Efficient hydrodeoxygenation of ketones, phenols, and ethers promoted by platinum-heteropolyacid bifunctional catalysts

Article abstract of DOI:10.1246/cl.140342

A Cs_2.5H_0.5PW₁₂O₄₀-supported platinum catalyst (Pt/CsPW) could act as an efficient heterogeneous catalyst for hydrodeoxygenation of various types of oxygen-containing compounds such as ketones, phenols, and ethers. The observed catalysis was truly heterogeneous, and the retrieved Pt/CsPW could be reused.

Full text of DOI:10.1246/cl.140342

CL-140342
Received: April 7, 2014 | Accepted: April 11, 2014 | Web Released: April 18, 2014
Efficient Hydrodeoxygenation of Ketones, Phenols, and Ethers
Promoted by Platinum-Heteropolyacid Bifunctional Catalysts
Shintaro Itagaki, Naoki Matsuhashi, Kento Taniguchi, Kazuya Yamaguchi, and Noritaka Mizuno*
Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656
(E-mail: tmizuno@mail.ecc.u-tokyo.ac.jp)
A Cs2.5H0.5PW12O40-supported platinum catalyst (Pt/CsPW)
could act as an efficient heterogeneous catalyst for hydro-
(step 1)
O
OH
R2
OH
R2
deoxygenation of various types of oxygen-containing com-
pounds such as ketones, phenols, and ethers. The observed
catalysis was truly heterogeneous, and the retrieved Pt/CsPW
could be reused.
H2
R1
R1
R1
R2
(step 2)
R1
−H2O
OR3
R2
(or −R3OH)
OH
R2
R1
R2
R1
Oxygen-containing compounds such as carbonyls, alcohols,
phenols, and ethers are versatile and readily available. They can
be employed as precursors for various types of chemicals.
Deoxygenation to alkanes (or alkenes) is one of the representa-
tive transformations and has frequently been performed in
laboratory-scale organic synthesis as well as bulk production.1
Since oxygen functionalities are poor leaving groups, deoxy-
genation often requires strong reductants. For example, in
laboratory-scale deoxygenation of ketones and aldehydes,
Clemmensen reduction using a zinc amalgam under strongly
acidic conditions, Wolff-Kishner reduction using hydrazine or
its derivatives under strongly basic conditions, and Mozingo
reduction through the sequential reaction of thioacetalization
and hydrogenolysis are still frequently been utilized despite
their production of large amounts of by-products.2
In comparison with the above-mentioned antiquated proce-
dures, hydrodeoxygenation (using H2 as the reductant) is a
promising reaction for deoxygenation of oxygen-containing
compounds.3-6 In particular, it has been utilized for upgrading
biomass and pyrolysis bio-oils.3,4 Although several classes of
catalysts such as cobalt-molybdenum and nickel-molybdenum
have industrially been utilized, they readily undergo deactivation
due to coke deposition.7 In addition, these procedures typically
require harsh reaction conditions (e.g., ²300 °C for phenols).3a
The above disadvantages can be overcome by the one-pot
strategy using metal-acid bifunctional catalysts.4-6 As shown in
Scheme 1, hydrogenation of carbonyls or phenols to saturated
alcohols proceeds (step 1), followed by the formation of alkenes
through dehydration of the alcohols (step 2). Finally, the alkenes
are hydrogenated to give the corresponding alkanes (step 3).
Although several metal-acid bifunctional catalysts have been
developed for this strategy, challenges still remain because they
have disadvantages of limited substrate scopes, high temper-
atures, high pressures of H2, and/or use of large excess of H2.4-6
Herein, we report that hydrodeoxygenation of oxygen-
containing compounds efficiently proceeded in the presence of a
Cs2.5H0.5PW12O40-supported platinum catalyst (Pt/CsPW) under
relatively mild reaction conditions (typically 120 °C, 5 atm of
H2). The present system could be applied to a wide variety of
oxygen-containing compounds such as aliphatic and aromatic
ketones, phenols, and even ethers, affording the corresponding
deoxygenated products (mainly alkanes) in moderate to high
yields. The observed catalysis was truly heterogeneous, and the
(step 3)
R1
R1
H2
R2
R2
Scheme 1. A possible reaction path for hydrodeoxygenation of
oxygen-containing compounds in the presence of metal-acid
bifunctional catalysts.
catalyst could be reused without a severe loss of high catalytic
performance.
We prepared various metal-acid bifunctional catalysts by
impregnation of metals on (acidic) supports using aqueous metal
chloride solutions, followed by reduction with H2 (denoted as
metal/support; see the Supporting Information for their prepa-
ration).8 With regard to metals for hydrogenation (steps 1 and 3
in Scheme 1), we used platinum group metals such as platinum,
palladium, rhodium, and ruthenium. Alcohol dehydration
(step 2 in Scheme 1) is expected to be included in the rate-
limiting step for hydrodeoxygenation using metal-acid bifunc-
tional catalysts.4a,4g,4h Therefore, we selected heteropolyacids
such as Cs2.5H0.5PW12O40 (CsPW), Cs3HSiW12O40 (CsSiW),
H3PW12O40 (HPW), and H4SiW12O40 (HSiW) as acidic supports
because of the following reasons: their strong Brønsted acidities
for protonation of hydroxy groups9 and bare nucleophilic surface
of polyanions for stabilization of carbocation-type intermediates
formed in step 2 in Scheme 1.10
By using metal/support catalysts, we initially carried out the
hydrodeoxygenation of 2-octanone (1a) to octane (2a) as the
model reaction (Table 1).11,12 The reaction was carried out at
120 °C (bath temperature) using 0.1 mol % (metal) catalysts
under 5 atm of H2. Under the present conditions, the reaction did
not proceed at all in the absence of the catalysts or the presence
of CsPW alone (Table 1, Entries 11 and 12). Among various
metal/CsPW catalysts examined, Pt/CsPW was the most
effective for the hydrodeoxygenation; 1a was completely
converted within 1 h, and 2a, 2-octanol (3a), and dioctyl ether
(4a) were obtained in 36, 46, and 12% yields, respectively
(Table 1, Entry 1). A side reaction of the intermolecular
dehydrative condensation of 3a to 4a took place in the present
1086 | Chem. Lett. 2014, 43, 1086–1088 | doi:10.1246/cl.140342
© 2014 The Chemical Society of Japan

Table 1. Hydrodeoxygenation of 1a using various catalystsa
Table 2. Pt/CsPW-catalyzed hydrodeoxygenation of various
kinds of oxygen-containing compoundsa
O
OH
Catalyst
n-C8H18
+
+
Yield
( )5
( )5
( )5
( )5
3a
O
Entry
Substrate
Product
/%b
1a
2a
4a
Yield/%b
O
1
92
90
76
Conv.
2c
3c
Entry
Catalyst
1a
1b
of 1a/%b
2a
3a
4a
1
2c
3
4
5
6
7
8
9
Pt/CsPW
Pt/CsPW
Pd/CsPW
Rh/CsPW
Ru/CsPW
Pt/CsSiW
Pt/HPW
Pt/HSiW
Pt/C
>99
>99
38
12
18
>99
92d
>99e
66
40
19
36
83
31
6
46
3
12
14
<1
<1
<1
7
O
4
92
<1
<1
<1
64
59
70
59
36
<1
<1
2
O
24
70
92
2
26
12
11
<1
<1
<1
<1
5d
1c
1d
1e
1f
4
<1
<1
<1
<1
<1
10
11f
12
Pt/Al2O3
CsPW
None
<1
OH
6
aReaction conditions: Metal/support (the molar ratio of metal to
heteropolyacid: 1/20; metal: 0.1 mol %), 1a (0.5 mmol), heptane
(1 mL), 120 °C, 1 h, H2 (5 atm). bConversions and yields were
determined by GC using naphthalene as an internal standard.
Yield/% = (Product/mol)/(1a/mol) © 100 (for 2a and 3a);
Yield/% = (Product © 2/mol)/(1a/mol) © 100 (for 4a). c3 h.
68
2
OH
7e
OCH3
dOctenes were formed in 14% total yield. Octenes were formed
e
OCH3
f
in 5% total yield. CsPW (160 mg).
system; however, this is not a problem because Pt/CsPW could
also catalyze hydrodeoxygenation of ethers to alkanes (see the
last section). When prolonging the reaction time to 3 h, the yield
of 2a reached up to 83% (Table 1, Entry 2). Pd/CsPW gave 2a
in a moderate yield (Table 1, Entry 3), while the hydrodeoxy-
genation hardly proceeded in the presence of Rh/CsPW and
Ru/CsPW (Table 1, Entries 4 and 5).
The selection of acidic supports was very crucial. As
summarized in Table 1, 2a was obtained in significant yields
only when heteropolyacids were used as supports for platinum.
In the case of Pt/C and Pt/Al2O3, 1a was selectively hydrogen-
ated to 3a without the formation of 2a (Table 1, Entries 9 and
10), thus indicating that heteropolyacids can efficiently promote
the dehydration of 3a. Indeed, we confirmed in separate
experiments that dehydration of alcohols was efficiently pro-
moted in the presence of heteropolyacids. Cesium salts (CsPW
and CsSiW) were more effective than the corresponding acid
forms (HPW and HSiW) (Table 1, Entries 1 and 6 vs. 7 and 8)
possibly owing to the large surface areas of the cesium salts.13,14
The phosphorous-centered CsPW was a better support than the
silicon-centered CsSiW (Table 1, Entries 1 vs. 6).15
The comparison of the results (conversions of 1a) of Pt/
CsPW with those of Pt/C and Pt/Al2O3 reveals that the
hydrogenation of 1a (ketone) to 3a (alcohol) was also
accelerated by the presence of heteropolyacids. Recently,
Kaneda and co-workers have shown that the heterolytic cleavage
of H2 proceeds at the interface between metals and basic oxides
(e.g., CeO2 and hydrotalcite as proton acceptors) and that
hydrogenation of polar multiple bonds, e.g., carbonyls, can be
promoted by the active hydrogen species.16 Similarly, in the
present case, the heterolytic cleavage of H2 likely proceeds at
the interface between platinum and bare nucleophilic surface of
78
2
O
8e
aReaction conditions: Pt/CsPW (the molar ratio of Pt to CsPW:
1/100; Pt: 0.1 mol %), substrate (0.5 mmol), heptane (1 mL),
120 °C, 3 h, H2 (5 atm). bYields were determined by GC using
naphthalene as an internal standard. Yield/% = (Product/mol)/
(1/mol) © 100 (for Entries 1-7); Yield/% = (Product/mol)/
(1f © 2/mol) © 100 (for Entry 8). cEntries 2 and 3 for the 1st
d
e
and the 2nd reuses, respectively. 60 °C. 9 h, H2 (7 atm).
polyanions, resulting in the promotion of ketone hydrogenation
(step 1 in Scheme 1).
To verify whether the observed catalysis was derived from
solid Pt/CsPW or leached metal species (platinum and/or
tungsten), the hydrodeoxygenation of 1a was performed under
the conditions described in Table 1, and Pt/CsPW was removed
from the reaction mixture by filtration at ca. 40% yield of 2a.
When the filtrate was again heated at 120 °C (bath temperature)
under 5 atm of H2, no further production of 2a was observed.
In addition, ICP-AES analysis confirmed that no platinum and
tungsten species were detected in the filtrate (Pt: <0.06%,
W: <0.007%). All these results rule out any contribution to
the observed catalysis from metal species that leached into the
reaction solution, and the observed catalysis for the present
hydrodeoxygenation is truly heterogeneous.17
After the hydrodeoxygenation of 1a was completed, Pt/
CsPW could easily be retrieved from the reaction mixture by
simple filtration (>89% recovery). We confirmed by IR and
Chem. Lett. 2014, 43, 1086–1088 | doi:10.1246/cl.140342
© 2014 The Chemical Society of Japan | 1087

5935. e) C. Zhao, J. A. Lercher, ChemCatChem 2012, 4, 64. f) C.
Zhao, Y. Kou, A. A. Lemonidou, X. Li, J. A. Lercher, Chem.
Commun. 2010, 46, 412. g) D.-Y. Hong, S. J. Miller, P. K.
Agrawal, C. W. Jones, Chem. Commun. 2010, 46, 1038. h) C.
Zhao, J. He, A. A. Lemonidou, X. Li, J. A. Lercher, J. Catal. 2011,
280, 8. i) C. Zhao, D. M. Camaioni, J. A. Lercher, J. Catal. 2012,
288, 92. j) T. T. Isimjan, Q. He, Y. Liu, J. Zhu, R. J. Puddephatt,
D. J. Anderson, ACS Sustainable Chem. Eng. 2013, 1, 381.
a) B. Török, G. London, M. Bartók, Synlett 2000, 631. b) V.
Kogan, Z. Aizenshtat, R. Neumann, Angew. Chem., Int. Ed. 1999,
38, 3331. c) X. Kong, W. Lai, J. Tian, Y. Li, X. Yan, L. Chen,
ChemCatChem 2013, 5, 2009.
Although Kozhevnikov and co-workers have recently reported the
hydrodeoxygenation of isobutyl ketone and diisobutyl ketone
using heteropolyacids-supported platinum catalysts under H2 flow
conditions (using large excess of H2), their use for other types
of substrates such as aromatic ketones, phenols, and ethers has
not been mentioned: M. A. Alotaibi, E. F. Kozhevnikova, I. V.
Kozhevnikov, Chem. Commun. 2012, 48, 7194.
E. Furimsky, F. E. Massoth, Catal. Today 1999, 52, 381.
Supporting Information is available electronically on J-STAGE.
a) M. Pope, Hetropoly and Isopoly Oxometalates, Springer-Verlag,
Berlin, 1983. b) I. V. Kozhevnikov, Catalysts for Fine Chemical
Synthesis: Catalysis by Polyoxometalates, John Wiley & Sons,
Ltd, Chichester, 2002, Vol. 2. c) C. L. Hill, C. M. Prosser-
McCartha, Coord. Chem. Rev. 1995, 143, 407. d) T. Okuhara, N.
Mizuno, M. Misono, Adv. Catal. 1996, 41, 113. e) R. Neumann,
Prog. Inorg. Chem. 1998, 47, 317.
XRD analyses that the local as well as bulk structures of CsPW
in the catalyst were preserved after reuse. The retrieved Pt/
CsPW could be reused for the hydrodeoxygenation of 1a at least
twice without a severe loss of its catalytic performance (Table 2,
Entries 2 and 3).
Finally, we turned our attention to the scope of the present
Pt/CsPW-catalyzed hydrodeoxygenation system toward various
types of oxygen-containing compounds (Table 2). For hydro-
deoxygenation, 1.3-3.8 equiv of H2 with respect to hydro-
genation was utilized. The hydrodeoxygenation of both acyclic
(1a) and cyclic (1b) aliphatic ketones proceeded smoothly to
give the corresponding alkanes in high yields (Table 2, Entries 1
and 4). In the case of acetophenone (1c), the reaction took place
even at 60 °C to form the corresponding deoxygenated products
in 94% total yields (Table 2, Entry 5). Beside ketones, lignin-
derived phenolic monomers such as phenol (1d) and guaiacol
(1e) also afforded the corresponding alkanes in high yields
(Table 2, Entries 6 and 7). Notably, even less reactive diphenyl
ether (1f) could be converted into cyclohexane in 78% yield
(Table 2, Entry 8).
In summary, we successfully developed an efficient hetero-
geneously catalyzed system for hydrodeoxygenation of various
types of oxygen-containing compounds such as ketones,
phenols, and ethers. In addition, Pt/CsPW could be reused. In
comparison with the previously reported systems, the present
system has the following advantages: a wide substrate scope,
milder reaction conditions (e.g., temperatures: ¯120 °C, H2
pressures: 5-7 atm), and/or the use of reduced amounts of H2
(1.3-3.8 equiv with respect to hydrogenation).
5
6
7
8
9
10 a) Y. Izumi, K. Hayashi, Chem. Lett. 1980, 787. b) K. Matsuo, K.
Urabe, Y. Izumi, Chem. Lett. 1981, 1315. c) Y. Izumi, K. Matsuo,
K. Urabe, J. Mol. Catal. 1983, 18, 299. d) Y. Ogasawara, S.
Itagaki, K. Yamaguchi, N. Mizuno, ChemSusChem 2011, 4, 519.
11 Typical procedure for hydrodeoxygenation: Into a Teflon vessel
were successively placed Pt/CsPW (Pt: 0.1 mol %), 1a (0.5 mmol),
heptane (1 mL), and a Teflon-coated magnetic stir bar. The Teflon
vessel was attached inside an autoclave, and the reaction was
carried out at 120 °C (bath temperature) in 5 atm of H2. After the
reaction was completed (3 h), an internal standard (naphthalene)
was added to the reaction mixture, and the conversion of 1a and
the product yields were determined by GC analysis. As for the
reuse experiment, Pt/CsPW was separated by filtration and washed
with heptane. The retrieved Pt/CsPW was dried at room temper-
ature prior to being used for the reuse experiment. The products
(mainly alkanes) were confirmed by the comparison of their GC
retention times and GC-MS spectra with those of authentic data.
12 Among the solvents examined, nonpolar solvents (e.g., heptane,
mainly utilized in this study) were suitable for the hydrodeoxy-
genation of 1a. In contrast, the desired deoxygenated product 2a
was hardly produced under the conditions described in Table 1
This work was supported in part by Grants-in-Aid for
Scientific Researches from the Ministry of Education, Culture,
Sports, Science and Technology of Japan.
References and Notes
1
a) D. V. Nadkarni, J. F. Hallissey, Org. Process Res. Dev. 2008, 12,
1142. b) G. A. Peterson, F.-A. Kunng, J. S. McCallum, W. D.
Wulff, Tetrahedron Lett. 1987, 28, 1381. c) D. A. Evans, M. R.
Wood, B. W. Trotter, T. I. Richardson, J. C. Barrow, J. L. Katz,
Angew. Chem., Int. Ed. 1998, 37, 2700.
2
3
M. B. Smith, J. March, March’s Advanced Organic Chemistry:
Reactions, Mechanisms, and Structure, 6th ed., John Wiley &
Sons, Inc., Hodoken, New Jersey, 2007.
a) T.-R. Viljava, R. S. Komulainen, A. O. I. Krause, Catal. Today
2000, 60, 83. b) D. C. Elliott, Energy Fuels 2007, 21, 1792.
c) M. J. Girgis, B. C. Gates, Ind. Eng. Chem. Res. 1991, 30, 2021.
d) Y. Nakagawa, K. Tomishige, Catal. Surv. Asia 2011, 15, 111.
e) Y. Nakagawa, K. Mori, K. Chen, Y. Amada, M. Tamura, K.
Tomishige, Appl. Catal., A 2013, 468, 418. f) A. Iino, A. Cho, A.
Takagaki, R. Kikuchi, S. T. Oyama, J. Catal. 2014, 311, 17. g) R.
Arundhathi, T. Mizugaki, T. Mitsudome, K. Jitsukawa, K. Kaneda,
ChemSusChem 2013, 6, 1345. h) Z. Xinghua, W. Tiejun, M.
Longlong, W. Chuangzhi, Fuel 2010, 89, 2697. i) A. D. Sutton,
F. D. Waldie, R. Wu, M. Schlaf, L. A. Pete Silks, III, J. C. Gordon,
Nat. Chem. 2013, 5, 428. j) K. Chen, M. Tamura, Z. Tuan, Y.
Nakagawa, K. Tomishige, ChemSusChem 2013, 6, 613.
when using polar solvents such as DMF and diglyme.
13 The BET surface areas of CsPW and HPW were 142 and 4 m2 g
¹1
,
respectively.
14 a) T. Okuhara, H. Watanabe, T. Nishimura, K. Inumaru, M.
Misono, Chem. Mater. 2000, 12, 2230. b) S. Tatematsu, T. Hibi, T.
Okuhara, M. Misono, Chem. Lett. 1984, 865.
15 Y. Izumi, M. Ono, M. Ogawa, K. Urabe, Chem. Lett. 1993, 825.
16 a) A. Noujima, T. Mitsudome, T. Mizugaki, K. Jitsukawa, K.
Kaneda, Angew. Chem., Int. Ed. 2011, 50, 2986. b) A. Noujima, T.
Mitsudome, T. Mizugaki, K. Jitsukawa, K. Kaneda, Molecules
2011, 16, 8209. c) A. Noujima, T. Mitsudome, T. Mizugaki, K.
Jitsukawa, K. Kaneda, Chem. Commun. 2012, 48, 6723.
17 R. A. Sheldon, M. Wallau, I. W. C. E. Arends, U. Schuchardt, Acc.
Chem. Res. 1998, 31, 485.
4
a) C. Zhao, W. Song, J. A. Lercher, ACS Catal. 2012, 2, 2714.
b) C. Zhao, Y. Kou, A. A. Lemonidou, X. Li, J. A. Lercher,
Angew. Chem., Int. Ed. 2009, 48, 3987. c) N. Yan, Y. Yuan, R.
Dykeman, Y. Kou, P. J. Dyson, Angew. Chem., Int. Ed. 2010, 49,
5549. d) C. Zhao, J. A. Lercher, Angew. Chem., Int. Ed. 2012, 51,
1088 | Chem. Lett. 2014, 43, 1086–1088 | doi:10.1246/cl.140342
© 2014 The Chemical Society of Japan