WO2006045951A1

WO2006045951A1 - Use of rare earth and metal mixed oxyhydrides for the conversion of alkanes into co and h2 at low temperature

Info

Publication number: WO2006045951A1
Application number: PCT/FR2005/002665
Authority: WO
Inventors: Hanan Zarrou; Louise Duhamel
Original assignee: Centre National De La Recherche Scientifique (C.N.R.S.); Universite Des Sciences Et Technologies De Lille
Priority date: 2004-10-25
Filing date: 2005-10-25
Publication date: 2006-05-04
Also published as: FR2876996A1

Abstract

The invention relates to the use of a material made from a mixed oxyhydride of at least one rare earth and at least one metallic element other than a rare earth, for the catalysis of a partial oxidation reaction of an alkane to give a mixture of H<SUB>2</SUB> and CO at a temperature below 200° C. The invention further relates to fuel cells which may be used at low temperature using said reaction.

Description

Use of mixed rare earth metal oxyhydrides for the conversion of alkanes to CO and H ₂ at low temperatures

The present invention relates to a process for converting alkanes to a mixture of CO and H ₂ by a partial oxidation reaction. This partial oxidation reaction can in particular be used to provide the anode of a SOFC type fuel cell with a mixture of CO and H ₂ , from an alkane such as methane present in natural gas or else still from cycloalkanes.

The partial oxidation of an alkane is a well-known reaction, whose balance equation can be written in the following form:

C _n H _{2n + 2} + (n / 2) O ₂ → (n + 1) H ₂ + n CO (C _n H _2n ⁺ (n / 2) O ₂ → n H ₂ + n CO, in the case of a cycloalkane)

For more details on this reaction, see in particular Science, vol. 259, p. 343 (1993) or Nature, vol. 344, p. 319 (1990).

This partial oxidation reaction is used in particular for the preparation of hydrogen from alkanes, in particular from methane, which is the alkane which is the most interesting in this respect, insofar as it has the highest H-ratio. /VS. Thus, the partial oxidation reaction is used in particular to convert the natural gas, rich in methane, into a mixture of CO and H ₂ (so-called "synthesis gas").

Whatever its use, the partial oxidation reaction of the alkanes is generally conducted in the presence of a catalyst. In this context, many types of catalysts have been proposed, including catalysts based on supported metals or even catalysts of the metal oxide type. Some of these catalysts have proven interesting in terms of conversionι_jje alkane and _selectivity, hydrogen formed. Nevertheless, to obtain such a catalytic activity, the use of high temperatures is most often required. Thus, Really interesting catalytic activities are rather obtained by implementing temperatures of the order of 700 to 800 ^° C.

A particular use of the partial oxidation reaction of alkanes in a mixture of CO and H ₂ is that of fuel cells, in particular fuel cells of SOFC type (solid oxide electrolyte fuel cell).

Fuel cells use an anode reduction reaction of hydrogen. Conventionally, the hydrogen used in this context is introduced as such into the cell, which requires a large amount of hydrogen storage. In particular, to avoid such storage of hydrogen, another technology has been developed, which consists in introducing into the cell not hydrogen but an alkane type fuel (in particular natural gas, rich in methane), which is converted in situ to syngas (CO + H ₂ ), thereby providing the anode with the hydrogen necessary for the reduction reaction.

To convert the alkane fuel into synthesis gas within the fuel cell, a method used is that of the reforming, which implements endothermic reactions, of the following type:

C _n H _{2n + 2} + n CO ₂ → (n + 1) H ₂ + 2n CO (dry reforming) C _n H _{2n + 2} + n H ₂ O → (2n + 1) H ₂ + n CO (steam reforming )

Given the endothermic nature of these reactions, the reforming processes have the major disadvantage of requiring the implementation of significant energy, which is reflected in particular in terms of process costs. To the above-mentioned reforming processes, processes are therefore preferably used which implement a partial oxidation of the fuel, which has the advantage of being exothermic, and therefore requires a lower energy input than the reactiOrïss ^~ deπ "étorrήagë7

However, the processes developed in this context require the implementation of high temperatures, typically well above 600 ⁰ C, to obtain efficient conversion of the alkane associated with a high selectivity of formation of hydrogen.

These high temperatures are likely to lead to the formation of carbon (coking phenomenon), which can poison the catalyst, or more simply, clog the battery and impair its effectiveness.

In addition, the need to implement high temperatures prohibits the implementation of certain technologies for fuel cells. Thus, for example, fuel cells employing a device of the steel plate reactor type, envisaged for example in J. Electrochem. Soc. 149, vol. 7, p.59 (2002), are generally used at temperatures of the order of 500 ^° C at most, temperatures at which most catalysts of the partial oxidation of alkanes currently known have poor catalytic activities.

There are rare documents describing catalysts made at less than 500 ° C. For example, US Pat. No. 5,111,927 discloses partial oxidation conducted between 200 ^° C. and 1000 ^° C.

An important issue would be obtaining fuel cells implementing the partial oxidation reaction of alkane capable of operating at even lower temperatures, for example between 15 and 200 ⁰ C, and preferably at room temperature (typically between 15 and 30 ^° C.), which catalysts currently used for the partial oxidation reaction of alkane do not make it possible to obtain with an acceptable efficiency.

An object of the present invention is to provide a process for converting alkanes to H ₂ and CO, which is economically interesting and is at least as effective as current processes in terms of alkane conversion and selectivity of the alkane. hydrogen formation, but at a lower temperature.

In this context, the object of the invention is in particular to provide a process for conversion of alkane into an effective hydrogen which is suitable for use within a fuel cell, in particular in a fuel cell. SOFC type fuel, without requiring high working temperatures.

For this purpose, according to a first aspect, the present invention proposes the use of a material based on a mixed oxyhydride of at least one rare earth and at least one metal element other than a rare earth to catalyze a partial oxidation reaction of an alkane in a mixture of H ₂ and CO, at a temperature below 200 ^° C.

By "rare earth" is meant, in the sense of the present description, an element selected from the group consisting of scandium, yttrium and lanthanides, the lanthanides being the elements of atomic number between 57 and 71, namely elements ranging from lanthanum to lutetium, inclusively.

Moreover, the meaning of the present description, the term "oxyhydride mixte- at least ^~ ^~ a rare earth and at least one metal element other than rare earth" refers to a solid which comprises metal cations of one or more rare earths, metal cations of one or more metallic elements other than rare earth, O ^{2 -} anions and hydride ions.

According to a first embodiment, this mixed oxyhydride has the structure of an intermetallic oxide of the rare earth (s) and of the metallic element (s) and further comprises hydride ions at within anionic gaps of the crystalline lattice of this intermetallic oxide.

Alternatively, the oxyhydride used according to the invention may also be a mixture of several distinct metal oxides based on the rare earth (s) and the other metallic element (s), where all or a portion of these oxides include hydride ions within anionic gaps of their lattice. Preferably, the mixed oxyhydrate preferably contains at least one oxyhydride of the rare earth (s) ( s), namely an oxide of the rare earth (s) including hydride ions within anionic gaps of its crystal lattice. Thus, according to one variant, the mixed oxyhydride may consist of a mixture of several oxyhydrides, this mixture being, for example, in the form of oxyhydride crystallites based on the metallic element (s) other (s). ) that rare earths dispersed within a matrix based on an oxyhydride of the rare earth (s).

According to another possible variant, the mixed oxyhydride may also be based on a mixture comprising, on the one hand, oxyhydrides and, on the other hand, oxides that do not comprise hydride ions. Where appropriate, the oxyhydrides advantageously comprise one or more oxyhydrides based on the rare earth (s) and an oxide based on the other metallic element (s). According to this particular mode, the catalyst may for example comprise oxide crystallites based on the element (s) metal (s) other (s) that rare earths dispersed within a matrix based on an oxyhydride of the rare earth (s).

The work of the inventors made it possible to demonstrate that, quite unexpectedly, materials based on a mixed oxyhydride of at least one rare earth and at least one metal element other than a rare earth of The above-mentioned type are particularly effective catalysts for the partial oxidation reaction of an alkane at CO and H ₂ , and at a low temperature.

Thus, these catalysts make it possible to obtain very interesting results both in terms of the conversion rate of the alkane and the selectivity for hydrogen formed, at temperatures below 200 ^° C.

By "conversion rate of the alkane" in a partial oxidation reaction of an alkane is meant, in the sense of the present description, the following ratio C (expressed as a percentage):

C = (Do alkane - alkane N) / N _has lcane where: - N _'a i _ca π _e represents the number of moles of alkane introduced

- N ^f _a | _Ca n _e represents the number of moles of alkane remaining after the reaction Furthermore, the term "hydrogen selectivity formed" in a partial oxidation reaction of an alkane means the following ratio S (expressed as a percentage):

S = N H2 / 2 (N ' _a | cane ~ N alkane) where: - N'aicane represents the number of moles of alkane introduced

- N ^f _a i _ca n _e represents the number of moles of alkane remaining after the reaction; and

- N ^f _H2 represents the number of moles of hydrogen formed during the reaction.

The inventors have in fact found that by using a mixed oxyhydride of at least one rare earth and at least one metal element other than a rare earth, it is possible to obtain conversions of alkanes which may be greater than 50%, for example greater than or equal to 60%, and most often greater than or equal to 70%, with, at the same time, hydrogen selectivities formed of up to 50%, or even at least 70%, and even 80% at temperatures below 200 ° C.

These interesting properties of low temperature catalysis are quite surprising in view of the results observed with the currently known alkane partial oxidation catalysts, where high temperatures are required to obtain both a high alkane conversion. and a formed hydrogen selectivity that is acceptable.

Even more unexpectedly, the work of the inventors has made it possible to demonstrate that mixed oxyhydrides of at least one rare earth and of at least one metal element other than a rare earth generally have a catalytic activity of interest on a particular surface. wide temperature range. Thus, most often, these oxyhydrides make it possible to obtain a good conversion of the alkane and a good selectivity for formed hydrogen, even at ambient temperature (ie at temperatures of 15 to 30 ^° C., for example of the order of 20 ⁰ C). Thus, it turns out that a mixed oxyhydride of at least one rare earth and at least one metal element other than a rare earth may be used to catalyze a partial oxidation reaction of an alkane into a mixture of H2 and CO at a temperature of between 10 ° C and 200 ° C, obtaining both high values of alkane conversion and hydrogenated selectivity formed. Interesting results are obtained for temperatures greater than or equal to 50 ^° C., and even more so for temperatures greater than or equal to 100 ° C. Nevertheless, in the most general case, it is not necessary that the temperature of implementation of the partial oxidation reaction is greater than 200 ⁰ C for interesting catalytic properties are observed. Thus, very advantageous properties are obtained for example at temperatures between 15 and 18O ⁰ C. Thus, partial oxidation reactions conducted at temperatures of the order of 15 to 100 ° C lead to obtaining interesting results. in terms of alkane conversion and selectivity to formed hydrogen.

The work of the inventors has made it possible to establish that advantageous results are in particular observed when the oxyhydride used is obtained by treating with hydrogen a dried or calcined mixture of oxides and / or hydroxides of the ( or rare earth (s) and metal element (s) other than rare earths.

Thus, according to a particularly advantageous embodiment, it is advantageous for the mixed oxide used according to the invention to be obtained according to a process comprising the following steps:

(A) making a mixture of hydroxides of the rare earth (s) and the metal element (s) other than rare earths;

(B) subjecting the hydroxide mixture of step (A) to drying and / or heat treatment; and

(C) contacting the solid from step (B) with hydrogen.

The "hydroxide mixture" formed in step (A) may, in general, be any mixture comprising metal cations of the (or) rare earth (s) and the metallic element (s) other than rare earths and OH ^' ions, this mixture possibly being, for example, a mixed intermetallic hydroxide or a physical mixture of several metal hydroxides. Advantageously, the hydroxide mixture produced in step (A) is an intermetallic hydroxide of the rare earth (s) and of the metallic element (s) other (s). ) only rare earths.

Preferably, step (A) is carried out by performing a coprecipitation of metal salts of the rare earth (s) and of the metallic element (s) other than rare earths in a basic medium, in general, by adding an aqueous or aqueous-alcoholic solution of the metal salts corresponding to a base, in particular of the amine type (for example triethylamine). In this context, the metal salts used are advantageously nitrates.

As a general rule, especially when the hydroxide mixture of step (A) is obtained by coprecipitation in a basic medium, the hydroxide mixture obtained is most often recovered by filtration, and is then advantageously washed, for example by water and / or by an alcohol (methanol or ethanol for example), this washing being, where appropriate, preferably carried out with a water / alcohol mixture, for example a water / methanol mixture.

Step (B) may, according to a particular embodiment, consist of a simple drying of the hydroxide mixture obtained in step (A).

According to another embodiment, step (B) comprises a heat treatment of the hydroxide mixture. If appropriate, this heat treatment is advantageously preceded by a step of drying the hydroxide mixture, in particular to allow a homogeneous temperature rise during the heat treatment.

preferably carried out at a temperature of at least 300 ^° C., advantageously at least 400 ^° C., this temperature nevertheless remaining preferably below 700 ° C., and more preferably below 600 ^° C. In a particularly advantageous manner, it is preferred that this temperature be of the order of 500 ° C. Preferably, this heat treatment is carried out by bringing the mixture of hydroxides of step (A) to the calcination temperature with a Controlled temperature rise gradient, this temperature rise gradient being advantageously between 10 ° C per hour and 500 ° C per hour, and preferably between 25 ° C per hour and 100 ° C per hour.

With regard to step (C), the inventors have demonstrated that the solid obtained at the end of step (B) behaves as a "hydrogen reservoir" particularly capable of incorporating hydride ions in its crystalline structure when it is brought into contact with hydrogen. Without wishing to be bound to a particular theory, the work of the inventors makes it possible to argue that the catalytic properties obtained for the oxyhydride are all the more interesting as the quantity of hydride ions incorporated in the solid during step (C ) is high. In this context, the inventors have demonstrated that there is an optimum treatment temperature in step (C), to obtain a maximum incorporation of hydride ions. This optimum temperature depends on the nature of the rare earth (s) and other metallic element (s) other than rare earths. It can easily be determined for a given solid by observing the amount of hydrogen absorbed by the solid at different temperatures. As a general rule, this optimum temperature is between 25 ° C. and 1000 ^° C., and most often between 150 ° and 350 ° C.

It is advantageous that the treatment of step (C) is carried out at a temperature of the order of the above-mentioned optimum temperature allowing a maximum incorporation of hydride ions into the catalyst. For this purpose, step (C) is typically conducted at a temperature of between 25 ° C. and 500 ^° C., for example between 150 ^° C. and 35 ^° C., for example between 180 and 250 ° C. (typically at a temperature of the order of 200 ° C).

According to another conceivable embodiment, the mixed oxide used according to the invention can also be obtained according to a process comprising the following steps: (A ') depositing a mixture based on hydroxides of the rare earth (s) on an oxide support of the metallic element (s) other (s) that rare earths;

(B ') subjecting the supported hydroxide mixture of step (A') to drying and / or heat treatment; and

(C) contacting the solid from step (B) with hydrogen.

Where appropriate, the steps (B ') and (C) are advantageously carried out under the same temperature conditions as the steps (B) and (C) above.

Whatever its exact mode of production, the mixed oxyhydride used according to the invention advantageously has a molar ratio rare earth (s) / other (s) element (s) metal (s) between 1: 0 , 01 and 1: 10, this ratio being preferably between 1: 0.05 and 1: 6.

Thus, according to a particularly advantageous embodiment, the mixed oxyhydride used according to the invention corresponds to the general formula (I) below:

T W1 ₃ O _x Hy (1) in which:

T represents a rare earth, or a mixture of rare earths, T being advantageously cerium or a mixture of rare earths comprising cerium;

M denotes a metallic element, or a mixture of metallic elements, other than a rare earth, M being advantageously chosen from the elements Zr, Al, Ni, Pt, Pd, Cu, Mn, Fe, Cr, Co, Rh, Ru, Ir, Os, Mo, V, Ti, W, Au, Zn, Nb, and mixtures thereof;

a is between 0.01 and 10, for example between 0.02 and 8 (typically between 0.05 and 6);

x is between 1 and 10; and - is between 0.1 and 100.

Even more advantageously, the mixed oxyhydride used corresponds to the general formula (II) below:

TM ¹ _a i M ^{2 a} ₂ θ _x Hy (11) in which:

T represents a rare earth, or a mixture of rare earths;

M ¹ denotes a metal chosen from Zr or Al;

M ² denotes a metallic element, or a mixture of metallic elements, other than zirconium, aluminum and rare earths, for example Ni, Pt, Pd, Cu, Mn, Fe, Cr, Co, Rh, Ru ₁ Ir, Os,

Mo, V, Ti, W, Au, Zn, Nb, or a mixture of two or more elements, M ² being advantageously nickel, or alternatively platinum or palladium (where nickel is preferred, because less expensive); - ai is between 0 and 1;

- a2 is between 0.01 and 10, a2 being generally less than or equal to 8, a2 being most often between 0.05 and 5;

x is between 1 and 10; and

- is between 0.1 and 100.

Thus, according to a first variant of the invention, the mixed oxyhydride used corresponds to the general formula (IIa) below:

in which

- T, M ² , a2, x and y have the aforementioned meanings; and - ai is between 0.1 and 1. In the context of this first variant, T advantageously represents cerium. Thus, the mixed oxyhydride advantageously corresponds to the following formula (IIa-1):

This Zr _a1 _a2 M ² O _x H _y (IIa-1) wherein M ^2, ai, a2, x and y have the abovementioned meanings.

More preferably still, the mixed oxyhydride has the following formula (Ila-2):

This Zr _is Ni ₂ O _x H _y (11a-2) in which a 1, a 2, x and y have the abovementioned meanings, where ai is preferably between 0.4 and 0.6, and a2 is preferably between 0 and , 5 and 5.

Thus, for example, the oxyhydride used may advantageously be a ternary oxyhydride of cerium, zirconium and nickel having the following general formula (IIa-3): This Zr _o , ₅ Ni a ₂ O _x H _y (11a-3) in wherein a2, x and y have the abovementioned meanings, a2 being preferably between 1 and 5.

Thus, as oxyhydrides that can be used according to the first variant of the invention, mention may be made in particular of the oxyhydrides which are described in application FR 2 846 648. Particularly interesting in this context are the oxyhydrides of formula (IIa-3) where a ₂ = 1, 3, 4 or 5.

According to a second variant of the invention, the mixed oxyhydride used corresponds to the general formula (IIb) below: Al f _a1 _a2 * M O _x H _y (Hb) wherein

- T, M ² , a2, x and y have the aforementioned meanings; and ai is between 0.1 and 1.

Here again, T advantageously represents cerium and the mixed oxyhydride (Hb) according to this second variant preferably corresponds to the following formula (IIb-1): This Al _a1 _a2 M ² O _x Hy (b-1) wherein M ^2, ai, a2, x and y have the abovementioned meanings.

More preferably, the mixed oxyhydride has the following formula (IIb-2):

This AI _a1 Ni ₃₂ O _x H _y (IIb-2) wherein ai, a2, x and y have the abovementioned meanings, have for example being between 0.4 and 0.6, and A2 being preferably between 0, 5 and 5.

Thus, for example, the oxyhydride used in this embodiment may advantageously be a ternary oxyhydride cerium, aluminum and nickel, having the general formula (IIb-3): This Alo, ₅ Ni ₃₂ O _x H _y (IIb- 3) in which a2, x and y have the abovementioned meanings, a2 being preferably between 1 and 5. Of particular interest are the oxides of formula (IIb-3) in which a2 = 1 or 3.

According to a third variant of the invention, the mixed oxyhydride used corresponds to the general formula (II) below:

_A2 TM ² O _x H _y (Ile) wherein T, M ^2, a2, x and y have the abovementioned meanings.

in the following formula (llc-1):

This M ^{2 a} ₂ O _x Hy (llc-1) wherein M ² , a 2, x and y have the aforementioned meanings.

Thus, for example, the oxyhydride used in this embodiment may advantageously be a binary oxyhydride cerium and nickel having the general formula (llc-2): This Ni ₃₂ O _x Hy (llc-2) wherein a2, x and y have the abovementioned meanings, a2 being preferably between 0.05 and 2, for example between 0.1 and 1 and typically between 0.2 and 0.8.

Whatever their exact nature, the oxyhydrides of the present invention are particularly useful for converting alkanes to a mixture of CO and H ₂ at low temperatures.

In this context, according to one particular aspect, the present invention specifically relates to the use of the oxyhydrides of the invention for converting methane, for example methane contained in natural gas, into a mixture of CO and H _2, in the aforementioned temperature ranges, advantageously between 10 and 200 ⁰ C, and preferably at a temperature below 180 ⁰ C, more preferably at a temperature below 15O ⁰ C, and typically between 15 and 100 ⁰ C, by example between 50 and 100 ° C.

According to another particular aspect, the subject of the present invention is also the use of the oxyhydrides of the invention for converting a cycloalkane, for example cyclohexane or a mixture containing it, into a mixture of CO and H 2 in the aforementioned temperature ranges, and preferably at a temperature below 200 ⁰ C, for example at a temperature between 15 and 100 ° C.

According to yet another more specific aspect, the oxyhydrides of the invention are advantageous for implementation within a fuel cell, in particular within a SOFC type fuel cell. In this context, the subject of the invention is in particular a method for generating a current or an electrical voltage by means of a fuel cell, most often an SOFC-type cell, where said fuel cell comprises , as anode, a material based on a mixed oxyhydride of at least one rare earth and au. minus a metallic element other than a rare earth as defined above, and wherein the fuel cell is used by supplying an alkane at said anode at an operating temperature of less than 200 ° C, the method being able to be used in the aforementioned low temperature ranges, for example at temperatures below 180 ° C, especially at less than 150 ° C, and typically between 15 and 100 ° C, for example between 25 and 100 ° C.

The invention also relates to fuel cells, in particular of the SOFC type, for the implementation of the aforementioned method, these fuel cells comprising: - an anode to. base of a mixed oxyhydride-d -'- at least one rare earth and at least one metal element other than a rare earth as defined above; and

means for conveying an alkane to said anode.

In these fuel cells, the anode may consist essentially of mixed oxyhydride. However, according to a more advantageous embodiment, in particular from an economic point of view, the anode comprises said mixed oxyhydride in the state supported on a solid support, in particular a support based on an inorganic oxide, such as, for example a silica support.

The fuel cells of the invention generally further include means for controlling the operating temperature at a temperature below 200 ° C, and preferably within the temperature ranges, for example between-15-and-1-00 - G.

However, according to a more particular aspect, the invention also relates to more specific fuel cells, intended to operate at ambient temperature (typically at temperatures between 10 and 50.degree. example between 15 ° C and 30 ^° C), which are devoid of heating means. The oxyhydrides of the invention, which have acceptable catalytic properties, or very good in some cases, allow the preparation of such fuel cells, in particular SOFC type, operating at very low temperatures.

The features and various advantages of the present invention will become even clearer in view of the illustrative examples set forth below.

EXAMPLES

Example 1

Preparation of catalysts based on ternary oxyhydrides of cerium, zirconium and nickel

Several catalysts (1A to 1F) based on ternary oxyhydrides of cerium, zirconium and nickel having a zirconium / cerium molar ratio of 0.5 and different nickel / cerium molar ratios were prepared. In other words, these catalysts are based on an oxyhydride of formula CeZro _, Ni _a2 θ _x H _y (formula IIIa-3) _, having different values of a2 which are indicated in Table 1 below. These catalysts 1A to 1F were prepared according to the following steps 1.1 to 1.3:

1.1. Preparation of a mixture of hydroxides of cerium, zirconium and nickel by coprecipitation of the corresponding metallic nitrates in basic medium.

A solution of nitrates of cerium, zirconium and nickel was made by mixing:

(i) 20 ml of a 0.5M aqueous solution of cerium nitrate;

(ii) 10 ml of a 0.5M aqueous solution of zirconium nitrate; and

(iii) a volume V1 of (20 x a2) ml of a 0.5M aqueous solution of nickel nitrate, where a2 is the desired nickel / cerium molar ratio for the oxyhydride of the catalyst. The volumes of aqueous nickel nitrate solution used in each case are reported in Table 1 below.

The resulting mixture was stirred for 10 minutes.

The solution obtained at the end of the mixture was added dropwise to a volume V2 of a solution of triethylamine at 1.5M in methanol. The volume V2 used in each case is reported in Table 1 below. During this addition, the formation of a precipitate of metal hydroxides was observed.

The hydroxide mixture thus formed was recovered by filtration (porosity filter 3) and then washed and rinsed with a total volume equivalent to the volume recovered, and this time with water and methanol.

1.2. Drying and possible calcination under air at 500 ° C.

The washed hydroxide mixture obtained at the end of the preceding step was dried at 120 ° C. in an oven for 12 hours. A solid was then obtained which was then ground in a mortar in the form of a fine powder. Except in the case of the preparation of catalyst 1 B, the powder obtained after the preceding grinding was then heated to 500 ° C in air, with a temperature rise rate of 30 ^° C. per hour. The solid was kept at 500 ° C for 4 hours, after which it was allowed to cool to room temperature. The catalysts subjected to the calcination step will be referred to herein as "calcined" catalysts as opposed to "dried" catalyst 1B.

1.3. Hydrogen treatment

The solid resulting from step 1.2 was then treated under a flow of hydrogen at a temperature of 200 ° C. for 12 hours, whereby the catalyst was obtained in the activated state, ready for implementation in the partial oxidation reaction of an alkane.

The different characteristics of the catalysts 1A to 1F and of their preparation process are reported in Table 1 below. TABLE 1 Catalysts 1A to 1F (CeZrO ₅ NJa _{2 type} )

(*): Catalyst 1C comprises the oxyhydride in the state supported on silica.

Example 2 Preparation of catalysts based on ternary oxyhydrides of cerium, aluminum and nickel

Two ternary oxyhydride catalysts (2A and 2B) of cerium, aluminum and nickel having an aluminum / cerium molar ratio of 0.5 and two distinct nickel / cerium molar ratios were prepared. These catalysts are based on an oxyhydride of formula CeAllo, 5Ni _a 2θ _x H _yι (formula _IIb -3), having different values of a2 which are specified in Table 2 below. These catalysts 2A and 2B were prepared according to the following steps 2.1 to 2.3: •

2.1. Preparation of a mixture of hydroxides of cerium, aluminum and nickel by coprecipitation of the corresponding metal nitrates in medium-basic.

A solution of nitrates of cerium, aluminum and nickel was made by mixing: (i) 20 ml of a 0.5M aqueous solution of cerium nitrate;

(ii) 10 ml of an aqueous solution of aluminum nitrate of concentration O ₁ 5M; and (iii) a volume V1 of (20 x a2) ml of a 0.5M aqueous solution of nickel nitrate, where a2 is the desired nickel / cerium molar ratio for the catalyst oxyhydride. The volumes of aqueous solution of nickel nitrate used in each case are reported in Table 2 below. The resulting mixture was stirred for 10 minutes.

The solution obtained at the end of the mixture was added dropwise to a volume V 2 of a solution of triethylamine at 1.5M in methanol. The volume V 2 used in each case is reported in Table 2 below. During this addition, the formation of a precipitate of metal hydroxides was observed. ^'

2.2. Drying and Calcination in Air at 500 ° C. The washed hydroxide mixture obtained at the end of the preceding step was dried at 120 ° C. in an oven for 12 hours. A solid was then obtained which was then ground in a mortar in the form of a fine powder.

The powder obtained after the preceding grinding was then heated to 500 ° C. in air, with a temperature rise rate of 30 ^° C. per hour. The solid was kept at 500 ° C for 4 hours, after which it was allowed to cool to room temperature.

2: 3 ^"Traitëmenf by IWD roqèn ^e.

The solid resulting from step 2.2 was then treated under a flow of hydrogen at a temperature of 200 ° C. for 12 hours, whereby the catalyst in the activated state, ready for implementation in the partial oxidation reaction of an alkane.

The different characteristics of the catalysts 2A to 2B and of their method of preparation are reported in Table 2 below.

Table 2: Catalysts 2A and 2B (CeAl type _n , sNi _a ?)

Example 3

Preparation of catalysts based on a binary oxyhydride of cerium and nickel

Several catalysts (3A to 3E) based on binary oxyhydrides of cerium and nickel having different nickel / cerium molar ratios were prepared. Thus, these catalysts are based on a formula of oxyhydride CeNi _a2 θχH _y (formula llc-2), with different values of a2, shown in Table 3 below. These catalysts 3A to 3E were prepared according to the following steps 3.1 to 3.3:

3-1- Preparation- d ¹ a ^~ -mélarrge of hvdroxydes cerium ^'and nickel copréeipitation of the corresponding metal nitrates in basic medium.

A solution of nitrates of cerium, zirconium and nickel was made by mixing: (i) 20 ml of a 0.5M aqueous solution of cerium nitrate; and

(ii) a volume V1 of (20 x a2) ml of a 0.5M aqueous solution of nickel nitrate, where a2 is the desired nickel / cerium molar ratio for the catalyst oxyhydride. The volumes of aqueous nickel nitrate solution used in each case are reported in Table 3 below.

The resulting mixture was stirred for 10 minutes.

The solution obtained at the end of the mixture was added dropwise to a volume V 2 of a solution of triethylamine at 1.5M in methanol. The volume V2 used in each case is reported in Table 3 below. During this addition, the formation of a precipitate of metal hydroxides was observed.

3.2. Drying and possible calcination under air at 500 ° C.

The washed hydroxide mixture obtained at the end of the preceding step was dried at 120 ^° C. in an oven for 12 hours. A solid was then obtained which was then ground in a mortar in the form of a fine powder.

The powder obtained after the preceding grinding was then heated to 500 ° C. in air, with a temperature rise rate of 30 ° C. per hour. The solid was kept at 500 ° C for 4 hours, after which it was allowed to cool to room temperature.

3.3. Hydrogen treatment

The solid from step 3.2 was then treated in a stream of hydrogen cTuπê ^the temperature 10 ^'0 ⁰ C for 12 hours, whereby the ready catalyst was obtained for its implementation in the reaction of partial oxidation of an alkane. The different characteristics of the catalysts 3A to 3E and of their method of preparation are reported in Table 3 below.

Table 3 Catalysts 3A to 3E (CeNi ₃₂ type)

Example 4

Use of the catalysts of Examples 1 to 3 for the partial oxidation reaction of methane.

Catalysts 1A to 1F ₁ 2A, 2B and 3A to 3E, obtained in the preceding examples, were used to catalyze the partial oxidation reaction of methane in a mixture of H ₂ and CO.

In each case, the reaction was carried out by circulating, in a stainless steel fixed bed reactor containing 200 mg of catalyst, a gaseous flow based on a mixture of CH ₄ , O ₂ and N ₂ , with a CH ₄ : O ₂ : N ₂ molar ratio of 3: 1: 3. In each case, the catalyst is deposited in the reactor on a bed of inert carborundum (SiC) organized in a succession of layers of decreasing grain diameter (bed of about-δ emβ-volumet), comprising a first grain diameter layer equal to 2.38 mm (volume: 2 cm ³ ), a second layer grain diameter equal to 1, 19 mm (volume: 1.5 cm ³ ) and a third layer grain diameter equal to 0.48 mm (This third layer contains an inert volume of carborundum equal to that of the catalyst, mixed with the catalyst)).

In practice, the hydrogen treatment steps 1.3, 2.3 and 3.3 of Examples 1 to 3 are carried out within the tubular reactor which is used for the partial oxidation reaction. Following the hydrogen treatment, the reactor is purged with a stream of helium for 30 minutes before the introduction of the reactive gas mixture for the partial oxidation reaction.

Once the equilibrium reached for the partial oxidation reaction, the gas flow leaving the reactor is analyzed by gas chromatography using a "Shimatdzu GC 9" chromatograph associated with an interface allowing the treatment of FID and katharometer signals, using the data software to establish and process the chromatogram. This analysis reveals the presence of H2, CO, N ₂ O 2, CH ₄ and CO 2 in the reactor outlet. On the basis of the quantitative data from the chromatography, the conversion of CH ₄ and oxygen as well as the selectivity into the various products formed are calculated, in equilibrium by the following formulas:

• methane conversion rate (expressed as a percentage):

CCH4 ⁼ (d ¹ CH4 - d cm) / d ¹ CH4

Oxygen conversion rate (expressed as a percentage): CO2 = (d 02 - d 02) / d 02

^• selectivity in formed hydrogen (expressed as a percentage):

S H2 ⁼ d H2 / 2 (from CH4 -d CH4)

^• selectivity in CO formed (expressed as a percentage):

S co ⁼ d co / (d ¹ CH4 - d CH4)

^• selectivity in CO ^ orm ^ (experiment.in_p.o_urcejQtage) -j.

S CO 2 = d CO 2 / (CH 4 - d cm)

with the following meanings: - cH4 and ₀₂ respectively represent the flows of methane and O ₂ entering the reactor; and

- d ^f CH4, _H 2 d ^f, d ^f o2, ^f d ^f _C co and o2 represent the methane flow, H _2, O _2, CO and CO ₂ in the reactor outlet.

The results obtained for the various catalysts at temperatures of between 50 ° and 200 ^° C. and with different flow rates of the reactive gas (CH ₄ + O ₂ + N ₂ ) are reported in Table 4 below. In the reaction, great care was taken in the regulation of the temperature. In particular, a thermocouple is used in particular for controlling the effective temperature of the catalytic bed.

Table 4: Catalytic Activities

Claims

1. Use of a material based on a mixed oxyhydride of at least one rare earth and of at least one metallic element other than a rare earth, for catalyzing a partial oxidation reaction of an alkane in one mixture of H ₂ and CO at a temperature below 200 ° C.

2. Use according to claim 1, for catalyzing a partial oxidation reaction of an alkane in a mixture of H ₂ and CO at a temperature between 15 and 100 ° C.

3. Use according to claim 1 or claim 2, wherein the mixed oxyhydride used is obtained by bringing into contact with. hydrogen with a mixture of oxides and / or hydroxide of the rare earth (s) and the metallic element (s) other than rare earths.

4. Use according to claim 1 or claim 2, wherein the mixed oxyhydride used is obtained by a process comprising the following steps: (A) producing a mixture of hydroxides of the (or) earth (s) rare (s) and metal element (s) other than rare earths;

(C) contacting the solid from step (B) with hydrogen.

.

5. Use according to one of claims 1 to 4, wherein in the mixed oxyhydride, the molar ratio rare earth (s) / other (s) element (s) metal (s) is between 1: 0.01 and 1: 10.

6. Use according to any one of claims 1 to 5, wherein the mixed oxyhydride has the general formula (I) below:

TM ₃ O _x H _y (I) wherein: - T represents a rare earth, or a mixture of rare earths;

M denotes a metallic element, or a mixture of metallic elements other than a rare earth;

a is between 0.01 and 10;

x is between 1 and 10; and - is between 0.1 and 100.

7. Use according to claim 6, wherein the mixed oxyhydride has the general formula (II) below:

in which: - T represents a rare earth, or a mixture of rare earths;

M ¹ denotes a metal chosen from Zr or Al;

M ² denotes a metallic element, or a mixture of metallic elements, other than zirconium, aluminum and rare earths; - ai is between 0 and 1;

- a2 is between 0.01 and 10;

x is between 1 and 10; and

- is between 0.1 and 100.

8. The use -according it sells ication-Tr-ΘÙ Foxyhydrure-mixed ^~ corresponds to the general formula (IIa) below:

T Zr _ai M ^{2 a} ₂ O _x H _y (lia) in which T ₁ M ² , a 2, x and y have the meanings given in claim 6; and ai is between 0.1 and 1.

9. Use according to claim 8, wherein the mixed oxyhydride has the following formula (Ila-1):

This Zr _3I M ² _α ² O _x H _y (1la-1) in which M ² , a 1, a 2, x and y are as defined in claim 7.

10. Use according to claim 9, wherein the mixed oxyhydride has the following general formula (Ila-2): This Zr _3I Ni ₃₂ O _x Hy (IIa-2) in which ai, a2, x and y are such that defined in claim 7.

11. Use according to claim 10, wherein the mixed oxyhydride has the following general formula (Ila-3):

This _o Zr ₅ Ni ₃₂ O _x H _y (IIa-3) wherein a2, x and y are as defined in claim 7.

The use of claim 7, wherein the mixed oxyhydride has the general formula (Hb) below:

wherein - T, M ² , a 2, x and y have the meanings given in claim 6; and ai is between 0.1 and 1.

13. Use according to claim 12, Ouj xyhy ^ ^ ^ jrj ejτiixte_ the formula (b-1): This _Al i M ² O _x H _y _a2 (b-1) wherein M ^2, a2, x and are there as defined in claim 11.

The use according to claim 13, wherein the mixed oxyhydride has the following general formula (11b-2):

This _AI i Ni ₃₂ O _x H _y (IIb-2) wherein ai, a2, x and y are as defined in claim 10.

15. Use according to claim 10, wherein the mixed oxyhydride has the following general formula (IIb-3):

This _{Alo, 5} Ni ₃₂ O _x H _y (IIb-3) wherein a2, x and y are as defined in claim 7.

16. Use according to claim 7, wherein the mixed oxyhydride has the general formula (II) below:

_A2 TM ² O _x H _y (Ile) wherein T, M ^2, a2, x and y have the meanings given in claim 6.

The use of claim 16, wherein the mixed oxyhydride has the formula (llc-1) below:

This M ² O _x H _y _a2 (llc-1) wherein M ^2, a2, x and y have the meanings given in claim 6.

18. Use according to claim 17, wherein the mixed oxyhydride has the following general formula (llc-2):

This Ni ₃₂ O _x Hy (llc-2) in which a2, x and y are as defined in claim 7.

19. Use according to any one of claims 1 to 18r-to-realize it -eonversion-methane in a mixture-of ^~ ^{^'~} CO e1rde ^{^"Hi"} to ^"a temperature below 200 ° C.

20. Use according to any one of claims 1 to 18, for converting a cycloalkane to a mixture of CO and H ₂ at a temperature below 200 ° C.

21. Use according to any one of claims 1 to 20, for producing, from an alkane, a mixture of CO and H2 at the anode of a fuel cell at a temperature below 200. ° C.

22. A method of generating a current or an electric voltage by means of a fuel cell, said fuel cell being a battery comprising, as anode, a mixed oxyhydride-based material. at least one rare earth and at least one metal element other than a rare earth as defined in one of claims 1 to 15, and wherein the fuel cell is used by providing an alkane at said at least one operating temperature below 200 ° C.

Fuel cell for carrying out the method of claim 22, comprising:

an anode based on a mixed oxyhydride of at least one rare earth and at least one metallic element other than a rare earth element as defined in one of claims 1 to 15; and

means for conveying an alkane to said anode.

24. Fuel cell according to claim 23, comprising means for regulating the operating temperature at a temperature below 200 ° C.

25. Fuel cell according to claim 23, for operation at ambient temperature, which is devoid of - - - heating means.

26. Fuel cell according to any one of claims 23 to 25, wherein the anode consists essentially of said mixed oxyhydride.

Fuel cell according to any of claims 23 to 25, wherein the anode comprises said mixed oxyhydride supported on a metal oxide support.