METAL OXIDE CATALYSTS, PREPARATION METHODS AND

APPLICATIONS"

Technical domain

The present invention reveals one type of supported catalyst, being the support one metal oxide or mixture of metal oxides and the catalyst metal or combination of metals. The present invention also reveals applications of these catalysts, namely for the methanol steam reforming reaction at low-temperature, and in the water-gas shift and in the dimethyl ether steam reforming.

State of art

During the last years the research and development on fuel cells technology has dramatically increased, targeting the development of applications for a wide range of sectors such as transportation, portable devices and stationary power plants. A common problem to all these applications is the use of hydrogen as fuel. Despite being the best fuel for high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) , hydrogen is difficult to transport and storage since it is extremely hazardous and has a low volumetric density. To increase the hydrogen density, different techniques are currently been considered: the use of tanks containing hydrogen at very high pressures, hydrogen liquefaction and the use of chemical substances that have the capacity of reacting reversely with hydrogen, such as metallic and organic hydrides. However, the former techniques are not able to achieve values of energy per unit of mass and volume for commercial use. As alternative, the use of fuels as hydrogen carriers, such as methanol, is being proposed by several researchers, like George Olah [1] . Methanol has unique advantages that explain its high interest as hydrogen carrier for fuel cells. It is the simplest of all alcohols, having only one carbon atom. The absence of a strong carbon to carbon bond facilitates the reforming at low temperatures (200-300 °C) . This range of reaction temperature is very low when compared with the reformation temperature of other fuels such methane (ca. 500 °C) or ethanol (ca. 400 °C) . Although methanol is highly toxic, it has the advantage of being biodegradable, liquid at atmospheric conditions and has high hydrogen to carbon ratio. In a steam reforming reactor three reactions, in addition to the overall steam reforming reaction, eq. (1), are commonly considered: methanol decomposition, eq.(2), and water gas shift, eq.(3):

CH ₃ OH+H ₂ 0 ^ C0 ₂ +3H ^■ 2 AH = 49,7 kJ mol -1

(1)

CH ₃ OH ^ CO+2H ₂ AH = 92,0 Id mol -1 (2)

CO+H ₂ O ^ C0 ₂ +H ₂ AH = -41,2 kJ mol -1 (3)

Besides methanol, dimethyl ether is a fuel that is being considered as an option for hydrogen production through steam reforming reaction. When a catalytic support that has acid groups, such as gamma alumina, is combined with a methanol steam reforming catalyst, the reaction of dimethyl ether steam reforming proceed through two successive reactions: dimethyl ether hydrolysis to methanol and methanol steam reforming. Since each dimethyl ether molecule produces two methanol molecules twice as much hydrogen is obtained by dimethyl steam reforming reaction:

CH ₃ OCH ₃ + H ₂ 0→ 2CH ₃ OH (4)

2CH ₃ OH + 2H ₂ 0→ 6H ₂ + 2C0 ₂ (5) Among the most promising applications of fuel cells are portable devices of small dimensions with power generation up to 100 W. The inherent limitations of the use of hydrogen represent a strong drawback for the commercialization of these devices: therefore, the direct feed of alternative fuels (methanol, ethanol, formic acid, dimethyl ether) is being pursued. Actually, among the organic fuels studied, methanol produces the higher performance. However, direct methanol fuel cells (DMFC) , still present several disadvantages when compared with polymer electrolyte membrane fuel cells (PEMFC) , namely: lower energy production per volume unit, lower life time, catalysts with higher costs and less energy due to methanol crossover. It is then concluded out the indirect feed of hydrogen, through methanol steam reforming, is a promising strategy. The advantages are not only related to the higher volumetric energy density of methanol, but also with the possibility of using the heat produced by the HT-PEMFC in the endothermic reforming reaction, which leads to a global energy efficiency of one fuel cell greater of 60 %. Moreover, a methanol reformer needs continuous feed of water steam, which can be again supplied by the HT-PEMFC. In fact, the amount of water produced by a HT-PEMFC is three times higher than the necessary for the methanol steam reforming reaction. Coupling a methanol reformer with a HT-PEMFC, besides providing the expected electrical power, recycles water and the heat is more efficiently used. However, this integration is only possible if the methanol steam reforming temperature is below the operation temperature of the HT-PEMFC. Typically, HT-PEMFCs operate between 120 °C and 200 °C, while the commercial available catalysts for methanol steam reforming work between 240 °C and 260 °C [2] . Another problem is the poisoning effect by carbon monoxide of HT-PEMFCs. Although the critical concentration increases with the operation temperature of HT-PEMFCs, lower concentrations of carbon monoxide are desirable, typically below 0.5 % for operation temperatures above 160 °C. Therefore, the ideal methanol steam reforming catalyst should have the following characteristics: a) Activity at temperatures below the 180 °C; b) High selectivity for hydrogen production; c) High thermal and chemical stability.

Presently, taking into account their chemical formulation, the methanol steam reforming catalysts can be divided in two main groups: copper-based catalysts and metals of group 8-10. Initially, the copper-based catalysts where used for methanol production and later become the most common formulation for methanol steam reforming. The main commercial available formulation is CuO/ZnO/Al ₂ 0 ₃ . However, this catalyst has several disadvantages, namely: small life time and pyrophoric behavior. To improve the commercial catalyst, several formulations that include rare metals in the catalysts were progressively revealed: U.S. Pat. N.° 6,576,217 [4], U.S. Pat. N.° 2002/0051747 [5] e U.S. Pat. N.° 2002/0169075 [6]. Despite some progress, the overall performance of copper-based catalysts is still far from the ideal, especially due to sintering deactivation mechanism. This phenomenon occurs, between 220 °C and 300 °C. As alternative to copper-based catalysts, Iwasa et al . was the first to report the Pd/ZnO catalyst highly selective for methanol steam reforming [7]. This surprisingly behaviour was attributed to the alloy between palladium particles and the zinc originated from the reduction of the ZnO support (PdZn) . The PdZn catalytic activity revealed to be promising when compared to copper-based catalysts, mainly due to their high thermal stability. Therefore, several studies focused in discovering which factors could contribute to improve that activity of PdZn catalysts were performed. Thus, the studied factors were: a) Surface area of the support; b) Preparation method; c) Alloy formation temperature; d) PdZn particle size.

The surface area of the support has been revealed to be an important factor. For example, U.S. Pat. N.° 2007/0191223 [8] describes a PdZn catalyst prepared on a high surface area A1 ₂ 0 ₃ support, this compound has surprisingly similar activities to copper-based catalysts. On the other hand, Karim et al . discovered that the PdZn catalyst presents a higher activity when the ZnO support is faceted [ 9 ] .

The active metals for methanol steam reforming are essentially Cu and PdZn. However, ZnO is ubiquitous in the main formulations. Despite the controversy about the role of ZnO, its promotional effect when combined with the active metal particles is well known. This effect is related to the increase of both selectivity and activity. Additionally, in copper-based catalysts is responsible by increasing the thermal stability. The surface area of the commercial ZnO support is approximately 10 m ² -g ^_1 [10] .

The majority of copper-based catalysts, including the commercially available, are prepared using the co- precipitation method, which allows the incorporation of high proportion of copper metal: 60-70 wt . % . Higher metal loadings originate higher H ₂ production. However, it would be desirable to achieve a high catalytic activities with metal loadings below to 20 wt . % which allows the reduction of the catalyst cost and the use of incipient wetness impregnation method for the deposition of active metal particles in the support. Compared to preparation methods, this method produces a higher number of active metal particles and a larger surface area.

Some inventions describe catalysts for methanol steam reforming that originates low CO concentration. For instance, U.S. Pat. No. 6,930,068 [11] reveals a catalyst that includes alloy particles of zirconium with palladium supported in a metal oxide. Although the carbon monoxide production has decreased, the incorporation of zirconium also had the effect of decreasing the activity when compared with PdZn catalysts. With the same purpose, U.S. Pat. N.° 7,569,511 [12] reveals a catalyst with yttrium in its formulation. Yttrium acts like a promoter, maintaining the typical activity for methanol steam reforming, while originating lower amounts of carbon monoxide.

Despite the efforts to found the ideal methanol steam reforming catalyst, slight advances were achieved in the last years. On one hand, copper-based catalysts are active but present low thermal stability; on the other hand PdZn- based catalysts are thermally stable but present lower activity than the copper-based ones.

The development of portable devices for generating electric power, using fuel cells integrated with methanol steam reforming only a few configurations were revealed. Generally, these devices use catalysts for the methanol reformer that are active at high temperatures (> 220 °C) and produce significant concentrations of CO. An catalyst active at lower temperatures, allows an efficiency improvement regarding the integration with a PEMFC. U.S.Pat. N.° 2007/0191223 [8], describes some configurations of microreformers for feeding hydrogen to PEMFCs, where the Pd-Zn/Al ₂ 0 ₃ catalyst should operate between 200 °C and 400 °C and preferentially between 220 °C and 300 °C; this patent does not mention the synergetic integration of the reformer with the fuel cell. US Pat 2002/0132145 [13] describes a compact system that has a synergetic integration of an PEMFC with the methanol steam reforming reaction. In this case, the non-selective membrane polydimethylsiloxane is used for separating the gases stream product of the methanol steam reforming from the gas stream that feeds the PEMFC. However, it is not revealed the catalyst used and its performance.

Description of the invention The present invention is related to methanol steam reforming catalysts, their preparation method and applications. The developed catalysts proved to be active at low temperatures, below 200 °C, producing low amounts of carbon monoxide, less than 0.5 %. For the catalysts preparation, metal oxides supports are first prepared using a method that allows the control of their morphology. As preferential support it was used ZnO. It was obtained an extremely faceted nanostructure (Figure 1); with nanosheets thinner than 100 nm - this structure is desirable to anchor active metal particles (Figure 2) .

In the developed supports, it is also possible to deposit metal particles that originate a low production of carbon monoxide, being yttrium the preferential used metal.

The principles here revealed for the methanol steam reforming catalysts preparation are suitable in the development of water-gas shift catalysts (Eq. 2) . The combination of the water-gas shift and methanol steam reforming reactions is an efficient strategy in mitigating CO production. Moreover, the copper-based catalysts are extensively used in industry for the water-gas shift reaction at low temperatures (190-250 °C) . Gold catalysts are also emerging as an alternative at low temperature range (180-250 °C) . This noble metal is not pyrophoric, and suffers less of the sintering mechanism. In copper-based catalysts, ZnO is the most used support, while in gold catalysts, the most used support is Ce0 ₂ .

The catalysts proposed in this invention demonstrated to be active even with the incorporation of low amounts of active particles. Therefore, the incipient wetness impregnation can be used as an alternative to co- precipitation method. The incipient wetness impregnation method allows the reduction of the catalysts preparation costs .

One promising application of the methanol steam reforming catalysts here revealed is the synergetic integration of the methanol steam reforming reactor with a HT-PEMFC.

Detailed description

The present invention reveals a new methanol steam reforming catalyst, its preparation and applications. The preparation method comprehends two major steps. The first one is the synthesis of the catalytic support, which is a metal oxide. The final step is the deposition of the metal active nanoparticles on the metal oxide support. The synthesized support is prepared with the purpose of maximizing the surface area. This is a desirable characteristic to increase the methanol steam reforming activity. The method here described was applied to the synthesis of several metal oxide supports. Especially zinc oxide (ZnO) has high methanol steam reforming activity; the BET (Brunauer, Emmett e Teller) surface area measurements confirmed that a high surface area ZnO support, superior to 100 m ² · g ^_1 was obtained. This value is one order higher than the 10 m ² -g ^_1 of the commercially available supports. The support morphology was analyzed by scanning electron microscopy (SEM); surprisingly, an extremely faceted morphology was obtained. Figure 1, shows the nanostructure of the synthesized ZnO support. In order to prepare a Pd/ZnO catalyst, ZnO was used as a catalyst support, originating high activity even at low temperatures, less than 180 °C. It was also verified that when the support was used with copper nanoparticles , the catalyst present activity at temperatures below 200 °C. Since, copper-based catalysts are prone to deactivate through sintering, this invention allows improving the thermal stability of copper- based catalysts, when they are operating at lower temperatures. The faceted nanostructure of the synthesized catalyst is on the basis of the described results. Carbon monoxide is an undesirable secondary product of methanol steam reforming, which is formed during methanol decomposition reaction (Eq. 2) . Being the methanol decomposition reaction a endothermic reaction, the preferential production of hydrogen through methanol steam reforming at lower temperatures decreases the amount of carbon monoxide produced. Therefore, the prepared catalysts produce less carbon monoxide when operating at 180 °C. However, it is still possible to reduce the amount of carbon monoxide produced by incorporating in the catalysts formulation promoters such zirconium, yttrium or both. It is well known that both promoters suppress the carbon monoxide production. Another strategy is the development of a water-gas shift catalyst based on the metal oxide supports here described. The application of this strategies, allows decreasing the carbon monoxide concentration in the hydrogen stream to less than 10 ppm, and therefore the direct feed to a low temperature PEMFC.

For the synthesis of the metal oxide support an aqueous solution containing 1-20 wt . % of urea and 10 wt . % of a metal salt is prepared. After obtaining a homogeneous solution the mixture is transferred to a teflon flask, which is closed and heated between 50-140 °C, for the period of time desirable to obtain the faceted nanostructure . Teflon is preferential to glass, since it avoids the deposition and grow of the precipitate particles in the flask walls. Thereafter, the flask is cooled at room temperature and the obtained precipitate is washed. This procedure allows controlling the morphology of the metal oxide support, affecting the former mentioned characteristics: high surface area and faceted structure. In other preferential application, during the metal oxide support synthesis it is added poly (ethylene glycol ) -block- poly (propylene glycol ) -block-poly (ethylene glycol) . The addition of less than 20 wt . % of this polymer to the initial aqueous solution enhances the surface area of the final metal oxide support, while maintaining its faceted structure .

After the preparation of the metal oxide support, two methods can be used for catalysts preparation: deposition- precipitation or incipient wetness impregnation. Preferentially, palladium or copper metals are used as active particles. The amount of active metal particles should be between 1-80 wt . % in the deposition-precipitation method; while in the incipient wetness impregnation method the amount of active metal particles should be between 1-30 wt . % .

In the deposition-precipitation method, a suspension is prepared, resulting from the mixture of the metal oxide support with the solution that contains the catalytic metal precursor. Then, the pH is slowly increased until it reaches the desirable value. Gradually, the catalytic metal will precipitate with the metal oxide structure. As final step, the obtained material isolated and calcined for a proper period of time.

Preferentially, the incipient wetness impregnation is applied due to its simplicity and quickness. Besides that, it is a less aggressive method towards the metal oxide support nanostructure . During the preparation, a solution that contains a metal salt is added dropwise to the support. The solvent should allow complete solvation of the metal oxide structure. Finally, the catalyst is dried, calcined and reduced.

In a preferential application of the incipient impregnation method, urea is added to the solution that contains the metal to impregnate. The deposition of urea in the catalytic support allows the improvement of the active nanoparticles . It should be added less than 10 wt . % of urea, to originate faceted nanoparticles like the support structure .

In the Pd/ZnO catalysts, the reduction can be performed during calcination with the passage of a hydrogen stream. The copper-based are reduced also with hydrogen but at a range of temperatures lower than which is used during calcination .

Preferentially to the reduction with hydrogen, it could be performed a chemical reduction of the catalysts that do not need alloy formation to be active for methanol steam reforming. After preparation, the active metal particles supported on the metal oxide should have a preferential size between 2 nm and 40 nm.

The present invention also reveals the application of methanol steam reforming catalysts in a reformer with the purpose of feeding hydrogen to an HT-PEMFC. The reformer should operate at temperatures below 200 °C, and preferentially between 160-180 °C, in the operation temperature range of the HT-PEMFCs . In this way, it is possible the synergetic integration of the HT-PEMFC with the reformer, being the heat released by the HT-PEMFC approximately 6 times superior to the heat needed for the methanol steam reforming reaction. On the other hand, the HT-PEMFC produces approximately 3 times more water than what is consumed during methanol steam reforming. This water can be recycled to the reformer, and therefore it is only needed a tank with methanol for feeding the combined system.

In the methanol steam reforming reaction, besides hydrogen, carbon monoxide and carbon dioxide are formed. The developed catalysts are active at low temperatures, with low production of carbon monoxide which is tolerated by the catalyst present in the HT-PEMFC anode (< 0.5%), when operating above 160 °C. However, with the consumption of hydrogen in the HT-PEMFC, its partial pressure diminishes which increases the concentration of the secondary products obtained during reformation as carbon dioxide and mainly of CO. To deal with this, three configurations are revealed to take advantage of the family of catalysts developed and the synergic integration between the reformer and HT-PEMFC units: 1 - Addition to the fuel cell electrocatalyst , a suitable amount of the methanol steam reforming catalyst. The fuel cell should be prepared to operate with a mixture of methanol, water and hydrogen, and therefore it could be a direct methanol fuel cell operating at high temperatures. Since, the electrochemical activity is superior in the presence of hydrogen, when using the methanol steam reforming catalyst the current density of the cell and its global efficiency should increase significantly, mainly with reduction of the crossover effect.

2 - Coupling one reactor for methanol steam reforming with a fuel cell. In this case, the mixture of water and methanol is added to the reformer, producing hydrogen that permeates preferentially through a membrane, facing on fuel cell anode. This membrane also allows the heat transfer from the fuel cell to the reformer. The source of water fed to the reformer is the obtained from the fuel cell cathode. The vaporization of the water/methanol mixture is done with the heat released by the fuel cell. The hydrogen that is not consumed in the fuel cell should be recycled to the reformer after purification through a suitable process, like a membrane process or cyclic adsorption.

3 - Use of an exterior reformer that feeds hydrogen, purified or not, directly to the fuel cell, receiving from it the heat and water necessary for the methanol steam reforming. In this configuration, the reformer should operate at inferior lower temperature than the fuel cell in order to promote an efficient heat transfer.

Finally, these catalysts can be used for producing hydrogen to other applications, even the ones that need a stream mainly free of carbon monoxide, such as low temperature PEMFC . In these cases, catalysts with promoters for suppressing the carbon monoxide production or a water- gas shift catalyst should be used (Eq. 3) . Preparation of a zinc oxide support with a controlled morphology to 100 ml of water are added 1.1 g of zinc acetate and 1.8 g of poly (ethylene glycol ) -block-ροΐγ (propylene glycol) - block-ροΐγ (ethylene glycol) (Pluronic P123). The mixture is placed in an ultrasonic bath until complete homogenization at room temperature. After that, if necessary, acetic acid is added until the solution becomes clear and placed again in the ultrasonic. Finally, the mixture is poured into a teflon flask. The flask is closed and the mixture is heated to 90 °C for 24 h. The obtained precipitate is washed with distillated water during a filtration process and calcined at 400 °C for 2 h. As result, the obtained surface area of the oxide support is superior to 100 m ² -g ^_1 . Figure 1 presents the obtained metal oxide particles morphology. It is visible a highly faceted structure.

Preparation of a Pd/ZnO catalyst by using the incipient wetness impregnation method

2 g of the ZnO support, prepared as described in the former example, are placed in the flask. A solution with 2.2 ml of chloroform and 168.7 mg of palladium acetate is added dropwise to the support. The wetted metal oxide is maintained in an ultrasonic bath for 2 h. The prepared catalyst is dried at 70 °C and calcined at 350 °C inside a tubular oven. During calcination hydrogen passes through the oven in order to reduce and promote the PdZn alloy particles formation. The atmosphere in the interior of the oven is reductive due to hydrogen flow at 100 cm ³ -min ^_1 .

Activity for hydrogen production during methanol steam reforming The methanol steam reforming activity was tested in a closed reactor that was placed inside an oven for temperature control - Figure 3. The preparation of the desired reactant mixture is performed inside a vessel, which is connected to the reactor through a valve. Both recipients are equipped with a magnetic stirrer that allows the complete mixture of the gas components. Two pressure sensors allow monitoring the pressure in both recipients. A Pd/ZnO catalyst with a surface area of 140 m ² · g ^_1 and with 4 wt . % loading was placed inside the reactor and maintained at constant agitation. After complete vacuum of the recipients, they were fed with 0.4 bar of argon at 25 °C. Following this, 380.4 mg of a water/methanol mixture, with molar fraction of 1.5, was injected to the mixture vessel. After feeding the reactants to the mixture vessel, the oven temperature was regulated to 180 °C. After temperature stabilization, the valve that connects both recipients was opened and closed after passing the reactants to the reactor. The reaction starts in the precise moment where the reactants contact with the catalyst. In the methanol steam reforming reaction the molar quantity of the products is the double of the reactants (Eq. 1) . Therefore, during the formation of hydrogen and carbon dioxide the pressure inside the reactor increases - Figure 4. The compounds present in the final reactional mixture were quantified by using an mass spectrometer: 19.40 % of hydrogen, 5.97 % of carbon dioxide, 0.43 % of carbon monoxide diluted in argon.

Summary

One object of the present invention is the preparation method of a metal oxide catalyst support, which comprises the following steps:

^■ Preparation of an two aqueous solutions, one containing urea and a metal salt and the other poly (ethylene glycol) -block-ροΐγ (propylene glycol ) -block-ροΐγ (ethylene glycol); ^■ correct the pH until solubilization of the mixture ;

^■ hydrothermal treatment of the solution;

^■ dry and heat treatment in order to obtain a metal oxide support with surface area superior to 80 m ² -g ^_1 ;

The poly (ethylene glycol ) -block-ροΐγ (propylene glycol) - block-ροΐγ (ethylene glycol) is available commercially with the following names: Pluronic L43, Pluronic L44, Pluronic L62, Pluronic L64, Pluronic P65, Pluronic F68, Pluronic P84, Pluronic P85, Pluronic F88, Pluronic P103, Pluronic P104, Pluronic P105, Pluronic F108, Pluronic P123 and Pluronic F127.

The polymer includes the following nominal formulations: E0 ₆ P0 ₂₂ E0 ₆ (molecular weight of 1850 g-mol ^-1 ), EO ₁₀ PO ₂₃ EO ₁₀ (molecular weight of 2200 g-mol ^-1 ), E0 ₆ P0 ₃₄ E0 ₆ (molecular weight of 2500 g-mol ^-1 ), EO ₁₃ PO ₃₀ EO ₁₃ (molecular weight of 2900 g-mol ^-1 ), E0 ₁₉ P0 ₂₉ E0 ₁₉ (molecular weight of 3400 g-mol ^-1 ), E0 ₇₆ P0 ₂₉ E0 ₇₆ (molecular weight of 8400 g-mol ^-1 ), E0 ₁₉ P0 ₄₃ E0 ₁₉ (molecular weight of 4200 g-mol ^-1 ), EO ₂₆ PO ₄₀ EO ₂₆ (molecular weight of 4600 g-mol ^-1 ), EO ₁₀₃ PO ₃₉ EO ₁₀₃ (molecular weight of 11400 g-mor ¹ ), EO ₁₇ PO ₆₀ EO ₁₇ (molecular weight of 4950 g-mol ^-1 ), E0 ₂₇ P0 ₆₁ E0 ₂₇ (molecular weight of 5900 g-mol ^-1 ), E0 ₃₇ P0 ₅₆ E0 ₃₇ (molecular weight of 6500 g-mol ^-1 ), EO ₁₃₂ PO ₅₀ EO ₁₃₂ (molecular weight of 1850 g-mol ^-1 ), E0 ₆ P0 ₂₂ E0 ₆ (molecular weight of 14600 g-mol ^-1 ), E0 ₁₉ P0 ₆₉ E0 ₁₉ (molecular weight of 5750 g-mol ^-1 ), EO ₁₀₀ PO ₆₅ EO ₁₀₀ (molecular weight of 12600 g-mol ^-1 ) .

In a preferential aspect the precipitate is dried until the metal oxide formation with a surface area superior to 120 m ² -g ^_1 , and preferentially 140 m ² -g ^_1

In another preferential aspect the mixture is heated until the formation of a faceted precipitate. In another preferential aspect, the metal oxide catalytic support is prepared by performing the following steps:

^■ prepare an aqueous solution containing, o 1-20 wt . % of urea; o 1-10 wt . % of metal salt; o 0.05-20 wt . % of poly (ethylene glycol) - block-ροΐγ (propylene glycol ) -block- poly (ethylene glycol), where the percentages correspond to the fraction of the component in water;

^■ correct the pH until solubilization of the mixture ;

^■ heat the mixture in a closed flask at a tempeture between the 40-130 °C, until formation of a precipitate;

^■ cooling the flask at room temperature;

^■ wash, dry and calcinate the precipitate until obtaining the metal oxide.

In other preferential aspect, the concentration of the poly (ethylene glycol ) -block-poly (propylene glycol ) -block- poly (ethylene glycol) is of 0.1-3 wt.%, and preferentially 2 wt.% and, the mixture is heated for 18-30 h and preferentially 24 h, until the precipitate formation.

In another preferential aspect, the mixture is heated in a closed flask at a temperature between 80-130 °C, preferentially 90-120 °C, more preferentially 40-130 °C and more preferentially 60-120 °C, being the referred flask of glass or polytetrafluoroethylene - PTFE . In another preferential aspect, the metal salts are Zn, Ce, Pr, Nd, Nb, Al, Y, Cu, La, Ga, In, Sn, Fe, Ti, Zr or Cr, or their mixtures and preferentially, the metal salts are nitrates or acetates.

In another preferential aspect, it are incorporated the metal active particles in the metal oxide support and it is added a promoter, preferentially Y, Zr.

In another preferential aspect of the present invention is a composite catalyst that contains:

-One metal or a combination of metal nanoparticles ;

-One metal oxide support, where the referred metal or metal nanoparticles are deposited and the referred support has surface area superior to 80 m -g ;

In another preferential aspect, the surface area of the support is superior to 10 n^-g ¹ , being the referred support of zinc oxide and has a structure with several faceted nanosheets (face 0001) and a superficial area superior to 120 m ² -g ^_1 , preferentially 140 m ² -g ^_1 .

In another preferential aspect, the catalyst has nanosheets with a thickness of 5-50 nm, and preferentially 20-40 nm, and even more preferentially 25, 28 or 30 nm.

In another preferential aspect the catalyst can be active at temperatures above 160 °C, and preferentially at 200 °C, and even more preferentially between 180-220 °C. In another preferential aspect, in the steam reforming reaction the concentration of carbon monoxide is less than 0.5 %, being lower with the incorporation of promoters in the catalyst such Y or Zr.

In another preferential aspect, the active metal is palladium, zinc, copper, gold, platinum or its mixtures.

In another preferential aspect, the support is ZnO, Y ₂ 0 ₃ , Ce0 ₂ , A1 ₂ 0 ₃ , La ₂ 0 ₃ , Ga ₂ 0 ₃ , ln ₂ 0 ₃ , Sn0 ₂ , Fe ₂ 0 ₃ , Ti0 ₂ , Zr0 ₂ , Nd ₂ 0 ₃ , NbO, Pr,0 _R or Cr,CL or its mixtures, or even more preferentially the catalyst is Pd-Zn-Y/Ce0 ₂ or Pd-Y/ZnO or Pd/ZnO or Cu-Zn/YCe0 ₂ or Cu/YZnO or Cu/ZnO or Cu-Zr/YCe0 ₂ or Cu-Ce-Zr or Cu-Ce-Zn or Cu-Ce-Y-Zn or Cu-Ce-Y-Zr or Cu-Ce- La-Zr or Cu-Ce-La-Zn or Cu-Ce-Pr-Zn or Cu-Ce-Pr-Zr.

In another preferential aspect, the catalyst contains copper and the support contains zinc oxide. In another preferential aspect, the catalyst contains gold (Au) and the support contains Ce0 ₂ .

In another preferential aspect, the metal nanoparticles , of the referred metal or metals, have a size between 2-40 nm, but of 2-5 nm to gold and 2-20 nm for copper nanoparticles .

In another aspect of the present invention is a fuel cell that contains a catalyst as above described, being the fuel cell a HT-PEMFC.

Another aspect of the present invention is the use of the catalyst described above, where the support is obtained by the method described above, in the methanol steam reforming reaction at 160 °C, and preferentially at 180-220 °C. Another aspect of the present invention is the use of the catalysts described above and obtained by the method described above in the water-gas shift reaction.

Another aspect of the present invention is the use of the catalyst described above and obtained by the method described above in the dimethyl ether steam reforming reaction. In this case, the catalyst here described should be combined with a metal oxide support that has acid groups for promoting dimethyl ether hydrolyses to methanol, and preferentially gamma-alumina ( *-Al ₂ 0 ₃ )

Summary description of the figures :

For easily understand this invention figures are that represent preferential aspects of the invention; however, they do not limit the application range of the present invention .

Figure 1 - ZnO particles image obtained by scanning electron microscopy.

Figure 2 - Nanosheets of the ZnO support image obtained by scanning electron microscopy.

Figure 3 - Scheme of the integrated system of reformer with fuel cell, where 1 is the methanol reformer, 2 the purification system of hydrogen, 3 the HT-PEMFC and 4 the synergetic integration (T _HT _ _PEMFC > T _reformer ) .

Figure 4 - Schematic representation of the experimental set-up used for testing the catalysts activity, where 5 is the inert gas, 6 is the vacuum line, 7 the mass spectrometer, 8 the vacuum pump, 9 the oven, 10 the injection of the H ₂ 0/CH ₃ OH mixture, 11 the pneumatic valve, 12 the mixing tank, 13 the reactor and 14 the magnetic stirrer .

Figure 5 - Steam reforming reaction pressure history in the closed reactor. It was used a 4 wt . % Pd/ZnO catalyst.

Figure 6 - Cerium oxide particles image obtained by scanning electron microscopy.

Figure 7 - Copper oxide particles image obtained by scanning electron microscopy.

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[12] C.R. Castellano, Y. Liu, A. Moini, G.S. Koermer, R.J. Farrauto, "Catalyst composition for alcohol steam reforming", US7569511, 2009.

[13] W. Preidel, "Fuel cell with internal reformer and method for its operation", US0132145, 2002.

The following claims set out a particular embodiment the invention.