Steam reforming of biomass-derived ethanol for the production of hydrogen for fuel cell applications

Article abstract of DOI:10.1039/b101455m

Ni/La₂O₃ catalyst exhibits high activity and good long term stability for steam reforming of ethanol to hydrogen production and is a good candidate for ethanol reforming processors for fuel cell applications.

Full text of DOI:10.1039/b101455m

Steam reforming of biomass-derived ethanol for the production of
hydrogen for fuel cell applications
Athanasios N. Fatsikostas, Dimitris I. Kondarides and Xenophon E. Verykios*
Department of Chemical Engineering, University of Patras, GR-26500 Patras, Greece.
E-mail: verykios@chemeng.upatras.gr
Received (in Cambridge, UK) 14th February 2001, Accepted 29th March 2001
First published as an Advance Article on the web 18th April 2001
Ni/La
2
O
3
catalyst exhibits high activity and good long term
two packed columns (Porapak, Carbosieve) and two detectors
(TCD, FID) and uses He as carrier gas. Porapak is used for the
stability for steam reforming of ethanol to hydrogen
production and is a good candidate for ethanol reforming
processors for fuel cell applications.
separation of C
Carbosieve is used for the separation of CO, CO
second gas chromatograph, which uses N as carrier gas, is
2
H
5
OH, H
2
O, CH
3
CHO, CH
4
, C
2
H
4
and C
2 6
H .
2
and CH . The
4
2
Fuel cells may be a promising alternative means of electricity
generation for stationary decentralized applications. They offer
significant advantages which include absence of pollutant
emission, since they use hydrogen as the fuel, and high
conversion efficiency, which may be even higher when they
operate on the co-generation mode. In recent years, fuel cells
have been seriously considered for electric vehicle operation,
making possible so-called Zero Emission Vehicles.
equipped with a Carbosieve column and a TCD detector and is
solely used for the analysis of the produced hydrogen.
Typical experimental results obtained are presented in Fig. 1,
in which the conversion of ethanol and the selectivities to
various reaction products are shown as a functions of reaction
temperature. At temperatures below 300 °C, steam reforming of
ethanol does not occur appreciably. Instead, dehydrogenation of
ethanol occurs to an appreciable extent producing acetaldehyde
and hydrogen. Increasing reaction temperature results in a
progressive decrease of selectivity toward acetaldehyde, which
drops to zero at temperatures above 550 °C. In this temperature
range the reforming reactions of both acetaldehyde and ethanol
prevail. It is interesting to observe that no ethylene is detected in
the reaction products, indicating that no dehydration of ethanol
is taking place, as might be expected. This is due to the fact that
An important source of hydrogen for stationary fuel cell
applications is natural gas, while for transportation, methanol
and gasoline are being considered. These fossil fuels do not
address the issue of carbon dioxide emissions, however, which
may only be addressed by the use of a renewable fuel as the
hydrogen source. Ethanol can be produced renewably from
several biomass sources, including energy plants, waste materi-
als from agroindustries or forestry residue materials, or even
organic fractions of municipal solid waste. Thus, in contrast to
the fossil-fuel-based systems, the bioethanol-to-hydrogen-
2 3
this particular catalyst, which utilizes La O as the carrier
material, does not possess any acidic sites, which are required
for the dehydration route. Steam reforming of ethanol takes
place to a significant extent at temperatures above 400 °C, as
evidenced by the sharp increase of ethanol conversion and by
system has the significant advantage of being nearly CO
2
neutral, since the carbon dioxide produced is consumed for
biomass growth, thus offering a nearly closed carbon loop. In
addition, the use of ethanol offers important storage and
handling safety advantages.
the increase of selectivities toward CO and H
products of the reaction are CO and CH , which are formed by
reaction of CO with water (shift reaction) and with hydrogen
(methanation), respectively. Selectivities toward CO and CH
2
(Fig. 1). By-
2
4
In the present communication, the catalytic steam reforming
of ethanol for hydrogen production is discussed, with respect to
catalyst performance characteristics. The steam reforming of
ethanol for hydrogen production has been shown to be entirely
feasible from a thermodynamic point of view.1 An issue of
major importance is then to develop highly active, selective and
durable catalysts for the reaction. Although much work has been
carried out on methanol reforming, only a limited number of
reports have appeared in the literature dealing with the
reforming of ethanol.4 Here, we report results obtained over a
2
4
–3
–6
2 3
Ni/La O catalyst, which has been previously found to exhibit
good performance characteristics under conditions of carbon
7
dioxide reforming of methane to synthesis gas. It is shown that
2 3
under certain operating conditions, the Ni/La O catalyst is very
active and stable for the steam reforming of ethanol and is
characterized by high selectivity toward hydrogen production.
The 17% Ni/La
was prepared by the wet impregnation method using Ni(NO
and La (Alfa Products) as starting materials, following a
procedure that has been described in detail elsewhere.
2 3
O catalyst employed in the present study
3 2
)
2 3
O
7
Catalytic performance tests have been conducted in the
temperature range 300–800 °C, over catalyst samples pre-
viously reduced in situ with hydrogen (500 °C, 2 h). In a typical
experiment, a water–ethanol mixture (molar ratio 3+1) is
pumped into a heated chamber and vaporized. The water–
ethanol gas stream (160 cm min ) is then fed to a quartz
micro-reactor containing 100 mg of catalyst. The composition
of the reactor effluent is analyzed by means of two gas
chromatographs, connected in series: the first is equipped with
Fig. 1 Effect of reaction temperature on the conversion of ethanol (XEtOH
)
and on selectivities toward acetaldehyde (SCH CHO), carbon monoxide
3
21
3
(
S
CO), carbon dioxide (SCO2), methane (SCH4) and hydrogen (S 2
over the 17% Ni/La catalyst. Experimental conditions: mass of catalyst:
100 mg; particle size: 0.25–0.50 mm; H O+EtOH molar ratio: 3+1; flow
H
), obtained
2 3
O
2
3
21
23
rate: 160 cm min (W/F = 0.0375 g s cm ); P = 1 atm.
DOI: 10.1039/b101455m
Chem. Commun., 2001, 851–852
851
This journal is © The Royal Society of Chemistry 2001

increase with increasing temperature and go through maxima at
ca. 550 °C. Above this temperature, the reformation of methane
2 2
with CO and with H O becomes thermodynamically feasible,
resulting in a decrease of the selectivities of both CH
since the Ni/La catalyst is known to be very active for these
reforming reactions. The observed decrease in the production
of CO may be due in part to the inverse shift reaction. At
temperatures above 600 °C, the conversion of ethanol reaches
4 2
and CO ,
2 3
O
7
2
1
1
00% and the selectivity toward hydrogen exceeds 90% (Fig.
). Under these conditions, the only undesirable product is
2
methane, which competes with H for hydrogen atoms.
However, from a practical point of view, a small concentration
of methane in the reformate may be tolerated since methane
present at the exhaust of the fuel cell can be burned, along with
unreacted hydrogen, to provide the heat necessary for the highly
endothermic reforming reaction. In any event, conversion of
2 2
methane via reforming with CO and H O proceeds at higher
reaction temperatures, resulting in increased yield of H
production.
2
The contact time dependence of the conversion of ethanol
and of the selectivity toward reaction products, as well as the
stability of the catalyst with time-on-stream were examined
Fig. 3 Conversion of ethanol and selectivities toward reaction products as
functions of time-on-stream, obtained over the (Ni/La )/Al catalyst.
Experimental conditions: mass of catalyst: 100 mg; particle size: 0.25–0.50
2
O
3
2 3
O
over a catalyst in which the active component (Ni/La
deposited on g-Al pellets (Engelhard) of a surface area of
80 m g . This type of catalyst formulation may be necessary
for a practical application since La is hydroscopic and
2 3
O ) was
3
21
2
mm; H O+EtOH molar ratio: 3+1; flow rate: 87 cm min (W/F = 0.0690
3
2 3
O
2
g s cm ); T = 750 °C; P = 1 atm.
2
21
1
2 3
O
pellets made out of this material do not possess the necessary
strength in the presence of steam, especially at low tem-
peratures. This problem is avoided if lanthana is dispersed over
the surface of materials which have the necessary strength, such
as alumina pellets. For the experiment described here, the g-
reformation products (CO and H
2
) and by an increase of the
CHO,
2 6
H . It is interesting to observe that at low contact
selectivity toward CO
2 3
and by-products, such as CH
C
2
H
4
and C
times (low ethanol conversion) appreciable amounts of ethylene
are formed, obviously by dehydration of ethanol over acidic
Al
calcined in air at 900 °C for 30 h. The resulting material was
then impregnated with Ni(NO , dried at 110 °C for 24 h,
reduced in H at 500 °C for 5 h and crushed to particles of
.25–0.50 mm in diameter.
The effect of contact time on the catalytic performance of the
Ni/La )/Al catalyst at the reaction temperature of 750 °C
2 3 3 3
O pellets were impregnated with La(NO ) and then
Al
La
2
O
2 3
3
sites. This reaction did not occur measurably over the Ni/
O catalyst which does not possess acidic sites.
3 2
)
2 3 2 3
The stability of the (Ni/La O )/Al O catalyst has been
2
examined at 750 °C and the results are shown in Fig. 3, in which
the alterations of activity and selectivity are plotted as functions
of time-on-stream. Under the experimental conditions em-
ployed (see legend of Fig. 3), a small deactivation of the catalyst
is observed during the first 80–100 h on stream, where
conversion of ethanol drops from 95 to 88%, while further
exposure of the catalyst to the reaction mixture does not result
in further deactivation. It is interesting to observe that
selectivity toward hydrogen does not change significantly and
slightly decreases from the initial value of 94 to 91% after 155 h
on stream. Selectivities toward the formation of other products,
0
(
2
O
3
2 3
O
is shown in Fig. 2, in which the conversion of ethanol and the
selectivities towards various reaction products are plotted as
functions of W/F. It is observed that for contact times > 0.1
3
g s cm the conversion of ethanol is 100% and the reaction is
highly selective toward hydrogen ( > 95%), the only unwanted
by-product being methane ( < 5%). As the contact time
decreases, the conversion of ethanol progressively drops,
accompanied by a decrease of the selectivity toward the
such as CO, CO
after 100–120 h.
Summarizing, the present results reveal that the Ni/La
catalyst, or the (Ni/La )/Al pelleted form, exhibits high
2 4 3 2 4 2 6
, CH , CH CHO, C H and C H also stabilize
2 3
O
2
O
3
2 3
O
activity and, most importantly, good long term stability for
steam reforming of ethanol to hydrogen production and is a
good candidate to be used in ethanol reforming processors for
fuel cell applications.
This work was funded in part by the Commission of the
European Community, under contract ERK6-CT-1999-00012,
and by the Hellenic General Secretariat of Research and
Technology (EPET II).
Notes and references
1
K. Vasudeva, N. Mitra, P. Umasankar and S. C. Dhingra, Int. J. Hydrogen
Energy, 1996, 21, 13.
2
3
G. Maggio, S. Freni and S. Cavallaro, J. Power Sources, 1998, 74, 17.
I. Fishtik, A. Alexander, R. Datta and D. Geana, Int. J. Hydrogen Energy,
000, 25, 31.
2
4
5
S. Cavallaro and S. Freni, Int. J. Hydrogen Energy, 1996, 21, 465.
F. Haga, T. Nakajima, H. Miya and S. Mishima, Catal. Lett., 1997, 48,
2
23.
Fig. 2 Effect of space time (W/F) on the conversion of ethanol and on the
6 F. Marino, E. G. Cerella, S. Duhalde, M. Jobbagy and M. A. Laborde, Int.
J. Hydrogen Energy, 1998, 23, 1095.
7 Z. Zhang and X. E. Verykios, J. Chem. Soc., Chem. Commun., 1995,
71.
2 3 2 3
selectivities toward reaction products, over the (Ni/La O )/Al O catalyst.
Experimental conditions: mass of catalyst: 100 mg; particle size: 0.25–0.50
mm; H
2
O+EtOH molar ratio: 3+1; T = 750 °C; P = 1 atm.
852
Chem. Commun., 2001, 851–852