EP1562861A1

EP1562861A1 - Storing hydrogen in solid compositions based on mixed oxides

Info

Publication number: EP1562861A1
Application number: EP03778410A
Authority: EP
Inventors: Louise Duhamel
Original assignee: Centre National de la Recherche Scientifique CNRS; Universite de Lille 1 Sciences et Technologies
Current assignee: Centre National de la Recherche Scientifique CNRS; Universite de Lille 1 Sciences et Technologies
Priority date: 2002-10-31
Filing date: 2003-10-20
Publication date: 2005-08-17
Also published as: AU2003285412A8; AU2003285412A1; FR2846648B1; WO2004041724A1; FR2846648A1

Abstract

The invention concerns solid compositions, consisting entirely or partly of a mixed oxide of formula (I): TZraMbOx, obtainable by heat treatment of a mixture of hydroxides of elements T (rare-earth(s)), Zr and M (metal element(s)). The invention also concerns the use of said compositions, in particular for hydrogen storage. In that context, the invention also concerns mixed oxohydride compositions of formula (I): TZraMbOx'Hy and their use as hydrogen reservoir.

Description

Storage of hydrogen in solid compositions based on mixed oxides

The present invention relates to solid compositions useful in particular for the storage of hydrogen in large quantities. The invention also relates to a process for the preparation of these compositions, as well as various specific uses of these solid compositions, in particular in the context of the constitution of anode materials for electrochemical systems, (for example of the fuel cell type), using a hydrogen reduction reaction.

The storage of hydrogen is at present a limiting stage with regard to the use of electrochemical systems of the fuel cell type, which require a continuous supply of hydrogen to supply electricity. The problem arises particularly for applications of fuel cell type systems in electric vehicles, on board which it is necessary to be able to store large quantities of hydrogen (in general, several kilograms).

For the storage of large quantities of hydrogen, storage in gaseous or liquid form poses problems in terms of spatial space. Consequently, systems have been developed for storing hydrogen in solids, which are more compact and which make it possible to store relatively large quantities of hydrogen. In this context, the use of metal alloys in which hydrogen is stored in the form of the corresponding metal hydride has been proposed, as in patent applications WO 01/74710, WO 01/44737 or even EP 554

649. These systems are however limited as to the quantity of hydrogen which they can store in the form of hydrides. In addition, during the storage of hydrogen in the form of metal hydride, the appearance of defects is often observed during the hydr ru ration / dehyd ru ration cycles.

More recently, systems have been developed implementing hydrogen storage in nanotubes or carbon nanofibers. These systems, as described for example in patent applications WO 99/40023 or WO 02/17427, have very large hydrogen storage capacities. Application WO 99/40023 describes systems capable of storing up to 15 to 20% by mass of hydrogen. However, systems based on nanotubes or carbon nanofibers currently known suffer from reproducibility problems (both with regard to their preparation and with regard to their properties during different implementation cycles).

However, the inventors have now discovered that certain mixed oxides based on zirconium, one or more rare earths (such as cerium in particular) and one or more other metals have very large hydrogen storage capacities. , most often without presenting neither the reproducibility problems observed with systems based on nanotubes or carbon nanofibers, nor the problems encountered with the storage of hydrogen in the form of hydrides of metal alloys. These large storage capacities obtained by avoiding the problems of prior art storage materials have been found to be particularly clear with ternary oxides of zirconium, a rare earth (in particular cerium) and another metal. .

In this context, the inventors have also demonstrated that mixed oxides based on zirconium, a rare earth and another metal allow hydrogen storage by transformation of said oxides into oxyhydrides, which has the advantage of storing hydrogen in the form of hydride ions in the crystal lattice of the compound, thus ensuring better stability for the structure obtained than in the context of storage in other oxides.

In this regard, the inventors have in particular demonstrated that mixed oxides based on zirconium, a rare earth and another metal, and in particular ternary oxides based on cerium and zirconium, can undergo several hydrogenation / dehydrogenation cycles without significant loss of their storage capacity. On the basis of these discoveries, the aim of the present invention is to provide solid compositions capable of ensuring the storage of large quantities of hydrogen within a solid material capable of undergoing several charge / discharge cycles of hydrogen, preferably without the appearance of defects and with good reproducibility.

The invention also aims to provide compositions capable of ensuring the transfer of hydrogen, in particular in the catalysis of reactions using dehydrogenations, or hydrogenation and or isomerization reactions.

The invention also sets itself the aim of providing a process for preparing the above-mentioned compositions.

Another objective of the invention is to provide solid compositions of the oxyhydride type useful as hydrogen reservoirs, suitable in particular for the constitution of anode materials in electrochemical systems implementing the hydrogen reduction reactions. , especially in fuel cell type systems.

Thus, according to a first aspect, the present invention relates to a solid composition, useful in particular for the storage of hydrogen or for the transfer of hydrogen, constituted in whole or in part by a mixed oxide corresponding to formula (I) ci below:

TZr _a M _b O _x (I) in which

T represents a rare earth, or a mixture of rare earths; a is between 0.1 and 1;

M denotes a metallic element different from zirconium and a rare earth, or a mixture of metallic elements other than zirconium and rare earths, M denotes preferably nickel, palladium, rhodium, gold, titanium , copper, manganese, aluminum, iron, chromium, cobalt, ruthenium, rhenium, platinum, iridium, osmium, molybdenum, vanadium, tungsten or a mixture of these compounds; - b is between 0.01 and 5; x is between 2 and 11, where the mixed oxide of formula (I) can be obtained according to a process comprising the steps consisting in:

(A) make a mixture of hydroxides of the rare earth (s) T, of zirconium and of the metallic element (s) M, with the following molar ratios for the elements in presence:

Zr / T = a; and

M / T = b, where a and b have the above values; and (B) subjecting the mixture of hydroxides of step (A) to a heat treatment so as to obtain the mixed oxide of formula (I).

Within the meaning of the present description, the term "rare earth" means an element chosen from the group consisting of yttrium, thorium and lanthanides (namely elements with an atomic number between 57 and 71, ranging from lanthanum to lutetium ). In formula (I), T preferably denotes cerium.

By “mixed oxide” is meant here an oxide or a mixture of oxides based on at least three metallic elements, comprising one or more intermetallic oxides and / or a mixture of several metallic oxides, this oxide or mixture of oxides being likely to be obtained according to the steps (A) and (B) above. The mixed oxides of the invention may comprise a matrix based on an oxide of one or more metals (this matrix generally comprising a zirconium and / or rare earth T oxide) within and / or at the surface of which are dispersed crystallites of another oxide based one or more metals (most often, this oxide is then a metal oxide M). Whatever their exact structure, the mixed oxides of the invention can be ternary oxides based on a rare earth T (preferably cerium), zirconium and a metal M. In the mixed oxide of formula (I) present in the solid composition of the invention, the molar ratio of zirconium to cerium (a) is specifically between 0.1 and 1, this ratio a being preferably greater than or equal to 0.2, and advantageously greater or equal to 0.3. In general, this ratio remains less than or equal to 0.8, and advantageously less than or equal to 0.7. Thus, the molar ratio a can advantageously be of the order of 0.5, typically between 0.4 and 0.6.

The metallic element M present in the mixed oxide of formula (I) is advantageously chosen from nickel or palladium, this metal more preferably being nickel. Whatever its nature, the metal M is present in the mixed oxide of formula (I) at the rate of a molar ratio M / Ce (b) specifically between 0.01 and 5. This molar ratio b is advantageously at least equal to 0.1 and preferably at least equal to 0.5. It is moreover more often preferred that this molar ratio remains less than or equal to 3 and even more advantageously less than or equal to 2. Thus, this ratio can advantageously be between 0.5 and 1.5.

Without wishing to be linked in any way to a particular theory, it seems to be possible to claim that the hydrogen storage capacity which is observed for the solid compositions of the invention is due to the fact that the mixed oxides of formula (I) have a strong ability to create, within their crystalline system, a large amount of anionic vacancies in the presence of hydrogen, in particular when they are obtained by steps (A) and (B) above. In particular so that the number of anionic vacancies created is as large as possible in the presence of hydrogen, it is generally preferable that, in formula (I), x is as high as possible. So, compounds of formula (I) of interest are those where x is at least equal to 3, advantageously at least equal to 4, and even more preferably at least equal to 4.4. It is understood, however, that the value of x can sometimes be limited by the nature of the different metals T and M present.

In formula (I), the metal M preferably denotes nickel. In this case, it is preferred that, in formula (I), a is at least equal to 0.2 and advantageously at least equal to 0.3, a then preferably remaining less than or equal to 0.8 and even more advantageously less than or equal to 0.7. Thus, when the metal M designates nickel, it is generally particularly advantageous for the ratio a to be between 0.4 and 0.6, this ratio a being particularly preferably equal to 0.5.

Furthermore, when the metal M designates nickel (and in particular when a is of the order of 0.5), the ratio b preferably remains greater than or equal to 0.2, and advantageously greater than or equal to 0.5 . In this context, it is further preferred that b remains less than or equal to 4 and, in a particularly preferred manner, less than or equal to 3. Thus, b is advantageously between 0.75 and 2, and it is typically of the order from 1.

According to a particularly advantageous variant, the compound of formula (I) present in the composition according to the invention corresponds to the following formula (la):

CeZr _a M _b O _x (la)

in which M, a, b and x have the same meanings in formula (I), it being understood that x is generally at least equal to 3, and advantageously greater than or equal to 4.

Even more advantageously, the mixed oxide of formula (I) present in the composition according to the invention corresponds to formula (Ib) below:

CeZr _0, ₅ _x NiO (Ib) in which x has the same meaning as in formula (I) and is advantageously greater than or equal to 4.

In general, in formula (Ib), x is between 4 and 7, and this ratio is advantageously at least equal to 4.3. However, x most often remains less than or equal to 6. Thus, in the oxides of formula (Ib) which are particularly suitable in the context of the present invention, the ratio can typically be between 4.4 and 5.5.

In the most general case, the compositions according to the invention consist wholly or partly of a mixed oxide of formula (I).

Thus, according to a first possible variant, the composition according to the invention may essentially consist of the mixed oxide of formula (I). In this case, it is most often made up of at least 95% by mass, preferably at least 97% by mass, and advantageously at least 98% by mass with the mixed oxide of formula (I). In the context of this first variant, it is generally preferred that the composition of the invention is in the form of a powder having the highest possible specific surface. According to another variant which may prove to be advantageous, in particular in terms of cost, a composition according to the invention can also comprise (or consist of) a support on the surface of which is deposited a layer based on the mixed oxide of formula (I). In the context of this variant, the support used advantageously has the highest possible specific surface. The support used according to this particular variant can in particular be a support of the metal oxide type, such as an alumina or silica support, for example a support of silica and / or alumina, generally microporous, mesoporous or nanoporous. The layer based on the oxide of formula (I) which is present on the surface of the support according to this variant can be a continuous or discontinuous layer. Preferably, it is a layer essentially consisting of the mixed oxide of formula (1), advantageously distributed continuously on the surface of the support. According to another aspect, the present invention also relates to a process for the preparation of a composition comprising a mixed oxide of formula (I) as defined above. This process includes the steps of:

Zr / T = a; and M / T = b, where a and b have the above values for the mixed oxides of formula (I); and

(B) subjecting the mixture of hydroxides of step (A) to a heat treatment so as to obtain the mixed oxide of formula (I).

By "mixture of hydroxides" within the meaning of the present invention, is meant a mixture of solids comprising metal cations of metals T, Zr and M and OH ions ^" , this mixture possibly taking the form of a mixed intermetallic hydroxide or of a physical mixture of several metal hydroxides. Advantageously, the mixture of hydroxides produced in step (A) of the process of the invention is an intermetallic hydroxide of zirconium, of the rare earth (s) ( s) T, and metallic element (s) M. Thus, to prepare a composition based on a mixed oxide of formula (la) or (Ib), it is particularly advantageous for the mixture of hydroxide from step (A) or a mixed intermetallic hydroxide of cerium, zirconium and nickel.

Most often, step (A) of the process of the invention is carried out by coprecipitation of metal salts of metals T, Zr and M in basic medium, and, in general, by adding an aqueous or hydroalcoholic solution of cerium salts , zirconium and the metallic element M to a base, in particular of the amine type (for example triethylamine). In this case, the salts used can advantageously be nitrates. Whatever the nature of the salts used, it is particularly advantageous for the addition of the salts to the base to be carried out as quickly as possible. The addition is thus advantageously carried out by a drop by drop as quickly as possible, and one can also envisage an instantaneous addition of the salts to the base.

As a general rule, when the mixture of hydroxides from step (A) is obtained by coprecipitation of T, Zr and M metal salts in basic medium, the mixture of hydroxides obtained (mixed intermetallic hydroxide) is most often recovered by filtration, and it is then advantageously washed, for example with water and / or with alcohol.

More generally, whatever its method of production, it is most often desirable for the mixture of hydroxides subjected to step (B) of heat treatment to consist essentially of hydroxides of the metals T, Zr and M , preferably in the dry state, that is to say essentially free of solvents and in particular essentially free of water, in particular so as to control the rise in temperature during the heat treatment.

The heat treatment step (B) is preferably carried out at a temperature at least equal to 300 ° C., advantageously at least equal to

400 ° C, this temperature advantageously remaining below 700 ° C, and preferably below 600 ° C. Particularly advantageously, it is preferred that this temperature is of the order of 500 ° C.

According to another conceivable mode, step (B) of heat treatment can be carried out at a temperature between 80 ° C and 150 ° C, for example between 80 ° C and 120 ° C. In this case, step ( B) generally consists of drying in the aforementioned temperature ranges.

It should be emphasized that the most advantageous mixed oxides of formula (!) Are generally obtained by bringing the mixed hydroxides of step (A) to the calcination temperature with a controlled temperature rise gradient, this rise gradient in temperature then being in generally between 10 ° C per hour and 500 ° C per hour, this gradient preferably being between 25 ° C per hour and 100 ° C per hour.

As has been pointed out, the compositions of the invention are in particular useful for carrying out the storage or the transfer of hydrogen. This particular use of the compositions of the invention constitutes another specific object of the present invention.

Given their affinity for hydrogen, the compositions of the invention can in particular be used as catalysts for carrying out reactions using one or more dehydrogenation steps. In this context, the compositions according to the invention can in particular be used to carry out alkane oxidation reactions, where the dehydrogenation step is decisive.

One of the main applications that can be envisaged for the compositions of the invention is the storage of hydrogen. In this context, the inventors have demonstrated that the oxides of formula (I) present in the compositions of the invention are capable of reacting with hydrogen under certain temperature and pressure conditions, to lead to an integration of l hydrogen in the form of hydride ions within anionic vacancies in their crystal lattice. In this context, it seems to be possible to say that a heterolytic hydrogen dissociation reaction takes place according to the following global reaction:

H ₂ + [oxide] DO ^{2 "} - [oxide] H ~ OH ^_ .

Thus, according to another particular aspect, the present invention also relates to a hydrogen storage process consisting in bringing together:

(i) hydrogen; and

(ii) a solid composition according to the invention comprising a mixed oxide of the above formula (I) (for example a compound of formula (la) or of formula (Ib)), whereby a solid composition is obtained comprising a mixed oxyhydride of cerium, zirconium and said metal M, within which a large quantity of hydrogen is stored, in the form of hydride ions.

The optimal temperature during hydrogen storage depends on the mixed oxide used. It is however generally between 25 and 1000 ° C.

The amount of hydrogen which can be stored in an oxide of formula (I) according to the invention measured according to the charging method described in application EP 208 405 is generally at least 0.03 and preferably at least 0.05 grams of hydrogen per gram of mixed oxide of starting formula (I).

Solid compositions based on oxyhydrides which can be obtained according to the hydrogen storage process of the invention, and which are useful as a hydrogen reservoir, constitute, according to a particular aspect, another object. of the present invention. Their use as a hydrogen reservoir also constitutes an object of the invention. The solid compositions which can be obtained according to the hydrogen storage process of the invention generally consist wholly or partly of a mixed oxyhydride corresponding to formula (II) below:

TZr _a M _b O _x .H _y (II)

in which T, M, a and b have the same meanings as in formula (I) and where: x 'is less than the value x of the starting compound (I), and is generally between 1 and 10; and - is between 0.1 and 100. The compounds of formulas (II) are oxyhydrides useful as hydrogen reservoirs. As such, they can present, at different stages of their successive charges and discharges, variable quantities of hydrogen (in the form of hydride ions), reflected by the value of y. The value of y depends on the capacity of the mixed oxides to incorporate hydrogen and their molar mass. It is obtained by multiplying the quantity of hydrogen incorporated in mol / g with the molar mass of the mixed oxide.

Thus, the compounds of formula (II) according to the invention can integrate hydrogen in a variable manner with values of y which can effectively vary between 0.1 and 1000. Generally, for compounds of molecular mass less than 1000, the value of y will be between 0.1 and 100. However, for certain compounds of formula (II), the value of y can only vary, during the charge and discharge cycles, between more restricted extreme values. However, y can go up to 25, preferably up to 28 at the end of a charge, and the discharge generally leads to a decrease in y to values less than or equal to 2, and preferably less than or equal to 1.

In a particularly preferred manner, in formula (II), the metal M denotes nickel. Where appropriate, the compound of formula (II) is advantageously obtained by treatment of a compound of formula (Ib) with hydrogen. In this case, y can generally vary at least between 0.2 and 30 during successive charges and discharges, and preferably between 0.1 and 31. In a particularly advantageous manner, in the solid compositions according to the invention useful for As hydrogen reservoirs, the mixed oxyhydride of formula (H) corresponds to the following formula (IIa):

CeZr _a M _b O _x H _y (lia) in which M, a, b, x 'and y have the above definitions.

More preferably, the mixed oxyhydride of formula (11) corresponds to the following formula (I Ib): CeZr _0, ₅ NiO _x H _y (IIb)

in which x 'and y have the above definitions.

In general, the compositions according to the invention based on oxyhydride compounds of formula (II) are useful as a hydrogen reservoir. These compositions can in general be used in several successive hydrogenation / dehydrogenation cycles without significantly losing their storage capacity, and without observing the formation of defects within their structure. The compositions of the invention based on oxyhydride compounds can in particular be used as anode materials in electrochemical systems implementing hydrogen reduction reactions, and in particular in systems of the fuel cell type. This specific use, as well as the electrochemical systems implementing a hydrogen reduction reaction (in particular of the fuel cell type) comprising an anode based on a composition based on an oxyhydride according to the invention, constitutes a another aspect of the present invention.

The characteristics and various advantages of the present invention will appear even more clearly in the light of the illustrative examples set out below.

Example 1: Preparation of a mixed oxide

1.1 - Preparation of a mixture of hydroxides by coprecipitation of cerium nitrate, zirconium and nickel

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

(i) 20 ml of an aqueous solution of cerium nitrate (concentration 0.5M) (ii) 10 ml of an aqueous solution of zirconium nitrate (concentration

0.5M)

(iii) 20 ml of an aqueous solution of nickel nitrate (concentration

0.5M). The mixture produced was stirred for 10 minutes.

The solution obtained was added dropwise to 62.5 ml of a 1.5M solution of triethylamine diluted in methanol. During the addition, the formation of a precipitate of metal hydroxides was observed.

The mixture of hydroxides formed was collected by filtration (porosity filter 3), then it was washed and rinsed 5 times with water and with methanol, then it was dried at 150 ° C. on a water bath. sand for 48 hours. The solid obtained was then ground in a mortar in the form of a fine powder.

1.2 - Calcination in air at 500 ° C. The powder obtained at the end of the preceding stage was brought to 500 ° C. under an atmosphere of air at a rate of temperature rise 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.

Example 2: Preparation of a mixed oxide CeZr ₀ , 5Ni ₀ , ₄ θ4, ι

2.1 - Preparation of a mixture of hydroxides by coprecipitation of cerium nitrate, zirconium and nickel

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

(i) 20 ml of an aqueous solution of cerium nitrate (concentration

0.5M)

(ii) 10 ml of an aqueous solution of zirconium nitrate (concentration

0.5M) (iii) 10 ml of an aqueous solution of nickel nitrate (concentration

0.5M).

The mixture produced was stirred for 10 minutes. The solution obtained was added dropwise to 50 ml of a 1.5M solution of triethylamine diluted in methanol. During the addition, the formation of a precipitate of metal hydroxides was observed.

2.2 - Calcination in air at 500 ° C. The powder obtained at the end of the preceding stage was brought to 500 ° C. under an atmosphere of air at a rate of temperature rise 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.

EXAMPLE 3 Preparation of a mixed oxide CeZr _0, 5Ni ₂ 9θ6,7

3.1 - Preparation of a mixture of hydroxides by coprecipitation of cerium nitrate, zirconium and nickel

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

(i) 20 ml of an aqueous solution of cerium nitrate (concentration 0.5M)

(ii) 10 ml of an aqueous solution of zirconium nitrate (concentration 0.5M)

(iii) 60 ml of an aqueous solution of nickel nitrate (concentration 0.5M).

The mixture produced was stirred for 10 minutes. The solution obtained was added dropwise to 112 ml of a 1.5M solution of triethylamine diluted in methanol. During the addition, the formation of a precipitate of metal hydroxides was observed.

The hydroxide mixture formed was recovered by filtration (porosity filter 3), then it was washed and rinsed 5 times with water and with methanol, then it was dried at 150 ° C on a sand bath for 48 hours. The solid obtained was then ground in a mortar in the form of a fine powder.

3.2 - Calcination in air at 500 ° C

The powder obtained at the end of the preceding step was brought to 500 ° C. under an atmosphere of air at a rate of temperature rise 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.

Example 4: Storage of hydrogen

The compositions of Examples 1 to 3 were successively placed in the presence of hydrogen at different temperatures, whereby compositions based on oxyhydrides were obtained incorporating variable amounts of hydrogen. The results obtained are collated in Tables 1 to 3 below.

TABLE 1: Storage of hydrogen in the composition of Example 1

TABLE 2: Storage of hydrogen in the composition of Example 2

TABLE 3 Storage of hydrogen in the composition of Example 3

Claims

1. Solid composition, consisting wholly or in part of a mixed oxide corresponding to formula (I) below:

TZr _a M _b O _x (I) in which:

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

- a is between 0.1 and 1;

M denotes a metallic element different from zirconium and a rare earth, or a mixture of metallic elements other than zirconium and rare earths; b is between 0.01 and 5; - x is between 2 and 11, said mixed oxide of formula (I) being capable of being obtained according to a process comprising the steps consisting in:

Zr / T = a; and M / T = b, where a and b have the above values; and

2. Composition according to claim 1, characterized in that T denotes cerium.

3. Composition according to claim 1 or according to claim 2, characterized in that the compound of formula (I) corresponds to the following formula (la):

CeZr _a M _b O _x (la)

wherein M, a, b and x are as defined in claim 1.

4. Composition according to one of the preceding claims, characterized in that M denotes nickel.

5. Composition according to claim 4, characterized in that the compound of formula (I) corresponds to the following formula (Ib):

CeZr _0l5 NiO _x (Ib)

wherein x is as defined in claim 1.

6. Composition according to any one of claims 1 to 5, characterized in that it is essentially constituted by the mixed oxide of formula (I).

7. Composition according to any one of claims 1 to 5, characterized in that it comprises a support, on the surface of which is deposited a layer based on the mixed oxide of formula (I).

8. Process for the preparation of a composition constituted in whole or in part by a mixed oxide corresponding to formula (I) below:

TZr _a M _b O _x (I) in which: - T represents a rare earth, or a mixture of rare earths

a is between 0.1 and 1; M denotes a metallic element different from zirconium and a rare earth, or a mixture of metallic elements other than zirconium and rare earths; b is between 0.01 and 5; - x is between 2 and 11, said method comprising the steps consisting in:

(A) make a mixture of hydroxides of the rare earth (s) T, of zirconium and of the metallic element (s) M, with the following molar ratios for the elements in presence: Zr / T = a; and

M / T = b, where a and b have the above values; and

9. Method according to claim 8, characterized in that step (B) is carried out at a temperature between 300 ° C and 700 ° C.

10. Method according to claim 8, characterized in that step (B) is carried out at a temperature between 80 and 150 ° C.

11. Use of a composition according to one of claims 1 to 7 or of a composition capable of being obtained according to the method of one of claims 8 to 10, for the storage or transfer of hydrogen.

12. Use of a composition according to one of claims 1 to 7 or of a composition capable of being obtained according to the process of one of claims 8 or 9, as catalyst for carrying out a hydrogenation reaction , dehydrogenation and / or isomerization.

13. Hydrogen storage process comprising a step consisting in bringing together:

(i) hydrogen; and

(ii) a composition according to any one of claims 1 to 7.

14. Solid composition capable of being obtained according to the hydrogen storage method of claim 12.

15. Solid composition according to claim 14, characterized in that it consists wholly or partly of a mixed oxyhydride corresponding to formula (II) below:

TZr _a M _b O _x H _y (II)

-in which T, M, a and b have the same meanings as in formula (I) of claim 1 and in which: - x 'is between 1 and 10; and is between 0.1 and 100.

16. Composition according to claim 15, characterized in that, in formula (II), the metal M is nickel.

17. Composition according to Claim 16, characterized in that the oxyhydride of general formula (II) corresponds to the following formula (IIa):

CeZr _a M _b O _x H _y (lia) in which M, a, b, x 'and y have the same meanings as in claim 15.

18. Composition according to claim 16, characterized in that the oxyhydride of general formula (II) corresponds to the following formula (llb):

CeZr _0l NiO _x H _y (llb) in which x 'and y have the same meanings as in claim 14.

19. Use of a composition according to any one of claims 15 to 18, as a hydrogen reservoir.

20. Use of a composition according to any one of claims 15 to 18 as anode material in an electrochemical system implementing a hydrogen reduction reaction.

21. An electrochemical system implementing a hydrogen reduction reaction, comprising an anode based on a composition according to any one of claims 15 to 18.