Hydrogen Production 1
-
Upload
biruk-zinabu -
Category
Documents
-
view
62 -
download
0
Transcript of Hydrogen Production 1
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 3 ( 2 0 0 8 ) 4 5 6 9 – 4 5 7 6
Avai lab le a t www.sc iencedi rec t .com
j ourna l homepage : www.e lsev ier . com/ loca te /he
Synthesis and characterization of bimetallic Cu–Ni/ZrO2
nanocatalysts: H2 production by oxidative steamreforming of methanol
R. Perez-Hernandeza,*, G. Mondragon Galiciaa, D. Mendoza Anayaa, J. Palaciosa,C. Angeles-Chavezb, J. Arenas-Alatorrec
aInstituto Nacional de Investigaciones Nucleares; Carretera Mexico-Toluca S/N La Marquesa, Ocoyoacac,
Estado de Mexico C.P. 52750, MexicobPrograma de Ingenierıa Molecular, Instituto Mexicano del Petroleo, Eje Central Lazaro Cardenas,
No. 152, C.P. 07730, Mexico D.F., MexicocInstituto de Fısica-UNAM, Apartado Postal 20-364, C.P. 01000, Mexico D.F., Mexico
a r t i c l e i n f o
Article history:
Received 19 May 2008
Received in revised form
11 June 2008
Accepted 13 June 2008
Available online 22 August 2008
Keywords:
Cu–Ni/ZrO2 catalysts
Bimetallic nanocatalysts
H2 production
Oxidative steam reforming of
methanol
HRTEM
STEM–EDX
TPR
* Corresponding author. Tel.: þ52 55 5329723E-mail address: [email protected] (
0360-3199/$ – see front matter ª 2008 Interndoi:10.1016/j.ijhydene.2008.06.019
a b s t r a c t
Cu/ZrO2, Ni/ZrO2 and bimetallic Cu–Ni/ZrO2 catalysts were prepared by deposition–
precipitation method to produce hydrogen by oxidative steam reforming of methanol
(OSRM) reaction in the range of 250–360 �C. TPR analysis of the Cu–Ni/ZrO2 catalyst showed
that the presence of Cu facilitates the reduction of the Ni at lower temperatures. In addi-
tion, this sample showed two reduction peaks, the former peak was attributed to the
reduction of the adjacent Cu and Ni atoms which could be forming a bimetallic Cu-rich
phase, and the second was assigned to the remaining Ni atoms forming bimetallic Ni-
rich nanoparticles. Transmission Electron Microscopy revealed Cu or Ni nanoparticles on
the monometallic samples, while bimetallic nanoparticles were identified on the Cu–Ni/
ZrO2 catalyst. On the other hand, Cu–Ni/ZrO2 catalyst exhibited better catalytic activity
than the monometallic samples. The difference between them was related to the Cu–Ni
nanoparticles present on the former catalyst, as well as the bifunctional role of the bime-
tallic phase and the support that improve the catalytic activity. All the catalysts showed
the same selectivity toward H2 at the maximum reaction temperature and it was w60%.
The high selectivity toward CO is associated to the presence of the bimetallic Ni-rich
nanoparticles, as evidenced by TEM–EDX analysis, since this behavior is similar to the
one showed by the monometallic Ni-catalyst.
ª 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights
reserved.
1. Introduction storage of H2 in the vehicle: gas compressed, liquid, H2 storage
The PEM (proton-exchange membrane) fuel cell generally
requires H2 as fuel; there are various strategies for on board
9; fax: þ52 55 53297240.R. Perez-Hernandez).ational Association for H
materials such as metal hydrides and carbon nanotubes.
However, all these options require a dedicated filling station
infrastructure which raises issues concerning safety and
ydrogen Energy. Published by Elsevier Ltd. All rights reserved.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 3 ( 2 0 0 8 ) 4 5 6 9 – 4 5 7 64570
cost. Olah [1] put forth a convincing case for why the chemical
storage of hydrogen in the form of methanol offers distinct
advantages over alternate means. The main advantage of
liquid fuels is their high energy density and ease of handling,
and the fact that they can be used for the on-demand produc-
tion of hydrogen for fuel cells, with applications in mobile and
stationary grid-independent power systems. Methanol is
readily available and can be catalytically reformed into an
H2-rich gas at moderated temperature (200–400 �C). Methanol
has high H/C ratio and no C–C bonds, hence minimizing the
risk for coke formation. Moreover, as methanol can be
produced from renewable sources, its reforming does not
contribute to a net addition of CO2 to the atmosphere. Conse-
quently, there are three processes available for H2 production
using methanol as a H2 source:
Steam reforming of methanol (SRM-endothermic reaction)
CH3OH þ H2O / CO2 þ 3H2 (1)
Partial oxidation of methanol (POM-exothermic reaction)
CH3OH þ 1=2O2 / CO2 þ 2H2 (2)
Oxidative Steam Reforming of Methanol (OSRM is a combi-
nation of SRM and POM)
CH3OH þ 1=2H2O þ 1=4O2 / CO2 þ 5=2H2 (3)
In the literature, copper based catalysts have received
considerable attention for H2 production by SRM [2–5]. Other
catalysts that have been extensively studied in the important
reforming industrial process for syngas production are
nickel-based catalysts; this reaction also allows the conver-
sion of two undesirable greenhouse gases like CH4 and CO2
[6–8]. However, the studies related with Ni-catalysts in the
steam reforming of liquid products mainly used ethanol
(SRE) as an H2 source [9–13]. Oxidative steam reforming of
methanol has not been extensively studied, but initial results
indicate low carbon monoxide and high hydrogen concentra-
tion in the products [14]. Velu et al. [15] studied the OSRM
reaction and found that the ZrO2-containing catalysts are
the best for H2 production with low CO levels. Agrell et al.
[16] studied the SRM, POM and OSRM reaction and found in
the OSRM reaction low CO levels with the following selec-
tivity toward H2: SRM>OSRM> POM. They observed that
the addition of O2 to the SRM reaction appears to be an effec-
tive way to decrease the CO content in the product. Navarro
et al. [17] studied the oxidative reforming of hexadecane
over Ni and Pt catalysts supported on Ce/La-doped Al2O3.
They found for both Ni and Pt catalysts, higher specific
activity when active metals were supported on alumina
modified with cerium and lanthanum. However, the catalytic
activity and H2 selectivity observed on Ni-based catalysts
were higher than on Pt-based catalysts.
The goal of this work was to develop new inexpensive Cu/
ZrO2, Ni/ZrO2 and Cu-Ni/ZrO2 catalysts by deposition–
precipitation for oxidative steam reforming of methanol to
produce H2-rich gas at relatively lower temperature. Catalysts
characterization included BET (N2 adsorption–desorption),
SEM (Scanning Electron Microscopy), EDX (Energy Dispersive
X-ray Spectroscopy), XRD (X-ray Diffraction), TEM (Transmis-
sion Electron Microscopy) and TPR (Temperature Programmed
Reduction).
2. Experimental
2.1. Preparation of catalytic materials
2.1.1. SupportZrO2 was prepared by a sol–gel method from Zirconium(IV)
propoxide (Fluka) as a precursor in n-propanol (Aldrich) solu-
tion and acid catalyst (HNO3–Baker) with constant stirring.
The solution was processed at room temperature, and the
deionized water was added dropwise to complete hydrolysis.
The molar ratio used for the synthesis was: propoxide/
alcohol/H2O/HNO3¼ 1:4:4:0.33 [18]. After the hydrolysis reac-
tion the temperature was increased at reflux and held for
50 min, then cooled at room temperature. The mixture was
aged for 24 h and the residual liquid was removed by decant-
ing. A xerogel was obtained after heating at 100 �C for 24 h.
The xerogel was first heated 1 h at 100 �C under an air stream
and then calcined at 650 �C for 5 h.
2.1.2. Catalysts preparation by deposition–precipitationwith ureaOne gram of ZrO2 was added to 100 ml of an aqueous solution
at pH z 2 and 4.2 M of urea with constant stirring. Cu(CH3-
CO2)2$H2O (Merck) or NiCl2$6H2O at an appropriate concentra-
tion was incorporated at the suspension to yield 3 wt% of
copper and nickel, respectively, in the monometallic catalysts.
For bimetallic sample the concentration of Ni and Cu was
1.5 wt% of each one of the metal to obtain 3 wt% of total
metallic phase. The temperature of the suspension was
increased at 80 �C for 20 h, and as the urea was decomposed
the pH was increased. Then the solids were recovered by
centrifugation and washed with deionized water and centri-
fuged again. This procedure was repeated 4 times. After
that, the solids were dried at 100 �C for 24 h. The catalysts
were calcined as follows: at 100 �C for 1 h and then the
temperature was increased at 300 �C for 2 h in air and cooled
at room temperature, next, the catalysts were reduced with
H2 (5%)/He (60 ml/min) at 600 �C for 2 h. The actual Cu and
Ni contents were determined by ICP and they were 2.80% of
Cu in Cu/ZrO2 catalyst, 2.44% of Ni in the Ni/ZrO2 catalyst,
and for bimetallic Cu–Ni/ZrO2 sample the Cu and Ni were
1.47 and 1.03%, respectively.
2.2. Characterization
Total surface area was calculated by the BET method from N2
adsorption by the single point method using a N2 (30%)/He gas
mixture, recorded at liquid nitrogen temperature in a RIG-100
multitask from ISR INC. X-ray diffraction (XRD) powder
patterns were recorded in a Siemens D-5000 diffractometer,
using Cu Ka (l¼ 0.15406 nm). The morphology and chemical
composition analysis of the samples were performed in
a LVSEM (Low Vacuum Scanning Electron Microscopy) JEOL
JSM5900LV fitted with an Energy Dispersive X-ray Spectrom-
eter (OXFORD). The analysis was performed in equipment
conditions of 20 kV and 20 Pa of pressure. The images were
obtained with the backscattering electron signal. Before the
analysis, the samples were fixed on an aluminum specimen
holder with aluminum tape. A Transmission Electron
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 3 ( 2 0 0 8 ) 4 5 6 9 – 4 5 7 6 4571
Microscope (TEM) JEOL JEM 2010 with resolution point to point
of 0.23 nm was used to determine the structure and lattice
parameters of the metallic nanoparticles on the support.
HRTEM and local chemical analysis of the bimetallic nanopar-
ticles were carried out in a microscope JEM 2200FS with a reso-
lution of 0.19 nm which has been fitted with an energy
dispersive X-ray Spectrometer (NORAN). The chemical anal-
ysis was made using the Scanning Transmission Electron
Microscopy (STEM)-EDX technique since the STEM mode led
us obtain a better control of the small probe size (less than
1 nm of diameter). The samples were prepared in a solution
with isopropanol and a drop was put on copper or gold grids.
Temperature-programmed reduction (TPR) experiments were
carried out on an automatic multitask unit RIG-100 from ISR
INC equipped with a Thermal Conductivity Detector (TCD)
with output to a computer. The oxidized catalyst (0.1 g) was
placed in the reactor and purged with UHP Ar at room temper-
ature and then the TPR measurement was performed using H2
(5%)/Ar gas mixture (30 ml/min). The temperature was
increased at a rate of 10 �C/min from room temperature to
700 �C. The effluent gas was passed through silica gel to
remove water before measuring the amount of hydrogen
consumed during the reduction by the TCD. The signal was
calibrated by 0.5 ml pulses of UHP H2 (5%)/Ar at the end of
the experiment. After testing the catalytic reaction, the cata-
lyst was cleaned by He stream (30 ml/min) for 30 min at
360 �C and cooled at room temperature, after this the sample
was purged with UHP Ar flow and the TPR was performed.
20 30 40 50 60 70 80 90
ll llllllllllllllllll
l
l
ll
°Cu/ZrO2
2 (theta)
*°Cu-Ni/ZrO2
Inte
nsity
(a.u
.)
*Ni/ZrO2
x2Cu-Ni/ZrO2 rxn
Fig. 1 – XRD patterns of the Cu/Ni/ZrO2 catalysts before and
after catalytic activity. (l)-monoclinic-ZrO2, (B)-Cu, (*)-Ni.
2.3. Catalytic reaction
The steady-state activity in the oxidative steam reforming of
methanol reaction was performed in a conventional fixed-
bed flow reactor (8 mm i.d.) using 0.1 g of the catalyst in
a temperature range from 250 to 360 �C with 4 h stabilization
time at each temperature and atmospheric pressure, with
a thermocouple in contact with the catalytic bed allowing the
control of the temperature inside the catalyst on an automatic
multitask unit RIG-100. The catalyst was first activated in
a stream of H2 (5%)/He (60 ml/min) from room temperature to
300 �C with a heating rate of 10 �C/min and held at this temper-
ature for 1 h. The catalyst was brought up to the reaction
temperature in He and the reaction mixture was introduced.
For the OSRM reaction, O2 (5%)/He mixture was used and the
total flow rate was kept at 50 ml/min (GHSV¼ 30,000 h�1 based
on the total flow) and added by means of a mass flow controller
(RIG-100) and bubbled through a tank containing mixture of
water and methanol, the partial pressure of CH3OH, H2O and
O2 was 75, 12.75 and 25.2 Torr, respectively. The effluent gas
of the reactor was analyzed by gas chromatography using
TCD. A 2-m packed Porapack Q column able to separate water,
methanol, methyl formate (MF) and CO2 was used. The gaseous
products such as H2, O2, CH4 and CO were separated with
a molecular sieve of 5 A. The following equations were used
to determine the methanol conversion and selectivity:
Xð%Þ ¼ Cin � Cout
Cin� 100;
SH2ð%Þ ¼ nH2-out
nH2-out þ nCH4-out þ nH2Oout� 100 ð4Þ
SCOð%Þ ¼nCO2-out
nCO2-out þ nCOout þ CH4-out� 100 (5)
The subscripts in and out indicate the inlet and the outlet
concentrations of the reactants or products.
3. Results and discussion
3.1. Textural and structural properties
The surface area calculated by the BET method from N2
adsorption–desorption by the single point method of the
bare ZrO2 was 30 m2/g, after the incorporation of the active
phase on the ZrO2 support, the surface area was slightly
increased to 33, 34 and 35 m2/g for Cu/ZrO2, Ni/ZrO2 and Cu–
Ni/ZrO2 catalysts, respectively. This slight increment of the
surface area could be attributed to the partial dissolution of
the ZrO2 support by the acid medium when the active phase
was impregnated. During the centrifuged, drying and thermal
treatments the dissolved material would be reprecipitated as
smaller particles, so accounting for the increase in the surface
area. Fig. 1 shows the experimental XRD patterns of the Cu/
ZrO2 and Ni/ZrO2 catalysts. Diffraction pattern of metallic
copper and nickel as well as diffraction peaks of the mono-
clinic ZrO2 phase were observed. Cu, Ni or Cu–Ni alloy were
not observed by XRD in the Cu–Ni/ZrO2 catalyst. After catalytic
reaction, the Cu–Ni/ZrO2 sample showed a similar diffraction
pattern to the pre-reaction catalyst.
The morphology of the three catalysts was analyzed by
LVSEM and a typical image of the Cu–Ni/ZrO2 catalyst, is illus-
trated on Fig. 2. All the samples studied exhibited nanopar-
ticles approximately 150 nm contained in large spongy
clusters. However, nanoparticles with semispherical
morphology approximately 10 nm of diameter deposited on
the surface of the ZrO2 crystalline were revealed by TEM tech-
nique. Ni nanoparticles of w10 nm of diameter were observed
on the Ni/ZrO2 catalyst (Fig. 3a). Fig. 3b shows the TEM results
of the bimetallic Cu–Ni/ZrO2 sample. The bright field STEM
image of the Cu–Ni/ZrO2 catalyst shows good dispersion of
Fig. 2 – SEM image of the fresh bimetallic Cu–Ni/ZrO2
catalyst.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 3 ( 2 0 0 8 ) 4 5 6 9 – 4 5 7 64572
the metal-containing nanoparticles. These images seem to
indicate a bimodal size distribution with a large grouping of
particles around 10 nm. In order to elucidate the chemical
composition of these nanoparticles the EDX analysis was
performed on it. Inset EDX spectrum in Fig. 3b, carried out in
the nanoparticles with 10 nm of diameter, clearly showed
the presence of Cu and Ni elements. These results reveal the
bimetallic nature of this system and they have the following
composition: 18% of the nanoparticles have a Ni/Cu w 4.6,
41% have a Ni/Cu w 1.7, 29% have a Ni/Cu w 1, 6% have a Ni/
Cu w 0.6 and 6% have a Ni/Cu w 0.25 weight ratio, respec-
tively. Cu nanoparticles on the Cu/ZrO2 catalyst were not
found during the TEM analysis, however, it was present in
the samples as was identified by EDX analysis, inset spectrum
in Fig. 3c.
3.2. Temperature-programmed reduction
Fig. 4 shows the TPR profiles of the fresh Cu/Ni/ZrO2 catalysts
calcined at 300 �C and the samples after catalytic reaction.
Reduction peaks observed on the catalysts at temperatures
below 350 �C were associated to the reduction of CuO and
NiO particles. The peak above 500 �C observed on the three
samples is related to the reduction of hydroxycarbonates
species (identified by FTIR, Figure not shown) which originate
from the urea decomposition during the synthesis of the
samples and remain present on the surface after calcinations.
TPR profile of the fresh NiO/ZrO2 sample shows a peak at
320 �C indicating that NiO is reduced to metallic Ni. Literature
reports that large NiO particles with lower interaction with the
ZrO2 on the Ni/ZrO2 catalyst could be reduced at low temper-
ature [19–21]. The reduction of CuO supported on ZrO2 shows
two peaks at 200 and 250 �C indicating the existence of two
different kinds of CuO species. Highly dispersed copper oxide
and CuO bulk were present on the Cu/ZrO2 sample [22]. TPR
profile of the bimetallic catalyst showed a similar behavior
like on the fresh Cu/ZrO2 sample, although Ni was also
present on the catalyst. On this sample a shoulder at 212
and a peak at 225 �C were observed, these temperatures are
closer to the monometallic Cu/ZrO2 catalyst but far from the
reduction peak observed on Ni/ZrO2 sample. This study clearly
exhibits differences in the interactions between Cu/Ni species
on the surface of the zirconia when they are together, and
could be explained as follows: during the TPR test, Cu probably
causes spillover of hydrogen onto the Ni inducing a concurrent
reduction of both copper oxide and NiO. For that, the presence
of Cu lowered the reduction temperature of Ni. A similar result
was reported by Arenas-Alatorre et al. [23] in the TPR experi-
ments on the Pt–Ni/SiO2 catalysts, they observed that the
presence of the Pt in the bimetallic catalysts contributes to
facilitate the reduction of the NiO. On the other hand, Vizcaıno
et al. [24] in the bimetallic Cu–Ni/SiO2 catalyst reported reduc-
tion peaks between 200 and 260 �C. The peak at low tempera-
ture was assigned to CuO reduction and the other was
attributed to NiO reduction. A detailed analysis of TPR profile
and the results of TEM and HRTEM techniques suggested that
the first reduction peak of the bimetallic catalyst could be
attributed to the reduction of adjacent Cu and Ni atoms, which
could be forming a bimetallic phase. The second reduction
peak could be assigned to the remaining Ni atoms forming
Ni-rich nanoparticles. This proposal could be supported with
the results from HRTEM technique. Fig. 5 shows HRTEM image
of a nanoparticle deposited on the zirconia support from Cu–
Ni/ZrO2 catalyst. The atomic interplanar distance measured
in the nanoparticle was 0.207 nm which corresponds to the
cubic system of the bimetallic Cu0.81Ni0.19 phase in (111)
plane with the unit cell parameter a¼ 0.3593 nm according
to the JCPDS card number 471406. Chemical analysis carried
out by EDX revealed strongly Cu and Ni elements.
Samples’ post-reaction also was characterized by TPR tech-
nique, and their experimental profiles show a tiny broad H2
consumption at low temperatures with long tail extending
to higher temperature than fresh catalysts. These results
suggest that the gas stream causes small oxidation in the
active phase having highly dispersed nickel and copper oxides
species on the catalysts at w220–300 �C and �200 �C, respec-
tively [2,22,25–29].
3.3. Catalytic performance on the oxidative steamreforming of methanol (OSRM) reaction
Fig. 6 shows the catalytic behavior of Cu/Ni/ZrO2 catalysts
during OSRM reaction at different temperatures. In the Cu/
ZrO2 catalyst, the conversion of methanol was 11% at the
beginning of the reaction (250 �C) and increased as tempera-
ture was raised, and at 300 �C the consumption of methanol
was w50%. Additional temperature increase did not result in
an increase in methanol conversion. However, when copper
was supported on ceria, 100% of methanol conversion at
260 �C was reported on catalysts with <6% of copper [25].
This effect is caused by the modification in feed concentra-
tions of fuel, oxygen or steam [30]. On the Ni/ZrO2 sample,
the conversion of methanol in the range of 250–300 �C was
<14%. After this temperature the methanol conversion
reached w100% at 350 �C. Vizcaıno et al. [24] reported a similar
behavior during SR of ethanol reaction. They observed high
catalytic activity on Ni/SiO2 sample than Cu/SiO2 catalyst. In
the case of the bimetallic Cu–Ni/ZrO2 catalyst, the catalytic
activity was higher than the monometallic samples in almost
Fig. 3 – TEM image of: (a) Ni/ZrO2, (b) bright field STEM image of the Cu–Ni/ZrO2, (c) Cu/ZrO2 catalysts.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 3 ( 2 0 0 8 ) 4 5 6 9 – 4 5 7 6 4573
all ranges of the reaction temperature with nearly complete
conversion reached by 350 �C. In the literature there are no
studies associated with the steam reforming of methanol
reaction on the bimetallic Cu–Ni catalysts. However, some
reports related with the catalytic activity of the bimetallic
Ni–Cu catalysts in the steam reforming (SR) and oxidative
steam reforming (OSR) have been done only with ethanol
[11,12,31]. Gallucci et al. [32] reported that the SR of methanol
is more suitable than SR of ethanol for hydrogen production.
Marino et al. [11,12] studied the effect of the nickel content
in the Cu/Al2O3 samples on the steam reforming of ethanol
reaction. They found that the conversion of the catalysts
improves when nickel content increases. This behavior was
attributed to the addition of Ni which favors the segregation
of Cu2þ ions to the catalytic surface and enhances the ethanol
conversion. In other report, the catalytic activity was related
with the high metal dispersion [26]. In our case, besides the
dispersion and segregation of metallic ions, the best catalytic
activity observed in the Cu–Ni/ZrO2 sample was associated to
the presence of the bimetallic phase nanoparticles on the
zirconia support. Because of the Cu/ZrO2 and Ni/ZrO2 catalysts
only Cu or Ni nanoparticles were identified, and their catalytic
activity was lesser at low temperatures than in bimetallic
catalyst. Thus the bimetallic alloy of the two metals can be
used efficiently as an active phase during OSRM reaction. In
addition, the bifunctional role of the bimetallic phase with
the ZrO2 had an important function in the catalytic activity.
Agrell et al. [16] reported that Cu/ZnO/ZrO2 catalyst exhibits
high activity for methanol conversion due to the high Zr/Cu
ratio which favors the possible copper-support interaction
increasing the bifunctional role between the active phases
and the ZrO2 beneficial for the reaction, in addition zirconia
100 200 300 400 500 600
571250200
Temperature (°C)
Cu/ZrO2
177 Cu/ZrO2 post-reaction
550
225212Cu-Ni/ZrO2
187
H2
Con
sum
ptio
n (a
.u.)
Cu-Ni/ZrO2 post-reaction
550320 Ni/ZrO2
306245Ni/ZrO2 post-reaction
Fig. 4 – Temperature-programmed reduction profiles of the
fresh catalysts (solid line), samples after catalytic reaction
(thin line).
0
20
40
60
80
100
250 270 290 310 330 350Temperature °C
Met
hano
l con
vers
ion
(%)
Cu/ZrO2Cu-Ni/ZrO2Ni/ZrO2
Fig. 6 – Effect of temperature on the catalytic performance
in the oxidative steam reforming of methanol over Cu/Ni/
ZrO2 catalysts. Partial pressure of CH3OH, H2O and O2 was
75, 12.75 and 25.2 Torr, respectively. GHVS [ 30,000 hL1.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 3 ( 2 0 0 8 ) 4 5 6 9 – 4 5 7 64574
avoids the deactivation of the catalyst by coke deposition
during the reaction and formation of CO. It is worth noting
a better correlation between catalytic conversion and the
reduction of the samples at low temperature. In this case
the most active catalysts had the lower temperature reduction
peaks.
The main products of the OSRM reaction from Cu/Ni/ZrO2
catalysts were H2, CO, CO2 and H2O. A few quantity of methyl
formate as by-product of the reaction was observed in three
samples. Methane was also produced in small amount on
the Ni/ZrO2 and Cu–Ni/ZrO2 catalysts. Fig. 7 showed the distri-
bution of hydrogen on the Cu/Ni/ZrO2 catalysts and it could be
produced by means of Eqs. (6)–(10) and (12). The selectivity of
the Cu/ZrO2 catalyst at 250 �C was w30% and 0% for the other
Fig. 5 – HRTEM image of bimetallic nanoparticle deposited
on the zirconia of the Cu–Ni/ZrO2 catalyst.
samples. When the temperature was increased up to 300 �C it
was observed that the H2 selectivity was also increased, after
this temperature it remained essentially unchanged on the
three samples. However, it can be observed that the methanol
conversion increased after 300 �C on the Ni-based catalysts
(Fig. 6) but the H2 did not raise, this result could be explained
by the oxidation of the H2 with O2 (Eq. (13)) [25] or another
possibility by means of Eq. (14). Thus stable hydrogen produc-
tions over 60% were obtained for the Cu/Ni/ZrO2 catalysts. At
the beginning of the reaction all samples showed high CO2
selectivity, Fig. 8. However, as the reaction temperature
increases from 250 to 350 �C the CO2 production decreases,
this effect could be correlated by rWGS reaction (Eq. (14)) in
the Ni-content samples. Nevertheless, another possibility to
obtain CO as by-product of the reaction is from methanol
decomposition at higher temperatures (Eq. (15)), so CO2
production decreases. Between them, the catalyst which
showed high methanol conversion also had faster drop in
the CO2 selectivity than the other samples. However, on the
monometallic Cu/ZrO2 catalyst only w10% of CO2 was lost at
0
20
40
60
80
100
250 270 290 310 330 350Temperature (°C)
H2 S
electivity (m
ol %
)
Cu/ZrO2Cu-Ni/ZrO2Ni/ZrO2
Fig. 7 – H2 selectivity as a function of reaction temperature.
Partial pressure of CH3OH, H2O and O2 was 75, 12.75 and
25.2 Torr, respectively. GHVS [ 30,000 hL1. The other H
containing product was the water and methane.
0
20
40
60
80
100
250 270 290 310 330 350Temperature (°C)
CO
2 S
elec
tivity
(mol
%)
Cu/ZrO2Cu-Ni/ZrO2Ni/ZrO2
Fig. 8 – CO2 selectivity as a function of reaction
temperature. Partial pressure of CH3OH, H2O and O2 was
75, 12.75 and 25.2 Torr, respectively. GHVS [ 30,000 hL1.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 3 ( 2 0 0 8 ) 4 5 6 9 – 4 5 7 6 4575
the maximum reaction temperature. Fig. 9 shows the CO
selectivity of the three catalysts. The CO2 depletion observed
on Fig. 8 essentially on the Ni-content samples is due to the
change in the selectivity toward CO production, and it can
be produced by following Eqs. (8), (10), (12), (14) and (15).
Because Ni/ZrO2 catalyst had high CO selectivity in the
OSRM reaction, the higher CO production observed on the
Cu–Ni/ZrO2 sample could be associated at the presence of
bimetallic Ni-rich nanoparticles as was identified by TEM–
EDX during the study. In addition, the presence of copper on
bimetallic sample reduces the CH4 formation. Selectivity
toward CH4 is presented in Fig. 9 and could be formed by
means of Eq. (11).
According to the results and reports on the literature [24,33]
the role of our catalysts in the OSRM reaction is: the major
reaction intermediates are located on the zirconia while the
role of copper and nickel active phase is to promote hydrogen
spillover and then release to the feed gas. It is clear that during
OSRM reaction, Ni-based catalysts produces relatively high
concentration of CO in special on the bimetallic sample, which
is still much higher than the upper limit of CO concentration in
the feed gas for PEM fuel cells. Thus, the integrated catalyst
system with a suitable function that promoted both OSRM
and WGS reactions should be developed. The following
0
20
40
60
80
100
250 270 290 310 330 350Temperature (°C)
CO
, CH
4 S
elec
tivity
(mol
%) Cu/ZrO2
Cu-Ni/ZrO2Ni/ZrO2
CH4
Fig. 9 – CO and CH4 selectivity as a function of reaction
temperature. Partial pressure of CH3OH, H2O and O2 was
75, 12.75 and 25.2 Torr, respectively. GHVS [ 30,000 hL1.
sequence of the reactions can be summarized during OSRM
reaction over these Cu/Ni/ZrO2 catalysts:
2CH3OH þ OðaÞ/ CH3OCHO þ H2O þ H2 (6)
2CH3OH / CH3OCHO þ 2H2 (7)
CH3OCHO / 2CO þ 2H2 (8)
CH3OH þ 2OHðaÞ / CO2 þ H2O þ 2H2 (9)
CH3OH þ OHðaÞ/ CO þ H2O þ 3=2H2 (10)
CH3OCHO / CH4 þ CO2 (11)
CH4 þ H2O 4 CO þ 3H2 (12)
H2 þ 1=2O2 / H2O (13)
CO2 þ H2 / CO þ H2O (14)
CH3OH / CO þ 2H2 (15)
4. Conclusions
In the present study, Cu/ZrO2, Ni/ZrO2 and Cu–Ni/ZrO2 cata-
lysts have been developed for oxidative steam reforming of
methanol to produce H2-rich gas at relative lower tempera-
ture. The TPR results revealed two different kinds of CuO: (i)
highly dispersed CuO species and CuO bulk present on the
CuO/ZrO2 catalyst and (ii) free NiO ,i.e., with no metal-support
interactions or highly dispersed NiO particles was evidenced
in the NiO/ZrO2 sample. The presence of Cu in the bimetallic
catalyst facilitates the reduction of Ni at lower temperatures.
Copper and nickel metallic nanoparticles on Cu/ZrO2 and Ni/
ZrO2 catalysts were observed by TEM, while bimetallic nano-
particles with different Cu/Ni weight ratios were identified
on the Cu–Ni/ZrO2 sample. The steady-state activity showed
that the Ni-based catalyst was more effective than the Cu-
based sample when was supported on ZrO2 for the OSRM reac-
tion at higher temperatures, indicating that Ni-based catalysts
is better for this reaction. The Cu–Ni/ZrO2 catalyst showed
the best catalytic performance at low temperatures than the
monometallic samples. This behavior was attributed to the
bimetallic nanoparticles present on the surface of the catalyst
that improves the bifunctional effect between the active
bimetallic phase and the support during the OSRM reaction.
All the catalysts showed the same selectivity toward H2 at
the maximum reaction temperature and it was w60%. The
high selectivity toward CO observed on the Cu–Ni/ZrO2
sample is associated to the presence of the Ni-rich bimetallic
nanoparticles, as evidenced by TEM and EDX analysis, since
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 3 ( 2 0 0 8 ) 4 5 6 9 – 4 5 7 64576
this behavior is similar to the one showed by the monome-
tallic Ni-catalyst.
Acknowledgements
Thanks to I.Q. Albina Gutierrez Martınez, Jorge Perez and Luis
Rendon for technical support and to the project ININ-CA-711
and CONACYT J-48924 for financial support.
r e f e r e n c e s
[1] Olah GA. After oil and gas: methanol economy. Catal Lett2004;93:1–2.
[2] Yao C-Z, Wang L-C, Liu Y-M, Wu G-S, Cao Y, Dain W-L, et al.Effect of preparation method on the hydrogen productionfrom methanol steam reforming over binary Cu/ZrO2
catalysts. Appl Catal A: Gen 2006;297:151–8.[3] Szizybalski A, Girgsdies F, Rabis A, Wang Y, Niederberger M,
Ressler T. In situ investigations of structure–activityrelationships of a Cu/ZrO2 catalyst for the steam reformingof methanol. J Catal 2005;233:297–307.
[4] Lindstrom B, Pettersson LJ. Hydrogen generation bysteam reforming of methanol over copper-basedcatalysts for fuel cell applications. Int J Hydrogen Energy2001;26:923–33.
[5] Purnama H, Girgsdies F, Ressler T, Schattka J-H, Caruso RA,Scomacker R, et al. Activity and selectivity ofa nanostructured CuO/ZrO2 catalyst in the steam reformingof methanol. Catal Lett 2004;94:61–8.
[6] ACW Koh, Chen L, Leong WK, Johnson BFG, Khimyak T, Lin J.Hydrogen or synthesis gas production via the partialoxidation of methane over supported nickel–cobalt catalysts.Int J Hydrogen Energy 2007;32:725–30.
[7] Venugopal A, Naveen Kumar S, Ashok J, Hari Prasad D, DurgaKumari V, Prasad KBS, et al. Hydrogen production bycatalytic decomposition of methane over Ni/SiO2. Int JHydrogen Energy 2007;32:1782–8.
[8] Liu Y, Liu D. Study of bimetallic Cu–Ni/g-Al2O3 catalysts forcarbon dioxide hydrogenation. Int J Hydrogen Energy 1999;24:351–4.
[9] Yang Y, Ma J, Wu F. Production of hydrogen by steamreforming of ethanol over a Ni/ZnO catalyst. Int J HydrogenEnergy 2006;31:877–82.
[10] Biswas P, Kunzru D. Steam reforming of ethanol forproduction of hydrogen over Ni/CeO2–ZrO2 catalyst: effect ofsupport and metal loading. Int J Hydrogen Energy 2007;32:969–80.
[11] Marino FJ, Cerrella EG, Duhalde S, Jobbagy M, Lombarde M.Hydrogen from steam reforming of ethanol. Characterizationand performance of copper–nickel supported catalysts. Int JHydrogen Energy 1998;23:1095–101.
[12] Marino FJ, Boveri M, Baronetti G, Lombarde M. Hydrogenproduction from steam reforming of bioethanol using Cu/Ni/K/g-Al2O3 catalysts. Effect of Ni. Int J Hydrogen Energy 2001;26:665–8.
[13] Sun J, Qui X-P, Wu F, Zhu W-T. H2 from steam reforming ofethanol at low temperature over Ni/Y2O3, Ni/La2O3 and Ni/Al2O3 catalysts for fuel-cell application. Int J HydrogenEnergy 2005;30:437–45.
[14] Velu S, Suzuki K, Osaki T. Oxidative steam reforming ofmethanol over Cu/ZnAl(Zr)-oxide catalysts; a new andefficient method for the production of CO-free hydrogen forfuel cells. Chem Commun 1999:2341–2.
[15] Velu S, Suzuki K, Okazaki M, Kapoor MP, Osaki T, Ohashi F.Oxidative steam reforming of methanol over CuZnAl(Zr)-oxide catalysts for the selective production of hydrogen forfuel cells: catalyst characterization and performanceevaluation. J Catal 2000;194:373–84.
[16] Agrell J, Birgersson H, Boutonnet M, Melian-Cabreara I,Navarro RM, Fierro JLG. Production of hydrogen frommethanol over Cu/ZnO catalysts promoted by ZrO2 andAl2O3. J Catal 2003;219:389–403.
[17] Navarro RM, Alvarez-Galvan MC, Rosa F, Fierro JLG.Hydrogen production by oxidative reforming of hexadecaneover Ni and Pt catalysts supported on Ce/La-doped Al2O3.Appl Catal A: Gen 2006;297:60–72.
[18] Perez-Hernandez R, Aguilar F, Gomez-Cortes A, Dıaz G. NOreduction with CH4 or CO on Pt/ZrO2–CeO2 catalysts. CatalToday 2005;107–108:175–80.
[19] Montoya JA, Romero-Pascual E, Gimon C, Del Angel P,Monzon A. Methane reforming with CO2 over Ni/ZrO2–CeO2
catalysts prepared by sol–gel. Catal Today 2000;63:71–81.[20] Shan W, Luo M, Lin P, Shen W, Li C. Reduction property and
catalytic activity of Ce1�xNixO2 mixed oxide catalysts for CH4
oxidation. Appl Catal A: Gen 2003;246:1–9.[21] Kirumakki SR, Shpeizer BG, Sagar GV, Chary KVR,
Clearfield A. Hydrogenation of Naphthalene over NiO/SiO2–Al2O3 catalysts: structure–activity correlation. J Catal 2006;242:319–31.
[22] Ratnasamy P, Srinivas D, Satyanarayana CVV,Manikandan P, Senthil Kumaran RS, Sachin M, et al.Influence of the support on the preferential oxidation of COin hydrogen-rich steam reformates over the CuO–CeO2–ZrO2
system. J Catal 2004;221:455–65.[23] Arenas-Alatorre J, Gomez Cortes A, Avalos Borja M, Dıaz G.
Surface properties of Ni–Pt/SiO2 catalysts for N2Odecomposition and reduction by H2. J Phys Chem B 2005;109(6):2371–6.
[24] Vizcaıno AJ, Carrero A, Calles JA. Hydrogen production byethanol steam reforming over Cu–Ni supported catalysts. IntJ Hydrogen Energy 2007;32:1450–61.
[25] Perez-Hernandez R, Gutierrez-Martınez A, Gutierrez-Wing CE. Effect of Cu loading on CeO2 for hydrogenproduction by oxidative steam reforming of methanol. Int JHydrogen Energy 2007;32:2888–94.
[26] Kugai J, Subramani V, Song C, Engelhard MH, Chin Y-H.Effects of nanocrystalline CeO2 supports on the propertiesand performance of Ni–Rh bimetallic catalyst for oxidativesteam reforming of ethanol. J Catal 2006;238:430–40.
[27] Molina R, Poncelet G. a-Alumina-supported nickel catalystsprepared from nickel acetylacetonate: a TPR study. J Catal1998;173:257–67.
[28] Frusteri F, Freni S, Chiodo V, Donato S, Bonura G, Cavallaro S.Steam and auto-thermal reforming of bio-ethanol over MgOand CeO2 Ni supported catalysts. Int J Hydrogen Energy 2006;31:2193–9.
[29] Arena F, Licciardello A, Parmaliana A. The role of Ni2þ
diffusion on the reducibility of NiO/MgO system: a combinedTRP–XPS study. Catal Lett 1990;6:139–49.
[30] Ahmed S, Krumpelt M. Hydrogen from hydrocarbon fuels forfuel cells. Int J Hydrogen Energy 2001;26:291–301.
[31] Marino F, Boveri M, Baronetti G, Lombarde M. Hydrogenproduction via catalytic gasification of ethanol. Amechanism proposal over copper–nickel catalysts. Int JHydrogen Energy 2004;29:67–71.
[32] Gallucci F, Basile A, Tosti S, Iulianelli A, Drioli E. Methanoland ethanol steam reforming in membrane reactors: anexperimental study. Int J Hydrogen Energy 2007;32:1201–10.
[33] Fisher IA, Bell AT. A mechanistic study of methanoldecomposition over Cu/SiO2, ZrO2/SiO2, and Cu/ZrO2/SiO2. JCatal 1999;184:357–76.