ethanol steam reforming and water gas shift over co-zno catalytic

7/30/2019 Ethanol Steam Reforming and Water Gas Shift Over Co-ZnO Catalytic

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Ethanol steam reforming and water gas shift over Co/ZnO

catalytic honeycombs doped with Fe, Ni, Cu, Cr and Na

Albert Casanovas a, Maria Roig a, Carla de Leitenburg b, Alessandro Trovarelli b,Jordi Llorca a,c,*a Institut de Tecniques Energetiques, Universitat Politecnica de Catalunya, Diagonal 647, Ed. ETSEIB, 08028 Barcelona, SpainbDipartimento di Scienze e Tecnologie Chimiche, Universita di Udine, via del Cotonificio 108, 33100 Udine, ItalycCentre for Research in NanoEngineering, Universitat Politecnica de Catalunya, Pasqual i Vila 1-15, 08028 Barcelona, Spain

a r t i c l e i n f o

Article history:

Received 17 February 2010

Received in revised form

7 May 2010

Accepted 24 May 2010

Available online 25 June 2010

Keywords:

Ethanol steam reforming

Water gas shift

Hydrogen

Catalytic honeycomb

Cobalt catalyst

a b s t r a c t

The effect of Fe, Ni, Cu, Cr, and Na (1%) addition over ZnO-supported Co (10%) honeycomb

catalysts in the steam reforming of ethanol (ESR) and water gas shift reaction (WGS) for the

production of hydrogen was studied. HRTEM and EEL spectroscopy revealed the formation

of metal alloys between Co and Fe, Ni, Cu, and Cr. Catalysts promoted with Fe and Cr

performed better in the ESR, and the sample promoted with Fe showed high activity for

WGS at low temperature. As deduced from TPR and oxidation pulse experiments, alloy

particles in catalysts promoted with Fe and Cr exhibited a rapid and higher degree of redox

exchange between reduced and oxidized Co, which may explain the better catalytic

performance.

2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

1. Introduction

The search for an active and selective catalyst for the gener-

ation of hydrogen through ethanol steam reforming (equation

(1)) at low temperature constitutes an active research area

because ethanol is a renewable fuel with low toxicity and high

energy density that is also easy to handle and distribute [1e3].

Moreover, a bioethanol-to-H2 system has the advantage of

being CO2 neutral.

C2H5OH 3H2O/6H2 2CO2 (1)

There arenumerous studies that demonstrate the feasibility

of generatinghydrogen from ethanolewatermixtures through

catalytic steam reforming, either with powder catalysts [4,5]

and over catalytic walls [6e10]. Among all catalysts tested so

far, those based on cobalt exhibit the highest activity and

selectivity towards hydrogen at low temperature [11e27].

Concerning the support, acidic supports should be avoided

since they favor massive carbon deposition through ethanol

dehydration into ethylene, whereas supports with basic and

redox characteristics are preferred, such as ZnO [28]. Thus,

much work has been carried out over the Co/ZnO system. It

has been demonstrated by in situ magnetic studies coupled to

reaction tests and by in situ diffuse reflectance infrared spec-

troscopy under real operation that the simultaneous presence

of metallic cobalt and cobalt oxide is required for the progress

of the reaction [29e31]. Two steps of the reaction have been

identified. First, ethanol dehydrogenates into acetaldehyde

* Corresponding author. Institut de Tecniques Energetiques, Universitat Politecnica de Catalunya, Av. Diagonal 647, Ed. ETSEIB, 08028Barcelona, Spain. Tel.: 34 93 401 17 08; fax: 34 93 401 71 49.

E-mail address: [email protected] (J. Llorca).

A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / h e

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 5 ( 2 0 1 0 ) 7 6 9 0 e7 6 9 8

0360-3199/$ e see front matter 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

doi:10.1016/j.ijhydene.2010.05.099
mailto:[email protected]://www.elsevier.com/locate/hehttp://dx.doi.org/10.1016/j.ijhydene.2010.05.099http://dx.doi.org/10.1016/j.ijhydene.2010.05.099http://dx.doi.org/10.1016/j.ijhydene.2010.05.099http://dx.doi.org/10.1016/j.ijhydene.2010.05.099http://dx.doi.org/10.1016/j.ijhydene.2010.05.099http://dx.doi.org/10.1016/j.ijhydene.2010.05.099http://www.elsevier.com/locate/hemailto:[email protected]


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and hydrogen (equation (2)) over cobalt oxide (Co3O4).

Hydrogen partly reduces the surface of cobalt particles into

metallic cobalt and then, the second step, the reforming of

acetaldehyde into the final products H2 and CO2, takes place

(equation (3)) with the participation of the water gas shift

reaction (equation (4)).

C2H5OH/

CH3CHOH2 (2)

CH3CHO 3H2O/5H2 2CO2 (3)

H2O CO4H2 CO2 (4)

C2H5OH/CH4 COH2 (5)

In order to favor the redox exchange between metallic

cobalt and cobalt oxide under reaction conditions, several

cobalt alloy formulations have been attempted. Alloying

cobalt with the more electronegative first-row transition

metals Ni and Cu did not improve the performance for the

ethanol steam reforming reaction [32]. Also, alloying cobalt

with noble metals favors the formation of methane through

ethanol decomposition at low temperature (equation (5)). In

contrast, alloying cobalt with the less electronegative first-row

transition metals Fe and Mn showed to be positive for the

steam reforming of ethanol in terms of both catalytic activity

and selectivity towards hydrogen [33e35]. In this work, we

extend the study of the steam reforming of ethanol (ESR) over

ZnO-supported, Co-based honeycomb catalysts by evaluating

the effect of Fe, Ni, Cu, Cr, and Na addition. We also report the

performance of these catalysts for the water gas shift reaction

(WGS), which participates in the reaction scheme (4). It is well

known that honeycomb structures are preferred for the

generation of hydrogen in industrial environments and for

mobile applications, such as fuel cell powered vehicles

equipped with internal reformers [8e10]. They are robust,

easy to scale up and replace, and offer homogeneous flow

distribution patterns with low pressure drop.

2. Experimental method

2.1. Preparation of powder catalysts and honeycombs

Co/ZnO catalysts (10% wt. Co) doped with Fe,Ni, Cu, Cr, and Na

(1% wt.) were prepared by incipient wetness co-impregnation

from nitrate aqueous solutions over ZnO (Kadox 15). Theresulting solids were dried at 383 K overnight and calcined in

air at 673 K for 6 h. Thesecatalystswerelabeled as Co(Fe)/ZnO,

Co(Ni)/ZnO, Co(Cu)/ZnO, Co(Cr)/ZnO, and Co(Na)/ZnO. For

comparative purposes, a monometallic cobalt catalyst sup-

ported on ZnO, Co/ZnO, was prepared in a similar way. For the

preparation of honeycomb catalysts, 400 cpsi (cells per square

inch) cordierite monolith cylinders with a diameter of 2 cm

and a lengthof 2 cm were used.They were obtained by cutting

larger monolith pieces with a diamond saw. Honeycomb

catalysts were prepared by the washcoating method from

vigorously agitated suspensions of powdered catalysts in de-

ionized water (w5% w/w). After each immersion, honeycombs

were dried at 373 K under continuous rotation and calcined at

673 K. This procedure was repeated several times in order to

obtain the desired weight gain (10e12% w/w).

2.2. Characterization

Mechanical stability of the catalyst coatings in honeycomb

samples was evaluated by direct exposure to mechanical

vibration. The vibration frequency was raised progressivelyfrom 20 to 50 Hz at a fixed acceleration value of 2 G, and at

50 Hz the acceleration was progressively increased from 2 to

10 G. Weight loss was monitored after 30 min at each

frequency and acceleration, and after 3 h under the most

severe vibration conditions (50 Hz, 10 G). G levels were

controlled directly on the vibration test board with a Bruel &

Kjaer 4370 accelerometer. Scanning electron microscopy was

accomplished using a JEOL JSM 6400 instrument at an accel-

eration voltage of 20 kV. X-ray diffraction profiles (XRD) were

collected at a step width of 0.02 degreesand by counting 10 s at

each step with a Siemens D-500 instrument equipped with

a Cu target and a graphite monochromator. High-resolution

transmission electron microscopy (HRTEM) was conducted at200kV with a JEOL JEM 2010F microscope equipped with a field

emission gun and an EELS detector. Samples were dispersed

in alcohol and deposited on grids with holey carbon films.

Temperature programmed reduction (TPR) was carried out

with a Micromeritics AutoChem II 2920 instrument using

a H2/Ar mixture (5% H2) at 10 K min1 and a TCD detector.

Oxidation experiments were carried out at 723 K with 30

consecutive 0.05 mL oxygen pulses (1 pulse/min). Surface area

measurements (BET) were performed with a Micromeritics

TriStar 3000 apparatus. Chemical composition was obtained

by optical emission spectroscopy with inductively-coupled

plasma (ICP-OES, PerkineElmer Optima apparatus).

2.3. Catalytic tests

Ethanol steam reforming was carried out over honeycomb

catalysts at atmospheric pressure and 473e773 K in a tubular

reactor at a total flow of 80 mL min1. C2H5OH(0.33 mL min1)

and H2O were fed separately at a C2H5OH:H2O molar ratio of

1:6 (S/C 3) and the mixture was balanced with He. The

effluent of the reactor was monitored on line with an MKS

Cirrus mass spectrometer or an Agilent micro-GC. Samples

were first pretreated inside the reactor with a H2:N2 mixture

(50 mL min1, 10% H2) at 723 K for 4 h, the temperature was

lowered to 473 K under N2, and then the reaction mixture was

introduced at 473 K. Monoliths operated under isothermalconditions as deduced from temperature monitoring inside

their channels, located either in contact with the reactor wall

or at the center of the reactor. Unaltered conversion level was

measured at various flowrates at reactor inlet while keeping

constant the ratio between the weight of catalyst and the

molar flow rate of ethanol at reactor inlet, thus ensuring the

absence of external mass transfer limitations. The water gas

shift reaction was carried out at atmospheric pressure in the

473e673 K temperature range using a CO:H2:H2O:N2 1:2:6:14

molar mixture (total flow 50 mL min1). Water was provided

with a syringe pump and vaporized before entering the reac-

tant stream. Analysis of products was performed with a Var-

ian micro-GC.

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 5 ( 2 0 1 0 ) 7 6 9 0e7 6 9 8 7691
http://dx.doi.org/10.1016/j.ijhydene.2010.05.099http://dx.doi.org/10.1016/j.ijhydene.2010.05.099http://dx.doi.org/10.1016/j.ijhydene.2010.05.099http://dx.doi.org/10.1016/j.ijhydene.2010.05.099


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3. Results and discussion

3.1. Redox and structural characterization of promoted

Co/ZnO catalysts

Table 1 compiles the catalysts prepared along with their

surface area (BET method) and chemical composition. Thesurface area values recorded for all samples were similar and

about ca. 10e12 m2 g1. In order to get insight into the redox

characteristics of the cobalt catalysts promoted with different

metals, detailed temperature programmed reduction (TPR)

and oxygen pulse experiments were carried out to study the

redox exchange between oxidized and reduced cobalt, which

has been demonstrated to be the clue for the production of

hydrogen by ethanol steam reforming over Co-based systems

[29e35]. Fig. 1 shows the TPR profiles of all samples after

oxidation at 673 K. All of them exhibit two main hydrogen

consumption peaks, which correspond to the well known

two-step transformation of cobalt spinel into metallic cobalt:

Co3O4/

CoO/

Co [8]. However, upon addition of only1% w/w promoter, the TPR profiles for the different promoted

catalysts differ significantly. For the bare Co/ZnO sample

(Fig. 1a), the two peaks are centered at about 560 and 690 K,

whereas for the promoted samples the first hydrogen uptake

(Co3O4 / CoO) occurs clearly at a lower temperature, ca.

520e540 K (Fig. 1bef). In contrast, the temperature of the

second hydrogen uptake and the relative intensity between

the two hydrogen consumption peaks vary considerably

among the different samples. The Co(Cr)/ZnO and Co(Na)/ZnO

samples exhibit a CoO/ Co transformation similar to that of

Co/ZnO, both in temperature and relative intensity, whereas

forthe Co(Ni)/ZnO catalyst the amount of hydrogen consumed

in the second peak is clearly larger with respect to the firsthydrogen uptake. On the other hand, the position of the

second hydrogen consumption peak is shifted towards

a higher reduction temperature in the Co(Fe)/ZnO catalyst and

towards a muchlower temperature in the Co(Cu)/ZnO sample.

In this case, the area of the second hydrogen uptake is rather

small compared to the other promoted samples. Finally, an

additional hydrogen uptake at low temperature, ca. 500 K, is

particularly observed in the sample promoted with Cu

(Fig. 1d). It is concluded that the reduction behavior of the

promoted samples does not follow a clear trend in electron

donation taking into account the electron affinity of the

promoters, and the variations in the TPR profiles may be due

to more complex effects, such as alloying.

In order to get insight into the amount of cobalt that can

reversibly participate in a redox exchange, several alternate

TPR and oxygen pulse experiments were carried out over

samples Co/ZnO, Co(Fe)/ZnO and Co(Cr)/ZnO. Three TPR

profiles and two oxidation experiments using oxygen pulses

(OP) at 723 K were alternated: TPR1/ OP1/ TPR2/ OP2/

TPR3. The amount of oxygen uptake on a metal basis recordedover the Co(Fe)/ZnO and Co(Cr)/ZnO samples in OP1 was

significantly higher than that of sample Co/ZnO. Taking into

account themetalloadingof thedifferent samples (Table1),the

extent of reoxidation for catalysts Co(Fe)/ZnO and Co(Cr)/ZnO

was about 90 and 85%, respectively, whereas for the Co/ZnO

sample the degree of reoxidation was much lower, about 70%.

In addition, the dynamics of the oxygen uptake differed

considerably between Co/ZnO and the samples promoted with

Fe and Cr. In the promoted samples, the transition between

complete oxygen uptake andnon-oxygen uptake wasfast (3e4

pulses), whereas the transition in the Co/ZnO catalyst was

significantly slower (9e10 pulses). It can be concluded that the

redox dynamics between oxidized and reduced cobalt is clearly

Table 1 e Chemical analysis, surface area, and meancobalt particle size of catalysts determined by X-raydiffraction and transmission electron microscopy.

Catalyst w/w Co(%)

w/w M(%)

BET(m2 g1)

dxRD(nm)

dTEM(nm)

Co/ZnO 9.8 e 11.3 17.1 15.6

Co(Fe)/ZnO 10.1 0.98 10.9 16.2 14.1

Co(Ni)/ZnO 9.7 1.05 12.2 19.1 17.4

Co(Cu)/ZnO 10.2 1.11 12.8 19.8 18.1

Co(Cr)/ZnO 9.9 0.97 11.4 18.3 16.7

Co(Na)/ZnO 9.4 0.89 11.8 18.5 16.2

Fig. 1 e Temperature programmed reduction profiles of

catalysts Co/ZnO (a), Co(Fe)/ZnO (b), Co(Ni)/ZnO (c), Co(Cu)/

ZnO (d), Co(Cr)/ZnO (e), and Co(Na)/ZnO (f).



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enhanced in the presence of these promoters. The TPR profiles

recorded over catalysts Co/ZnO and Co(Fe)/ZnO before and

after each oxygen pulse experiment are reported in Fig. 2. The

TPR profiles recorded afterthe oxygen pulseexperiments, TPR2

andTPR3 (b-c),differedfrom TPR1 (a). In both samples, the area

of the second hydrogen consumption peak increased consid-

erablywith respect to thelow temperature hydrogen uptake. In

addition, in the Co(Fe)/ZnO sample, extra hydrogen uptakesignals appeared at ca. 570 and 710 K after reoxidation, sug-

gesting the formation of new active sites upon redox cycling.

Similar results were obtained with the Co(Cr)/ZnO sample.

The structure of all catalysts prepared in this work have

been characterized in detail. After calcination at 673 K, all

catalysts showed by X-ray diffraction (XRD) the characteristic

peaks of the Co3O4 spinel phase. In addition to ZnO peaks, no

other signals appeared in the diffraction patterns due to the

low promoter loading (1% w/w). In addition, no differences

were observed in the position and shape of the spinel

diffraction peaks. After reduction at 673 K, peaks due to

metallic cobalt(fcc) and/orcobalt-metal alloys appeared in the

XRD patterns of all catalysts and no cobalt oxide phases(Co3O4, CoO) were observed. Table 1 compiles the mean

particle size of cobalt/cobalt alloy particles as deduced from

the Scherrer equation. Particle size of about 16e20 nm were

calculated in all cases, indicating that the incorporation of

promoter had no significant effect on particle size. Since XRD

did not provide information about the phases where the

promoters were present, a detailed microstructural study was

carried out on the reduced samples by combined high-reso-

lution transmission electron microscopy and energy electron-

loss spectroscopy (HRTEM-EELS) in order to determine if

cobalt and promoter entities were in contact, or occurred as

separate phases. This is important for elucidating the role of

promoters in the catalytic behavior of these catalysts withrespect to Co/ZnO in ESR and WGS reactions. More than 150

metal particles covering various parts of the samples were

used forsize distribution measurements and more than 40 EEL

spectra were recorded for each sample.

Fig. 3 shows representative bright field and lattice fringe

TEM images of all samples along with EEL spectra recorded

over individual metal particles. As a general rule, well

dispersed metal particles over ZnO support were present in

all catalysts, with similar particle size distribution centered at

about 14e18 nm, which is well in accordance with values

calculated from XRD (Table 1). The dispersion of cobalt

particles over the support in the Co/ZnO catalyst is wellexemplified in Fig. 3a. The insets show an HRTEM image and

an EEL spectrum recorded over one individual cobalt particle.

The particle shows lattice fringes according to a single

metallic Co crystallite oriented along the [012] direction. As

expected, the EEL spectrum showed peaks characteristic of

cobalt at 769.7 and 816.4 eV corresponding to Co L3 edge.

A similar analysis performed over Co/ZnO from a different

preparation batch showed similar results, thus indicating

that the preparation method used in this work is fully

reproducible. Fig. 3b corresponds to the Co(Fe)/ZnO sample.

Again, a good dispersion of metal particles is encountered.

The inset in Fig. 3b shows an HRTEM image of a single particle

oriented along the [001] crystallographic direction. An accu-rate analysis of lattice fringes in individual metal particles did

not reveal any significant modification of the cobalt fcc

structure. However, it should be taken into account that the

lattice parameter of metallic cobalt is not expected to change

significantly with the addition of 1% w/w iron, and that such

modification would be under the accuracy of the HRTEM

images in such small particles. In contrast, EELS showed to be

very useful for determining the occurrence of cobalt alloying

with iron. In all single particles analyzed, both Co and Fe

peaks (at 683.8 eV) were identified in the EEL spectra (see

inset), with an approximate Co:Fe atomic ratio of 9:1, which

corresponds well with the cobalt and iron content of the

sample. Therefore, the Co(Fe)/ZnO sample is constituted byCoeFe alloy particles well dispersed over ZnO. Similarly, the

EEL spectra recorded over individual particles in samples Co

(Ni)/ZnO, Co(Cu)/ZnO, and Co(Cr)/ZnO (Fig. 3cee) showed the

simultaneous occurrence of Co and promoter peaks with an

Fig. 2 e Temperature programmed reduction profiles of catalysts Co/ZnO and Co(Fe)/ZnO recorded over the fresh samples (a),

and after consecutive oxygen pulse experiments (b,c).



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approximate Co:M atomic ratio of 9:1, indicating that alloying

between Co and the promoter occurred in these samples, too.

As discussed above, lattice fringe analysis could not distin-

guish between pure Co particles and those alloyed with the

promoters, but served to unambiguously identify the cobalt-

based particles. The alloy particles were sometimes covered

by a layer of Co3O4 (Fig. 3ced), with distinctive lattice spacing

at 4.67 and 2.86 A corresponding to (111) and (220) planes,

respectively. Finally, the sample promoted with sodium,

Co(Na)/ZnO (Fig. 3f), was virtually identical to the non-

promoted Co/ZnO catalyst, indicating that, in this case,

sodium is likely atomically dispersed and not incorporated

into the cobalt structure. No signals corresponding to the

NaeK edge at 1050e1150 eV appeared in the EEL spectra. From

the microstructural characterization results it is concluded

that the different redox behavior exhibited by the samples is

likely related to the formation of cobalt alloys and not to

a particle size effect.

Fig. 3e

Transmission electron microscopy images and EEL spectra corresponding to catalysts Co/ZnO (a), Co(Fe)/ZnO (b),Co(Ni)/ZnO (c), Co(Cu)/ZnO (d), Co(Cr)/ZnO (e), and Co(Na)/ZnO (f).



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3.2. Catalytic tests over honeycomb catalysts

Catalytic honeycombs were imaged by scanning electron

microscopy (SEM) in frontal and transverse views as well as by

confocal imaging and a good catalyst coating homogeneity

was observed in all cases. The mean catalytic layer thickness

was about 150 mm. Mechanical stability of the catalytically

active phase in honeycomb catalysts is a critical issue forpractical application purposes because coating loss and

banking up should be completely avoided. The weight loss of

the catalytic coatings in all honeycombs was less than 5%

after 5 h of exposure to mechanical vibration (up to 50 Hz and

10 G), which means an excellent adherence.

Catalytic honeycombs were tested for the ethanol steam

reforming reaction (ESR) with a steam to carbonratio of S/C 3

and W/FEtOH 42 min gcat mol1 (volume hourly space

velocity, VHSV 2500 h1). Fig. 4 shows the evolution of

ethanol conversion as well as the distribution of products at

different reaction temperatures for all samples. For the sake of

clarity, only the main products H2, CO2, CO, CH4, and C2H4O

(acetaldehyde) have been plotted. Other products identifiedwere ethylene and ethane in trace amounts ( Co(Na)/ZnOw Co(Ni)/ZnO > Co/ZnO > Co(Cu)/ZnO.It is observed that the incorporation of Cu promoter in the

catalyst results in a strong enhancement of ethanol dehy-

drogenation, but the capability for the ulterior reforming of

acetaldehyde with steam is inhibited. On the other hand,

catalysts promoted with Cr, Fe, and Na are more active and

Fig. 4 e Catalytic performance of honeycombs Co/ZnO (a), Co(Fe)/ZnO (b), Co(Ni)/ZnO (c), Co(Cu)/ZnO (d), Co(Cr)/ZnO (e), and

Co(Na)/ZnO (f) in the ethanol steam reforming. S/C[ 3, 0.33 mL C2H5OH minL1, VHSV [ 2500 hL1. Ethanol conversionC.

Selectivity to H2B, CO2 6, CO>, CH4 *, and acetaldehyde ,.



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selective towards the reforming products, H2 and CO2, with

respect to the bare Co/ZnO catalytic honeycomb. Promotion

by Ni results in larger amounts of methane among the reac-

tion products, specially at high temperature. From the TPR

and OP results discussed in Section 3.1, it appears that cata-

lysts that perform better in ESR are also those that exhibit

a higher amount of cobalt which is able to participate in redox

exchange mechanisms. This correlation was first proposed in[35] for Co/ZnO catalysts promoted with Mn.

Figure 5 shows the results attained at 673 and 773 K in

a two-dimensional plot, where the amount of hydrogen

obtained on a molar basis with respect to ethanol in the

reactor inlet is plotted against the amount of carbon dioxide.

From the stoichiometry of the steam reforming of ethanol

(equation (1)), the expected molar ratio H2/CO2 is 3. This is

indicated in the graph as a dashed line (the reforming line).

Other competitive routes for ethanol transformation (ethanol

decomposition, dehydration, etc.) result in deviations from

the reforming line, making this type of graph very useful,

since the position of the different catalysts serve as a measure

of both their activity and selectivity to the reforming products

H2 and CO2.

At low temperature (673 K, Fig. 5a), the honeycomb cata-

lyst containing only ZnO-supported cobalt, Co/ZnO, was

active for ethanol transformation, but it plots to the right

side of the reforming line, thus indicating that ethanolreforming is accompanied by ethanol decomposition, origi-

nating H2/CO2 < 3. At this temperature, honeycomb catalyst

Co(Ni)/ZnO plots even worse in the graph, according to

a larger ethanol decomposition to methane. In contrast,

sample Co(Cu)/ZnO exhibits a similar hydrogen yield but

a much lower CO2/C2H5OH ratio. It plots to the left side of the

reforming line (H2/CO2 > 3), which means a higher dehy-

drogenation activity with respect to the other catalytic

honeycombs. Honeycomb promoted with Na and particularly

honeycombs promoted with Cr and Fe progressively show

higher hydrogen yields and plot closer to the reforming line,

indicating that these samples are more active and selective

for ESR with respect to the Co/ZnO catalytic honeycomb. Asexpected from thermodynamics (ESR is an endothermic

process), at high temperature (773 K, Fig. 5b) all samples

exhibit a better performance towards the reforming prod-

ucts. However, and in spite that all samples cluster around

the reforming line at high H2/C2H5OH and CO2/C2H5OH

values, catalytic honeycombs Co(Fe)/ZnO and Co(Cr)/ZnO

still perform better than the non-promoted Co/ZnO sample.

Over Co(Fe)/ZnO and Co(Cr)/ZnO catalytic honeycombs,

complete ethanol transformation was attained at ca. 673 K

and acetaldehyde transformed almost completely at 723 K

(0.2% C2H4O for Co(Fe)/ZnO and 2.9% C2H4O for Co(Cr)/ZnO on

a dry basis). At this temperature, the CO2/CO molar ratio was

5.3 and 3.8 for Co(Fe)/ZnO and Co(Cr)/ZnO, respectively,whereas in both samples CO2/CH4 molar ratios greater than

10 were recorded.

Finally, catalysts were tested in the water gas shift reaction

(WGS, equation (4)) under conditions simulating the outlet of

an ethanol steam reformer (CO:H2:H2O 1:2:6). Table 2 shows

the catalytic activity of all samples in terms of CO conversion

temperature, both for CO conversion values of 25% (T25) and

50% (T50). As expected from the ESR results reported above, no

methane was formed in the WGS catalytic tests. The values of

T50 for the different samples did not substantially differ, and

temperatures in the range 540e550 K were recorded. In

contrast, catalyst Co(Fe)/ZnO showed higher activity for WGS

Fig. 5 e Yields of H2 and CO2 in the ethanol steam

reforming at 673 K (a) and 773 K (b). S/C[ 3, 0.33 mL

C2H5OH minL1, VHSV [ 2500 hL1.

Table 2 e Catalytic performance of catalysts in the watergas shift reaction. CO:H2:H2O:N2[ 1:2:6:14, GHSV[15,000 hL1.

Catalyst T25 (K) T50 (K)

Co/ZnO 526 542

Co(Fe)/ZnO 512 549

Co(Ni)/ZnO 526 542

Co(Cu)/ZnO 534 547

Co(Cr)/ZnO 530 545

Co(Na)/ZnO 523 540



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at low temperature, with T25 512 K vs. 526 K for Co/ZnO,

suggesting that the low amount of CO obtained under ESR

conditions over the Co(Fe)/ZnO catalytic honeycomb at low

temperature was related to its WGS activity.

4. Conclusions

Co/ZnO honeycomb catalysts promoted with Fe, Ni, Cu, Cr,

and Na containing 10% w/w Co and M/Co w 0.1 are effective

for hydrogen production at low temperature from ethanol

steam reforming and water gas shift reaction. The presence of

Fe facilitates the redox exchange between reduced and

oxidized Co, which has a clear positive effect on both reac-

tions. Also, incorporation of Cr and Na promoters results in

a better catalytic performance towards ethanol steam

reforming. In contrast, a negative effect in encountered with

honeycomb samples doped with Ni andCu, since the presence

of Ni favors ethanol decomposition at lowtemperature and Cu

promotes the formation of acetaldehyde. Alloying of Co withFe, Ni, Cu, and Cr has been evidenced by high-resolution TEM

and electron energy loss spectroscopy.

Acknowledgements

This work was supported by grant CTQ2009-12520. A.T. and

C.d.L. thanks regione Friuli Venezia Giulia and MIUR for

financial support. J.L. is grateful to ICREA Academia Program.

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ethanol steam reforming and water gas shift over co-zno catalytic

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