Fuel 104 (2013) 711–716

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Fuel

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CuZn/ZrO2 catalytic honeycombs for dimethyl ether steam reformingand autothermal reforming

Cristian Ledesma, Jordi Llorca ⇑Institut de Tècniques Energètiques and Centre de Recerca en Nanoenginyeria, Universitat Politècnica de Catalunya, Av. Diagonal 647, Ed. ETSEIB, 08028 Barcelona, Spain

h i g h l i g h t s

" CuZn/ZrO2 catalytic monoliths perform excellent for DME steam reforming." The best selectivity to H2 and CO2 is exhibited by a catalyst with a Cu:Zn molar ratio of 1:10." SEM and XPS show that better Cu dispersion is attained by increasing Zn/Cu ratio." CuZn/ZrO2 catalysts deactivate under DME autothermal reforming due to the prevalence of methoxy species.

a r t i c l e i n f o

Article history:Received 1 January 2012Received in revised form 15 April 2012Accepted 28 June 2012Available online 13 July 2012

Keywords:Dimethyl etherCopper–zinc catalystCatalytic monolithSteam reformingAutothermal reforming

0016-2361/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.fuel.2012.06.116

⇑ Corresponding author. Address: Institut de TècniqPolitècnica de Catalunya, Av. Diagonal 647, Ed. ETSEIB+34 93 401 17 08; fax: +34 93 401 71 49.

E-mail address: jordi.llorca@upc.edu (J. Llorca).

a b s t r a c t

Dimethyl ether (DME) steam reforming simulating practical applications was tested over catalytichoneycombs coated with ZrO2 and loaded with different amounts of Cu and Zn. The best catalytic perfor-mance in terms of activity and yield towards the reforming products, H2 and CO2, was exhibited by CuZn/ZrO2 with a Cu:Zn molar ratio of 1:10, which also showed high stability. SEM and XPS characterizationshowed that this catalyst contains very well-dispersed copper particles in contact with ZnO. Catalyticmonoliths were also tested in the DME autothermal reforming reaction, but a strong deactivation wasobserved, probably due to the prevalence of methoxy species that lead to the formation of methaneand carbon residues, as evidenced by in situ FTIR and XPS experiments.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

In recent years, fuel cells are considered a promising alternativeas energy devices since they can convert the chemical energy ofhydrogen to electrical energy with higher efficiency and lowerpollutant emission compared to conventional processes [1–4].Typically, an electrochemical reaction of a fuel at an anode (gener-ally H2) and of and oxidant at a cathode (generally O2) generateselectricity in a fuel cell, where only water is produced onsite as asingle chemical product. Nowadays, hydrogen is mainly producedfrom fossil fuels, but it can also be produced from renewablesources in order to develop a more sustainable energy model, suchas renewable bio-derived fuels [5,6]. Steam reforming (SR) is con-sidered an attractive method to produce hydrogen due to its highhydrogen yield and lower rate of side reactions when comparedto partial oxidation processes [7,8]. Dimethyl ether (DME) has been

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ues Energètiques, Universitat, 08028 Barcelona, Spain. Tel.:

recently recognized as an alternative clean fuel for multi purposesdue to its high hydrogen to carbon ratio and, therefore, high energydensity. DME is easily liquefied at low pressure and it is corrosion-safe, easy to handle, store and transport. Therefore, it fulfils therequirements for a good hydrogen carrier. In addition, DME has alow reforming temperature, similar to methanol, but DME is pre-ferred because of its non-toxicity [9–12]. Finally, a single-step pro-duction process from the product of the gasification of biomass(H2/CO) to DME has recently been developed [13–16], so the directproduction of DME from syngas is economically profitable.

The steam reforming of DME (Eq. (1)) consists of two consecu-tive, moderately endothermic reactions: DME hydrolysis to meth-anol (Eq. (2)) and subsequent methanol steam reforming tohydrogen and carbon dioxide (Eq. (3)) [17]. The overall reactionyields 6 mol H2 per mol DME, and half of H2 comes from water.However, other side reactions usually occur, such as the watergas shift reaction (Eq. (4)), DME decomposition (Eq. (5)) and COor CO2 methanation (Eqs. (6) and (7)).

ðCH3Þ2Oþ 3H2O�2CO2 þ 6H2 ð1Þ

Table 1Catalytic monoliths prepared in this work. Chemical composition referred as weightpercent with respect to monolith weight.

Catalyst ZrO2 (%) CuO (%) ZnO (%)

Cu(1)Zn(1)/ZrO2 10.6 4.0 5.2Cu(1)Zn(1)b/ZrO2 10.4 2.1 2.5Cu(2)Zn(1)/ZrO2 11.7 7.1 3.7Cu(1)Zn(2)/ZrO2 10.4 3.1 6.3Cu(1)Zn(10)/ZrO2 10.4 0.8 8.7

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ðCH3Þ2OþH2O�2CH3OH ð2Þ

CH3OHþH2O�CO2 þ 3H2 ð3Þ

COþH2O�CO2 þH2 ð4Þ

ðCH3Þ2O�CH4 þ COþH2 ð5Þ

COþ 3H2�CH4 þH2O ð6Þ

CO2 þ 4H2�CH4 þ 2H2O ð7Þ

Generally, DME hydrolysis is catalyzed over solid-acid catalystssuch as zeolites, alumina and various inorganic oxides while ametallic function (Cu-, Zn-, Pt- or Pd-based) is needed for methanolsteam reforming. Thus, bifunctional catalysts consisting of bothacidic and metallic functions are required for accomplishing thesteam reforming of DME. Several research groups have studiedDME SR processes employing a number of Cu-based catalyst sys-tems, such as copper ferrite spinels combined with various acidcatalysts [18–20], Al2O3–Cu/SiO2 [21], H-mordenite-Cu/CeO2 [22],WO3/ZrO2–Cu/CeO2 [22,23] or Cu/GaxAl10�xO15 [24]. Other metalshave been studied as well, such as palladium, but there are onlya few examples and usually they are compared to other noble met-als such as platinum or rhodium [21,25]. We have recentlyreported the use of catalytic monoliths coated with Cu, Zn and/orPd over several inorganic oxides, such as Al2O3, CeO2, ZrO2, Ce0.5

Zr0.5O2, SnO2, MnO2, WO3 and WO3–ZrO2 for the DME steamreforming reaction under diluted conditions [26–28]. The catalyticmonoliths coated with ZrO2 were also studied in the DME steamreforming reaction using pure mixtures (DME and H2O mixturesnot diluted in inert gas) since they showed the best performanceunder diluted conditions [26]. The catalytic monolith coated withCuZn/ZrO2 showed a very good stability and selectivity towardsthe reforming products H2 and CO2 at 823 K under a pure DME-water mixture with S/C = 3 and VHSV = 450 h�1 [28] (VHSV refersto volume hourly space velocity on a honeycomb volume basis).This work extends the study of the catalytic monoliths coated withCuZn/ZrO2 by studying the effect of metal loading and the Cu/Znratio. Moreover, characterization of the surface composition andthe distribution of the active phase were carried out with SEM-EDX and XPS. In addition to DME SR, we also evaluated the perfor-mance for autothermal reforming (ATR). The autothermal reform-ing reaction, also termed oxidative steam reforming or combinedreforming, is considered the most thermally efficient and dynamicmethod of producing hydrogen [29]. In ATR, the DME is reactedwith air and steam (Eq. (8)) in order to combine the endothermicsteam reforming (Eq. (1)) and the exothermic partial oxidationreaction (Eq. (9)), which produces heat to sustain the endothermicreaction [30].

ðCH3Þ2Oþ 2H2Oþ 1=2O2�2CO2 þ 5H2 ð8Þ

ðCH3Þ2Oþ 1=2O2�2COþ 3H2 ð9Þ

2. Materials and methods

2.1. Preparation of catalytic monoliths

400 cpsi (cellspersquareinch) cordierite monolith cylinders witha diameter of 2 cm and a length of ca. 2 cm were used. They wereobtained by cutting larger monolith pieces (Corning Inc.) with a dia-mond saw. Monoliths were first coated with ZrO2 using an aqueoussolution of ZrOCl2�8H2O as precursor. Following immersion, mono-liths were dried at 373 K under continuous rotation and calcined inair at 773 K for 2 h. This procedure was repeated several times in

order to obtain the desired weight gain (10–12% w/w) of the sup-port. Once the ZrO2 was bound to the monoliths walls, the activemetals were loaded over the monoliths by incipient wetnessimpregnation from Cu(NO3)2�3H2O and Zn(NO3)2�6H2O ethanolicsolutions. The resulting monoliths were finally dried at 373 K undercontinuous rotation and then calcined in air at 773 K for 5 h. Table 1compiles the catalytic monoliths prepared in this work and theirchemical composition.

2.2. Characterization techniques

The microstructure, morphology and composition of monolithchannels were studied by scanning electron microscopy (SEM)and energy dispersive X-ray analysis (EDX). High resolution SEMimages were recorded at 5 or 10 kV using a Neon40 Crossbeam Sta-tion (Zeiss) instrument equipped with a field emission (FE) source.About one hundred particles were considered in each sample forparticle size distribution estimation. X-ray photoelectron spectra(XPS) were collected with a SPECS system using a Al X-ray source(150 W) and a 9-channel Phoibos detector at a pressure below5 � 10�7 Pa. XPS quantification of surface elements was carriedout using Shirley baselines and Gaussian-Lorentzian (1:1) line-shapes. Oxidative Methanol-TPD was studied using infrared spec-troscopy (FTIR). These experiments were performed in situ usinga Shimadzu FTIR-8400S instrument equipped with a HarrickHTC-3 high temperature transmission cell. Spectra were averagedover 20 scans in the mid-IR range (400–4600 cm�1) at a nominal2 cm�1 resolution. The sample was first reduced in situ under10% H2/Ar at 573 K for 30 min and the background spectra were ta-ken at different temperature intervals under Ar. The sample wasthen exposed to a steady stream of MeOH/air for 30 min and thespectra were subsequently collected at different temperatures upto 673 K under Ar.

2.3. Catalytic tests

Dimethyl ether steam reforming was carried out simulating realapplication at atmospheric pressure in a stainless steel tubular reac-tor under different DME loads (2.5–10 cm3 min�1) and volumehourly space velocity (VHSV) values (240–900 h�1). H2O was fedusing a HPLC Knauer Smartline 100 pump to obtain a DME:H2O mo-lar ratio of 1:6 (S/C = 3). The effluent of the reactor was monitored online with an Agilent 3000A micro-GC equipped with PLOT U,Stabilwax and 5 Å Molsieve columns, which allowed a careful quan-tification of H2, O2, CO, CO2, CH4, CH3OH and CH3OCH3 concentra-tions. All lines were heated at 323 K to avoid condensation. Carbonbalance closure calculations were always within experimental error(5%). Several analyses were conducted at each reaction condition.The catalytic monoliths were first pretreated inside the reactor witha 10% H2/He mixture (50 cm3 min�1) at 573 K for 2 h. Then the tem-perature was lowered to 473 K under He flow and the reaction mix-ture was introduced at this temperature. The reaction was followedfrom 473 to 823 K (2 K min�1) and then it was maintained at 823 Kfor 40–80 h on stream. Monoliths operated under isothermal condi-tions as deduced from temperature monitoring inside the channels,

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located either in contact with the stainless steel housing wall or atthe center of the reactor. Autothermal reforming was performed at823 K using a DME flow rate of 5 cm3 min�1, S/C ratios between 1and 3, O2/DME = 0.5 and different VHSV values (350–600 h�1). A sta-bility test was also carried out using a DME flow rate of 5 cm3 min�1,S/C = 1 and O2/DME = 0.5 at 823 K over 48 h on stream. Conversion,selectivity and yield values are defined as follows:

DME conversionð%Þ ¼ nDMEconv

2� nDMEin� 100 ð10Þ

Selectivity toCi speciesð%Þ ¼ nCiPnCi

� 100 ð11Þ

CiYieldð%Þ ¼%DMEconversion �%SelectivityCi

100ð12Þ

where nDMEconv represents the moles of DME converted mea-sured as the sum of moles of CO2, CO, CH4 and CH3OH at the reactoroutlet and nDMEin represents the moles of DME at the reactor inlet.

3. Results and discussion

3.1. DME steam reforming over CuZn/ZrO2 catalytic monoliths withdifferent Cu and Zn contents

Fig. 1 shows the yields attained for all products on a dry basis inthe reforming reaction at 823 K for each monolith tested under dif-ferent DME loads. The results of the Cu(1)Zn(1)/ZrO2 catalyticmonolith were previously reported by our group [28].

The catalytic monolith Cu(1)Zn(1)b/ZrO2 shows a remarkablelower activity compared to the catalytic monolith Cu(1)Zn(1)/ZrO2. Both catalytic monoliths have a Cu:Zn molar ratio of ca.1:1, being the only difference the total amount of active phase(the Cu(1)Zn(1)b/ZrO2 sample has half of the metal load of the cat-alytic monolith Cu(1)Zn(1)/ZrO2, see Table 1). This result indicatesthat an increase of the acidic properties of the surface due to an in-crease of ZrO2 exposure does not improve the activity becausethere is no increase of MeOH formation among the reaction prod-

Fig. 1. Catalytic performance of CuZn/ZrO2 monoliths under DME steam reformingconditions at 823 K ( = CO2, = H2, h = CO, j = CH4, =CH3OH). Experimentalconditions: 5 cm3 min�1 DME and VHSV = 460 h�1 (a), 10 cm3 min�1 DME andVHSV = 920 h�1 (b) and 2.5 cm3 min�1 DME and VHSV = 240 h�1 (c).

ucts, thus suggesting that the determining step of the reaction overthis type of catalysts under the conditions tested is the MeOHreforming (Eq. (3)) rather than DME hydration (Eq. (2)). Neverthe-less, other effects related to the amount of active phase, such asdispersion and metal interaction, cannot be completely ruled out.

The catalytic monolith with the active phase containing doubleamount of copper than zinc (Cu(2)Zn(1)/ZrO2) also shows lowactivity, probably due to copper sintering. In this case, higheramounts of decomposition products (Eq. (5)), CO and CH4, are ob-served. When the total load of active phase is maintained but theamount of copper is decreased, a remarkable increase of the activ-ity is observed, as depicted in Fig. 1. The DME conversion increasesup to 65% when doubling the amount of zinc with respect to thecopper amount (catalytic monolith Cu(1)Zn(2)/ZrO2) and reaches80% when the amount of zinc is ca. ten times the amount of copper,sample Cu(1)Zn(10)/ZrO2. In both cases the selectivity is main-tained towards the reforming products H2 and CO2. Only a smallamount of CO is detected (<4%) for the Cu(1)Zn(2)/ZrO2 catalyticmonolith and <2% for the catalytic monolith coated withCu(1)Zn(10)/ZrO2 (Fig. 1a), which is ascribed to the promoter effectof ZnO towards the formation of CO2 in the water gas shiftequilibrium.

An increase of VHSV leads to a decrease of DME conversion fol-lowing the decrease in the contact time between the reactants andthe surface of the catalyst. As depicted in Fig. 1b, the selectivity isalmost equal to that obtained using less reactant loading (Fig. 1a).Accordingly, when the loading of DME is decreased to 2.5 cm3

min�1, the DME conversion increases (Fig. 1c). In this case, theselectivity to the reforming products, H2 and CO2, is very similarto that obtained under higher DME loads, being the most remark-able difference the increase of CO concentration, probably becausethe reverse water gas shift reaction is now favored to achieve theequilibrium concentrations (73% H2, 19% CO2 and 8% CO at 823 K).

An example of the experiments that were carried out with eachcatalytic monolith over time is depicted in Fig. 2 (Cu(1)Zn(10)/ZrO2). The vertical lines indicate changes of DME load (segmentsa, b and c). As explained before, the changes in the load of reactantsresult in different DME conversion values, which barely affect theselectivity. It merits to be highlighted that no signs of deactivationwere observed in any catalytic monolith under the different DMEloads tested over time on stream (in some cases up to 80 h).

3.2. Sample characterization

3.2.1. Scanning electron microscopy (SEM)Representative high resolution SEM images corresponding to a

single channel of monoliths coated with Cu(1)Zn(1)/ZrO2 orCu(1)Zn(10)/ZrO2 catalysts after DME steam reforming (long-termexperiment, Fig. 1) are shown in Fig. 3. A good distribution andhomogeneity of the zirconia support over cordierite was observedin all cases. Moreover, copper and zinc were well distributed in thechannels of both catalytic monoliths, as determined by EDX. Inmonolith Cu(1)Zn(1)/ZrO2, both individual and aggregate copperparticles were encountered over ZrO2 (Fig. 3a). Examination ofmultiple parts of the sample revealed that the ratio between num-ber of copper particles in aggregates vs. individual copper particleswas about 3:1, thus indicating a poor dispersion of copper. In con-trast, in monolith Cu(1)Zn(10)/ZrO2, only individual, very well-dis-tributed copper particles were identified over zinc particles andZrO2 (Fig. 3b). The average particle diameter of individual copperparticles was calculated from the mean diameter frequency distri-bution with the formula: d = Rnidi/Rni, where ni is the number ofparticles with particle diameter di in a certain range. Well-dis-persed copper particles in the Cu(1)Zn(10)/ZrO2 catalytic monolithexhibited a mean particle size of about 50 nm. Hence, the betterperformance of the Cu(1)Zn(10)/ZrO2 catalytic monolith in the

Fig. 2. Catalytic performance of Cu(1)Zn(10)/ZrO2 monolith over time on streamunder DME steam reforming conditions at 823 K and S/C = 3. Experimentalconditions: 5 cm3 min�1 DME and VHSV = 460 h�1 (a), 10 cm3 min�1 DME andVHSV = 920 h�1 (b) and 2.5 cm3 min�1 DME and VHSV = 240 h�1 (c).

Table 2XPS data of CuZn/ZrO2 catalytic monoliths after steam reforming reaction at 823 K.

Catalyst BE (eV) Cu/Zn ratio

Cu 2p3/2 Zn 2p3/2 Zr 3p3/2 Theoretical Experimental

Cu(1)Zn(10)/ZrO2 932.2 1021.9 333.1 0.10 0.05Cu(1)Zn(2)/ZrO2 933.1 1022.5 334.8 0.50 0.17Cu(1)Zn(1)/ZrO2 933.2 1022.5 333.7 1.00 0.13

Table 3Experimental conditions for the oxidative steam reforming reaction at 823 K.

Step cm3 min�1 DME S/C O2/DME VHSV h�1

DME SR 5 3 – 460ATR 3 5 3 0.5 600ATR 2 5 2 0.5 480ATR 1.5 5 1.5 0.5 420ATR 1 5 1 0.5 350

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DME steam reforming reaction could be related to a better copperdispersion with respect to the other catalytic honeycombs withhigher copper contents.

3.2.2. X-ray photoelectron microscopy (XPS)The surface composition after reaction of the catalytic mono-

liths Cu(1)Zn(10)/ZrO2, Cu(1)Zn(2)/ZrO2 and Cu(1)Zn(1)/ZrO2 wasstudied in order to establish a connection between the surfacecomposition and the catalytic performance observed. The bindingenergies (referenced to the adventitious C 1s signal at 284.8 eV)and the theoretical bulk and experimental surface atomic Cu/Zn ra-tios are compiled in Table 2. The XPS results show that the propor-tion of copper that is on the surface decreases with respect to thetheoretical value when the amount of copper increases in the cat-alyst, probably due to agglomeration of copper in accordance toSEM results. The measured surface atomic Cu/Zn ratio closer tothe theoretical value corresponds to the catalytic monolithCu(1)Zn(10)/ZrO2, which shows the best catalytic performance.Thus, to achieve high activity under DME reforming conditions, a

Fig. 3. Scanning electron microscopy images corresponding to a single channel of a monosteam reforming reaction at 823 K, 2.5–10 cm3 min�1 DME, S/C = 3 and VHSV = 240–900

large amount of copper is not needed, it is more important tomaintain a good dispersion of copper to avoid sintering under reac-tion. On the other hand, no surface carbon deposition was ob-served, in accordance to the high stability of these catalytichoneycombs under DME steam reforming conditions discussedabove.

3.3. DME autothermal reforming over Cu(1)Zn(1)/ZrO2 catalyticmonolith

The Cu(1)Zn(1)/ZrO2 catalytic monolith with more than 80 h onstream under DME steam reforming was tested under oxidativesteam reforming conditions using different S/C ratios (Table 3). Inthe autothermal reaction, the amount of water was progressivelydecreased to reach the strictly stoichiometric value (Eq. (8)).Fig. 4 shows the yields attained for all products on a dry basis at823 K for each condition.

As depicted in Fig. 4, the catalytic monolith achieves 50% ofDME conversion in the DME SR, a value similar to that reportedin Fig. 1a for the fresh sample, which again shows the remarkablestability of this formulation under DME steam reforming condi-tions. The selectivity is also very similar, obtaining mostly thereforming products H2 and CO2. The level of DME conversionreached under each condition in the oxidative steam reformingtests cannot be compared directly since the residence time is dif-ferent. However, the selectivity is similar in all cases, despite thedifferences in contact time. The addition of air and the progressivedecrease of water cause a concomitant increase of CH4, suggestingthat decomposition of DME and/or CO/CO2 methanation reactions

lith coated with Cu(1)Zn(1)/ZrO2 (a) and Cu(1)Zn(10)/ZrO2 (b) after 40 h under DMEh�1.

Fig. 4. Catalytic performance of Cu(1)Zn(1)/ZrO2 monolith under different DMEoxidative reforming conditions at 823 K ( = CO2, = H2, h = CO, j = CH4,

= CH3OH) (Table 3).

Fig. 6. In situ FTIR spectra recorded over Cu(1)Zn(1)/ZrO2 under MeOH-TPDexperiments in the temperature range 423–573 K simulating steam reforming (a)and oxidative steam reforming (b) conditions.

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are favored. At similar conversion level of DME (experiments DMESR and ATR 1 in Fig. 4), the amount of hydrogen obtained understeam reforming (73%) is higher than that produced under auto-thermal conditions (61%), as predicted by the stoichiometry ofthe reaction.

A stability test was also performed at 823 K under autothermalconditions using stoichiometric ratios of S/C and O2/DME (Eq. (8))for more than 40 h. Fig. 5 shows the conversion and selectivityvalues over time on stream. A progressive deactivation is detectedduring the experiment, as observed in the conversion plot. Deactiva-tion cannot be attributed to sintering because the metal particle sizerecorded by SEM is similar before and after reaction. On the otherhand, deactivation is accompanied by a progressive decrease ofthe amount of hydrogen and a simultaneous increase of the amountof CH4 (up to 2% at the end of the experiment), whereas no signifi-cant changes in methanol, CO and CO2 concentrations are observedduring all the experiment. As Nilsson and co-workers have reported,the mechanism of the DME partial oxidation involves methoxyspecies, as a result of the dissociative adsorption of DME on thecatalyst surface [31,32]. We have conducted a comparative studyof the species adsorbed at the surface of the Cu(1)Zn(1)/ZrO2 sampleby in situ FTIR MeOH-TPD under oxidative steam reforming (thiswork) and under steam reforming conditions [28]. The spectrarecorded for both processes are shown in Fig. 6. Methoxy species

Fig. 5. Catalytic performance of Cu(1)Zn(1)/ZrO2 monolith over time on streamunder DME autothermal reforming reaction. Experimental conditions: 5 cm3 min�1

DME, S/C = 1, O2/DME = 0.5, VHSV = 350 h�1, T = 823 K.

are readily formed in both cases but, whereas under steam reform-ing conditions they evolve with temperature readily into formatespecies (Fig. 6a), methoxy species prevail under oxidative steamreforming conditions (Fig. 6b). In a previous work, we related thepresence of methoxy species to the formation of CH4 and carbonresidues, which led to the deactivation of a CuPd/ZrO2 catalyst un-der DME steam reforming (whereas formate species led to thereforming products, H2 and CO2) [28]. The presence of methoxy spe-cies could explain the increase of CH4 over CuZn/ZrO2 and the cata-lyst deactivation under autothermal conditions, since methoxyspecies evolves to the formation of carbon residues, as evidencedby XPS analysis on the sample after the stability test and in accor-dance with previous observations [27,28]. These results are not inconcordance with the extended belief that catalysts are more stableunder ATR than under steam reforming conditions, possibly due tothe complex reaction mechanism of DME reforming. According tothe results obtained, catalytic monoliths CuZn/ZrO2 that performexcellent for the DME steam reforming reaction do not seem to begood candidates for the autothermal reaction.

4. Conclusions

Catalytic monoliths containing ZrO2 as support and differentamounts of Cu and Zn were prepared and tested in the dimethylether (DME) steam reforming reaction simulating real application.In all cases the selectivity towards the reforming products, H2 andCO2, was high and no signs of deactivation were observed, even un-der high DME loads. The activity was strongly influenced by theamount of copper in the catalyst, being catalyst formulations withhigh Zn/Cu ratios preferred. In these cases, SEM and XPS character-ization after reaction showed a better dispersion of copper parti-cles and lack of sintering. In contrast, strong deactivation of the

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catalysts occurred under autothermal reforming conditions. Thisdeactivation was likely caused by the presence of methoxy species,which was related to the formation of methane and carbonresidues.

Acknowledgements

This work was funded through MICINN Grant CTQ2009-12520and FEDER funds. C.L. acknowledges MEC for a PhD Grant(ENE2006-06925). J.L. is grateful to ICREA Academia program.

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