Quenched skeletal Ni as the effective catalyst for selective partial hydrogenation of polycyclic aromatic hydrocarbons

Article abstract of DOI:10.1039/c3ra44871a

Quenched skeletal Ni is an active and selective catalyst for selective partial hydrogenation of polycyclic aromatic hydrocarbons (PAHs). The molecular structure of PAHs significantly dominate the hydrogenation process and furthermore, the distribution of hydrogenated products.

Full text of DOI:10.1039/c3ra44871a

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Quenched skeletal Ni as the effective catalyst for
selective partial hydrogenation of polycyclic aromatic
Cite this: RSC Adv., 2013, 3, 23984
hydrocarbons†
Received 3rd September 2013
Accepted 8th October 2013
*
Chengyun Liu, Zeming Rong, Zhuohua Sun, Yong Wang, Wenqiang Du, Yue Wang
and Lianhai Lu
DOI: 10.1039/c3ra44871a
www.rsc.org/advances
Quenched skeletal Ni is an active and selective catalyst for selective now, numerous works have focused on increasing catalyst's
partial hydrogenation of polycyclic aromatic hydrocarbons (PAHs). activity in the hydrogenation of PAHs,10 nevertheless the
The molecular structure of PAHs significantly dominate the hydro- controllability for products remain highly unsatised. Fu et al.
genation process and furthermore, the distribution of hydrogenated studied the regioselective hydrogenation of PAHs over Pd/C and
products.
Pt/C and found out that over Pd/C, the reaction afforded
regiospecically the corresponding K-region dihydroarenes,
while analogous reactions over Pt/C take place regioselectively
on terminal rings to provide the related tetrahydroarenes.11
Nieuwstad et al. studied the hydrogenation of alkyl-substituted
naphthalene over Pd/C and results showed that the equilibra-
tion between pairs of alkyltetralins were kinetically controlled
and bulky alkyl substituents weaken the strength of adsorp-
tion.12 Yu et al. employed group-V metal aryloxide compounds
for PAHs hydrogenation and found the cis-conguration
dominated the products.13 Girgis and Gates studied the hydro-
genation networks of several PAHs over sulded Ni–Mo/g-Al2O3
and the reactions in each network are approximated as rst
order in the reactant.14 Minabe and Nakada studied the partial
hydrogenation of pyrene over RANEYꢀ Ni and found the ratio of
deep hydrogenated products was increased with prolonging of
reaction time; however, the reaction speed decreased simulta-
neously.15 It is obvious that the hydrogenation process of PAHs
is complex and different catalytic systems exhibit different
reaction selectivity. Therefore, it is important to have a deep
understanding of the reaction mechanism and design an active,
selective controllable hydrogenation catalytic system for the
clean and efficient synthesis of partial saturated PAHs.
Polycyclic aromatic hydrocarbons (PAHs) form a class of
hazardous compounds which originate from coal tar, crude oil
but mainly arise from the incomplete combustion of fossil fuels
and organic matters.1 Because of the carcinogenic properties
and wide distribution in the environment, PAHs have been
universally acknowledged to be potent environmental pollut-
ants and have been taken seriously regarding problems for
ecological environments.2 In contrast, the partial saturated
PAHs being formed by reduction of corresponding PAHs are
less toxic and widely used in pharmaceuticals,3 dyes4 and fuels.5
Therefore, converting the toxic PAHs into high-valued partial
saturated PAHs will be a meaningful protocol for both the
environment and chemical production.
Usually, PAHs could be reduced using dissolved alkali metal
in the process of Birch reduction,6 LiAlH4,7 biodegradation over
special enzymes8 and catalytic hydrogenation over different
kinds of catalysts,9 such as carbon supported Pd nanoparticles,
sulded Ni–Mo/g-Al2O3 and RANEYꢀ Ni. However, the
conventional chemical reduction method has been challenged
due to the serious pollution and the biological reduction has the
shortcoming of low efficiency with long reaction time using a
large quantity of biocatalyst. The selective catalytic hydrogena-
tion seems to be a better choice for partial saturated PAHs
preparation, which is environmentally benign and offers several
advantages over chemical and biochemical reductions. Until
In recent years, the skeletal Ni prepared with quenching
technique (QS Ni) has attracted much attention because it is
lack of long-range order; the surface is rich in low-coordination
sites and defects which are essential for adsorption and acti-
vation of the reactants.16 These characters signicantly improve
the catalytic performance compared with normal RANEYꢀ Ni
and made QS Ni widely used in hydrogenation of ne
chemicals.17,18
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian
116024, China. E-mail: zeming@dlut.edu.cn; Tel: +86-411-84986242
† Electronic supplementary information (ESI) available: Catalytic hydrogenation
experiment, preparation and characterization of catalyst, quantum calculations
of molecular structure, analytical and spectral characterization data were
described in ESI. See DOI: 10.1039/c3ra44871a
In this communication, we report a green and highly effi-
cient catalytic methodology for chemoselective hydrogenation
of various PAHs compounds into corresponding partial
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saturated PAHs over QS Ni. The molecular structure of PAHs solvent was replaced by ethanol and cyclohexane, the reaction
signicantly dominate the process of hydrogenation and rate and the selectivity to tetralin changed signicantly, which
furthermore, the distribution of partial hydrogenated products. might be caused by the different hydrogen solubility in those
solvents.20
The relationships of component concentration versus reac-
tion time are shown in Fig. 1. At early stage of the reaction, the
Results and discussion
concentration of naphthalene decreased with reaction time and
naphthalene totally converted into tetralin without detection of
decalin in 50 min. Even prolonging the reaction time to 100
min, tetralin was still the exclusive product indicating its
stabilization in reaction system. Theoretically, the resonance
energy for naphthalene hydrogenation to tetralin will be
reduced 105 kJ molÀ1, while the resonance energy for tetralin
hydrogenation to decalin is accompanied by a loss of as large as
152 kJ molÀ1. Also, it is more difficult for tetralin to adsorb on
QS Ni's surface than naphthalene due to the steric hindrance.
Therefore, take both factors into account; tetralin could stably
exist in the reaction conditions, which resulted into only satu-
rating single ring for naphthalene hydrogenation.
Inspired by these results, we investigated a series of bicyclic
PAHs with QS Ni catalyst to corresponding partial saturated
PAHs and the results are summarized in Table 2. It was
noticeable that all the bicyclic PAHs can be hydrogenated into
single ring saturated PAHs. As shown in entries 1–3 and entry
14, both rings for the substrate with symmetric structure have
equal chance to adsorb on the surface of QS Ni and single ring
saturated PAHs were exclusively obtained. In contrast, in entries
4–12, the balance was broken when naphthalene was asym-
metrically substituted with different groups. The isomer prod-
ucts were obtained aer different benzene ring was separately
hydrogenated. Basically, the electron-donating groups
promoted the unsubstituted ring to be preferentially hydroge-
nated (except entry 11) and by contrast, the electron-with-
drawing groups promoted the substituted ring to be
preferentially hydrogenated. These results probably caused by
the changes of steric hindrance and the distribution of electron
density for both rings. The balance between these two factors
The catalytic hydrogenation reaction was carried out in a 70 mL
stainless-steel autoclave. All products were analyzed by GC and
GC-MS. The Skeletal Ni catalyst was prepared by rapidly
quenching technique according to the literature.17 Structural
characteristics of the QS Ni as well as experimental details are
described in the (ESI†).
Naphthalene is typical PAHs and was chosen to be the model
substrate in this study. Theoretically, naphthalene hydrogena-
tion is a typical consecutive reaction containing at least two
steps as illustrated in Scheme 1. Tetralin is the half-hydroge-
nated intermediate and decalin is the full-hydrogenated
product.
Initially, we screened the naphthalene hydrogenation by 8
different catalysts with THF solvent under the same reaction
conditions (373.15 K and 1.5 MPa H2, Table 1). Among the noble
metal catalysts Pt/C, Pd/C, Ru/C and Rh/C, Rh/C provided 48%
conversion and 99% selectivity to tetralin. In addition, RANEYꢀ
Ni, Ni–B and Ni–P were investigated in this model reaction and
up to 100% selectivity to tetralin was achieved, simultaneously.
Furthermore, QS Ni prepared by quenching technique was
employed for the naphthalene hydrogenation. Obviously, QS Ni
showed best performance in the model experiment, which is
probably attributed to the structural properties of QS Ni derived
from the quenching process.19 From Fig. S1–4,† it can be found
that the QS Ni hold the typical porous structure which could
offer abundant active centers for the reaction. When THF
Scheme 1 Reaction network of naphthalene hydrogenation.
Table 1 Naphthalene hydrogenation to tetralin with different catalysts and
solventsa
Catalysts
Solvent
Conv.%
Sele.%
5 wt% Pt/C
5 wt% Pd/C
5 wt% Ru/C
5 wt% Rh/C
Ni–B
Ni–P
RANEYꢀ Ni
QS Ni
THF
THF
THF
THF
THF
THF
THF
THF
<1
2
5
48
23
12
57
89
26
>99
100
100
100
99b
100
100
100
100
100
82c
QS Ni
QS Ni
Ethanol
Cyclohexane
a
Fig. 1 The concentration-time plots for the selective hydrogenation of naph-
thalene over QS Ni. Reaction conditions: 373.15 K, 1.5 MPa, 11.7 mmol naph-
thalene, 20 mL THF, 0.2 g QS Ni. The conversion and selectivity were determined
by GC.
Reaction conditions: 373.15 K, 1.5 MPa, 11.7 mmol naphthalene, 20 mL
solvent, 0.25 g catalysts, 30 min, tert-Butylcyclohexane as the internal
standard. The results were repeated 5 times and taken the average
number. b 1% decalin was detected. c 18% decalin was detected.
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Table 2 Chemoselective Hydrogenation of bicyclic PAHs to partial saturated
PAHs over QS Nia,b
Table 2 (Contd. )
Entry Substrate
Products
t minÀ1 Conv./% Sele./%
Entry Substrate
1
Products
t minÀ1 Conv./% Sele./%
285
15
>99
>99
100
100
50
60
>99
>99
100
100
15
2
3
16
a
Reaction conditions: 373.15 K, 1.5 MPa, 11.7 mmol substrates, 20 mL
THF, 0.2 g QS Ni, used tert-butylcyclohexane as the internal standard.
The results were repeated 5 times and taken the average number. The
conversion and selectivity were determined by GC and the products
were conrmed by GC-MS and. b 1H NMR (shown in ESI†).
15
30
>99
>99
100
4
5
6
16 : 23 : 60
determined the distribution of hydrogenated products. When
the same functional groups substituted at the different sites of
naphthalene-a site and b site (entries 4–9), the reaction rates of
these two series are obviously different—the a-substituted
series are faster. Moreover, the substituted rings will prefer to
be hydrogenated along the increase of steric hindrance of the
substituted groups at a site. In order to better understand these
phenomena, transformations of molecular congurations
during the hydrogenation process were simulated as shown in
Fig. S5–S8.† It can be found that relative to the b-substituted
series, the peri strain (van der Waals interaction of the 1 R group
with the 8-hydrogen atom) presented in a-substituted series.
During the reaction process, the hydrogenations of the
substituted rings will partial released the strain, especially with
the bulky substituted group. These results are similar with the
results reported by Nieuwstad et al. whose used Pd/C as the
catalyst.12 In entries 13–17, when heteroatoms substituted on
the skeleton of the PAHs, the hydrogenation reaction would
only occur at the substituted ring caused by the strong coordi-
nation ability of heteroatoms. In order to further identify this
mechanism; the hydrogenation was carried out in the system
where naphthalene and quinoline were coexisted. The rela-
tionships of component concentration versus reaction time are
shown in Fig. S9.† It is clear that with the prolonged reaction
time quinoline was quickly hydrogenated into 1,2,3,4-tetrahy-
droquinoline, by contrast, the concentration of naphthalene
was almost unchanged. This indicated that though naphtha-
lene and quinoline have the similar molecular structures, the
coordination between heteroatom and the unsaturated surface
of QS Ni favored the reaction preferably happened at the ring
containing heteroatoms.
120
300
>99
>99
57 : 43
4 : 69 : 27
7
8
9
540
40
>99
>99
>99
74 : 26
45 : 55
39 : 61
90
10
11
50
75
>99
>99
47 : 53
53 : 47
12
750
>99
70 : 30
Furthermore, we studied the hydrogenation of the PAHs with
more than double rings (Table 3), which hold more reactive
sites and therefore, the hydrogenation process will proceed via
several different intermediates. It is notable that hydrogenation
of these PAHs is a consecutive reaction and can be mainly
divided into two stages. At the rst stage, the substrates can be
quickly consumed and converted into different kinds of
intermediates. At the second stage, the rate of hydrogenation
gradually decreased and isomerization or disproportionation
between the products occurred during the course of
13
14
90
30
>99
>99
100
100
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Table 3 Chemoselective Hydrogenation of PAHs more than two cycles over QS Nia
Entry
1
Substrate
Products
t minÀ1
Conv./%
Sele./%
5
>99
>99
1 : 41 : 6 : 52
15 : 84b
165
20
>99
>99
8 : 23 : 37 : 32
26 : 73c
2
3
120
25
>99
11 : 15 : 52 : 22
5790
15
>99
>99
77 : 11d
100
4
36000
>99
99e
a
Reaction conditions: 373.15 K, 1.5 MPa, 11.7 mmol substrates, 20 mL THF, 0.2 g QS Ni, used tert-butylcyclohexane as the internal standard. The
results were repeated 5 times and taken the average number. The conversion and selectivity were determined by GC and the products were
b
c
conrmed by GC-MS and 1H NMR (shown in ESI†). 1.3% Perhydroanthracene was detected. 0.7% Perhydrophenanthrene was detected.
d
e
12% Perhydropyrene was detected. 1% Perhydroperylene was detected.
hydrogenation (shown in Fig. S10–S13†]. The distribution of the hydrogenated into 1,2,3,3a,4,5,6,7,8,9-H10P (C), 1,2,3,10,11,12,
products was determined by the molecular structure and the 12a,12b-H8P (D) and 1,2,3,3a,4,5,6,7,8,9,9a,10,11,12-H14P (E),
terminal rings preferred to be hydrogenated.
simultaneously. Due to the steric hindrance, the terminal ring
To probe the hydrogenation mechanism of PAHs with more of B is easily absorbed on the catalyst's surface than the middle
than double rings, perylene was chose as a model substrate and rings (shown in Fig. S14†). So the hydrogenation preferred to
the reaction network which based on the relationships of take place at the terminal rings and converted into D and E as
component concentration versus reaction time (Fig. S13†) was the principle products. With further increase of reaction time,
shown in Fig. 2.
both C and D will be further hydrogenated into E and the
At the rst stage of the reaction, perylene (P) was quickly
hydrogenated into 1,2,3,10,11,12-H6P (B in Fig. 2) without
detection of any other hydrogenated products. This phenom-
enon maybe as caused by following reasons: rstly, perylene is a
kind of symmetric planar molecule containing two C2 axes.
When perylene absorbed on the surface of catalyst, each ring of
perylene had the equal chance to be hydrogenated. According to
the theoretical calculation,21 formation of B with phenanthrene
structural unit requires approximately 32 KJ molÀ1 less energy
than formation of 1,2,3,7,8,9-H6P which contains the anthra-
cene structural component. So perylene preferred to be hydro-
genated into B as the intermediate. Secondly, the steric
hindrance of B is much bigger than the case of perylene, which
makes perylene prior adsorbed on the surface of QS Ni and be
hydrogenated when perylene and B coexisted in the reaction
system. At the second stage of the reaction, B will be further
Fig.
2
The schematic representation of perylene hydrogenation products.
A: perylene; B: 1,2,3,10,11,12-H6perylene; C: 1,2,3,3a,4,5,6,7,8,9-H10perylene;
D: 1,2,3,10,11,12,12a,12b-H8perylene; E: 1,2,3,3a,4,5,6,7,8,9,9a,10,11,12-H14
-
perylene; F: peryhydro perylene.
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reaction rate will further slow down due to the increase of steric
hindrance (shown in Fig. S14†).
6 T. J. Donohoe, R. Garg and C. A. Stevenson, Tetrahedron:
Asymmetry, 1996, 7, 317.
In summary, this communication provides a predicable and
controllable method to obtain partial saturated PAHs by selec-
tive hydrogenation of PAHs over QS Ni. The molecular structure
of PAHs strongly inuenced the hydrogenation process and
furthermore, the distribution of hydrogenated products. Since
partial saturated PAHs can be further converted to highly
valuable compounds through several reactions, this result will
generally contribute to the synthetic methodology of partial
saturated PAHs derivatives.
7 Y. Segawa and D. W. Stephan, Chem. Commun., 2012, 48,
11963.
8 A. L. Juhasz, M. L. Britz and G. A. Stanley, J. Ind. Microbiol.,
2000, 24, 277; A. Robert, Kanaly and H. Shigeaki, Appl.
Microbiol. Biotechnol., 2002, 68, 5826; B. Sudarat,
M. L. Britz and G. A. Stanley, Appl. Microbiol. Biotechnol.,
2000, 66, 1007.
9 Q. Lin, K. Shimizu and A. Satsuma, Appl. Catal., A, 2010, 387,
166; S. Murcia-Mascaros, B. Pawelec and J. L. G. Fierro, Catal.
Commun., 2002, 3, 305; A. M. Venezia, V. La Parola and
B. Pawelec, Appl. Catal., A, 2004, 264, 43.
10 A. Zhao, X. Zhang and C. Liang, J. Phys. Chem. C, 2010, 114,
3962; B. Pawelec, V. L. Parola and J. L. G. Fierro, J. Mol. Catal.
A: Chem., 2006, 253, 30; T. Tang, C. Yin and L. Wang,
J. Catal., 2007, 249, 111; M. J. Jacinto, O. H. C. F. Santos
and R. Landers, Appl. Catal., B, 2009, 90, 688.
11 P. P. Fu, H. M. Lee and R. G. Harvey, J. Org. Chem., 1980, 45,
2797.
Acknowledgements
This work was nancially supported by the National Natural
Science Foundation of China (21206015), Specialized Research
Fund for the Doctoral Program of Higher Education
(20120041120022), Fundamental Research Funds for the
Central Universities (DUT13LK29).
12 T. J. Nieuwstad, P. Klapwijk and H. Van Bekkum, J. Catal.,
1973, 29, 404.
Notes and references
1 G. W. vanLoon and S. J. Duffy, Environmental Chemistry: A 13 J. S. Yu, B. C. Ankianiec and M. T. Nguyen, J. Am. Chem. Soc.,
Global Perspective, Oxford University Press Inc., New York, 1992, 114, 1927.
2005; D. L. Poster, M. M. Schantz and L. C. Sander, Anal. 14 M. J. Girgis and B. C. Gates, Ind. Eng. Chem. Res., 1994, 33,
Bioanal. Chem., 2006, 386, 859.
2301.
2 T. T. Bovkun, M. Grayevsky and Y. Sasson, J. Mol. Catal. A: 15 M. Minabe and K. Nakada, Bull. Chem. Soc. Jpn., 1985, 58,
Chem., 2007, 270, 171; W. B. Wang, S. M. Lu and
1962.
P. Y. Yang, J. Am. Chem. Soc., 2003, 125, 10536; K. Fujita, 16 K. Klement, R. H. Willens and P. Duwez, Nature, 1960, 187,
C. Kitatsuji and S. Furukawa, Tetrahedron Lett., 2004, 45,
3215; Y. Cheng, H. Fan and S. Wu, Green Chem., 2009, 11,
1061.
869; X. Chu, P. Guo and Y. Pei, J. Phys. Chem. C, 2007, 111,
17535.
17 L. Lu, Z. Rong and W. Du, ChemCatChem, 2009, 1, 369.
3 F. W. Vierhapper and E. L. Eliel, J. Org. Chem., 1975, 40, 2729; 18 X. Yu, H. Li and J. Deng, J. Mol. Catal. A: Chem., 2000, 199,
´
V. Sridharan, P. A. Suryavanshi and J. C. Menendez, Chem.
Rev., 2011, 111, 7157.
191; K. Gorp, E. Boerman and P. H. Berben, Catal. Today,
1999, 13, 349; H. Li, W. Wang and J. Deng, J. Catal., 2000,
191, 257; B. Liu, L. Lu and K. Iwatani, J. Mol. Catal. A:
Chem., 1998, 171, 117.
ˇ
4 P. Soustek, M. Michl and N. Almonasy, Dyes Pigm., 2008, 78,
139.
5 M. Pang, C. Liu and C. Liang, Green Chem., 2012, 14, 1272; 19 H. Hu, M. Qiao and X. Zhang, J. Catal., 2004, 221, 612.
T. Kotanigawa, M. Yamamoto and T. Yoshida, Appl. Catal., 20 C. H. Yen, H. Lin and C. Tan, Catal. Today, 2011, 174, 121.
A, 1997, 164, 323.
21 W. C. Herndon, J. Am. Chem. Soc., 1973, 95, 2404.
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