effect
amine ligands considerably elevated the activity of PVP-Ru on the activity of PVP-Pt comparing with the addition of
Fig 2. The metal ethylenediamine complex effect on the selective
hydrogenation of chlorobenzene over PVP-Pt colloidal nanoca-
talyst—the metal complexes were Cr(en)3(NO3)3, Co(en)(NO3)2,
Fig 1. Hydrogenation of chlorobenzene over multiamine ligands Ni(en)(NO3)2, and Zn(en)2(NO3)2 successively. & D conversion
modified PVP-Pt nanocatalyst at 5 h reaction time.
of chlorobenzene, & D selectivity to cyclohexane.

906
Li et. al
Ni2C, while Co(en)(NO3)2 improved both the activity and the
selectivity compared to the nickel ethylenediamine complex
(the average rate of reaction was improved from 5.54 to
6.03 mol H2/[mol Pt h], and the selectivity to cyclohexane
was increased from 34.7% to 41.6%, respectively). The data
mentioned above showed that metal complexes exerted par-
ticular effect on the selective hydrogenation of chloroben-
zene, which is different from the effect of either metal central
ions or ligands. Because Zn2C caused PVP-Pt to lose all the
activity, the addition of Zn(en)2(NO3)2 poisoned the catalyst
seriously and hindered the hydrogenation of chlorobenzene.
There were different results about zinc complexes in different
reaction systems.[15,17] In Yang et al.’s[15] paper, Zn(en)2Cl2
performed as a poison in the hydrogenation of o-CNB in
PVP-Pt and caused the whole activity to lose. Yan[17]
reported that the incorporation of Zn (II) cation with multi-
amines enhanced the activity of PVP-Ru and performed
superior to ligands alone, despite Zn2C causing a decrease in
the activity of PVP-Ru colloidal catalyst in the hydrogena-
tion of o-CNB. Particularly in the case of Zn(trien)2Cl2, the
activity of the as-modified PVP-Ru increased by 30 times
more than that of the unmodified PVP-Ru. Our results con-
cerning the activity of PVP-Pt modified by zinc complexes in
the hydrogenation of chlorobenzene were consistent with
Fig 3. The metal ethylenediamine complex and metal 8-hydrox-
ylquiline complex effect on the selective hydrogenation of chlo-
robenzene over PVP-Pt colloidal nanocatalyst—the metal
complexes were Cr(acac)3(NO3)3, Fe(acac)3(NO3)3, Fe(8-HQ)
(NO3)3, Co(8-HQ)(NO3)2, and Ni(8-HQ)(NO3)2, successively.
& D conversion of chlorobenzene, & D selectivity to cyclohex-
ane, ––acac complex, - - - D 8-HQ complex).
those results reported by Yang et al.[15] In different catalytic modifier, a better selectivity to o-chloroaniline and a
systems, the same metal complex had different modification higher activity were obtained.
on the catalytic hydrogenation reaction.
Figure 3 also shows that the effect of metal 8-hydroxylqui-
With respect to the equilibrium of step dissociation of line complexes on the selective hydrogenation of chloroben-
metal complexes, there was no unitary of species but a mix- zene. The 8-hydroxylquiline complexes with the different
ture of multistep complexes coexisted in the reaction system. metal central ions had different effects. The hydrogenation
Take PVP-Pt-[Cr(en)3]3C as an example, where [Cr(en)]3C
,
rate of chlorobenzene and selectivity decreased obviously
[Cr(en)2]3C, and[Cr(en)3]3C coexisted in the reaction medium with the introduction of Fe(8-HQ)(NO3)3 and Co(8-HQ)
in different concentrations. The mixture made the complexes (NO3)2. However, with Co(8-HQ)(NO3)2 introduced, the
effect on the catalytic activity and selectivity very compli- activity was considerably enhanced compared to the PVP-Pt-
cated. In conclusion, the effect of the metal complexes is dif- Co2C system (entry 5) whereas the selectivity was slightly
ferent from both the metal central ions and the ligands, and it changed. With respect to the PVP-Pt-Ni2C (entry 6) and
is not the sum of the effects of each.
PVP-Pt systems, the selectivity was greatly promoted to
In the study of ligands as modifiers, PVP-Pt-Hacac 77.5% and the catalytic performance of the catalyst was mod-
(entry 18) had the best effect on both the activity and the ulated slightly when Ni(8-HQ)(NO3)2 was used as a modifier.
selectivity (the average rate of reaction was improved In Yan et al.’s[17] paper, Co(8-HQ)2 performed as a spectator,
from 9.30 to 10.90 mol H2/[mol Pt h], and the selectivity while 8-HQ ligand enhanced the activity of PVP-Ru without
to cyclohexane was increased from 66.0% to 68.4%, any loss in the selectivity for o-CAN. Tu et al.[16] reported
respectively). Metal acetylacetonate complexes had infe- that the metal 8-hydroxyquinoline complexes had inferior
rior influences on the hydrogenation of chlorobenzene in influences on the selectivity of the hydrogenation of m-CNB
both activity and selectivity except that Cr(acac)3(NO3)3 and many metal 8-HQ complexes exerted favorable effect on
performed as a spectator (Figure 3). Fe(acac)3(NO3)3 hin- the selectivity of the hydrogenation of p-CNB considerably.
dered the hydrogenation rate and caused the activity and They found that Fe(8-HQ)2C exerted the best favCorable influ-
selectivity decrease evidently, while Mn(acac)2Cl2 (entry ence on the selectivity to CAN than Fe(8-HQ)2 and Fe(8-
20) performed as a poison (the activity fell into 0.32 mol HQ)3 did. Thus, the behavior of metal complexes was closely
H2/[mol Pt h], while the selectivity increased up to 100%). related to the number of the ligands coordinated to the metal
The metal cations Cr3C, Mn2C, and Fe3C (entries 2–4) central ions. They suspected that the complex effect was
exerted inferior influences on the hydrogenation (the aver- related to the interaction of metal complex with reaction sub-
age rate was 8.40, 0.00, and 3.51 mol H2/[mol Pt h], strate, reaction product, or the metallic catalyst.
respectively). However, upon the addition of the acac
ligand, the metal complexes weakened the inferior influen-
ces of these metal cations. Yang et al.[15] also found that Conclusions
the metal acetylacetonate complexes showed a more
favorable effect in comparison with the metal cations. In conclusion, the metal complex effect on the hydrogenation
When the complex Ni(acac)2 was introduced as
a
of chlorobenzene over PVP-Pt has been studied under 298 K

Hydrogenation of Chlorobenzene
907
and atmospheric pressure. When the neat platinum nanopar- 10. Liu, M. H.; Yu, W. Y.; Liu, H. F. J. Mol. Catal. A Chem. 1999,
138, 295.
ticles was served as the catalyst, only 77.5% conversion and
moderate selectivity to cyclohexane (65.58%) were obtained.
11. Liu, M. H.; Yu, W. Y.; Liu, H. F.; Zheng, J. M. J. Colloid Interface
Sci. 1999, 214, 231.
The metal complexes and ligands employed to the catalytic
12. Liu, M. H.; Yan, X. P.; Liu, H. F.; Yu, W. Y. J. Mol. Catal. A
system had great effect on both the activity and the selectivity
of the catalyst.
Chem. 1999, 138, 273.
13. Liu, M. H.; Xiao, H. L.; Shan, H. B.; Li, X. H.; Liu, Y. Y.; Wang,
A. M. Synth. React. Inorg. Met.-Org. Nano-Met. Chem. 2013, 43,
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Funding
144, 123.
This work was supported by the National Natural Science
Foundation of China (21077062, 61225018, 51272084,
16. Tu, W. X.; Liu, H. F.; Tang, Y. J. Mol. Catal. A Chem. 2000, 159,
115.
21105053, 21301103), the Taishan Scholar, and the Shan- 17. Yan, X. P.; Liu, M. H.; Liu, H. F.; Liew, K. Y.; Zhao, N. J. Mol.
Catal. A Chem. 2001, 170, 203.
18. Smith, M. B.; March, J. March’s Advanced Organic Chemistry:
dong Natural Science Foundation (ZR2012FZ007).
Reactions, Mechanisms, and Structure; Wiley Interscience, New
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