Hydrodeoxygenation of bio-derived phenols to hydrocarbons using RANEY Ni and Nafion/SiO2 catalysts

Article abstract of DOI:10.1039/b916822b

A simple, green, cost- and energy-efficient route for converting phenolic components in bio-oil to hydrocarbons and methanol has been developed, with nearly 100% yields. In the heterogeneous catalysts, RANEY Ni acts as the hydrogenation catalyst and Nafion/SiO₂ acts as the Bronsted solid acid for hydrolysis and dehydration.

Full text of DOI:10.1039/b916822b

View Article Online / Journal Homepage / Table of Contents for this issue
COMMUNICATION
www.rsc.org/chemcomm | ChemComm
Hydrodeoxygenation of bio-derived phenols to hydrocarbons using
RANEYs Ni and Nafion/SiO2 catalystsw
Chen Zhao,a Yuan Kou,b Angeliki A. Lemonidou,ac Xuebing Lia and Johannes A. Lercher*a
Received (in Berkeley, CA, USA) 14th August 2009, Accepted 23rd October 2009
First published as an Advance Article on the web 18th November 2009
DOI: 10.1039/b916822b
A simple, green, cost- and energy-efficient route for converting
phenolic components in bio-oil to hydrocarbons and methanol
has been developed, with nearly 100% yields. In the hetero-
geneous catalysts, RANEYs Ni acts as the hydrogenation
catalyst and Nafion/SiO2 acts as the Brønsted solid acid for
hydrolysis and dehydration.
Table 1 Aqueous-phase hydrodeoxygenation of 4-n-propylphenol
using Pd and/or Ni based catalysts and acids at 473 Ka
Cycloalkane
select. [C%]
Catalyst
Acid
Conv. (%)
Pd/C
Pd/C
Pd/C
Pd/C
Pd/C
Pd/C
Ni/SiO2
H3PO4
100
100
100
100
100
100
9
37
51
96
84
74
1.5
5.2
98
98
43
50
36
64
99
98
—
—
CH3COOH
Zeolite (H-Beta)
Zeolite (H-Y)
Nafion solution
Nafion/SiO2
Nafion/SiO2
Nafion/SiO2
Nafion/SiO2
Nafion/SiO2
Nafion/SiO2
Nafion solution
H3PO4
While bio-oil production has been commercialized, the lack of
suitable upgrading techniques limits its direct use as transporta-
tion fuel.1 Two key problems in bio-oil upgrading processes
have to be addressed. (1) Crude bio-oil contains approximately
30 wt% water, which is difficult to be removed from the
original solution, because the bio-derived oxygen containing
compounds easily oligomerize during the thermal separation.2
Therefore, bio-oil upgrading should be performed preferentially
in the raw aqueous solution with water tolerant catalysts. Water
also proves to be a good medium for conversion of bio-derived
polyols and terpenes.3 (2) Crude bio-oil contains large concen-
trations of reactive oxygen containing compounds, which are
very unstable.4 Thus, bio-oil upgrading should be performed
under mild conditions with minimum phase transfer.
Ni/ASA
RANEY Nis2400
RANEY Nis4200
RANEYs Ni
RANEYs Ni
RANEYs Ni
RANEYs Ni
100
100
0
CH3COOH
0
a
Reaction conditions: 4-n-propylphenol (1.36 g, 0.010 mol), 0.05 wt%
H3PO4/H2O solution (80 mL), 5 wt% CH3COOH/H2O solution
(80 mL), H2O (80 mL), 10 wt% Nafion/H2O solution (1.00 g),
13 wt% Nafion/SiO2 (0.80 g), zeolite H-Beta (0.080 g), zeolite H–Y
(0.095 g), Pd/C (5 wt%, 0.040 g), RANEYs Ni (freshly prepared,
0.30 g), RANEY Nis2400 (0.30 g), RANEY Nis4200 (0.30 g),
60 wt% Ni/SiO2 (0.50 g), 65 wt% Ni/ASA (0.50 g), 4 MPa H2,
0.5 h, stirred at 1000 rpm.
The currently reported upgrading techniques use two
approaches. One is based on hydrogenation and hydro-
deoxygenation with sulfide catalysts such as cobalt or nickel
doped molybdenum sulfides. These catalysts are, however,
sensitive to water and poisoned by the high concentrations
of oxygen containing compounds.5 The other is based on
zeolite catalysts at high temperatures (623 to 723 K) on which
the oxygenates are mostly converted to carbonaceous deposits
and to a much lesser extent to alkanes.6
For the efficient use of the phenolic bio-oil, especially for the
oil derived from lignin, we report here a new green route based
on low-cost RANEYs Ni catalysts and an environmentally
friendly solid acid, i.e., Nafion/SiO2, to convert the aqueous
phenolic monomers (phenols, guaiacols and syringols) in bio-oil
to hydrocarbons and methanol.
Recently, we have developed a new highly efficient (nearly
100% cycloalkane and methanol yields) one-pot route for
hydrodeoxygenation of aqueous phenolic bio-oil to cyclo-
alkanes over bifunctional catalysts combining the metal
function of Pd/C with mineral acids.7 However, the bottleneck
for the industrial application of such a process is related to the
use of a noble metal catalysts and an added liquid acid, leading
to a relatively corrosive reaction environment.
To find a suitable green solid acid to replace mineral liquid
acid, a series of liquid and solid acids were tested on the
hydrodeoxygenation of 4-n-propylphenol in the presence of
Pd/C catalysts (see Table 1).z Under mild conditions (473 K,
5 MPa H2, 0.5 h), Pd/C yielded 84 and 74% of n-propyl-
cyclohexane from 4-n-propylphenol with H3PO4 and
CH3COOH, respectively. To replace liquid acids, the solid
acid has to be thermally stable to temperatures above 473 K in
the aqueous phase7 and has a high acid density. Amberlyst
a Catalysis Research Center, Department of Chemistry,
Technische Universitat Munchen, Garching 85747, Germany.
¨
¨
meets the requirement of high acid density (ca. 5.4 equiv. kgꢀ1
)
E-mail: johannes.lercher@ch.tum.de; Fax: (+) 49-89-28913544;
Tel: (+) 49-89-289-13540
and high surface area (50 m2 gꢀ1), but it decomposes above
473 K.8 Thus, robust solid acids were explored including
zeolites and Nafion, which are very stable at elevated
temperatures in aqueous solution.9 The zeolites H-beta and
zeolite H-Y were not selective to the formation of alkanes,
producing only 1.5 and 5.2% yields of n-propylcyclohexane
from 4-n-propylphenol, respectively. The main product obtained
with both zeolites was 4-n-propylcyclohexanone. The zeolites
b PKU Green Chemistry Center, Beijing National Laboratory for
Molecular Sciences, College of Chemistry and Molecular
Engineering, Peking University, Beijing 100871, China
c Department Chemical Engineering, Aristotle University of
Thessaloniki, Thessaloniki 54124, Greece
w Electronic supplementary information (ESI) available: The GC-MS
product spectrum, a photo of the hydrocarbon product after reactions,
the proposed reaction pathways and phenolic monomer hydro-
deoxygenation reactions. See DOI: 10.1039/b916822b
ꢁc
This journal is The Royal Society of Chemistry 2010
412 | Chem. Commun., 2010, 46, 412–414

View Article Online
Table
2
Aqueous-phase hydrodeoxygenation of 2-methoxy-4-n-
a
unsupported Nafion. In contrast to the highly dispersed Nafion
in water, the solid Nafion/SiO2 composite, however, can be reused
and was, therefore, selected for the following catalytic tests.
In the next step, replacement of the supported noble metal
(Pd) catalysts by base metals, in particular by Ni, was
explored. Supported Ni/SiO2 and Ni/ASA catalysts led to
conversions of 9 and 37%, respectively, with about 50%
cycloalkane selectivity. It should be noted, however, that
supported Ni catalysts are quite effective in the reduction of
functional groups in aromatic molecules, but are rather
inactive for the hydrogenation of the aromatic ring.11 The full
metal Ni catalysts, i.e., RANEY Nis2400, RANEY Nis4200
and freshly prepared RANEYs Ni exhibited higher hydro-
genation ability than supported Ni catalysts under identical
conditions (473 K, 4 MPa H2), as shown in Table 1.
Together with the Nafion water suspensions and the Nafion/
SiO2 composite, freshly prepared Ni catalysts led to
100% n-propylcyclohexane, while the other two commercial
RANEY Nis2400 and RANEY Nis4200 showed conversions
of 51 and 96% and n-propylcyclohexane selectivities of 36 and
64%, respectively. The lower activities of RANEY Nis2400
propylphenol using RANEYs Ni and Nafion/SiO2
Selectivity (C%)
T/K
Conv. (%)
Cycloalkanes
Methanol
473
523
573
1
38
80
89
88
86
9.3
8.4
8.7
a
Reaction conditions: 2-methoxy-4-n-propylphenol (1.66 g, 0.010 mol),
H2O (80 mL), 13 wt% Nafion/SiO2 (0.80 g), RANEYs Ni (freshly
prepared, 0.30 g), 4 MPa H2, 0.5 h, stirred at 1000 rpm.
used contain Lewis and Brønsted acidity,9 but their effective
acidity in aqueous solution is very low.10 Nafion, a perfluorinated
polymer with terminal –CF2CF2SOOH groups, is a very
strong Brønsted solid acid catalyst (Table S1, ESIw). When
the Nafion water suspension (10 wt%; the –SO3H concentration
was equal to the Al concentration in the experiment with
zeolite) was tested (Table S2, ESIw), 98% yield of n-propyl-
cyclohexane was produced. Nafion supported on SiO2 (loading:
13 wt%) also led to 98% n-propylcyclohexane production.
This shows that the material is able to act as efficiently as
Table 3 Aqueous-phase hydrodeoxygenation of phenolic monomers in bio-oil over RANEYs Ni catalysts with Nafion/SiO2 at 573 Ka
a
Reaction conditions: reactant (0.010 mol), RANEYs Ni (freshly prepared, 0.30 g), 13 wt% Nafion/SiO2 (0.80 g), H2O (80 mL), 4 MPa H2, 2 h, stirred
at 1000 rpm.b Trace amounts of by-products (less than 2 C%): ethers from intermolecular dehydration between phenolic monomer reactants.
ꢁc
This journal is The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 412–414 | 413

View Article Online
and RANEY Nis4200 are attributed to the partial oxidation
of the Ni surface on the commercial catalysts or formation of
aluminum oxide overlayers.12 It should be emphasized at this
point that molecular acids such as H3PO4 or CH3COOH led to
no hydrogenation activity at all in the presence of fresh
RANEYs Ni catalysts. This is caused by the dissolution
and oxidation of RANEYs Ni catalysts in the acidic aqueous
solution under reactions conditions. The Nafion polymer was
hardly ionized as the pH of aqueous solution remained nearly
neutral (pH = 6) during the course of the reaction.
acid for hydrolysis and dehydration (Fig. S3a, ESIw). Acid
promoted carbon-backbone transformation led also to
isomerized cycloalkanes, but did not lead to ring opening
(Fig. S3b, ESIw). The relatively high temperature (573 K)
induces cycloalkane dehydrogenation to form some cyclo-
alkenes and aromatic molecules with full metal Ni catalysts
(Fig. S3c, ESIw).13 The new catalyst combination opens the
possibility to tailored hydrodeoxygenation and hydrogenation
of lignin derived bio-products.
This research was performed in the framework of network
of excellence IDECAT.
This combination of catalysts, however, hardly showed
activity (1% conversion) with substituted phenols such as
2-methoxy-4-n-propylphenol at 473 K (Table 2) implying that
the methoxy group stabilizes the aromatic ring and increases
the difficulty for hydrogenation. Increasing the reaction
temperature to 523 and 573 K led to 38 and 80% conversions
with very high selectivities to cycloalkanes and methanol (490%).
With the optimized catalyst combination, a series of repre-
sentative bio-derived phenolic monomers (phenols, guaiacols
and syringols) were efficiently converted to hydrocarbons and
methanol under optimized conditions (573 K, 4 MPa H2, 2 h)
(see Table 3 and Scheme S1, ESIw). Phenolic monomers
containing six to nine carbon atoms directly linked in the
backbone were investigated. The one-pot aqueous phase pro-
cess led to over 90% yields of hydrocarbons and methanol
(Fig. S1, ESIw), being highly atom economic and energy
efficient. The product mixtures mainly include cyclohexane/
alkylcylcohexane, with low concentrations in cyclohexene/
alkylcyclohexene and benzene/alkylbenzene. The selectivities
for dehydrogenated products (cycloalkenes and benzene
derivatives) ranged from 7 to 15%. Acid catalyzed ring
contraction of isomerization products derived from cycloalkane,
such as 1-ethyl-2-methyl-cyclopentane and ethylcyclopentane,
were obtained for the C9 backbone phenolic-monomer
conversion, with selectivities from 0.5 to 2.7%. Minor hydro-
genolysis led to cycloalkanes with shorter carbon chains, e.g.,
n-propylcyclopentane (C8 cycloalkane) from 2-methoxy-4-n-
propylphenol (C9 backbone phenol). Hydrolysis of methoxy
groups selectively led to methanol.7 These results suggest that
the one-pot approach with two catalytic functions can be
applied for widely diverse phenolic monomer conversion.
To simulate real crude bio-oil, an equimolar mixture of
phenolic monomers including 4-n-propylphenol, 2-methoxy-
4-n-propylphenol and 4-allyl-2-methoxyphenol was hydro-
deoxygenated. After reactions (Fig. S2, ESIw), the metal and
acid catalysts were deposited in the bottom of the reactor and
a top hydrocarbon layer was formed. Thus catalysts and the
liquid phases can be easily separated. The process realized
nearly quantitative conversions with 100% selectivities to
hydrocarbons and methanol. No product from polymerization
among phenolic compounds was observed.
Notes and references
z For phenolic monomer hydrodeoxygenation: in
a typical test,
phenolic monomer (0.010 mol), Nafion/SiO2 (13 wt%, 0.80 g), freshly
prepared RANEYs Ni (0.30 g) and H2O (80 mL) were added to a Parr
reactor (reactor volume, 300 mL). After purging the reactor with H2, the
reaction was carried out with 4 MPa H2 (room temperature) at 473 K
for 0.5 h or 573 K for 2 h at a stirring speed of 1000 rpm. After reaction,
the reactor was cooled to room temperature. Ethyl acetate was used to
extract the organic mixture and the aqueous phase was also gathered.
The aqueous and organic layers were both analyzed by GC and
GC–MS. Gas chromatography (GC) and GC-mass spectroscopy
(GC–MS) analysis were performed on a Shimadzu 2010 gas chromato-
graph with a flame ionization detector (FID) and a Shimadzu QP 2010S
GC-mass spectroscope, both equipped with a 30 m (0.25-mm-i.d) HP-5
column. Internal standards (i.e., 2-isopropylphenol for the organic
phase and acetone for the aqueous phase) were used to determine the
product amount and carbon balance. The gas phase products were
analyzed by GC (HP 6890, Porapak Q column, FID). The calculations
of conversion and selectivity were based on mol carbon basis.
Conversion = (amount of raw material changes/total amount of
aromatic compounds in the starting material) ꢂ 100%. Selectivity =
(C atom in each product/total C atoms in the products) ꢂ 100%. The
carbon balance is better than 94 ꢃ 3% in this work.
1 S. Czernik and A. V. Bridgwater, Energy Fuels, 2004, 18, 590.
2 S. Czernik, D. Johnson and S. Black, Biomass Bioenergy, 1994, 7,
187.
3 (a) R. D. Cortright, R. R. Davda and J. A. Dumesic, Nature, 2002,
418, 964; (b) G. W. Huber, J. W. Shabaker and J. A. Dumesic,
Science, 2003, 300, 2075; (c) N. Yan, C. Zhao, C. Luo, P. J. Dyson,
H. Liu and Y. Kou, J. Am. Chem. Soc., 2006, 128, 8714; (d) C. Zhao,
W. J. Gan, X. B. Fan, Z. P. Cai and P. J. Dyson amd Y. Kou,
J. Catal., 2008, 254, 244; (e) N. Yan, C. Zhao, P. J. Dyson, C. Wang,
L. Liu and Y. Kou, ChemSusChem, 2008, 1, 626.
4 M. Garcia-Perez, A. Chaala, H. Pakdel, D. Kretschmer and
C. Roy, Biomass Bioenergy, 2007, 31, 222.
5 (a) E. G. Baker and D. C. Elliott, US Pat., 5 180 868, 1993;
(b) E. Laurent and B. Delmon, J. Catal., 1994, 146, 281;
(c) E. Furimsky and F. E. Massoth, Catal. Today, 1999, 52, 381;
(d) J. S. Shabtai, W. W. Zmierczak and E. Chornet, US Pat.,
5 959 167, 1999.
6 (a) S. Vitolo, M. Seggiani, P. Frediani, G. Ambrosini and L. Politi,
Fuel, 1999, 78, 1147; (b) S. Vitolo, B. Bresci, M. Seggiani and
M. G. Gallo, Fuel, 2001, 80, 17.
7 C. Zhao, Y. Kou, A. A. Lemonidou, X. Li and J. A. Lercher,
Angew. Chem., Int. Ed., 2009, 48, 3987.
8 M. A. Harmer and Q. Sun, Appl. Catal. A, 2001, 221, 45.
9 S. Kotrel, J. H. Lunsford and H. Knozinger, J. Phys. Chem. B,
2001, 105, 3917.
10 (a) T. Okuhara, Chem. Rev., 2002, 102, 3641; (b) G. Sartori and
R. Maggi, Chem. Rev., 2006, 106, 1077.
11 J. Relvas, R. Andrade, F. G. Freire, F. Lemos, P. Araujo,
M. J. Pinho, C. P. Nunes and F. R. Ribeiro, Catal. Today, 2008,
133–135, 828.
12 A. Chojecki, M. Veprek-Heijman, T. E. Muller, P. Scharringer,
S. Veprek and J. A. Lercher, J. Catal., 2007, 245, 237.
13 L. A. Zhang, G. H. Xu, Y. An, C. P. Chen and Q. D. Wang, Int. J.
Hydrogen Energy, 2006, 31, 2250.
The detailed reaction pathway for hydrodeoxygenation of
phenolic compounds in which the noble metal catalyzes the
hydrogenation of the aromatic ring and of cycloalkene and
H3PO4 catalyzes ether hydrolysis and alcohol dehydration has
been explored previously.7 In the present fully heterogeneous
catalyst combination, RANEYs Ni acts as the hydrogenation
metal catalyst and Nafion/SiO2 acts as the Brønsted solid
ꢁc
This journal is The Royal Society of Chemistry 2010
414 | Chem. Commun., 2010, 46, 412–414