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Hydrogen production from oxidative steam reformingof methanol: Effect of the Cu and Ni impregnation on ZrO2

and their molecular simulation studies

P. Lopez a,b, G. Mondragon-Galicia a, M.E. Espinosa-Pesqueira a, D. Mendoza-Anaya a,Ma.E. Fernandez a, A. Gomez-Cortes c, J. Bonifacio a, G. Martınez-Barrera d,R. Perez-Hernandez a,*a Instituto Nacional de Investigaciones Nucleares, Carr. Mexico-Toluca S/N La Marquesa, Ocoyoacac, Edo. de Mexico C. P. 52750, MexicobEstudiante del Programa de Maestrıa en Ciencia de Materiales, de la Facultad de Quımica, Universidad Autonoma del Estado de Mexico,

Mexicoc Instituto de Fısica-Universidad Nacional Autonoma de Mexico, Apdo. Postal 20-364, Mexico 01000 D.F., Mexicod Laboratorio de Investigacion y Desarrollo de Materiales Avanzados, Facultad de Quımica, Universidad Autonoma del Estado de Mexico,

Km. 12 Carretera Toluca-Atlacomulco, San Cayetano 50200, Mexico

a r t i c l e i n f o

Article history:

Received 8 April 2011

Received in revised form

16 February 2012

Accepted 17 February 2012

Available online 4 April 2012

Keywords:

H2 production

Oxidative steam reforming

of methanol

CueNi/ZrO2 catalysts

Coreeshell nanoparticles

Molecular simulation

Structureesensitive reaction

* Corresponding author. Tel.: þ52 55 5329723E-mail address: raul.perez@inin.gob.mx (

0360-3199/$ e see front matter Copyright ªdoi:10.1016/j.ijhydene.2012.02.105

a b s t r a c t

CuandNiwere supported on ZrO2 by co-impregnation and sequential impregnationmethods,

and tested in the oxidative steam reforming ofmethanol (OSRM) reaction for H2 production as

a functionof temperature. Surfacearea of the catalysts showeddifferences as a functionof the

order in which the metals were added to zirconia. Among them, the Cu/ZrO2 catalyst had the

lowest surface area. XRD patterns of the bimetallic catalysts did not show diffraction peaks of

theCu,Nior bimetallicCueNialloys. Inaddition,TPRprofilesof thebimetallic catalystshad the

lowest reduction temperature comparedwith themonometallic samples. The reactivity of the

catalysts in the rangeof 250e350 �Cshowedthat thebimetallic samplespreparedbysuccessive

impregnationhadhighest catalytic activity among all the catalysts studied. These resultswere

also confirmed by theoretical calculations. The reactivity of the monometallic and bimetallic

structures obtained by molecular simulation followed the next order: NishellCucore/

ZrO2yCushellNicore/ZrO2>Ni/Cu/ZrO2>Cu/Ni/ZrO2>CueNi/ZrO2>Cu/ZrO2>Ni/ZrO2.These

findings agree with the experimental results, indicating that the bimetallic catalysts prepared

by successive impregnation show a higher reactivity than the CueNi system obtained by co-

impregnation. In addition, the selectivity for H2 production was higher on these catalysts.

This result could be associated also to the presence of the bimetallic CueNi and coreeshell Ni/

Cunanoparticles on the catalysts, aswas evidenced by TEMeEDXanalysis, suggesting that the

OSRM reactionmay be a structureesensitive reaction.

Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

reserved.

9; fax: þ52 55 53297240.R. Perez-Hernandez).2012, Hydrogen Energy Publications, LLC. 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 en e r g y 3 7 ( 2 0 1 2 ) 9 0 1 8e9 0 2 7 9019

1. Introduction

Fuel cells have recently attracted much attention as a poten-

tial device for energy transformation. Hydrogen is a most

promising fuel for fuel cell, and steam reforming of natural

gas, methanol, and gasoline can produce it. One method of

great interest in recent years is hydrogen production from

methanol via steam reforming over palladium [1e3] or

copper-based catalysts [4e6]. The advantage of using meth-

anol for H2 production is its high hydrogen/carbon ratio. This

makes the steam reforming of methanol (SRM) energetically

favorable and has the advantage of reducing the soot forma-

tion due to the absence of carbonecarbon bonds, which

otherwise may lead to catalyst deactivation [7,8]. Copper-

based catalysts have received considerable attention for H2

production via SRM [4e7]. Another interesting reaction is the

oxidative steam reforming (OSR), this reaction combine the

steam reforming and partial oxidation reactions. This process

can be adiabatic by using the energy produced from partial

oxidation to supply the endothermic steam reforming reac-

tion [9]. Oxidative steam reforming of methanol (OSRM)

studies, indicate low carbon monoxide yield and high

hydrogen concentration in the products [10e15]. Mainly

studies on NieCu-base catalysts in the steam reforming for H2

production used ethanol [16e20], however, a significant

amount of by-products were obtained. In WGS reaction, it has

been observed that the addition of Cu into Ni catalyst causes

an increase in the catalyst activity. A similar result was

reported for the OSRM reaction and this positive effect was

ascribed to the amount and formation of the bimetallic NieCu

species [12,21].

The goal of this work was to study the effect of the metal

addition to ZrO2 by impregnation method in the oxidative

steam reforming of methanol to produce H2-rich gas. Cata-

lysts were characterized by DSC/TGA, BET (N2 adsorp-

tionedesorption), SEM (Scanning Electron Microscopy), EDX

(Energy Dispersive X-ray Spectroscopy), XRD (X-ray Diffrac-

tion), TEM (Transmission Electron Microscopy), Simulation

method and TPR (Temperature-Programmed Reduction).

2. Experimental

2.1. Synthesis of the ZrO2 and catalysts

ZrO2 was prepared by the solegel method, initially a sol was

prepared by mixing Zirconium (IV) propoxide (Fluka) (as

precursor) with n-propanol (Aldrich) and a basic catalyst

(NH4OH) (Fluka) under constant stirring. The resulting sol was

processed at reflux temperature (85 �C) and water was added

drop wise to it. The reflux temperature was kept constant

during 1 h and the resulting gel was cooled down to room

temperature (r.t.) and aged for 24 h. The residual liquid was

removed by decanting. The molar ratio used for the synthesis

was: Zr(OCH2CH2CH3)4/C3H8O/H2O/NH4OH¼ 1:4:4:0.33. Finally

the sample was dried at 100 �C 24 h. The xerogel was heated at

100 �C for 1 h and then heated at 450 �C for 6 h under an air

stream. The prepared zirconia was then impregnated with an

aqueous solution of Cu(CH3COO)2�H2O (Merck) or NiNO3�6H2O

at an appropriate concentration to obtain 3 wt.% of copper or

nickel respectively onto the monometallic catalysts. The

excess of water was then evaporated at 80 �C under constant

stirring and the resulting solids were dried at 110 �C overnight.

The catalysts were calcined at a rate of 5 �C/min up to 400 �Cunder static air and holding this temperature for 2 h, then

slowly cooling down to r.t. Three bimetallic samples were

prepared at 80%Cu and 20%Ni respectively to obtain 3 wt.% of

total metallic phase. For the first sample, ZrO2 was succes-

sively impregnated with an aqueous solution of Cu(CH3-

COO)2�H2O (Merck), after that, the excess of water was

removed at 80 �C under constant stirring and the catalyst was

dried at 110 �C and calcined at 400 �C for 2 h followed by

cooling down to r.t. Then, an aqueous solution of NiNO3�6H2O

was added and the resulting solid was calcined at the same

temperature and time. The as prepared catalysts will be

referred as Ni/Cu/ZrO2. For the second catalyst, the synthesis

procedure was changed to the above sample mentioned. The

labeling of this catalyst will be referred as Cu/Ni/ZrO2. The

third sample (CueNi/ZrO2) was prepared by using a simulta-

neous impregnation (also called co-impregnation): an

aqueous solution of Cu(CH3COO)2 and NiNO3�6H2O were

added to ZrO2 and calcined at 400 �C for 2 h. All the samples

were reduced at 450 �C using a mixture of H2 (5%)/Ar (50 mL/

min) stream for 1.5 h before characterization, except for TPR

technique in which the sample was calcined.

2.2. Characterization

The DSC/TGA analysis of xerogel was carried out in Calorim-

eter SDT Q600 (TA Instruments-Waters) under N2 atmosphere

in the range of 20e1000 �C for TGA analysis at a heating rate of

10 �C/min. The details of catalysts characterization have been

reported in our earlier reports [3,10e13,22e24]. Nitrogen

adsorptionedesorption of the samples was measured at

�196 �C on a Belsorp-max Bel Japan equipment. Prior to the

measurements the samples were degassed at 150 �C for 1 h.

The surface area and pore size distribution were determined

using the BET and BJHmethods respectively. HRTEM and local

chemical analysis of the bimetallic nanoparticles were carried

out in a JEM 2200FS microscope with a resolution of 0.19 nm

and fitted with an energy dispersive X-ray Spectrometer

(NORAN) and a JEM 2010-HTwith a point resolution of 0.19 nm

fitted with an EDX microprobe Thermo-scientific. JEOL-2010

microscope with a point resolution of 0.19 nm fitted with an

NORAN microprobe Thermo-scientific. The samples were

dispersed in isopropanol and a drop of such a solution was

placed onto copper and gold 300 mesh grids.

Oxidative steam reforming of methanol was carried out at

an atmospheric pressure by placing the fixed bed flow reactor

(8 mm i.d.) in an electric furnace consisting of two heating

zones equipped with omega temperature controllers, using

a commercial flow system RIG-100-ISRI. Prior to OSRM reac-

tion, 0.1 g of catalyst was reduced in-situ, using a stream of H2

(5%)/Ar (50 mL/min) increasing temperature from room to

450 �C with a heating rate of 10 �C/min and holding this

temperature for 1.5 h. A thermocouple in contact with the

catalytic bed was utilized in order to monitor and control the

temperature inside the catalyst. For the reaction, O2 (5%)/He

mixture was passed through stainless steel saturator

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 9 0 1 8e9 0 2 79020

containing methanol and water mixture (we use a hot line in

the saturator in order to maintain constant the

temperaturew 20 �C). This gas was added bymeans of a mass

flow controller (RIG-100). The total flow ratewas kept at 40mL/

min (GHSV ¼ 24,000 h�1 based on the total flow). Reaction

products were analyzed by Gow-Mac 580 Gas chromatograph

with thermal conductivity detector equipped with two

columns system (molecular sieve 5 A and Porapack Q

columns), double injector controlled by Clarity software

V.2.6.04.402 and TCD. The first column was used to separate

the gaseous products such as H2, O2, CH4 and CO. The second

column was used to separate water, methanol, methyl

formate (MF) and CO2. All the reported data were collected

after a run time of 7 h. The following equations were used to

determine the methanol conversion and selectivity:

Xð%Þ ¼ Cin � Cout

Cin� 100

H2 production ¼ mmol H2 producedmmol CH3OH feed

SCO2ð%Þ ¼ nCO2�out

nCO2�out þ nCOout� 100

The subscripts in and out indicate the inlet and the outlet

concentrations of the reactants or products.

2.3. Simulation method

The bimetallic models were building up with Cu (80%) and Ni

(20%) in order to obtain the Cu0.80Ni0.20 system using the

program Cerius2, which required appliedmolecular dynamics

algorithms [25e27]. The geometry optimization calculations

were performed at each structure through a process in which

coordinates of the atoms are adjusted to achieve a system as

close to a real physical system in equilibrium, and determined

the minimum energy structures, the procedure was carried

out with the algorithm BroydeneFletchereGoldfarbeShanno

(BFGS). The models were: CueNi, where the calculation of

molecular dynamics is performed by adding simultaneously

copper and nickel atoms, then a simulated heating process to

500 �C was applied. Ni/Cu, which is computed first with Cu

atoms and a theoretical heating to 500 �C was applied, then Ni

atoms were added followed with a simulated heating process

to 500 �C was performed again. Cu/Ni structure where the

molecular dynamics calculation is performed first with Ni and

then added with Cu atoms, notice that the addition of the

metallic atoms was changed but the simulated heating

Table 1 e TPR peaks positions, �C and concentrations (%) of th

Catalyst Surface area Total pore volume

m2/g cm3/g

ZrO2 42 0.0736

Cu/ZrO2 12 0.0271

Cu/Ni/ZrO2 28 0.0512

CueNi/ZrO2 11 0.0262

Ni/Cu/ZrO2 37 0.0582

Ni/ZrO2 21 0.0333

Theoretical value of the H2/CuO (H2/NiO) ¼ 1 for complete reduction of m

process was as the above mentioned. Also a Cu(core)eNi(shell)and Cu(shell)eNi(core) structures were built. After bimetallic and

monometallic models were obtained, they were deposited on

a surface of ZrO2 and molecular properties were performed.

The frontier orbitals like HOMO (Highest Occupied Molecular

Orbital) and LUMO (Lowest Unoccupied Molecular Orbital)

were calculated by Dmol3 code [28]. This code is based in the

density functional theory which uses the Local Density

approximation and generalized gradient approximation to

achieve molecular properties.

3. Results and discussion

3.1. Thermal analysis, textural and structural propertiesof the catalysts

ZrO2 Xerogel was studied by means of TGA in order to select

an appropriate calcination temperature leading to total

decomposition of carbonaceous products from the synthesis

toward the corresponding oxide. The obtained TGA-DSC

curves for the xerogel (Figure not included) showed 22% of

the weight loss and it was attributed to the elimination of the

physically adsorbed water, physical and chemical adsorbed

alcohol and residual organic material coming from the

synthesis. The observed exothermic peak at 433 �C on the

zirconia xerogel was ascribed to a change of phase from an

amorphous material to crystalline tetragonal zirconia

[25,29,30]. The specific surface area of bare ZrO2 was 42 m2/g.

After metallic phase impregnation and thermal treatments

(calcination and reduction), the surface area of the catalysts

diminished and was lower than bare support. Among them,

the Cu/ZrO2 and CueNi/ZrO2 catalysts had the lowest surface

area, as well as, the total pore volume (Table 1). Fig. 1 showed

a representative zone of the SEM image of the Ni/Cu/ZrO2

catalyst. It is important to mention that the bare ZrO2 and the

other catalysts had the same morphology, so, particles with

spherical tendency. This is understandable because we used

the ZrO2 previously stabilized at 450 �C to obtain the catalysts.

Fig. 2 shows the XRD patterns of the catalysts before and after

catalytic reaction in the range of 20e90� 2q. An expanded scale

was used in order to illustrate the peaks of pure Cu and Ni

phases or Cu/Ni alloys present on the ZrO2. XRD patterns of

the samples before the catalytic test evidenced diffraction

peaks of the tetragonal and monoclinic phases of the ZrO2. In

addition, diffraction peaks of the metallic Cu and Ni phases

e reducible species in the Cu/Ni-base catalysts.

Reduction temperature (�C) H2/MO

Before After Before After

e e e e

217, 248, 290, 340 174 0.77 0.11

192, 222 171 0.93 0.26

203, 259 183 0.76 0.09

185, 220 174 0.83 0.21

349, 443 326, 447 0.76 0.63

etal oxide.

Fig. 1 e Typical SEM images of the fresh Ni/Cu/ZrO2

catalyst.

100 200 300 400 500

Cu/Ni/ZrO2

Cu-Ni /ZrO2

Ni /ZrO2

Temperature ºC

Ni/Cu /ZrO2

H2 C

onsu

mpt

ion

(a.u

.)

Cu/ZrO2

Fig. 3 e H2-TPR profiles of the CueNi base catalysts

supported on ZrO2 (before-solid line and after-clear line)

catalytic reaction.

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 en e r g y 3 7 ( 2 0 1 2 ) 9 0 1 8e9 0 2 7 9021

were identified on the Cu/ZrO2 and Ni/ZrO2 catalysts respec-

tively. The bimetallic catalysts did not exhibit diffraction

peaks related to metallic Cu, Ni or bimetallic CueNi alloys.

However, the possibility cannot be ruled out for the presence

of crystallites with small particle size, which is beyond the

detection capacity of the XRD technique. After catalytic test,

some changes were observed in the XRD patterns of the Ni/

ZrO2 and the bimetallic CueNi/ZrO2 catalysts (the later

prepared by simultaneous impregnation). On the former

catalyst, NiO phase was identified and on the bimetallic

sample, a peak of the metallic copper appears. This finding

evidences that the active phase is not stable on these catalysts

and it was modified by the stream of the reaction.

3.2. Temperature-programmed reduction

In order to study the reducibility of the active phase in the

fresh and spent catalysts, TPR analysis was performed and the

results are showed in Fig. 3. Peaks corresponding to the

reduction of bare ZrO2 did not appear in the whole range of

Fig. 2 e XRD patterns of the CueNi base catalysts supported

on ZrO2 (before and after catalytic reaction).

studied temperature. Calcined Cu/ZrO2 samples displayed

a broad multipeak reduction profile within two temperature

range, one of 150e250 �C and the second from 350 to 400 �C.This suggests the presence of the mixture of CuOx species,

and it corresponds to copper species highly disperse in the low

temperature range and Cu with strong interaction with the

support at high temperature range. In contrast, only a reduc-

tion peak can be distinguished in the TPR profile of the Ni/ZrO2

catalyst in the temperature range of 315e375 �C. It has been

reported that large NiO particles with lower interaction with

the ZrO2 on the Ni/ZrO2 catalyst could be reduced at low

temperature [12,31e33]. NiO particles strongly bonded with

the ZrO2were observed close to 350 �C [13]. The reduction peak

observed in both, Ni/ZrO2 and Cu/ZrO2 catalysts was shifted at

low temperature when Ni and Cu are together. Clearly, the

bimetallic system not only promoted the dispersion of the

active phase on the catalysts as previously discussed within

the XRD results, but also improved the reducibility of CuO and

NiO by modifying the interaction of the active phase with the

support. TPR profiles of the bimetallic Cu/Ni/ZrO2 and Ni/Cu/

ZrO2 catalysts synthesized by successive impregnation had

the most intense reduction peak at a lower temperature

compared to the CueNi/ZrO2 sample. However, the reduction

temperature in these bimetallic catalysts was lower than on

themonometallic samples. Vizcaıno et al. [34] reported, on the

bimetallic CueNi/SiO2 catalyst, that the reduction peaks

appeared between 200 and 260 �C. The peak at the lowest

temperaturewas assigned to CuO reduction and the otherwas

attributed to NiO reduction. In a previous study [12] on CueNi/

ZrO2 system, it has been reported that Cu causes spillover of

hydrogen onto Ni. This induces a simultaneous reduction of

both, copper oxide andNiO, and causes a shift in the reduction

of the active phase at low temperatures, as was reported for

the PteNi/SiO2 system [35]. In addition, it has been suggested

that the first reduction peak observed in the TPR profile of the

bimetallic catalyst, corresponded to the reduction of adjacent

Cu and Ni atoms, which could be forming a bimetallic phase.

The second reduction peak was assigned to the remaining Ni

atoms forming Ni-rich nanoparticles. That proposal was

supported with HRTEM technique results [12]. In our case,

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 9 0 1 8e9 0 2 79022

a similar behavior could be occurring. This is because a bime-

tallic particle on CueNi/ZrO2 sample was identified (Fig. 4a).

The measured interplanar distance in the nanoparticle was

1.81 A, which corresponds to the (200) plane, associated with

the cubic phase of the bimetallic Cu3.8Ni system, as was

confirmed by EDX analysis (inset EDX spectrum in Fig. 4a).

Another possibility to explain the shift of the reduction peaks

at lower temperature on the bimetallic system; could be

related to the particle size of the active phase. On these

Fig. 4 e a) HREM image of a CueNi nanoparticle in the (200)

crystallographic plane was identified on the CueNi/ZrO2

catalyst. Inset image, EDX of the CueNi nanoparticle. b)

TEM image of Ni/Cu/ZrO2 catalyst, coreeshell nanoparticles

were identified, the left side area shown two particles

building the core. Inset image, EDX of the Ni/Cu coreeshell

nanoparticle. EDX analyses were performed in-situ with

a spot of 10 nm and the electron beamwas located at the Ni

shell area.

samples, diffraction peaks of the active phase were not

observed by XRD technique, suggesting a high dispersion of it.

Fig. 4b showed the TEM image of the Ni/Cu/ZrO2 catalyst. It

showed two coreeshell nanoparticles of around 40 nm in

diameter, the Cu-core had an average diameter ofw34 nmand

the thickness of the shell was around 5.69 nm. This kind of

structures could be a consequence of the synthesis method,

EDX analysis (inset EDX spectrum in Fig. 4b) demonstrated the

presence of the Ni (8.78%), Cu (38.16%), Zr and O elements; the

metal Ni/Cu (1:4) ratio was coincident with the molar Ni(1)/

Cu(4) ratio used for the synthesis. This kind of particles could

be also responsible of the shift of the reduction peaks at lower

temperature on the bimetallic system, as observed on Fig. 3.

Breen and Ross [36] observed that if the catalysts are reduced

at lower temperatures, higher reactivity on the methanol

steam reforming reaction is obtained. The peaks position and

the percentage of the metal oxide reduction given by the H2/

MO ratio are summarized in Table 1. The H2 consumption

during the TPR analysis on the fresh Cu/Ni-base catalysts was

low; this indicates incomplete reduction of the active phase.

Among all the catalysts studied, the bimetallic samples

prepared by successive impregnation showed the highest H2/

MO ratio, indicating further reduction of the active phase. TPR

profiles of the samples after catalytic reaction showed lower

H2 consumption, indicating that under OSRM conditions the

active phase is present for both oxidized and reduced states,

but the metallic state prevails as was confirmed by XRD

analysis of the spent samples. After OSRM reaction, by EPR

technique was found that in Cu/CeO2 samples, the ion Cu2þ is

forming a nano-sized two-dimensional structure [10,37,38].

Oguchi et al. [39] observed a reduction peak on the CuO/ZrO2

sample post-reaction. They concluded that the Cu2O catalyst

was stabilized during the SRM reaction. Turco et al. [40] sug-

gested that there was a zone within the catalytic bed where

the catalyst is oxidized, and another zone where it was

reduced. This phenomena could be occurred on our samples,

because, generally in oxidative steam reforming process,

evidence suggest that the front of the catalyst bed is partially

oxidized and the downstream of the catalyst bed remains in

the reduced state.

3.3. Simulation method

Fig. 5 shows the theoretical calculations of the monometallic

and bimetallic models over ZrO2. After the geometry optimi-

zation of the theoretical models, the total energy and the

energy gap had the following values: Ni(shell)/Cu(core)/ZrO2

(�3193.49, 0.0027) eV, Cu(shell)/Ni(core)/ZrO2 (�3429.43, 0.0159)

eV, Ni/Cu/ZrO2 (�3419.37, 0.0185) eV, Cu/Ni/ZrO2 (�3488.39,

0.021) eV, CueNi/ZrO2 (�3655.28, 0.108) eV, Cu/ZrO2 (�3810.23,

0.385) eV and Ni/ZrO2 (�3832.18, 0.565) eV respectively. The

HOMO-LUMO gap of the systems along with the total energy

calculated, allows to evaluate the reactivity behavior of the

system. According to Fukui’s theory [41] a low reactivity will

be expected in a system having a large energy gap combined

with a low total energy. While, if the gap of the system is low

and the total energy is large, high reactivity will be expected.

From this theory, it is understood then that the reactivity is

reflected in the ability to facilitate the adsorption or desorp-

tion of amolecule for a specific reaction in these systems. This

Fig. 5 eMolecular models of the bimetallic clusters: Top graph corresponds to gap-energy, in bottom graph showed the total

energy of the systems. It showed that as the energy gap increases, the total energy of the system decreases, this indicates

that the Ni(30 atomos)(shell)Cu(13 atomos)(core)/ZrO2 and Cu(30atomos)(shell)Ni(13 atomos)(core)/ZrO2 are the most reactive,

while the CueNi/ZrO2 is less reactive on the bimetallic models. Eads [ EA D EM L EA/M, EA[methanol Energy, EM[ System

Energy of the models [42].

200 225 250 275 300 325 3500

20

40

60

80

100

Met

hano

l Con

vers

ion

(mol

%)

Temperature (ºC)

Cu/ZrO2 Ni/Cu/ZrO2 Cu/Ni/ZrO2 Cu-Ni/ZrO2 Ni/ZrO2

Fig. 6 e Steam reforming of methanol over copper-nickel-

base catalysts supported on ZrO2 (GHVS [ 24,000 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 en e r g y 3 7 ( 2 0 1 2 ) 9 0 1 8e9 0 2 7 9023

suggests that as the band gap of the bimetallic models

decreases, an electron transfer mechanism is favored at the

interface between the bimetallic structures and the support.

This facilitates the redox properties of the catalysts, giving

a higher OSRM activity. Theoretical results obtained after the

simulation of the successive impregnation process, based on

coreeshell structures, show higher reactivity than in the co-

impregnation (CueNi/ZrO2) and monometallic simulated

process. The reactivity of these systems followed the next

order: Ni(shell)/Cu(core)/ZrO2 y CushellNicore/ZrO2 > Ni/Cu/

ZrO2 > Cu/Ni/ZrO2 > CueNi/ZrO2, > Cu/ZrO2 > Ni/ZrO2. In

addition, the energy adsorption between methanol and the

surface of these catalytic models were calculated (inset table

in Fig. 5). The energy adsorption was calculated according

with reference [42]. The results obtained confirm also, that the

models prepared by successive impregnation process had the

low energy adsorption, so, the ability to facilitate the adsorp-

tion or desorption of a methanol for this reaction. Mainly in

the literature, the theoretical studies reported are on unsup-

ported coreeshell particles and their alloys like CueAu parti-

cles, on this systems the studies have concentrated on the

structural behavior of the clusters [43,44], but no correlation

with the catalytic activity was associated.

3.4. Oxidative steam reforming of methanol reactionover Cu/Ni-base catalysts

Oxidative steam reforming (OSR) of methanol reaction was

carried out in the Cu/Ni/ZrO2 samples. Fig. 6 shows the cata-

lytic activity of the copperenickel-base catalysts supported on

ZrO2 as a function of the reaction temperature. It was possible

to observe that the Cu/ZrO2 catalyst was better than Ni/ZrO2

sample in the temperatures range studied in this work. This

indicates that methanol conversion occurs preferentially on

monometallic copper than on nickel one. It is important to

mention that the H2 chemisorption process did not occur in

these samples, for this reason the metal dispersion was not

estimated and as a consequence the TOF could not be deter-

mined for each catalyst, having a real comparison in the

200 225 250 275 300 325 3500.0

0.4

0.8

1.2

1.6

2.0

2.4H

2 yie

ld

Temperature (ºC)

Cu/ZrO2 Ni/Cu/ZrO2 Cu/Ni/ZrO2 Cu-Ni/ZrO2 Ni/ZrO2

200 225 250 275 300 325 3500

20

40

60

80

100

Open-CO

Solid-CO2

Sele

ctiv

ity (m

ol %

)

Temperature (ºC)

Cu/ZrO2 Ni/Cu/ZrO2 Cu/Ni/ZrO2 Cu-Ni/ZrO2 Ni/ZrO2

0

20

40

60

80

100

a

b

Fig. 7 e a) H2 yield as a function of the metal addition and

temperature. (GHVS [ 24,000 hL1). b) Evolution on the

selectivity of CO2 and CO as a function of the metal

addition and temperature. (GHVS [ 24,000 hL1).

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 9 0 1 8e9 0 2 79024

methanol conversion. When Ni was supported on ZrO2-

monoclinic [12], the catalytic activity was similar to the

obtained in this work up to 300 �C. On the other hand, it is

clear that the preparation method of the catalyst has

a significant influence on the OSRM reaction. The addition of

0.2 wt.% of Ni to Cu/ZrO2 catalyst leads to a considerable

improvement in themethanol conversion, compared with the

Ni/ZrO2 sample. The CueNi/ZrO2 sample had a similar

behavior to the Cu/ZrO2 catalyst until 300 �C. After this

temperature the CueNi/ZrO2 sample exhibited the same

catalytic activity than the other bimetallic samples. In addi-

tion, was observed that the active phase of the CueNi/ZrO2

catalyst was not stable, because, it was sinterized after cata-

lytic reaction (Fig. 2). This effect could be explained the lower

catalytic activity observed on this sample than on the other

bimetallic samples prepared by successive impregnation.

Among bimetallic samples, those prepared by the successive

impregnationmethod showed high reactivity than the sample

synthesized by simultaneous co-impregnation. Although

experimentally the catalyst surface is different in the samples

prepared by successive impregnation method, the theoretical

reactivity predictions determined from the energy gap is

similar in both bimetallic models, as seen in the Fig. 5. This

may explain the catalytic behavior between the two catalytic

species. Shu et al. [45] observed that the impregnation

sequence of Pt and Ni on g-Al2O3 does not seem to play

a significant role in the catalytic activity for the dispropor-

tionation of cyclohexene. By EXAFS studies revealed the

formation of PteNi bonds in both catalysts. They suggested

that the surfaces of both samples are Pt-terminated, from the

segregation of Pt to the surface during hydrogen reduction. In

recently paper Strasser et al. [46] concluded that the platinum-

rich shell on PteCu nanoparticles, exhibits compressive

strain, which results in a shift of the electronic band structure

of platinum and weakening chemisorption of oxygenated

species. These activityestrain relationships were consistent

with computational predictions that compressive strain

enhances oxygenereduction reaction. In our casewe observed

that the catalytic activity is strongly related with the crystal-

linity and morphology of the active phase, the above mention

was corroborated by means of XRD and TEM. The TEM anal-

ysis of the bimetallic particle with coreeshell morphology;

showed that there is no crystalline arrangement point to point

or even line to line, which can be observable in the shell of the

particle (Fig. 5b). The crystalline anisotropy plays an impor-

tant role in the methanol conversion in this research, because

in the case of the coreeshell Ni/Cu structure, the catalytic

property increases in both cases, so the activity is not

restricted by any preferred crystallographic direction. In the

case of the Cu/ZrO2 system having a crystalline arrangement

in the (111) crystal direction, as seen in the XRD pattern of

Fig. 2, indicates that there are more particles with this type of

crystalline plane which favors the catalytic activity but not as

in the case of bimetallic coreeshell particles; while in the case

of Ni-base catalyst was observed that it has a poor crystallinity

as observed in the XRD pattern (Fig. 2) with the (111) crystal-

line direction. This showed that there are few planes in the

(111) crystalline direction influencing the catalytic anisotropic

response. This means that even if there is a poorly crystalline

monometallic active phase, the response in the catalytic

activity does not resemble bimetallic systems with coreeshell

morphology, as well as, when the active phase is a metallic

alloy (CueNi). This finding suggests that the OSRM reaction

may be structureesensitive. Yu-Hua et al. [47] studied the

methanol decomposition on Ni(1 1 1) and Ni(1 0 0) surfaces

using DFT-GGA (density functional theory-generalized

gradient approximation). The different behavior observed in

the methanol interaction with Ni(1 1 1) or Ni(1 0 0), suggests

that the methanol decomposition might be a structur-

eesensitive reaction, as it has been observed in our samples.

Marino et al. [19,20] found that the conversion of ethanol on

the SRE reactionwas improvedwhen nickel content increased

on the bimetallic CueNi system. This behavior was attributed

to the addition of Ni, which favors the segregation of Cu2þ ions

in the catalytic surface that causes an increase in the catalytic

activity. Thus the enhancement on the catalytic activity could

be attributed to the bimetallic CueNi species as was previ-

ously reported [12,19e21], and coreeshell nanoparticles

identified with TEM technique on the Ni/Cu/ZrO2 catalyst. As

well as, the reactivity of these systems calculated by

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 en e r g y 3 7 ( 2 0 1 2 ) 9 0 1 8e9 0 2 7 9025

theoretical calculations. However, the possibility cannot be

ruled out for the presence of crystallites with small particle

size, which is beyond the detection capacity of the XRD

technique. It is worth notice, that the BET surface area of the

Cu/ZrO2 sample is two times lower than Cu/Ni/ZrO2 and Ni/

Cu/ZrO2 samples. Thus, the catalytic activity observed on the

Cu/ZrO2 could be attributed to the presence of highly

dispersed Cu species rather than Cu bulk as reported for Cu/

CeO2 catalysts [10].

During the OSRM reaction with copperenickel-base cata-

lysts supported on ZrO2, the main products observed were H2,

CO, CO2 and H2O. However, a small quantity of methyl

formate was also present at temperatures below 275 �C in

almost all samples. Above this temperature, the methyl

formate was unstable and was not detected. On copper-ZrO2

systems [48], the production of (CH3)2O and CH2O during the

OSRM was observed and it was suggested that they were

produced on the support. Fig. 7a shows the hydrogen yield as

a function of reaction temperature during the catalytic tests of

the copperenickel-base catalysts on the OSRM reaction.

Hydrogen production was negligible up to 225 �C and increase

when the temperature was raised. Cu/Ni/ZrO2 and Ni/Cu/ZrO2

catalysts prepared by successive impregnation had the same

H2 yield after 250 �C and it was higher than all samples. At the

maximum reaction temperature, the H2 yield is about 2.0 mmol

for the Cu/Ni/ZrO2 andNi/Cu/ZrO2 catalysts, this is close to the

theoretical value (2.5) if a total reagents conversion is

assumed. At this temperature the methanol conversion was

nearly 100%. On the other three samples the H2 production

was close to 1.5 mmol. The CO2 selectivity (Fig. 7b) is important

at the beginning of the reaction and diminished as tempera-

ture was increased. This drop in the CO2 selectivity was

pronounced on the samples where the catalytic activity was

nearly 100%. In the case of the CO selectivity, this was produce

after 275 �C. The CO production at 350 �C was 10% for the

monometallic samples and close to 40% for the bimetallic

0 500 1000 1500 2000 2500 30000

10

20

30

40

50

60

70

80

90

100

Methanol CO2 H2 CO

Mol

(%)

Time (min)

Fig. 8 e Methanol conversion and selectivity versus time

on stream in OSRM. Reaction temperature [ 300 �C. Cu/Ni/

ZrO2 catalyst (GHVS [ 24,000 hL1).

SH2

�%�[

nH2Lout

nH2LoutDnCOoutDnCO2out� 100.

catalysts. The decrease in the CO2 selectivity and the forma-

tion of CO is probably due to the reverse water-gas shift (WGS)

reaction that occurred on the bimetallic samples. Taking in

account the results frommethanol conversion and selectivity,

it is considered that CH3OH form CH3OCHO and H2 on the

surface of the catalysts as the first step of the OSRM reaction.

Then, CH3OH is oxygenated to CH3OCHO, and then decom-

posed to H2 and CO. CH3OHwas hydrated in order to formCO2,

H2O and H2 respectively as reported previously [12].

Considering the catalytic activity of the catalysts, we

analyzed the stability of the Cu/Ni/ZrO2 catalyst in the OSRM

reaction over 2500 min on stream operation at 300 �C and the

results are displayed in Fig. 8. As showed in Fig. 8, the meth-

anol conversion close to 85%was obtained,whileH2 selectivity

of around 43%, CO2 of about 55% and CO close to 2%. It is clear

that the catalyst showed excellent catalytic stability without

apparent deactivation during the testing. This suggests that

the active bimetallic phase is strongly interacted with ZrO2

and did not suffer agglomeration; thus, the main structure of

this catalyst can be maintained as was demonstrated by XRD.

4. Conclusion

In the present study, Cu/ZrO2, Ni/ZrO2 and three bimetallic

copper-nickel catalysts supported on ZrO2 were prepared by

the impregnation method. The bimetallic Cu/Ni/ZrO2 and Ni/

Cu/ZrO2 catalysts showed higher catalytic activity than bime-

tallic sample prepared by simultaneous impregnation and the

monometallic catalysts on the OSRM reaction. Molecular

simulation HOMO and LUMO properties of the bimetallic

system prepared by successive impregnation with coreeshell

particles, confirm that these systems hadmore reactivity than

bimetallic system obtained by simultaneous impregnation.

This suggests that as the band gap of the bimetallic models

decreases, an electron transfer mechanism is favored at the

interface between the bimetallic structures and the support,

facilitating the redoxpropertiesof the catalysts, givingahigher

OSRM activity. In addition, the H2 selectivity was higher on

these bimetallic Cu/Ni/ZrO2 and Ni/Cu/ZrO2 catalysts. The

former catalyst exhibited excellent stability in OSRM reaction

and has great potential in fuel cell applications. These results

couldbeassociated to thepresenceof thebimetallicCueNiand

coreeshell Ni/Cu nanoparticles present on the catalysts, as

was evidenced by HREM-TEMeEDX and to the crystalline

anisotropy of the active phase that plays an important role in

themethanol conversion and selectivity. This finding suggests

that the OSRM reactionmay be a structureesensitive reaction.

Acknowledgments

Thanks to I.Q. Albina Gutierrez Martınez, Carlos Salinas

Molina and Jorge Perez for technical support and to the project

ININ-CA-711, ININ-CA-009, CONACYT CB-2008-01-104540 and

CONACYT J-48924 for financial support. Authors would like to

acknowledge Dra. Reyna Natividad Rangel and Dr. Carlos

Angeles for its valuable comments and suggestions on the

manuscript.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 9 0 1 8e9 0 2 79026

r e f e r e n c e s

[1] Iwasa N, Mayanagi T, Nomura W, Arai M, Takezawa N. Effectof Zn addition to supported Pd catalysts in the steamreforming of methanol. Appl Catal A Gen 2003;248:153.

[2] Ranganathan SE, Bej KS, Thompson LT. Methanol steamreforming over Pd/ZnO and Pd/CeO2 catalysts. Appl Catal AGen 2005;289:153e62.

[3] Perez-Hernandez R, Avendano AD, Rosas E, Rodrıguez-Lugo V. Hydrogen production by methanol steam reformingover Pd/ZrO2-TiO2 catalysts. Topic Catal 2011;54:572e8.

[4] Yao C-Z, Wang L-C, Liu Y-M, Wu G-S, Cao Y, Dai 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.[5] 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.

[6] Purnama H, Girgsdies F, Ressler T, Schattka JH, Caruso RA,Scomacker R, et al. Catal Lett 2004;94:61.

[7] Lindstrom B, Pettersson LJ. Hydrogen generation by steamreforming of methanol over copper-based catalysts for fuelcell applications. Int J Hydrogen Energy 2001;26:923e33.

[8] Pettersson LJ, Westerholm R. State of the art of multi-fuelreformer for fuel cell vehicles: problem identification andresearch needs. Int J Hydrogen Energy 2001;26(3):243e64.

[9] Ahmed S, Krumpelt M. Hydrogen from hydrocarbon fuels forfuel cells. Int J Hydrogen Energy 2001;26:291.

[10] 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;32:2888e94.

[11] Perez-Hernandez R, Longoria LC, Palacios J, Aguila MM,Rodrıguez V. Oxidative steam reforming of methanol forhydrogen production over Cu/CeO2-ZrO2 catalysts. EnergMater Mater Sci Eng Energ Syst 2008;3(3):152e7.

[12] Perez-Hernandez R, Mondragon-Galicia G, Mendoza-Anaya D, Palacios J, Angeles-Chavez C, Arenas-Alatorre J.Synthesis and characterization of bimetallic CueNi/ZrO2

nanocatalysts: H2 production by oxidative steam reformingof methanol. Int J Hydrogen Energy 2008;33:4569e76.

[13] Perez-Hernandez R, Gutierrez-Martınez A, Palacios J, Vega-Hernandez M, Rodrıguez-Lugo V. Hydrogen production byoxidative steam reforming of methanol over Ni/CeO2eZrO2

catalysts. Int J Hydrogen Energy 2011;36:6601e8.[14] Velu S, Suzuki K, Kapoor MP, Ohashim F, Osaki T. Selective

production of hydrogen for fuel cel via oxidative steamreforming of methanol over CuAnAl(Zr)-oxide catalysts. ApplCatal A Gen 2001;213:47e63.

[15] Velu S, Suzuki K, Okasaki M, Kapoor MP, Osaki T, Ohashi F.Oxidative steam reforming of methanol over CuZnAl(Zr)-oxide catalysts for the selective production oh hydrogen forfuel cell: catalyst characterization and performanceevaluation. J Catal 2000;194:373e84.

[16] Sun J, Qui X-P, Wu F, Zhu W-T. H2 from steam reforming ofethanol at low temperaure over Ni/Y2O3, Ni/La2O3 and Ni/Al2O3 catalysts for fuel cell application. Int J Hydrogen Energy2005;30:437e45.

[17] Yang Y, Ma J, Wu E. Production of hydrogen by steamreforming of ethanol over a Ni/ZnO catalyst. Int J HydrogenEnergy 2006;31:877e82.

[18] Biswas P, Kunzru D. Steam reforming of ethanol forproduction of hydrogen over Ni/CeO2eZrO2 catalyst: effect ofsupport and metal loading. Int J Hydrogen Energy 2007;32:969e80.

[19] Marino FJ, Cerrella EG, Duhalde S, Jobbagy M, Lombarde M.Hydrogen from steam reforming of ethanol. Characterizationand performance of copperenickel supported catalysts. Int JHydrogen Energy 1998;23:1095e101.

[20] 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;26:665e8.

[21] Huang T-J, Yu TC, Jhao S-Y. Weighting variation ofWater�Gas shift in steam reforming of methane oversupported Ni and Ni�Cu catalysts. Ind Eng Chem Res 2006;45:150.

[22] Perez-Hernandez R, Gutierrez-Martınez A, Mayoral A,Deepak FL, Fernandez-Garcıa ME, Mondragon-Galicia G, et al.Hydrogen production by steam reforming of methanol overa Ag/ZnO one dimensional catalyst. Adv Mater Res 2010;132:205e19.

[23] Perez-Hernandez R, Gutierrez-Wing C. Design of new Ag-Au(1-D)-CeO2 catalysts for hydrogen production by steamreforming of methanol. EuropaCat IX, Salamanca, Spain;2009:1e3.

[24] Perez-Hernandez R, Gutierrez-Martınez A, Gutierrez-Wing C.Hydrogen production by steam reforming of methanol overNew Ag-Au(1-D)-CeO2 catalyst. Mater Res Soc Symp Proc2010;127:1e4.

[25] Perez-Hernandez R, Mendoza-Anaya D, Fernandez ME,Gomez-Cortes A. Synthesis of mixed ZrO2-TiO2 oxides bysolegel: microstructural characterization and infraredspectroscopy studies of NOx. J Mol Catal A Chem 2008;281:200.

[26] Pfrommer BG, Cote M, Louie SG, Cohen ML. Relaxation ofcrystals with the quasy Newtonmethod. J Comput Phys 1997;131:233e40.

[27] Fernandez ME, Angeles-Chavez C, Mondragon-Galicia G,Rodriguez-Lugo V. TEM and molecular simulation studies onthe hydroxylapatite structure with Si and Mg impurities. JMat Sci Mater Med 2004;15:735e40.

[28] Fukui K. The role of frontier orbitals in chemical reactions.Nobel Lecture; 8 December 1981.

[29] Knell A, Barnicken P, Baiker A, Wokaun A. CO oxidation overAu/ZrO2 catalysts: activity, deactivation behavior, andreaction mechanism. J Catal 1992;137:306e21.

[30] Perez-Hernandez R, Gomez-Cortes A, Arenas-Alatorre J,Rojas S, Mariscal R, Fierro JLG, et al. SCR of NO by CH4 on Pt/ZrO2-TiO2 solegel catalysts. Catal Today 2005;107-108:149e56.

[31] Montoya JA, Romero-Pascual E, Gimon C, Angel PD,Monzon A. Methane reforming with CO2 over Ni/ZrO2-CeO2

catalysts prepared by solegel. Catal Today 2000;63:71e85.[32] Kirumakki SR, Shpeizer BG, Sagar GV, Chary KVR,

Clearfield A. Hydrogenation of Naphthalene over NiO/SiO2-Al2O3 catalysts: structure-activity correlation. J Catal 2006;242:319e31.

[33] Shan W, Luo M, Lin P, Shen W, Li C. Reduction property andcatalytic activity of Ce1�XNiXO2 mixed oxide catalysts for CH4

oxidation. Appl Catal A Gen 2003;246:1e9.[34] Vizcaıno AJ, Carrero A, Calles JA. Hydrogen production by

ethanol steam reforming over CueNi supported catalysts. IntJ Hydrogen Energy 2007;32:1450e61.

[35] 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.

[36] Breen JP, Ross JRH. Methanol reforming for fuel-cellapplications: development of zirconia-containing CueZneAlcatalysts. Catal Today 1999;51:521e33.

[37] Ratnasamy P, Srinivas D, Satyanarayana CVV,Manikandan P, Senthil-Kumaran R, Sachin M, et al. Influence

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 en e r g y 3 7 ( 2 0 1 2 ) 9 0 1 8e9 0 2 7 9027

of the support on the preferential oxidation of CO inhydrogen-rich steam reformates over the CuO-CeO2-ZrO2

system. J Catal 2004;221:455e65.[38] Harrison PG, Ball IK, Azelee W, Daniell W, Goldfarb F. Nature

and surface redox properties of copper(ii)-promotedcerium(IV) oxide CO oxidation catalysts. Chem Mater 2000;12:3715e25.

[39] Oguchia H, Nishiguchia T, Matsumotoa T, Kanaia H, Utania K,Matsumurab Y, et al. Steam reforming of methanol over Cu/CeO2/ZrO2 catalysts. Appl Catal A Gen 2005;281:69e73.

[40] Turco M, Bagnasco G, Costantino U, Marmottini F,Montanari T, Ramis G, et al. Production of hydrogen fromoxidative steam reforming of methanol II. Catalytic activityand reaction mechanism on Cu/ZnO/Al2O3 hydrotalcite-derived catalysts. J Catal 2004;228:56.

[41] Yang W, Parr RG. Hardness, softness, and the fukui functionin the electronic theory of metals and catalysis. Proc NatiAcad Sci USA 1985;82:6723e6.

[42] Pepley BA, Amphlett JC, Korns LM, Mann RF. Methanol-Steam reforming on Cu/ZnO/Al2O3. Part 1 reaction networkAppl Catal A Gen 1999;179:21e9.

[43] Bracey CL, Ellis PR, Hutchings GJ. Application of copperegoldalloys in catalysis: current status and future perspectives.Chem Soc Rev 2009;38:2231e43.

[44] Rodrıguez-Lopez JL, Montejano-Carrizales JM, Jose-Yacaman M. Molecular dynamics study of bimetallicnanoparticles: the case of AuxCuy alloy clusters. Appl SurfSci 2003;219:56e63.

[45] Shu Y, Murillo LE, Bosco JP, Huang W, Frenkel AI, Chen JG.The effect of impregnation sequence on the hydrogenationactivity and selectivity of supported Pt/Ni bimetalliccatalysts. Appl Catal A Gen; 2008:169e79.

[46] Strasser P, Koh S, Anniyev T, Greeley J, More K, Yu C, et al.Lattice-strain control of the activity in dealloyed core-shellfuel cell catalysts. Nat Chem 2010;2:454e60.

[47] Zhou Y-H, Lv P-H, Wang G-C. DFT studies of methanoldecomposition on Ni(1 0 0) surface: compared with Ni(1 1 1)surface. J Mol Catal A Chem 2006;258:203e15.

[48] Esposito S, Turco M, Bagnasco G, Cammarano C, Pernice P,Aronne A. Highly dispersed solegel synthesized CueZrO2

materials as catalysts for oxidative steam reforming ofmethanol. Appl Catal A Gen 2010;372:48e57.