Effect of Cu loading on CeO2 for hydrogen production by oxidative steam reforming of methanol

International Journal of Hydrogen Energy 32 (2007) 2888 – 2894 www.elsevier.com/locate/ijhydene

Effect of Cu loading on CeO2 for hydrogen production by oxidative steam reforming of methanol R. Pérez-Hernández ∗ , A. Gutiérrez-Martínez, C.E. Gutiérrez-Wing Instituto Nacional de Investigaciones Nucleares, Carr. México-Toluca S/N La Marquesa, Ocoyoacac, Edo. de México C.P. 52750, México Received 31 July 2006; received in revised form 21 March 2007; accepted 1 April 2007 Available online 23 May 2007

Abstract Catalytic performance of Cu/CeO2 catalysts was studied as a function of Cu loading in the oxidative steam reforming of methanol (OSRM) reaction. The reduction of CuO/CeO2 catalysts evidenced the existence of different kinds of CuO species. Their reduction peaks shift to higher temperatures as a function of the CuO loading. The catalyst which exhibited a reduction peak at 242 ◦ C showed low activity on the OSRM reaction and poor H2 selectivity. SEM, XRD and TPR analyses of this sample revealed the strong influence of the large crystallites of Cu on the catalyst performance. Catalysts with 2 and 6 wt% of copper showed a similar activity in the OSRM reaction. However, the highest H2 selectivity was observed on the 2Cu/CeO2 catalyst in the range of 210.230 ◦ C. Above 230 ◦ C, H2 selectivity was improved on the 6Cu/CeO2 sample and decreased in the 2Cu catalyst. A diminished H2 selectivity is attributed to the loss of the active copper phase by oxidation during catalytic reaction, as confirmed by TPR and EPR studies on the 2Cu catalyst after catalytic reaction. 䉷 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. Keywords: Cu/CeO2 ; H2 production; Methanol-oxidative steam reforming; TPR; EPR

1. Introduction Fuel cells have recently attracted much attention as a potential device for energy transformation. Their performance is based on a clean process, without forming harmful by-products such as sulphur oxides and nitrogen oxides, while having a highly efficient energy transformation compared to conventional power generation processes as in heat engines. Hydrogen is a promising fuel for fuel cells and can be produced by steam reforming of natural gas, methanol and gasoline. Olah [1] explains the advantages of having a chemical storage of hydrogen in the form of methanol. Alternate approaches, such as cryogenic liquid H2 , storage on carbon nanotubes and highly pressurized gas, are either too energetic and costly or unproven for off-board storage of H2 for transportation. This has motivated this research focused on on-site hydrogen production from liquid fuel such as methanol or ethanol [2]. Literature suggests that in the steam-reforming reaction Cubased catalysts provide high CO2 selectivity versus undesirable ∗ Corresponding author. Tel.: +52 55 53297239; fax: +52 55 53297240.

E-mail address: [email protected] (R. Pérez-Hernández).

CO [3,4]. This is attributed to a reaction pathway, where adsorbed intermediate HCHO (formaldehyde) species react with water to directly produce H2 and CO2 without forming a CO intermediate. Takezawa and Iwasa [3] found that a catalyst composed of Pd supported on ZnO demonstrated high reaction selectivity to CO2 similar to that of Cu catalysts, while providing high activity comparable to the activity of precious metals. Liu et al. [5] reported that CuO/CeO2 is effective for steam reforming of methanol (SRM). Steam reforming is an endothermic reaction and thus requires energy input, which makes transient operation difficult when bursts of energy are needed. Oguchi et al. [6] found that the optimum amount of CuO in CuO/CeO2 was 80% wt, and the addition of ZrO2 had an accelerating effect in the SRM. Partial oxidation of methanol (POM) is another possibility to produce H2 ; POM has a higher reaction rate than steam reforming, but half the hydrogen selectivity [2]. Furthermore, POM is highly exothermic, so temperature control can be difficult. Oxidative steam reforming (OSR) is a combination of steam reforming and partial oxidation. This process uses the energy produced from partial oxidation to supply the endothermic, steam-reforming reaction, and thus can be run adiabatically [7]. This eliminates the need to transfer heat

0360-3199/$ - see front matter 䉷 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2007.04.012

R. Pérez-Hernández et al. / International Journal of Hydrogen Energy 32 (2007) 2888 – 2894

across a heat-conducting boundary and allows the reaction to proceed at much higher rates in a smaller reactor volume. Oxidative steam reforming of methanol (OSRM) has not been extensively studied, but initial results indicate low carbon monoxide yield and high hydrogen concentration in the products [8]. Some authors [9–11] studied the OSR of methanol over Cu and Pd catalysts supported over ZnO promoted by Zr–Al. They found that oxygen concentration in the gas phase is the main parameter determining the reactor performance and suggested an oxidation/decomposition followed by reforming scheme for the process. This work reports the effect of the copper supported on CeO2 in the OSRM as a function of temperature on H2 production. Catalysts characterization included BET (N2 adsorption–desorption), SEM (scanning electron microscopy), EDS (energy dispersive X-ray spectroscopy), XRD (X-ray diffraction), TPR (temperature-programmed reduction) and EPR (electron paramagnetic resonance). 2. Experimental 2.1. Catalyst preparation Cerium nitrate (Ce(NO3 )3 • 6H2 O) (Sigma) was heated at 100 ◦ C for 1 h in air stream and then calcined at 700 ◦ C for 4 h. The prepared support was impregnated with the Cu(acetate)2 (Merck) at an appropriate concentration to yield 2, 6 and 10 wt% of Cu in the catalysts. The samples were dried at 100 ◦ C for 1 h and then calcined at 500 ◦ C for 2 h in static air and finally reduced with a H2 (5%)/He stream at 330 ◦ C for 1 h before the characterization and activity test. The labelling of different catalysts will be referred as nCu/CeO2 where n = 2, 6 and 10 wt% of Cu in the catalyst, respectively. 2.2. Characterization Total surface area was calculated by the BET method from N2 adsorption by the single point method using a 30% N2 /He gas mixture, recorded at the temperature of liquid nitrogen. XRD powder patterns were recorded in a Siemens D-5000 diffractometer, using Cu K ( = 0.15406 nm). The morphology and chemical composition of the samples were determined in a Philips XL-30, with a resolution of 3.5 nm, fitted with an energy dispersive X-ray Spectrometer (EDAX) at an acceleration voltage of 25 kV, obtaining the images with the backscattering electron signal. Before the analysis, the samples were fixed on aluminium specimen holder with an aluminium tape. TPR experiments were carried out on an automatic multitask unit RIG-100 from ISRI equipped with a thermal conductivity detector (TCD) with output to a computer. The oxidized catalyst (0.1 g) was placed in the reactor and purged with UHP Ar at room temperature and then the TPR measurement was performed using 5% H2 /Ar gas mixture (30 ml/min). The temperature was increased at a rate of 10 ◦ C/ min from room temperature to 700 ◦ C. The effluent gas was passed through silica gel to remove water before measuring the amount of hydrogen consumed during the reduction by the TC detector. The signal

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was calibrated by 0.5 ml pulses of 5% H2 /Ar at the end of the experiment. After testing the catalytic activity reaction, the surface of these catalysts was cleaned by a He stream (30 ml/min) for 30 min at 260 ◦ C and cooled at room temperature, then the sample was purged with UHP Ar flow and the TPR was performed. The EPR experiments were performed after catalytic test following a procedure reported on literature [12]. 2.3. Catalytic reaction The steady-state activity in the OSRM reaction was performed in a conventional fixed-bed flow reactor (8 mm i.d.) using 0.1 g of the catalyst in a temperature range from 200 to 260 ◦ C at atmospheric pressure, with a thermocouple in contact with the catalytic bed to control the temperature inside the catalyst. The catalyst was first activated in a stream of H2 (5%)/He (60 ml/min) from room temperature to 330 ◦ C with a heating rate of 10 ◦ C/ min and held at this temperature for 1 h. The catalyst was brought up to the reaction temperature in He and the reaction mixture was introduced. For the OSRM reaction, the mixture O2 (5%)/He was used with a total flow rate kept at 50 ml/min (GHSV = 30, 000 h−1 based on the total flow), fed by a mass flow controller and bubbled through a tank containing a mixture of water and methanol (cooled with ice). The partial pressure used was 30, 4.6 and 25.2 Torr for CH3 OH, H2 O and O2 , respectively (molar ratio O2 /CH3 OH = 0.83 and H2 O/CH3 OH = 0.15). The effluent gas of the reactor was analysed by gas chromatography using TCD. A 2-m packed Porapack Q column able to detect water, methanol, methyl formate (MF) and CO2 was used. MF (m/e = 60) was identified with a MAT-GCQ GC-MS Finningan model 9001. A cold trap was used to retain the liquids, for this reason these were not quantified. The gaseous products such as H2 and O2 were detected with a molecular sieve 5A. The 2Cu catalyst used was tested again in a second cycle of catalytic activity. So at the end of the reaction (260 ◦ C) the catalyst was cleaned with He for 30 min. Then the catalyst was activated in a H2 /He stream at 330 ◦ C for 1 h and the catalytic activity for the second cycle was determined. Diagram 1 shows the system reaction used to test the catalytic activity of the catalysts. 3. Results and discussion 3.1. Textural and structural properties The specific surface area of pure CeO2 support was 43 m2 /g and the catalysts after thermal treatments (calcination and reduction) were 42, 39 and 38 m2 /g for 2, 6 and 10% of copper, respectively. Fig. 1 shows the XRD patterns of the Cu/CeO2 catalysts corresponding to the reduced samples; all of them are characteristic of the cubic structure of ceria (fluorite structure). Cu was not detected in the 2Cu/CeO2 catalyst (before and after catalytic activity); this could be due to its low concentration (2.0 wt%) or because the particle size of the Cu is below the detection limit of the technique. However, on the 6Cu/CeO2 and 10Cu/CeO2 samples, additional diffraction peaks were observed, which correspond to the metallic copper, and their

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Diagram 1. Reaction system for the catalytic activity test.

Cu

Intensity (a.u.)

10Cu/CeO2

6Cu/CeO2

2Cu/CeO2 after reaction 2Cu/CeO2 20

30

40

50 60 2-theta

70

80

90

Fig. 1. XRD patterns of the Cu/CeO2 catalysts before and after catalytic activity.

intensity increases proportionally to the Cu loading on CeO2 . This result is associated with the growth of Cu particle size and is more evident in the 10Cu/CeO2 catalyst. SEM observation of Cu/CeO2 catalysts reveals the morphology of the samples, as well as the particle size of the Cu. Fig. 2 shows a representative image of the 10Cu/CeO2 catalyst where large particles of porous metallic Cu of about 4.5 m were observed. On the other catalysts these types of particles were not present. After the catalytic reaction this kind of particles remain on the 10Cu sample and are absent on the 2Cu and 6Cu catalysts as before the reaction. This result indicated that an addition of 10% wt. of Cu to the CeO2 matrix with 40 m2 /g mainly produces large copper particles.

Fig. 2. SEM image of the 10Cu/CeO2 catalyst. Arrows show the semi-spherical porous Cu particles.

3.2. Temperature-programmed reduction and electron paramagnetic resonance TPR profiles of CuO supported over CeO2 of the fresh catalysts (solid line) and the samples after catalytic reaction (dotted line) are shown in Fig. 3. The reduction of bare CeO2 is also included for reference. A broad peak above 556 ◦ C is observed for the CeO2 support and its intensity was very weak, indicating that only a very small amount of surface ceria could be reduced [13,14]. Reduction of CuO supported on CeO2 is observed at temperatures below 330 ◦ C. At least two or three reduction peaks were observed in the fresh CuO/CeO2 catalysts, indicating the existence of two or three kinds of CuO species.

R. Pérez-Hernández et al. / International Journal of Hydrogen Energy 32 (2007) 2888 – 2894

The TPR profile of the 2CuO/CeO2 catalyst has two reduction peaks at 165 and 199 ◦ C, respectively. The 6Cu/CeO2 catalyst showed reduction peaks at 170, 197 and 225 ◦ C, while on the 10Cu/CeO2 catalyst the TPR profile showed peaks at 156, 196 and 242 ◦ C. All catalysts had the characteristic small reduction peak at 500 ◦ C attributed to the reduction of the ceria support. The intensity of the high temperature peak increased significantly and was shifted to the high-temperature region when the amount of Cu was increased, because the large crystallites tend to be reduced slower than the small ones due to their relatively lower surface area exposed to H2 [11]. The peak positions and their contributions to CuO reduction derived from deconvolution of TPR profiles are given by the H2 /CuO ratio and summarized in Table 1. The H2 uptake by reduction of fresh 2CuO/CeO2 catalyst was much higher than the expected for the reduction of the CuO on the sample. This result could be associated to the fact that, in the TPR study, small particles probably cause spill over of hydrogen onto the support inducing a concurrent reduction of both copper oxide and the surface of the CeO2 [13,14]. On the 6Cu and 10Cu catalysts the low hydrogen consumption indicates incomplete reduction of the copper oxide. Luo et al. [15] studied CuO supported on CeO2 by TPR, using Cu(NO3 )2 as a Cu source. They observed two reduction peaks in the samples with a CuO concentration of up to 15%. The first peak was observed near 160 ◦ C for all the

H2 consumption (a.u.)

10Cu/CeO2

6Cu/CeO2

2Cu/CeO2 0

100

200

300

400

500

600

700

TEMPERATURE (°C)

Fig. 3. Temperature-programmed reduction profiles of the fresh catalysts (solid line), samples after catalytic reaction (dotted line) and bare CeO2 (clear line).

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catalysts. The position of the second peak shifts to higher temperatures (c.a. 180.235 ◦ C) as a function of the CuO loading, and the intensity also increases. On this study the peak at low temperature is attributed to the reduction of the highly dispersed CuO (small contribution), and the peak above 200 ◦ C is associated with the presence of bulk CuO [16,17] as the abundant phase. XRD and SEM analyses of the 10Cu catalyst confirm that the Bulk CuO species increase with the Cu loading. 3.2.1. TPR and EPR after catalytic reaction The TPR profiles of the catalysts after OSRM reaction (dotted line) showed reduction peaks at 160 ◦ C for the samples with 6 wt% of Cu, similar to the samples before the reaction; however, for the sample with 10% of copper the reduction peak was observed at 200 ◦ C and it corresponds to the second specie of the fresh catalyst (Fig. 3). The fraction of the copper species that were reduced from the total copper present in each one of the catalysts has the following order 6Cu < 10Cu < 2Cu. This means that only a small fraction of the highly dispersed copper observed on 6Cu catalyst is reoxidized. Agrell [11] reported that on highly dispersed copper, the metallic surface area is easily oxidized in the presence of O2 . This explains why in the 2Cu catalyst more copper is oxidized during the catalytic reaction than in 6Cu sample. In the 10Cu catalyst, the highly dispersed Cu present prior to the reaction was sinterized into large Cu particles and these were oxidized during OSRM reaction. This is why highly dispersed copper was practically not observed by TPR on the sample after catalytic test (Fig. 3). To determine the type of Cu specie oxidized during the catalytic reaction, EPR experiments were performed on the samples after OSRM reaction. The g values on the spectra of these samples correspond to Ce3+ , Ce4+ and Cu2+ paramagnetic ions (Fig. 4). The CuO type 2D-cluster after OSRM reaction was identified at g = 2.049 (attributed at isolated Cu2+ in lattice sites or in surface sites) and interacting Cu2+ forming a nano-sized two-dimensional structure (g = 2.10) [18,19]. Intensity of these signals reached a maximum on the 2Cu sample, so this is proportional to the spin concentration of paramagnetic ions on the surface of the ceria. The reduction in the EPR signal intensity observed on the 6Cu and 10Cu catalysts can be attributed to the decrease in the amount of these types of species due to the increase of the copper concentration on the surface of the catalysts. The signal at g = 2.155 can be assigned to aggregates of Cu(II) in close proximity. On the other hand, the highest intensity of the Cu2+ signals was detected on the 2Cu catalyst, indicating that

Table 1 TPR peaks positions, ◦ C and concentrations (%) of the reducible species in the CuO/CeO2 catalysts Catalyst 2Cu/CeO2 2Cu/CeO2 10Cu/CeO2

Peak 1 165 (41) 170 (6) 156 (5)

160a 160a 200a

Peak 2

Peak 3

Peak 4

199 (59) 197 (52) 196 (6)

500 255 (42) 242 (89)

— 500 500

H2 /CuO 1.43 0.93 0.68

0.66a 0.19a 0.26a

Values in parentheses are the contribution to Cu reduction (%) derived from deconvolution of TPR profiles. Theoretical value of the H2 /CuO = 1 for complete reduction of CuO. a Catalysts after catalytic reaction.

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2.15

2.097

Ce

+3

2.05 Ce

10Cu

+4

-

-O 2 Ce+4-O2 Ce

+3

6Cu 2Cu

2950

3050

3150

3250

3350

3450

O2 conversion (%)

Intensity (a.u.)

2.043

80 60 40 2Cu/CeO2 6Cu/CeO2 10Cu/CeO2 2Cu/CeO2-2°

20

H/Gaus Fig. 4. EPR spectra of the Cu/CeO2 catalysts after oxidative steam reforming of methanol reaction.

210

220

230

240

250

260

TEMPERATURE (°C)

Fig. 6. Conversion of oxygen as a function of reaction temperature in the oxidative steam reforming of methanol over nCu/CeO2 catalysts. CH3 OH partial pressure 30 Torr, H2 O partial pressure 4.6 Torr and O2 (5%)/He mixture (50 ml/min). GHVS = 30,000 h−1 . Solid symbol corresponds to the second run in the OSRM reaction. Molar ratio O2 /CH3 OH = 0.83 and H2 O/CH3 OH = 0.15.

100 Methanol conversion (%)

0 200

80 60 40 2Cu/CeO2 6Cu/CeO2 10Cu/CeO2 2Cu/CeO2-2°

20 0 200

210

220

230

240

250

260

TEMPERATURE (°C)

Fig. 5. Effect of temperature on the catalytic performance in the oxidative steam reforming of methanol over nCu/CeO2 catalysts. CH3 OH partial pressure 30 Torr, H2 O partial pressure 4.6 Torr and O2 (5%)/He mixture (50 ml/min). GHVS = 30,000 h−1 . Solid symbol corresponds to the second run in the OSRM reaction. Molar ratio O2 /CH3 OH = 0.83 and H2 O/CH3 OH = 0.15.

this kind of copper is easier to be oxidized during the reaction than 6Cu and 10 Cu samples. TPR experiments after OSRM reaction confirm this result, where the 2Cu catalyst requires more H2 to reduce this specie. Therefore, Cu(II) and isolated Cu2+ ions could be assigned to the peak at 160 ◦ C, while the CuO type 2D-clusters could be assigned to the peak at 200 ◦ C observed on the samples after catalytic reaction by TPR. 3.3. Catalytic performance on the OSR of methanol Fig. 5 shows the catalytic activity of the OSRM reaction on Cu/CeO2 catalysts. The light-off temperature for all samples is approximately 200 ◦ C. At 210 ◦ C the 2Cu/CeO2 catalyst presented 28% of methanol conversion, while the 6Cu/CeO2 and 10Cu/CeO2 catalysts reached 13% conversion at the same reaction temperature. At 220 ◦ C the 2Cu/CeO2 and 6Cu/CeO2 catalysts reached near 85% conversion, after this temperature they showed the same conversion. However, the 10Cu/CeO2 catalyst was the less active at every temperature of reaction, reaching 19% conversion at 220 ◦ C. The catalytic activity of the samples at 260 ◦ C showed the following order:

2Cu/CeO2 ≈ 6Cu/CeO2 > 10Cu/CeO2 . Methanol conversion reached almost 100% in the 2Cu and 6Cu catalysts, while in the 10Cu sample only 84% conversion was observed at the maximum reaction temperature. A similar behaviour was reported by Reitz et al. [20]; they observed that the catalytic activity decrease with increasing CuO crystallite size in the OSMR on CuO/ZnO. Sintering of highly dispersed copper on sample 10Cu during the OSRM reaction explains the low activity of this sample (Fig. 5). This finding suggests that highly dispersed copper is the active specie for the OSRM reaction. Catalytic activity of the 2Cu/CeO2 sample was evaluated in a second run, and it was found that the overall activity was similar to the first cycle with a slight decrease in it. This behaviour is understandable because the catalyst was stabilized first at 330 ◦ C and the reaction was completed before reaching that temperature (Fig. 5). XRD confirmed that in this catalyst the active highly dispersed copper does not sinterize. The diffraction pattern of the 2Cu catalyst after a second cycle of reaction does not show characteristic peaks of Cu phases, indicating that the sample maintains the same Cu species after the OSRM reaction, which can be regenerated during the catalytic reaction. However, these highly dispersed Cu species are much more susceptible to be oxidized during the reaction, as evidenced by TPR and EPR analysis of the sample after the catalytic test. A similar behaviour was observed in the O2 conversion (Fig. 6) but slightly higher than methanol. At the beginning of the reaction, the formation of CO2 , H2 O and a small quantity of methyl formate (MF as by-product of the reaction) was observed. H2 is produced until the methanol conversion approaches 18% by increasing the temperature. When the H2 production starts no CO or CH4 was detected in the outflow gas stream (within the detection limit of TCD). Fig. 7 shows the H2 selectivity (mol%) as a function of methanol conversion from the OSRM reaction on the Cu/CeO2 catalysts. The 2Cu sample showed the best H2 selectivity up to 230 ◦ C, compared to the other catalysts; after this temperature

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Since the methanol conversion remains almost unaffected after 230 ◦ C, the drop in the hydrogen yield observed in the 2Cu/CeO2 catalyst might be caused by the oxidation of H2 with O2 (Eq. (3)) promoted by the Cu oxidation, because in this sample more copper was oxidized during OSRM reaction as discussed in TPR and EPR results and this oxidized specie is inactive for H2 generation:

Selectivity tohydrogen (%)

35 30

2Cu 6Cu 10Cu

25 20 15 10

H2 + 21 O2 → H2 O.

5 0 200

210

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220

230

240

250

260

TEMPERATURE (°C) Fig. 7. H2 selectivity as a function of reaction temperature. %S(H2 ) = mol(H2 )/(mol(H2 +CO2 ))∗ Xa; %S(CO2 )=mol(CO2 )/(mol(H2 +CO2 ))∗ Xa; Xa = % methanol conversion (mol%).

the H2 selectivity decreases in this sample and increases in the 6Cu catalyst. At the maximum reaction temperature in which almost all methanol is consumed, the final products were H2 , H2 O and CO2 . The H2 depletion observed on the 2Cu sample can be explained by the loss of active copper phase for the H2 generation (Cu oxidation during the OSRM reaction). This agrees with TPR and EPR results of the sample analysed after the catalytic reaction, where more copper, assigned as highly dispersed Cu species, oxidizes easier on 2Cu sample than on 6Cu sample. If copper is well dispersed, the metallic surface is easer to be oxidized in the presence of O2 than in large crystallites [11], rendering the catalyst inactive for H2 production. Therefore, the Cu species that were oxidized during OSRM reaction could be assigned as Cu+2 . Reitz et al. [21] studied the OSRM reaction over Cu/ZnO catalysts by time-resolved XANES and found that under low-conversion conditions, Cu+2 was the dominant copper species, where water and CO2 are the primary products formed on the methanol combustion. They observed that an increase in the O2 concentration in the OSRM reaction over CuO/ZnO accelerates the reduction of CuO, as a result of the exothermicity of the methanol oxidation reaction. After complete conversion of O2 , Cu+2 was reduced to form Cu0 accompanied by the initiationof H2 production through SRM. Cu+ was observed as a transient species in the reduction of Cu+2 to Cu0 , but no activity on the OSRM reaction was attributed to it. Therefore, Cu+2 showed negligible activity for H2 formation, producing instead water and CO2 , while metallic copper is active for H2 production. If the highly dispersed Cu is oxidized to Cu+2 during OSRM reaction, the hydrogen yield decreases. This confirms the behaviour of the 2Cu catalyst. MF was detected at temperatures below 230 ◦ C in almost all the catalysts, after this temperature it is unstable and was not detected. A similar result was observed by Ranganathan et al. [22]. They found formato species adsorbed over Pd/CeO2 catalyst on the SRM. The following sequence of reaction may occur over our catalysts: 2CH3 OH → CH3 OCHO + 2H2 ,

(1)

CH3 OCHO + 2O2 → 2CO2 + 2H2 O.

(2)

(3)

Consequently the performance of the Cu/CeO2 catalysts can be explained on the basis of the combination of copper states (Cu0 /Cu+ /Cu2+ ), highly dispersed Cu; however, reaction intermediaries cannot be rule out. 4. Conclusions The catalysts with 2 and 6 wt% of copper over CeO2 were found to be very active in the production of hydrogen by oxidative steam reforming of methanol (OSRM) reaction. The catalytic activity of the samples revealed that the most active catalysts (2Cu and 6Cu) had the CuO reduction peaks at the lowest temperature. The presence of highly dispersed Cu is therefore likely to be an important factor in determining the efficiency of the Cu/CeO2 catalysts in the OSRM reaction. The 2Cu/CeO2 sample proves to be a good catalyst to produce hydrogen-rich gas mixture in the temperature range of 210.230 ◦ C with high activity in the OSRM reaction and low MF selectivity. At higher temperatures the 6Cu catalyst had the best performance towards H2 . The H2 depletion observed on the 2Cu catalyst is attributed to the loss of the active copper phase by oxidation during catalytic reaction according to our TPR and EPR results in the catalyst after OSRM reaction. Finally, the lowest H2 selectivity was observed in the catalyst with a high Cu content, in this sample high contribution of the large crystallites of Cu was observed by SEM, XRD and TPR. This confirms that having large Cu particles is not effective for H2 production as in the case of highly dispersed Cu. Acknowledgements Thanks to I.Q. Leticia Carapia for technical support. Dra. G. Cisniega for analysis on GC-MS and F. Ureña for EPR analysis and to the project ININ-CM-520, ININ-CA-711 and CONACyT J-48924 for financial support. References [1] Olah GA. After oil and gas: methanol economy. Catal Lett 2004;93:1–2. [2] Brown LF. A comparative study of fuels for on-board hydrogen production for fuel-cell-powered automobiles. Int J Hydrogen Energy 2001;26:381–97. [3] Takezawa N, Iwasa N. Steam reforming and dehydrogenation of methanol: difference in the catalytic functions of copper and group VIII metals. Catal Today 1997;36:45–56. [4] Breen JP, Ross JRH. Methanol reforming for fuel-cell applications: development of zirconia-containing Cu–Zn–Al catalysts. Catal Today 1999;51:521–33.

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