Hydrogen Production 1

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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.

mailto:[email protected]

http://www.elsevier.com/locate/he


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.


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.


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.


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 %

)


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

%)


Fig. 8 – CO2 selectivity as a function of reaction

temperature. Partial pressure of CH3OH, H2O and O2 was



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


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


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.

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