Low temperature hydrodeoxygenation of phenols under ambient hydrogen pressure to form cyclohexanes catalysed by Pt nanoparticles supported on H-ZSM-5

Article abstract of DOI:10.1039/c5cc05607a

The hydrodeoxygenation of various phenols to form cyclohexanes was achieved at 110 °C under an H₂ atmosphere at ambient pressure using a Pt/H-ZSM-5 catalyst and octane as the solvent.

Full text of DOI:10.1039/c5cc05607a

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Low temperature hydrodeoxygenation of phenols
under ambient hydrogen pressure to form
cyclohexanes catalysed by Pt nanoparticles supported
on H-ZSM-5
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
a
a
a
b
Hidetoshi Ohta,* Kentaro Yamamoto, Minoru Hayashi, Go Hamasaka, Yasuhiro
DOI: 10.1039/x0xx00000x
b
a
Uozumi and Yutaka Watanabe*
www.rsc.org/
The hydrodeoxygenation of various phenols to form were successful in allowing lower reaction temperatures to be
used, but high H pressures (4‒5 MPa) were still required. Here
we report that Pt/HꢀZSMꢀ5 efficiently catalyses the conversion
of various phenols into cyclohexanes under mild conditions
2
cyclohexanes was achieved at 110 °C under an H atmosphere
at ambient pressure using a Pt/H-ZSM-5 catalyst and octane
as the solvent.
2
(
110 °C, under H at 0.1 MPa, using octane as the solvent).
2
Interest in the development of a mild and efficient process for
converting lignin into fuels or other chemicals has been
growing because this1 would be an effective use of
lignocellulosic biomass. Lignin is an abundant and renewable
biopolymer that is formed by the polymerisation of phenolic
monomers in plants. The hydrodeoxygenation of lignin and
ligninꢀrelated phenols to produce cyclohexanes (which are used
as fuels, solvents and precursors in the synthesis of other useful
chemicals) has been the subject of investigations for a long
OH
O
OH
H2
metal
H2
metal
H2
metal
H
2
H O
Scheme 1 General reaction mechanism for the hydrodeoxygenation of
phenol catalysed by a metal–acid bifunctional catalyst.
Various zeoliteꢀsupported Pt catalysts were prepared.
Several kinds of the zeolites (HꢀZSMꢀ5, Hꢀ
Y) were impregnated with an aqueous solution of H PtCl to
load each zeolite with 2 wt% of Pt, and the zeolites were then
dried and reduced in the presence of H . Subsequently, each
catalyst was then characterised by Xꢀray diffraction (XRD),
transmission
adsorption/desorption measurements and acidꢀbase titration.
The characterisation results are summarised in Table S1, Fig.
S1 and S2 in the electronic supplementary information.† Of the
catalysts that were prepared, Pt/HꢀZSMꢀ5 had the smallest Pt
particle size (5.6 ± 2.0 nm, by TEM analysis) and the lowest
acid content (0.24 mmol g ).
Each Pt catalyst was used to hydrodeoxygenate 4ꢀ
propylphenol (1) in octane at 110 °C for 10 h under H at 0.1
MPa, and the catalytic performances of the different systems
were evaluated (Table 1). Pt/HꢀZSMꢀ5 was an excellent
catalyst, giving propylcyclohexane (2) in 99% yield (entry 1).
The Pt/HꢀZSMꢀ5 catalyst was reused twice without any loss of
catalytic activity (entries 2 and 3). A blank test using only Hꢀ
ZSMꢀ5 as a catalyst afforded no products, showing the
importance of Pt nanoparticle as a hydrogenation catalyst (entry
β, HꢀMOR and Hꢀ
2
6
1
,2
time. Many catalyst systems have been developed for the
reactions of some ligninꢀrelated phenols. However, most of
these reactions have been conducted under harsh conditions,
2
with high temperatures (higher than 300 °C) and high H2
electron
microscopy
(TEM),
nitrogen
pressures (2‒10 MPa), and the catalyst often becomes
deactivated mainly because of coking and waterꢀinduced3
structural changes in the catalyst at high temperatures.
Furthermore, harsh reaction conditions are undesirable in terms
of facility costs and safety. The development of a novel system
for catalysing the hydrodeoxygenation of phenols under milder
conditions is therefore desirable.
−
1
4
5
Lercher and Jones showed that the hydrodeoxygenation of
phenols to form cyclohexanes can be performed at relatively
low temperatures using a metal–acid bifunctional catalyst. For
example, the reactions of various phenols proceed at 200‒
2
2
50 °C in the presence of the catalysts Pd/C and H PO in
3 4
4
a,4c
water
via the metalꢀcatalysed hydrogenation of the aromatic
ring or a double bond and the acidꢀcatalysed dehydration of the
cyclohexanol intermediate (Scheme 1). Similarly, Chen
reported that Ru/HꢀZSMꢀ5 catalysed the hydrodeoxygenation
4
(
). Pt/Hꢀ
β
and Pt/HꢀMOR provided
2
in slightly lower yields
in 8% yield and
6
of phenols in water at 150‒200 °C. Kou and Dyson developed
entries 5 and 6). In contrast, Pt/HꢀY gave
many byproducts including phenol (7%) and 2,4ꢀ
dipropylphenol (17%), which were probably formed via the
acidꢀcatalysed transalkylation of
2
an efficient catalyst system composed of nanoparticles of a
noble metal and acidꢀfunctionalised imidazolium salts, and this
catalyst promoted the hydrodeoxygenation of phenol and 4ꢀ
8
1 (entry 7). Higher acid
7
alkylphenols in ionic liquids at 130 °C. These catalyst systems
contents of Pt/Hꢀβ, Pt/HꢀMOR and Pt/HꢀY (0.63‒1.41
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DOI: 10.1039/C
C
5
h
C
e
C
m
05
C
6
o
07
m
A
m
a
2
Table 1 Hydrodeoxygenation of 4ꢀpropylphenol (1) at 110 °C under H at 0.1 MPa, catalysed by different zeoliteꢀsupported metal nanoparticles.
b
b
Entry
Catalyst
Solvent
Conv. (%)
Yield based on carbon (%)
c
2
3
4
5
6
1
2
3
4
5
6
7
8
9
Pt/HꢀZSMꢀ5
Octane
Octane
Octane
Octane
Octane
Octane
Octane
Octane
Octane
Octane
Isoamyl acetate
Dibutyl ether
>99
>99
>99
6
>99
>99
59
>99
42
8
>99
>99
63
7
4
99
99
98
0
92
89
8
88
3
2
39
32
2
2
<1
0
0
0
0
0
0
0
3
0
<1
<1
1
0
3
<1
2
0
<1
0
<1
0
0
0
0
0
0
0
0
0
0
0
0
0
51
37
43
0
1
0
<1
<1
<1
1
Pt/HꢀZSMꢀ5 (2nd use)
Pt/HꢀZSMꢀ5 (3rd use)
HꢀZSMꢀ5
0
Pt/Hꢀβ
<1
<1
<1
2
0
0
1
21
0
0
0
Pt/HꢀMOR
Pt/HꢀY
Rh/HꢀZSMꢀ5 + HꢀZSMꢀ5
Pd/HꢀZSMꢀ5 + HꢀZSMꢀ5
Ru/HꢀZSMꢀ5 + HꢀZSMꢀ5
Pt/HꢀZSMꢀ5
Pt/HꢀZSMꢀ5
Pt/HꢀZSMꢀ5
Pt/HꢀZSMꢀ5
Pt/HꢀZSMꢀ5
Pt/HꢀZSMꢀ5
Pt/HꢀZSMꢀ5
0
d
d
<1
18
2
0
1
2
2
0
0
d
10
11
12
13
14
15
16
17
e
e
2
H O
1,4ꢀDioxane
Butanol
DMF
<1
12
0
0
No solvent
0
0
3
a
Reaction conditions:
1
(1.0 mmol), 2 wt% Pt/zeolite (98 mg, 1 mol% Pt) or HꢀZSMꢀ5 (96 mg), solvent (1.0 mL), 110 °C, H
2
(balloon, 0.1 MPa),
b
c
d
1
0 h. Determined by gas chromatography. The sum of the yields of all the isomers. 2 wt% metal/HꢀZSMꢀ5 (51‒53 mg, 1 mol% metal) +
e
additional HꢀZSMꢀ5 (the total amount of HꢀZSMꢀ5 was 96 mg). At 100 °C.
1
0
1
0). It should be noted that the solvent used had a great
1
1
influence on the catalytic activity of the Pt/HꢀZSMꢀ5. The
complete conversion of was observed in isoamyl acetate as in
octane, but the former case gave in only 39% yield, and 4ꢀ
propylcyclohexanol ( ) and bis(4ꢀpropylcyclohexyl)ether (6)
1
2
5
were also obtained in 51% and 1% yields, respectively (entry
1). Similar result was produced with dibutyl ether (entry 12).
1
The formation of
2 was almost completely suppressed when
H O, 1,4ꢀdioxane, butanol, DMF and neat conditions were used
2
(
entries 13‒17). H O is an inevitable byproduct of
2
hydrodeoxygenation, but it will depress the activity of the
catalyst compared to octane (entries 1 vs 13). Octane forms an
azeotrope with H O and could allow a certain amount of H O to
2
2
be removed from the reaction system through azeotropic
1
2
distillation (the azeotropic temperature is 90 °C). In addition,
the nonꢀpolar octane would have poorly coordinated to the
Fig. 1 Time course of the hydrodeoxygenation of 1, catalysed by Pt/HꢀZSMꢀ catalyst surface and have little effect on the catalytic activity.
5
in octane. Reaction conditions: 1 (1.0 mmol), 2 wt% Pt/HꢀZSMꢀ5 (98 mg, 1
The reaction could therefore be accelerated more efficiently by
using octane as the solvent.
mol% Pt), octane (1.0 mL), 110 °C, H (balloon, 0.1 MPa).
2
−
1
The time course of the hydrodeoxygenation of
by Pt/HꢀZSMꢀ5 in octane is shown in Fig. 1. It can be seen that
was gradually hydrogenated as the reaction time increased,
1 catalysed
mmol g ) than Pt/HꢀZSMꢀ5 may cause undesirable side
reactions. Pt/HꢀZSMꢀ5 has appropriate amount of acid sites,
which would be suitable for efficient and selective
hydrodeoxygenation. The catalytic activities of other metal
nanoparticles (Rh, Pd and Ru) supported on HꢀZSMꢀ5 were
examined using the same HꢀZSMꢀ5 loadings as were used for
1
and was completely consumed after 1.8 h. After 15 minutes,
was formed as a major product in 10% yield. The amount of
4
4
present then decreased over time, and the amount of
increased, reaching a yield of 49% after 1.8 h. It can be seen,
therefore, that was hydrogenated to via . After 1.8 h, the
amounts of and present increased as the amount of present
decreased, suggesting that and were formed from . Finally,
was completely consumed and converted into after 10 h.
5 produced
Pt/HꢀZSMꢀ5. As is shown in entry 8, the yield of
when Rh/HꢀZSMꢀ5 was used than when Pt/HꢀZSMꢀ5 was used.
Pd/HꢀZSMꢀ5 selectively converted to 4ꢀpropylcyclohexanone
) in 18% yield with the formation of , propylbenzene (
and many unidentified byproducts (entry 9). Ru/HꢀZSMꢀ5 was
not active under the reaction conditions that were used, and it
2 was lower
1
5
4
2
6
5
1
9
2
6
5
(
4
2
3)
6
2
gave only a trace of
2 and a very low conversion rate (entry
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DOI: 10.1039/C5CC05607A
a
Table 2 Control experiments using
5
and
6
as substrates.
b
b
Entry
Substrate
Catalyst
Gas
Time (h)
Conv. (%)
Yield based on carbon (%)
c
d
e
2
<1
1
54
>99
<1
<1
97
4
0
0
4
0
5
‒
‒
‒
6
0
0
7
8
18
19
20
21
22
23
24
5
5
5
5
6
6
6
HꢀZSMꢀ5
H
2
N
2
H
2
H
2
H
2
N
2
H
2
1
1
1
4
6
6
6
34
39
91
>99
65
10
15
0
12
13
0
Pt/HꢀZSMꢀ5
Pt/HꢀZSMꢀ5
Pt/HꢀZSMꢀ5
HꢀZSMꢀ5
Pt/HꢀZSMꢀ5
Pt/HꢀZSMꢀ5
15
<1
‒
‒
‒
‒
0
0
<1
<1
0
13
11
0
29
25
0
56
>99
0
0
a
Reaction conditions:
5 (1.0 mmol) or 6 (0.50 mmol), HꢀZSMꢀ5 (96 mg) or 2 wt% Pt/HꢀZSMꢀ5 (98 mg, 1 mol% Pt for 5, 2 mol% Pt for 6), octane
b c d
(
4
1.0 mL), 110 °C, gas pressure 0.1 MPa supplied using a balloon. Determined by gas chromatography. The sum of the yields of all the isomers.
ꢀpropylcyclohexene. 1ꢀpropylcyclohexene.
e
1
5
into
Pt/HꢀMOR showed less catalytic activities, giving
0% yields, respectively (the results are not shown in Table 3).
The reactions of the sterically demanding compounds 2,4,6ꢀ
2
in 67% yield (entry 25). For this reaction, Pt/Hꢀ
β and
2
in 39% and
4
trimethylphenol (11) and 2ꢀtertꢀbutylꢀ6ꢀmethylphenol (13
proceeded smoothly to afford 1,3,5ꢀtrimethylcyclohexane (12
)
)
in 91% yield and 1ꢀtertꢀbutylꢀ3ꢀmethylcyclohexane (14) in 95%
yield, respectively (entries 26 and 27). The strong catalytic
activity of Pt/HꢀZSMꢀ5 is noteworthy because the
hydrogenation of sterically hindered phenols usually requires
1
6
high pressure H2.
methylcyclohexane was not obtained when the sterically more
encumbered compound 2,6ꢀdiꢀtertꢀbutylꢀ4ꢀmethylphenol (15
was used, but the deꢀtertꢀbutylated product 14 was formed in
5% yield together with 2,6ꢀdiꢀtertꢀbutylꢀ4ꢀ
The expected 1,3ꢀdiꢀtertꢀbutylꢀ5ꢀ
Fig. 2 Proposed reaction pathways for the conversion of 5 to 2.
)
Control experiments using
performed to clarify the reaction pathways involved in the
conversion of to (Table 2). We consider that is generated
through the protonation of to form the corresponding
oxonium cation and then the nucleophilic attack on by
another molecule of with Hꢀ
ZSMꢀ5 under H (entry 18) and with Pt/HꢀZSMꢀ5 under N2
5 and 6 as substrates were
4
methylcyclohexanone (16) in 8% yield (entry 28). A C4
product, derived from the tertꢀbutyl group in 15, should be
formed in at least 17% yield; however, we could not detect it
probably due to the evaporation or the reaction with other
compounds during the reaction (some unidentified byproducts
were observed by GC analysis). In this reaction, 14 may have
been formed through the acidꢀcatalysed deꢀtertꢀbutylation of 15
5
2
6
5
9
9
1
3
5
.
However, the reactions of 5
2
(
entry 19) for 1 h did not give any
were actually 4ꢀpropylcyclohexene
propylcyclohexene (
doubleꢀbond isomerisation of
Pt/HꢀZSMꢀ5 under H afforded
6
, and the dominant products
(7)
and 1ꢀ
followed by the hydrodeoxygenation of the resulting 2ꢀtert
ꢀ
8
), formed through the acidꢀcatalysed
17
butylꢀ4ꢀmethylphenol to give 14
. With Pt/Hꢀβ and Pt/HꢀMOR,
1
4
7
.
In contrast, the reaction with
and after 1 h with higher
1
5
was converted to 14 (8% and 8%, respectively) and 16 (<1%
2
6
2
and 37%, respectively) together with many unidentified
byproducts which were formed probably via the acidꢀcatalysed
reactions caused by the zeolites with high acid content (the
results are not shown in Table 3). The reaction of methyl 4ꢀ
conversion of
was highly dependent on the reaction conditions. With Pt/Hꢀ
ZSMꢀ5 under H2, was fully converted into after 4 h (entry
1). We found that was converted into and by HꢀZSMꢀ5
under H (entry 22) and by Pt/HꢀZSMꢀ5 under N (entry 23).
5 (entry 20), suggesting that the formation of 6
5
2
2
6
7
8
hydroxybenzoate
(
17
)
successfully
provided
methyl
2
2
cyclohexanecarboxylate (18) in 67% yield without causing the
Under H , the reaction with Pt/HꢀZSMꢀ5 resulted in the full
18
2
ester moiety to be reduced (entry 29). This kind of
conversion of
From these results, we propose the reaction pathways involved
in the conversion of to (Fig. 2). First, is protonated by Hꢀ
ZSMꢀ5 to give , which is then transformed into through
nucleophilic attack by and/or into through dehydration. is
gradually converted into via because and are at
equilibrium under acidic conditions. The formation of is
promoted by the irreversible hydrogenation of and its isomer
by Pt/HꢀZSMꢀ5 to afford the final product
We performed the hydrodeoxygenation reaction using
various phenols in octane at 110 °C under an H atmosphere
6 after 6 h, giving 2 in 97% yield (entry 24).
transformation would be difficult to achieve using conventional
catalyst systems that require harsh reaction conditions.
5
2
5
In summary, we have developed
a
system for
9
6
hydrodeoxygenating phenols to form cyclohexanes under mild
5
7
6
conditions (ambient H pressure and 110 °C) using Pt/HꢀZSMꢀ5
2
7
9
6
5
as a catalyst and octane as the solvent. The catalyst system
facilitated the reaction of various phenols, including the
generally less reactive ligninꢀrelated methoxyphenol, sterically
hindered alkylphenols and an esterꢀfunctionalised phenol.
Detailed mechanistic studies and studies of reactions using a
broad range of phenols are ongoing, and the results will be
reported in due course.
7
7
8
2.
2
(
0.1 MPa) at different reaction times to demonstrate the
effectiveness of Pt/HꢀZSMꢀ5 as a catalyst. Selected results are
shown in Table 3. 2ꢀMethoxyꢀ4ꢀpropylphenol (10), which is
one of the most important ligninꢀrelated phenols, was converted
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Table 3 Hydrodeoxygenation of various phenols catalysed by Pt/Hꢀ
ZSMꢀ5 in octane.
4
(a) C. Zhao, Y. Kou, A. A. Lemonidou, X. Li and J. A. Lercher,
a
Angew. Chem. Int. Ed., 2009, 48, 3987; (b) C. Zhao, Y. Kou, A. A.
Entry
Substrate
Conv.
Product
Yield
(%)
Lemonidou, X. Li and J. A. Lercher, Chem. Commun., 2010, 46
412; (c) C. Zhao and J. A. Lercher, ChemCatChem, 2012, , 64; (d)
C. Zhao and J. A. Lercher, Angew. Chem. Int. Ed., 2012, 51, 5935;
(e) C. Zhao, D. M. Camaioni and J. A. Lercher, J. Catal., 2012, 288
92; (f) C. Zhao, S. Kasakov, J. He and J. A. Lercher, J. Catal., 2012,
96, 12; (g) J. He, C. Zhao and J. A. Lercher, J. Catal., 2014, 309
362.
,
b
b,c
(%)
4
2
5
6
90
67
,
10
11
13
15
17
2
2
,
d
e,f
2
>99
91
5
6
7
8
D.ꢀY. Hong, S. J. Miller, P. K. Agrawal and C. W. Jones, Chem.
Commun., 2010, 46, 1038.
12
14
14
18
W. Zhang, J. Chen, R. Liu, S. Wang, L. Chen and K. Li, ACS
e
27
28
29
>99
>99
>99
95
Sustainable Chem. Eng., 2014, 2, 683.
N. Yan, Y. Yuan, R. Dykeman, Y. Kou and P. J. Dyson, Angew.
Chem. Int. Ed., 2010, 49, 5549.
g
h
e
(a) I. V. Kozhevnikov, S. M. Kulikov, M. N. Timofeeva, A. P. Krysin
and T. F. Titova, React. Kinet. Catal. Lett., 1991, 45, 257; (b) J. Das,
Y. S. Bhat and A. B. Halgeri, Catal. Lett., 1994, 23, 161.
Selective hydrogenation of phenols to cyclohexanones by Pd
catalysts: see, (a) H. Liu, T. Jiang, B. Han, S. Liang and Y. Zhou,
Science, 2009, 326, 1250; (b) A. K. Talukdar, K. G. Bhattacharyya
and S. Sivasanker, Appl. Catal. A: Gen., 1993, 96, 229.
45
9
67
a
Reaction conditions: substrate (1.0 mmol), 2 wt% Pt/HꢀZSMꢀ5 (98 mg,
mol% Pt), octane (1.0 mL), 110 °C, H (balloon, 0.1 MPa), 24 h.
Determined by gas chromatography. Calculated based on carbon. 6 h.
The sum of the yields of the isomers. The molar ratio of the cis,cisꢀ
b
2
10 Ru/HꢀZSMꢀ5 showed high catalytic activity under high pressure H .
1
2
c
d
The details were shown in the electronic supplementary information.
1 Dibutyl ether solvent was slightly hydrolysed over Pt/HꢀZSMꢀ5 to
form butanol after the reaction (Table 1, entry 12). No
decomposition was observed with the other solvents.
e
f
1
1
g
h
and cis,transꢀisomers was 2:3. 2 mol% Pt. 48 h.
This work was supported by a GrantꢀinꢀAid for Scientific
Research (KAKENHI, 24760633) from the Japan Society for
the Promotion of Science (JSPS). We thank the Applied Protein
Research Laboratory and the Integrated Center for Science
2 Azeotropic Data for Binary Mixtures, in CRC Handbook of
Chemistry and Physics, Internet Version 2005, David R. Lide, ed.,
<http://www.hbcpnetbase.com>, CRC Press, Boca Raton, FL, 2005.
(
INCS) at Ehime University for NMR and gas chromatographyꢀ 13 A. Vjunov, M. Y. Hu, J. Feng, D. M. Camaioni, D. Mei, J. Z. Hu, C.
mass spectrometry measurements.
Zhao and J. A. Lercher, Angew. Chem. Int. Ed., 2014, 53, 479.
4 D. M. Brouwer, J. Catal., 1962, , 22.
(1% yield), (3% yield), 2ꢀmethoxyꢀ4ꢀpropylcyclohexanone (3%
1
1
1
Notes and references
5
4
5
a
yield) and 2ꢀmethoxyꢀ4ꢀpropylcyclohexanol (3% yield) were
observed on GC. Methanol (at least 8% yield) should be formed in
this reaction although it was not detected due to the evaporation
under the reaction conditions (110 °C).
Department of Materials Science and Biotechnology, Graduate School
of Science and Engineering, Ehime University, 3 Bunkyo-cho, Matsuyama
7
b
90-8577, Japan.
Institute for Molecular Science, Myodaiji, Okazaki 444-8787, Japan.
1
6 (a) T. Maegawa, A. Akashi, K. Yaguchi, Y. Iwasaki, M. Shigetsura,
E-mail: ota.hidetoshi.mx@ehime-u.ac.jp; Tel: +81-89-927-9944
Electronic Supplementary Information (ESI) is available: see
DOI: 10.1039/c000000x/
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32
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