Low-temperature hydrogen production by highly efficient catalytic system assisted by an electric field

Article abstract of DOI:10.1021/jp906137h

We investigated four catalytic reactions assisted with an electric field to promote catalytic activity, and we could achieve an effective process for hydrogen production at low temperatures, such as 423 K. In the presence of the electric field, four reactions of steam reforming of ethanol, decomposition of ethanol, water gas shift, and steam reforming of methane proceeded at very low temperature, such as 423 K, where a conventional catalytic reaction hardly proceeded. Conversion of reactant was greatly increased by the electric field, and apparent activation energies for these four reactions were lowered by the application of the electric field. This process can produce hydrogen and syngas by using a considerably small energy demand and has quick response.

Full text of DOI:10.1021/jp906137h

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3824
J. Phys. Chem. A 2010, 114, 3824–3833
Low-Temperature Hydrogen Production by Highly Efficient Catalytic System Assisted by
an Electric Field†
Yasushi Sekine,* Masayuki Haraguchi, Masahiko Tomioka, Masahiko Matsukata, and
Eiichi Kikuchi
Department of Applied Chemistry, Waseda UniVersity, 3-4-1, Okubo, Shinjuku, Tokyo, 169-8555 Japan
ReceiVed: June 30, 2009; ReVised Manuscript ReceiVed: August 23, 2009
We investigated four catalytic reactions assisted with an electric field to promote catalytic activity, and we
could achieve an effective process for hydrogen production at low temperatures, such as 423 K. In the presence
of the electric field, four reactions of steam reforming of ethanol, decomposition of ethanol, water gas shift,
and steam reforming of methane proceeded at very low temperature, such as 423 K, where a conventional
catalytic reaction hardly proceeded. Conversion of reactant was greatly increased by the electric field, and
apparent activation energies for these four reactions were lowered by the application of the electric field.
This process can produce hydrogen and syngas by using a considerably small energy demand and has quick
response.
1. Introduction
Ethanol is being paid a lot of attention as an alternative fuel.
It can be easily produced by fermentation of carbohydrate of
biomass, so ethanol is expected to be a clean energy source
having many possibilities. In addition, development of effective
use of ethanol as a fuel is important because petroleum will be
in short supply in the future.
Hydrogen production from various energy sources such as
fossil fuel and biomass is desired in the near future. Today, a
major route for hydrogen production is catalytic steam reforming
of methane, other hydrocarbons, or ethanol. The reaction is
highly endothermic and requires a high temperature. As for high-
temperature catalytic processes, there are many problems, such
as selection of strong materials to heat, deactivation of the
catalyst, and the difficulty of using wasted heat at a low
temperature after the heat exchanger. The heat loss is a one of
the reasons for the depression of the total energy efficiency of
chemical processes. In the case of small commercial chemical
processes without a heat exchanger, application of high tem-
perature is a serious problem because of the high heat loss, so
a low temperature catalytic process that works at a lower
temperature without a heat exchanger is desirable for high
energy efficiency.
Steam reforming of ethanol is an endothermic reaction and
requires high temperature, about 773 K or higher.
C2H5OH(g) + H2O(g) f 2CO + 4H2
∆H298 ) 255.9 kJ mol-1
C2H5OH(g) + 3H2O(g) f 2CO2 + 6H2
∆H298 ) 173.5 kJ mol-1
If this reaction could proceed at low temperature using wasted
heat, a novel process for effective hydrogen production would
be realized.
To solve such problems, many researchers have investigated
hybridization of nonequilibrium plasma and catalysts as novel
chemical processes.1-14 In addition, there have been many
investigations for the utilization of electric power to convert
such fuels into hydrogen/syngas.15-19 In contrast, we have
investigated catalytic reactions in an electric field. Since an
electric field needs less energy than a nonequilibrium electrical
discharge, the reaction can be conducted under milder condi-
tions. We have reported the effect of an electric field on the
catalytic decomposition of ethanol.20 The reaction proceeds at
a lower temperature region in which conventional catalytic
reaction cannot take place. The electric field is not plasma, is
milder than plasma, and has properties of lower consumption
energy and no emission spectra.
Many researches have investigated steam reforming of ethanol
at the lower temperature region.21-41 Supported Co catalyst
exhibited high activity for steam reforming of ethanol,21 and
noble metals such as Pt, Pd, Rh, and Ru have shown high
catalytic activities at 573-723 K.28,32,33 We also investigated
this steam reforming reaction over Co supported catalyst on
perovskite oxide, such as SrTiO3,39,40 and we found that the
reaction mechanism for steam reforming of ethanol was a
combination of the following five reactions:
(1) dehydrogenation of ethanol to form acetaldehyde,
C2H5OH(g) T CH3CHO(g) + H2 ∆H298 ) 68.9 kJ mol-1
In this research, we investigated steam reforming of ethanol
and another three elemental reactions: ethanol decomposition,
water gas shift reaction, and steam reforming of methane.
∆G573 ) -4.2 kJ mol-1, Kp573 ) 6.4 × 103, ∆G673
)
-19.8 kJ mol-1, Kp673 ) 2.8 × 106
† Part of the special issue “Green Chemistry in Energy Production
Symposium”.
* Corresponding author. Phone and Fax: +81-3-5286-3114. E-mail:
ysekine@waseda.jp.
(2a) steam reforming of acetaldehyde to form carbon mon-
oxide and hydrogen,
10.1021/jp906137h  2010 American Chemical Society
Published on Web 09/18/2009

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Novel Catalytic Reactions with Electric Field
J. Phys. Chem. A, Vol. 114, No. 11, 2010 3825
CH3CHO(g) + H2O(g) f 2CO + 3H2
∆H298 ) 186.9 kJ mol-1
(2b) decomposition of acetaldehyde to form methane and
carbon monoxide,
CH3CHO(g) f CH4 + CO ∆H298 ) 19.2 kJ mol-1
(3) steam reforming of methane,
CH4 + H2O(g) T CO + 3H2 ∆H298 ) 206.1 kJ mol-1
∆G573 ) 18.9 kJ mol-1, Kp573 ) 6.5 × 10-8, ∆G673
)
13.0 kJ mol-1, Kp673 ) 5.9 × 10-5
(4) and water gas shift of carbon monoxide to carbon dioxide.
CO + H2O(g) T CO2 + H2 ∆H298 ) -41.2 kJ mol-1
Figure 1. Schematic images for two catalytic reaction modes with/
without an electric field.
∆G573 ) -4.2 kJ mol-1, Kp573 ) 3.9 × 10,
∆G673 ) 3.3 kJ mol-1, Kp673 ) 1.2 × 10
In these sequential reactions, reaction 3, steam reforming of
methane, is a highly endothermic reaction, so a high temperature
is required. For this reaction, the Gibbs free energy at 573 K is
positive, 18.9 kJ/mol; 13.0 kJ/mol at 673 K. As a result, the
thermodynamic equilibrium constant for this reaction is only
6.5 × 10-8 at 573 K, 5.9 × 10-5 at 673 K. Although many
researchers have investigated steam reforming of methane,42-54
it is still a difficult problem to achieve a lower reaction
temperature, higher conversion, and lower carbon deposits on
the catalyst. On the other hand, reaction 4, a water gas shift
reaction, is an exothermic reaction, but a conventional catalyst
for the reaction, such as Cu/ZnO/Al2O3 or Pt/CeO2, is not so
highly active, not stable.55-75
In this research, we investigated steam reforming of ethanol,
and we also conducted three reactions of ethanol decomposition,
water gas shift reaction, and steam reforming of methane. In
each reaction, a conventional catalytic reaction (mode A) and
catalytic reaction in an electric field (mode B: named “electre-
forming”) were conducted and compared. Schematic images of
the reaction systems in this research are shown in Figure 1.
Figure 2. Reaction apparatus.
In all experiments, a quartz tube (6.0 mm o.d.) was used as
a flow-type reactor, as shown in Figure 2. Two stainless steel
rods (2.0 mm o.d.) were inserted from each end of the quartz
tube as electrodes. In each reaction, reactant was supplied at a
rate of 0.5 mmol min-1. Steam by carbon ratio was 2. In the
cases of both mode A and mode B, 100 mg of catalyst was
charged into the quartz reactor. The height of the catalyst bed
was 4 mm, and the gap distance of each electrode was 5 mm,
so the catalyst bed did not contact the tip of the upper electrode.
The catalyst was pretreated in situ in a 5% hydrogen flow (Ar
balance) at 723 or 823 K before the reaction to reduce the
catalyst. Liquid reactants such as ethanol and water were
supplied using a microfeeder (0.5 mmol min-1), evaporated in
a preheating zone (423 K), and carried into the reactor through
a gas line (393 K) with Ar (20 cc min-1). After the reaction,
product gases were analyzed using a GC-FID and a GC-TCD
after passing a cold trap (2-buthanol). Liquid products were
analyzed using a GC-FID before passing a cold trap. In this
research, the conversion of reactant was calculated from product
gases such as CO, CH4, CO2, C2H4, C2H6, and CH3CHO in each
reaction.
2. Experimental Section
In previous research, we have found that noble metals such
as Pt showed highly catalytic performance for steam reforming
of ethanol. We choose Pt, Rh, and Pd as the supported metals
for comparison in this research. We choose CeO2 as the best
catalyst support from previous investigations. CeO2 shows a
highly synergetic effect with an electric field,20 so we prepared
the following catalysts of 1 wt % Pt/CeO2, 1 wt % Pd/CeO2,
and 1 wt % Rh/CeO2. The catalysts were prepared by an
impregnation method. CeO2 was soaked in distilled water and
stirred and deaerated for 2 h at room temperature. An aqueous
solution of the precursor of the supported metals
(Pt(NH3)4(NO3)2, Pd(OCOCH3)2, Rh(NO3)3) was added, stirred
for 2 h, evaporated to dryness, then calcined at 973 K and
crushed into particles with sizes of 355-500 µm.
conversion (%) )
output moles of carbon atom in product gases
× 100
input moles of carbon atom in reactant
The yield of each product without hydrogen was defined as
below:

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3826 J. Phys. Chem. A, Vol. 114, No. 11, 2010
Sekine et al.
carbon moles of product species
yield (%) )
× 100
input moles of reactant
The yield of hydrogen was defined as below:
moles of hydrogen
H2 yield (%) )
× 100
input moles of reactant
A DC high-voltage power supply was used to generate the
electric field. The electric field was controlled by input current
with a fixed value of 3 mA, so the impressed voltage depended
on the nature of the catalyst. Waveforms of the current and
voltage were observed by a digital signal oscilloscope (Tektronix
TDS3052B). The profile was flat for the voltage, and micro-
pulse-shaped for the current. The applied electric pressure
(voltage) was about 130-600 V, depending on the reactant and
catalysts. The total input power was about 0.4-2 W.
Figure 3. Effect of temperature on the conversion of catalytic steam
reforming of ethanol without the electric field (mode A) and with the
electric field (mode B: electreforming).
3. Results and Discussion
3.1. Steam Reforming of Ethanol. First of all, we conducted
steam reforming of ethanol over various catalysts with/without
the electric field. Figure 3 shows the conversion of ethanol at
423-523 K by catalytic reaction without the electric field (mode
A) and by catalytic reaction in the electric field (mode B:
electreforming). Figure 4 shows the yield of products over each
catalyst and in each reaction mode. From Figure 3, mode A
shows low conversion for all catalysts about 10% or lower at
523 K, and conversion increased with an increase of reaction
temperature. In mode B: electreforming, conversion was greatly
increased for all catalysts by impressing the electric field to the
catalyst bed. In the case of Pd/CeO2 and Rh/CeO2, conversion
was about 60% at 423 K that conventional catalytic steam
reforming hardly proceeded, and maximum conversion of
ethanol was 70.2% at 523 K over Pd/CeO2 catalyst. In the case
of Pt/CeO2 catalyst, conversion was lower than the other two
catalysts, and the maximum conversion of ethanol was 61.6%
at 523 K. For the required reaction temperature to obtain the
same conversion level between modes A and B, the application
of the electric field can decrease the reaction temperature about
150 K or more for all catalysts.
Figure 4 indicates the effect of the electric field on the product
distribution. In general, the reaction path of catalytic steam
reforming of ethanol without the electric field is known as
described above. Dehydrogenation of ethanol and formation of
acetaldehyde and hydrogen is observed at very low conversion
(initial step of the reaction). Sequential decomposition of
acetaldehyde or steam reforming of acetaldehyde proceeds, and
CO, CH4 and H2 are produced on the catalyst. Then CO reacts
with water as a water gas shift (WGS) reaction, and CO2 and
H2 are produced.
Figure 4. Effect of temperature on the yield of products for catalytic
steam reforming of ethanol without the electric field (mode A) and
with the electric field (mode B: electreforming).
reaction rate of steam reforming and the decomposition of
acetaldehyde. If the steam reforming of acetaldehyde is the
dominant reaction over decomposition of it, the value of rR/rD
would become larger. The WGS ratio means the reactivity for
the WGS reaction on this condition. Notice that these parameters
are calculated supposing CO and CH4 are generated from only
reactions of steam reforming or decomposition of acetaldehyde,
and no methanation has been considered. This assumption was
based on the experimental result in which we could not observe
the formation of methane by steam reforming of “methanol”
with the same catalyst at the same temperature (results are not
shown), and CO2 is assumed to be generated only by the WGS
reaction.
Table 1 shows the ratio of rR/rD and WGS for each catalyst
and in each reaction mode. In mode A with Pd/CeO2 or Pt/
CeO2 catalyst, steam reforming of acetaldehyde slightly pro-
ceeded, and decomposition of acetaldehyde was a dominant
reaction because the rR/rD ratio was almost 0. Over Rh/CeO2
catalyst, these two reactions proceeded simultaneously because
rR/rD ratio was about 0.2-0.3. Over Pd/CeO2 or Rh/CeO2
catalyst, WGS ratio was about 10-30%, and over Pt/CeO2
As characteristic parameters for this reaction, we examined
the ratio of rR/rD and the WGS ratio, which are defined as
follows;
f(CO) + f(CO2) - f(CH4)
rR/rD(-) )
f(CH4)
f(CO2)
WGS ratio (%) )
× 100
f(CO) + f(CO2)
In the formula, f(product) means formation rate of each
product. The parameter of rR/rD represents the ratio of the

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Novel Catalytic Reactions with Electric Field
J. Phys. Chem. A, Vol. 114, No. 11, 2010 3827
TABLE 1: Steam-Reforming/Decomposition Ratio and Water Gas Shift Ratio over Three Catalysts with/without EF (electric
field) on Steam Reforming of Ethanol
Pd/CeO2
WGS ratio, %
Rh/CeO2
WGS ratio, %
Pt/CeO2
WGS ratio, %
temp, K
rR/rD, -
rR/rD, -
rR/rD, -
mode A (without EF)
mode B, electreforming
with EF
523
423
473
523
0.01
0.74
0.50
0.62
8.2
47.4
50.6
49.0
0.34
1.39
1.27
1.31
21.2
57.9
58.3
41.1
0.07
0.13
0.38
0.28
42.9
62.9
60.2
61.0
TABLE 2: Reaction Enthalpy and Energy Gain for the Steam Reforming of Ethanol over Three Catalysts with/without the
Electric Field at Each Temperature
formation rate (C-base)/µmol min-1
a
b
d
catalyst with/
without EF
CH3
CHO
∑∆Hc-P
,
∆Hc-EtOH
,
∆Hrc,
∆Eef ,
temp, K
423
conversion, %
H2
8.3
C2
CO2
0.1
87.3 105.7
0.1
CH4
0.8
CO
0.5
97.1
0.3
91.4
0.0
17.7
5.8
85.5
2.2
98.8
0.4
40.7
17.4
J min-1
J min-1
J min-1 J min-1
Pd/CeO2
Pd/CeO2 with EF
Rh/CeO2
Rh/CeO2 with EF
Pt/CeO2
Pt/CeO2 with EF
Pd/CeO2
Pd/CeO2 with EF
Rh/CeO2
Rh/CeO2 with EF
Pt/CeO2
Pt/CeO2 with EF
Pd/CeO2
Pd/CeO2 with EF
Rh/CeO2
1.1
61.4
0.5
65.0
0.4
21.1
6.4
60.8
3.7
71.2
1.6
45.2
10.4
70.2
8.7
58.8
7.6
61.6
8.6
0.0
13.5
362.7
6.1
428.3
4.9
155.3
50.8
342.1
27.6
444.1
19.5
340.1
74.0
408.9
77.0
361.9
78.1
8.0
432.7
3.6
457.8
2.6
148.7
45.0
428.3
26.3
502.0
11.6
318.7
73.4
494.7
61.0
414.2
53.6
5.4
-70.0
2.5
691.4 22.9 10.8
4.6 3.7 0.0
986.0 28.5 3.8 125.6
4.0 3.1
-75.4
-32.0
4.4
0.3
90.8
0.1
42.1
7.3
-29.5
0.0
1.9
0.0
1.5
0.0
0.2
30.0
4.5
87.6 115.7
5.7 2.7
2.3
6.6
5.8
262.6 29.3
29.7 28.7
624.2 28.7
18.5 16.2
1012.4 23.1
10.4 13.2
502.0 91.8
63.6 28.3
784.6 25.6
46.9 44.2
726.5 38.8
45.6 48.7
660.6 44.1
473
523
-86.2
-92.1
-59.1
13.4
1.3
4.1 138.2 104.5
-57.8
8.0
21.4
0.6
-85.9
16.0
-52.3
24.6
-55.0
0.0
6.2
0.3
0.4
61.6
1.6
0.8
74.4
18.8
6.9 101.3 127.7 105.6
-86.5
-68.3
-79.6
0.1
1.8
0.0
6.7
2.6
78.4
3.0
9.0
9.5
Rh/CeO2 with EF
Pt/CeO2
Pt/CeO2 with EF
82.6 112.2
6.6
4.0
61.7
96.8 123.6
378.9
434.0
a ∑∆Hc-P: summation of standard combustion enthalpy of products. b ∆Hc-EtOH: summation of standard combustion enthalpy of consumed
ethanol. c ∆Hr: endothermic enthalpy of the reaction. d ∆Eef: the difference of ∆Hr (without the electric field) and ∆Hr (with the electric field) at
the same temperature.
catalyst, the WGS ratio was about 50%. In mode B, rR/rD and
the WGS ratio were increased over all the catalysts by the
application of the electric field. Especially on the Rh/CeO2
catalyst, rR/rD greatly increased up to 1.3. It was supposed that
the reason for the increase in rR/rD was the shift of the reaction
path from decomposition of acetaldehyde to steam reforming
of acetaldehyde or promotion of steam reforming of methane,
which was generated by the decomposition of acetaldehyde. The
WGS ratio also increased up to 50-60% for all catalysts by
the application of the electric field. Thus, by impressing of the
electric field, hydrogen production was promoted by the change
of the reaction path.
Table 2 shows the formation rate of products; their combus-
Figure 5. Effect of temperature on the conversion of catalytic
tion enthalpy; and the endothermic enthalpy gain, ∆Eef. The
decomposition of ethanol without the electric field (mode A) and with
respective energies were about from 13.4 J/min (endothermic)
the electric field (mode B: electreforming).
to -92.1 J/min (exothermic) for the catalysts Rh, Pd, and Pt/
CeO2. The input electric energy at 473 K was 72.4 J/min ()
Figure 5 shows the conversion of ethanol for the catalytic
decomposition of ethanol without the electric field (mode A)
1.21 W; Pd/CeO2), 98.2 J/min () 1.64 W; Rh/CeO2), and 92.0
J/min () 1.53 W; Pt/CeO2), respectively. Although the syner-
and for the catalytic decomposition of ethanol in the electric
field (mode B: electreforming). Figure 6 shows the yield of
products over each catalyst and in each reaction mode. In Figure
5, the conversion of ethanol was increased for all catalysts by
impressing the electric field to the catalyst bed. The rate of
conversion was in the following order: Pd/CeO2 > Rh/CeO2 >
Pt/CeO2. The promotion effect was smaller than that of steam
reforming of ethanol. It seems that the existence of steam in
the reaction field promoted synergetic interaction between the
catalyst and the electric field. In Figure 6, the effect of the
electric field on catalytic decomposition of ethanol (mode A)
getic effect of noble metal and CeO2 support with the electric
field was observed, electric energy was consumed as heat, and
the reactant ethanol lost a part of its caloric value by exothermic
reaction in the cases of Pd or Rh catalysts.
3.2. Decomposition of Ethanol. Next, we examined decom-
position of ethanol over various catalysts to investigate the role
of steam in the electric field.
catalytic decomposition of ethanol: C2H5OH f CO +
CH4 + H2