The present invention deals with the chemical storage of hydrogen by means of metal borohydride-based materials. It notably deals with a process for preparing compounds for manufacturing an ammine metal borohydride starting from the said ammine metal borohydride which has been dehydrogenated.

Metal borohydride-based materials have been intensively investigated for their potential as high-capacity hydrogen storage materials. The thermolysis of a metal borohydride MBH4 results in hydrogen release at a dehydrogenation temperature which is inversely proportional to the electronegativity of the metal M cation. Hence, high electronegativity metal borohydrides are well suited for mobile applications due to their low decomposition temperature. For instance, some transition metal borohydrides present a decomposition temperature lower than room temperature.

A method is known for preparing an ammine metal borohydride of formula A _x M(BH4)x+m(NH3)n wherein A is an alkali metal, M is a metal different from an alkali metal, 0 < x < 2, n > 0, and m > 0. This known method comprises performing a nucleophilic addition reaction, implemented in liquid ammonia NH3, of a metal hydride of formula AxMHx+m and a borane complex of formula L*BH3, L being a solvent forming a complex with a borane compound BH3, such as to obtain a metal borohydride complex of formula A _x M(BH4)x+mLn, and a displacement reaction between the metal borohydride complex and liquid ammonia to obtain the ammine metal borohydride.

It is also known that the ammine metal borohydride can be regenerated by implementing a specific process, starting from the product of formula A _x M(BNH)x+m obtained as a reaction by-product of the dehydrogenation of the ammine metal borohydride of formula AxM(BH4)x+m(NH3) _n . However, this specific process requires heating the product of formula A _x M(BNH)x+m at a temperature greater than the melting temperature of the metal compound AxM, usually greater than 400 °C. This lowers its energetic yield.

Therefore, there is a need for a process for preparing starting compounds for manufacturing a preparing an ammine metal borohydride of formula AxM(BH4)x+m(NH3) _n which alleviates the hereabove drawback.

The aim of the invention is to satisfy this need. Embodiments according to a first aspect of the invention relate to a process for preparing a metal hydride of formula A _x MH _s+m and a borane compound BH3, starting from a product of formula A _x M(BNH) _x+m , wherein:

A is an alkali metal,

M is a metal different from an alkali metal,

0 < x < 10 m>0, the process comprising: a) contacting the product of formula A _x M(BNH) _x+m with a catalyst comprising a transition metal in solution in an aprotic polar solvent, such as to separate the metal hydride of formula A _x MH _x+ m and a hydrogenated boron nitride compound BNH, b) the synthesis of the borane compound BH3, from the hydrogenated boron nitride compound BNH, the synthesis comprising:

- a digestion reaction of the boron nitride compound BNH in a gaseous atmosphere containing, even consisting in, an anhydrous hydrogen halide acid gas comprising at least one halogen element Y, such as to produce a boron halide BY3,

- a hydrodehalogenation of the boron halide in a hydrogen gas atmosphere to obtain the borane compound BH3.

Preferred embodiments according to the first aspect of the invention relate to a process for preparing a metal hydride of formula A _x MH _x+m and a borane compound BH3, starting from a product of formula A _x M(BNH) _x+m , wherein:

A is an alkali metal,

M is a metal different from an alkali metal,

0 < x < 2 m>0, the process comprising: a) contacting the product of formula A _x M(BNH) _x+m with a catalyst comprising a transition metal in solution in an aprotic polar solvent, such as to separate the metal hydride of formula A _x MH _x+ m and a hydrogenated boron nitride compound BNH, b) the synthesis of the borane compound BH3, from the hydrogenated boron nitride compound BNH, the synthesis comprising: - a digestion reaction of the boron nitride compound BNH in a gaseous atmosphere containing, even consisting in, an anhydrous hydrogen halide acid gas comprising at least one halogen element Y, such as to produce a boron halide BY3,

- a hydrodehalogenation of the boron halide in a hydrogen gas atmosphere to obtain the borane compound BH3.

Embodiments according to a second aspect of the invention also relate to a process for preparing a metal hydride of formula A _x MH _x+m and a borane compound BH3, starting from a product of formula A _x M(BNH) _x+m , wherein:

A is an alkali metal,

M is a metal different from an alkali metal,

0 < x < 10 m>0, the process further comprising: a’i) reacting the metal hydride of formula A _x M(BNH) _x+m with ammonia such as obtain an ammoniated product of formula A _x M(NH2) _x+ m and a hydrogenated boron nitride compound BNH, a’ 2) the hydrogenation of the ammoniated product of formula A _x M(NH2) _x+ m such as to obtain an metal hydride of formula A _x MH _x+m , the process comprising the separation of the hydrogenated boron nitride compound BNH from the ammoniated product of formula A _x M(NH2) _x+ m before step a’ 2) or from the metal hydride of formula A _x MH _x+m after step a’ 2), and b) the synthesis of the borane compound BH3, from the hydrogenated boron nitride compound BNH, the synthesis comprising:

- a digestion reaction of the boron nitride compound BNH in a gaseous atmosphere containing, even consisting in, an anhydrous hydrogen halide acid gas comprising at least one halogen element Y, such as to produce a boron halide BY3,

- a hydrodehalogenation of the boron halide in a hydrogen gas atmosphere to obtain the borane compound BH3.

Preferred embodiments according to the second aspect of the invention relate to a process for preparing a metal hydride of formula A _x MH _x+m and a borane compound BH3, starting from a product of formula A _x M(BNH) _x+m , wherein:

A is an alkali metal, M is a metal different from an alkali metal,

0 < x < 2 m>0, the process further comprising: a’i) reacting the metal hydride of formula A _x M(BNH) _x+m with ammonia such as obtain an ammoniated product of formula A _x M(NH2) _x+ m and a hydrogenated boron nitride compound BNH, a’ 2) the hydrogenation of the ammoniated product of formula A _x M(NH2) _x+ m such as to obtain an metal hydride of formula A _x MH _x+m , the process comprising the separation of the hydrogenated boron nitride compound BNH from the ammoniated product of formula A _x M(NH2) _x+ m before step a’ 2) or from the metal hydride of formula A _x MH _x+m after step a’ 2), and b) the synthesis of the borane compound BH3, from the hydrogenated boron nitride compound BNH, the synthesis comprising:

- a digestion reaction of the boron nitride compound BNH in a gaseous atmosphere containing, even consisting in, an anhydrous hydrogen halide acid gas comprising at least one halogen element Y, such as to produce a boron halide BY3,

- a hydrodehalogenation of the boron halide in a hydrogen gas atmosphere to obtain the borane compound BH3.

The process of the invention, according to anyone of its first and second aspects, presents an improved yield. It also provides an easy chemical route to produce the starting materials which are required to the manufacture of the ammine metal borohydride.

The process according to the invention, according to anyone of its first and second aspects, can comprise one or more of the following optional features.

The product of formula A _x M(BNH) _x+m can be obtained from a dehydrogenation of a least one ammine metal borohydride of formula A _x M(BH4) _x +m(NH3) _n , with n > 0. In particular, the product of formula A _x M(BNH) _x+m can be obtained from a dehydrogenation of a mixture of an ammine metal borohydride of formula A _x M(BH4) _x +m(NH3) _n , n > 0, and at least one compound chosen among a metal borohydride of formula A(BH4), a metal borohydride of formula M(BH4)m, a metal hydride of formula AH, a metal hydride of formula MH _m , ammonia borane NH3BH3, a metal amidoborane of formula A(NH2BH3), a metal amidoborane of formula M(NH2BH3) _m and their mixtures. The product of formula A _x M(BNH) _x+m can be obtained from a dehydrogenation of a compound or a mixture of compounds chosen among:

- an ammine metal borohydride of formula A _x M(BH4) _x +m(NH3) _n ;

- a mixture of an ammine metal borohydride of formula A _x M(BH4) _x +m(NH3) _n and at least one, notably both, of a metal borohydride of formula A(BH4) and a metal borohydride of formula M(BH4) _m ;

- a mixture of an ammine metal borohydride of formula A _x M(BH4) _x +m(NH3) _n and at least one, notably both, of a metal hydride of formula AH and a metal hydride of formula MH _m ;

- a mixture of an ammine metal borohydride of formula A _x M(BH4) _x +m(NH3) _n and ammonia borane NH3BH3;

- a mixture of an ammine metal borohydride of formula A _x M(BH4) _x +m(NH3) _n and least one, notably both, of a metal amidoborane of formula A(NH2BH3) and a metal amidoborane of formula M(NH2BH3) _m , with n > 0.

For instance, Yang et al. (J. Phys. Chem. C, 2013) relates to the dehydrogenation of Mg(BH ₄ )2-6NH ₃ .

The product of formula A _x M(BNH) _x+m is preferably obtained from the dehydrogenation of an ammine borohydride fuel of formula A _x M(BH4) _x +m(NH3) _n with n > 0. The product of formula A _x M(BNH) _x+m can be in the form of a mixture wherein A _X M and BNH can be aggregated together and/or interact with each other.

The coefficient x can be greater than or equal to 0.1, greater than or equal to 0.2, greater than or equal to 0.5, greater than or equal to 1.0, greater than or equal to 1.5, greater than or equal to 1.8, greater than or equal to 1.9.

The coefficient x can be equal to 2.

The coefficient x can be lower than or equal to 10, lower than or equal to 2, lower than or equal to 1.9, lower than or equal to 1.8, lower than or equal to 1.5, lower than or equal to 1.0, lower than or equal to 0.5, lower than or equal to 0.2, lower than or equal to 0.1.

Preferably, the coefficient m ranges between 2 and 4. It can be equal to 2. The alkali metal A can be chosen among Li, Na, K and their mixtures. In particular, the alkali metal A can be Li.

The metal M can be chosen among transition metals, earth alkali metals, posttransitions metals and their mixtures.

Preferably, the metal M is chosen among Mg, Sc, Y, Ti, Zr, Mn, Zn, Al and their mixtures.

Preferably, the metal M is chosen among Zn, Al, Mg and their mixtures. Preferably, the metal M is chosen among Mg, Al and their mixtures. In particular, the metal M can be Mg.

In some embodiments, the product of formula A _x M(BNH) _x+m can be AZn(BNH) _x+m wherein A is chosen among Li, Na, K and their mixtures.

In some preferred embodiments, the product of formula A _x M(BNH) _x+m can be Li _x Al(BNH) _3+x .

In some preferred embodiments, the product of formula A _x M(BNH) _x+m can be A2Mg(BNH)4 wherein A is chosen among Li, Na, K and their mixtures. More especially, it can be of formula Li2Mg(BNH)4.

According the first aspect of the invention, preferably, step a) is performed at a temperature lower than the melting temperature of the metal compound A _X M.

Preferably, step a) is performed at a temperature ranging between 0°C and 150 °C.

Step a) can be performed in a H2 gas atmosphere, preferably in an autoclave, at a pressure greater than 0.1 MPa, for instance greater than 1.3 MPa, and lower than 35 MPa.

Notably, at step a), the product of formula A _x M(BNH) _x+m , the catalyst and the solvent can be introduced, into a chamber of the autoclave, for instance at a temperature ranging between 20 °C and 35 °C and at atmospheric pressure, notably in a neutral gaseous atmosphere. The autoclave chamber can be sealed after and the H2 pressure, and optionally the temperature, can be increased inside the chamber for improving the yield of the catalysis reaction.

Prior to being put in contact with the solvent, the product of formula A _x M(BNH) _x+m and the catalyst can be mixed, for instance by ball milling, in order to increase the surface of contact between the catalyst and the product of formula A _x M(BNH) _x+m . For example, in an embodiment the catalyst comprises Ti and the metal M is Al, and mixing results in the formation of Ti-catalyzed Al.

The product of formula A _x M(BNH) _x+m can be in the form of a solid chunk. For instance, the product of formula A _x M(BNH) _x+m can comprise a mixture of A _X M and BNH based polymers or an amorphous A-M-B-N-H compound.

The catalysis aims at catalysing the hydrogenation reaction occurring between hydrogen and the product of formula A _x M(BNH) _x+m . The catalyst can be in liquid or solid, notably in the form of a powder.

The catalyst comprises a transition metal which is preferably chosen among Ti, Zr, Fe and their mixtures.

Preferably the transition metal is titanium.

The catalyst can be chosen among an halogenide of the transition metal, an alkoxide of the transition metal and their mixtures. For instance, the catalyst can be chosen among a fluoride of the transition metal, a chloride of the transition metal, and a bromide of the transition metal. The catalyst can be chosen among titanium chloride TiCF, n-butoxide Ti(OBu)4, zirconium n-propoxide Zr(OPr)3, fer-ethylate Fe(OEt)2, TiFs. TiBrs and their mixtures. More especially, it can be chosen among TiCF, Ti(OBu)4 and their mixtures. Preferably, the catalyst is TiCh.

The solvent is a polar and aprotic. It can be chosen among an ether, an amine of formula RR’R”N, wherein R, R’ and R” can each be of formula CnEhn-i, in particular CH3 and C2H5, and phosphoramide, notably hexamethylphosphoramide.

Preferably, the solvent is chosen among tetrahydrofuran, dimethyl sulphide, triethylamine, diethyl ether, dimethyl ether, diglyme (bis(2-methoxyethyl) ether) and their mixtures. Preferably the solvent is tetrahydrofuran, also known as the acronym “THF”.

At the end of step a), the product of formula A _x MH _x+m and the boron nitride compound BNH are separated.

Preferably the product of formula A _x MH _x+m is dissolved in the solvent and the boron nitride compound BNH is solid. In particular, the boron nitride compound BNH can be extracted from the solution comprising the product of formula A _x MH _x+m by filtering.

As a variant, at the end of step a), the product of formula A _x MH _x+m and the boron nitride compound BNH can both be dissolved or solid and can be extracted through a density-base separation technique, which takes advantage of the differences of density between boron nitride and the product of formula A _x MH _s+ m.

According to the second aspect of the invention, preferably, at least one, preferably both of steps a’i) and a’2) are performed at a temperature lower than the melting temperature of the metal compound A _X M. More especially, at least one, preferably both of steps a’i) and a’2) can be performed at a temperature ranging between 15 °C and 150 °C.

Preferably, step a’i) is performed at a temperature ranging between 15 °C and 40 °C, notably at room temperature.

Step a’i) can be performed by mixing A _x M(BNH) _x+m and liquid ammonia. Mixing is preferably performed by ball milling, preferably for a period ranging between 400 minutes and 800 minutes.

Step a’i) can be performed at a pressure greater than 0.7 MPa. Preferably, step a’i) is performed at a pressure of 1 MPa.

Preferably, step a’i) is performed by reacting the metal hydride of formula A _x M(BNH) _x+m with liquid ammonia.

Step a’2) can be performed in a H2 gas atmosphere, preferably in an autoclave, at a pressure greater than 0.1 MPa, for instance greater than 1.3 MPa, and lower than 35MPa.

Step a’2) can be performed at a temperature ranging between 20 °C and 150 °C.

Step a’2) can be performed in a polar and aprotic solvent, preferably, the solvent being chosen among tetrahydrofuran, dimethyl sulphide, diethyl ether, dimethyl ether, diglyme (bis(2-methoxyethyl) ether) and their mixtures. Preferably the solvent is tetrahydrofuran.

In a variant, the process comprises the separation of the hydrogenated boron nitride compound BNH the ammoniated product of formula A _x M(NH2) _x+ m before step a’2).

In particular, at the end of step a’i), the hydrogenated boron nitride compound BNH and the ammoniated product of formula A _x M(NH2) _x+ m can be separated by taking advantage of the difference of their solubility in liquid ammonia. Notably, the hydrogenated boron nitride compound BNH can be solid whereas the ammoniated product of formula A _x M(NH ₂ ) _x+ m can be dissolved in ammonia. For instance, the hydrogenated boron nitride compound BNH can be separated from the ammoniated product of formula A _x M(NH2) _x+ m by filtering. After separation, the ammoniated product of formula A _x M(NH2) _x+ m can be precipitated before the hydrogenation step a’2). In another variant, the process comprises the separation of the hydrogenated boron nitride compound BNH from the metal hydride of formula A _x MH _x+m after step a’ 2). Preferably, the product of formula A _x MH _x+m is dissolved in the solvent and the boron nitride compound BNH is solid. In particular, the boron nitride compound BNH can be extracted from the solution comprising the product of formula A _x MH _x+m by filtering. As a variant, the product of formula A _x MH _x+m and the boron nitride compound BNH can both be dissolved or solid and can be extracted through a density-base separation technique, which takes advantage of the differences of density between boron nitride and the product of formula A _x MH _x + _m .

Step a’ 2) can be performed by contacting the mixture comprising the ammoniated product of formula A _x M(NH2) _x+ m and the hydrogenated boron nitride compound BNH with H2. Said contacting can be made in presence of the solvent, for instance tetrahydrofuran, or in the absence of the solvent. In a variant, step a’ 2) can be performed by hydrogenating only the ammoniated product of formula AxM(NH2) _x+m .

According to anyone of the first and second aspects of the invention, at step b), the halogen element Y can be chosen among F, Cl, Br, I and their mixtures. Preferably, the halogen element can be chosen among Cl and Br. Preferably the halogen element Y is chlorine Cl.

Prior to the digestion reaction, a solution can be prepared comprising the hydrogenated boron nitride compound BNH, a solvent chosen among toluene, tetrahydrofuran, diethyl-ether, 1,4-dioxane, l-butyl-3-methylimidazolium chloride, CS2, CCI4, C2CI4 and their mixtures and a compound chosen among AICI3, CuCh and their mixtures that form together with the halide acid a superacid/solvent system.

Preferably, the digestion reaction results in the formation of an ammonia halide of formula NH4Y and the process comprises the production of ammonia NH3 from the ammonia halide, for instance by means of a heating that results in the decomposition of the ammonia halide into ammonia and at least one hydrogen halide gas HY, which can be reused.

The digestion reaction can be implemented at a temperature ranging between 20°C and 100°C and at a pressure ranging between 1 bar and 80 bar, for instance at a pressure of about 40 bar.

For instance, the digestion reaction can be performed by mixing the BNH compound with CS2 and AICI3 and submitting the obtained solution in anhydrous HC1 gas at a temperature of 80°C and at a pressure of 40 bar. In a variant, the digestion reaction can be performed by mixing the BNH compound with CS2 and AIBrs in anhydrous HBr gas at a temperature of 80°C and a pressure of 30 bar.

The process can comprise the synthesis of the borane compound BH3, complexed in a solvent L in the form of a complex of formula L*BH3.

According to some embodiments, step b) can comprise a preparation of a solution of the boron halide BY3 in the solvent L such as to form a L*BY3 complex and the hydrodehalogenation is performed with boron halide being so complexed in the form of the L*BY3 complex, such as to obtain the borane compound BH3, complexed in a solvent L in the form of a complex of formula L*BH3.

The preparation of the solution of BY3 in the solvent L can comprise the stirring of the solvent L in a gaseous BY3 atmosphere or the stirring of the solvent L with a solution of BY3 at a temperature less than or equal to 30°C, preferably less than 15°C, preferably less than 5 °C, notably at 0°C or at -78 °C.

Once the complex L*BY3 is formed, the process can comprise mixing the L*BY3 complex in the solvent L.

According to some preferred embodiments, the process comprises a step c), successive to step b), comprising the preparation a solution of the boron compound BH3 with a solvent L such as to form a borane complex of formula L*BH3.

The solvent L is preferably an amine solvent.

The amine solvent can be of formula NR3 where R is chosen among CH3, C2H5, C3H7, C4H9, CeHs and their mixtures.

The amine solvent can be of formula NR2R or NRR R wherein R is different from R’ and R’ ’ and R’ is different from R’ ’ and any of R, R’ and R’ ’ can be chosen among CH ₃ , C2H5, C3H7, C4H9 and C ₆ H ₅ .

Preferably, solvent L is triethylamine N(CH2CH3)3.

The hydrodehalogenation of boron halide BY3, optionally complexed in the form of L*BY3, in a hydrogen gas atmosphere to obtain the borane compound BH3, respectively the borane complex L*BH3, is preferably implemented in the presence of a catalyst, preferably chosen among M _m B, M _m BN and their mixtures, wherein M is chosen among Ni, Pd, Fe, Co, Cu and their mixtures. Examples of hydrodechlorination of N(CH2CH3)3*BC13 in the presence of NEB catalyst is for instance described in C. Reller and F. Mertens, “A self- contained regeneration scheme of spent ammonia borane based on the catalytic hydrodechlorination of BClf Angew. Chem. Int. Ed., 2012, 51, 11731-11735, doi:10.1002/anie.201201134. This article also provides details on how to proceed to a reaction of a boron nitride compound BNH in a gaseous hydrogen halide HY atmosphere.

The hydrodehalogenation of boron halide BY3, optionally complexed in the form of L*BY3, can be performed at a temperature greater than or equal to 20°C, notably greater than or equal to 50°C and preferably lower than or equal to 160°C, notably about 130°C and/or at a pressure greater than 1 bar, notably greater than or equal to 10 bar and preferably lower than 80 bar. In example, the hydrodehalogenation of boron halide BCI3, optionally complexed in the form of L*BC13, can be performed at a temperature ranging between 100°C and 160°C and at a pressure of 60 bar. In another example, the hydrodehalogenation of boron halide BBn, optionally complexed in the form of L*BBr3, can be performed at a temperature ranging between 100°C and 130°C and at a pressure of 60 bar.

The hydrodehalogenation of boron halide BY3, optionally complexed in the form of L*BY3, can be implemented for a duration of less than 72 hours.

In some embodiments, the hydrodehalogenation of boron halide BY3 complexed in the form of L*BY3, can result in the formation of L*HY, which can be reduced such as to obtain the anhydrous hydrogen halide acid HY. In some other embodiments, the hydrogen halide acid complex L*HY can be reacted with ammonia such as to form NH4Y, especially if the temperature to proceed to the reduction of said halide acid complex is greater than the degradation temperature of solvent L.

The yield of the production of BH3 can be improved by eliminating the produced L-HY, such as to shift the reactions to the desired product and/or by conducting at least two hydrodehalogenation reactions.

In particular, in order to increase said yield, step b) preferably comprises at least:

- performing a first hydrodehalogenation reaction of boron halide BY3 complexed in the form of L*BY3 in the hydrogen gas atmosphere in the presence of the catalyst such as to obtain a first composition comprising a solid phase and a liquid phase comprising L*BH3 and at least one borane compound, such as of L*BY3, L*BHY2 and L*BH2Y,

- recovering the liquid phase from the first composition and prepare a second composition by dissolving the solid phase in the solvent L, in order that at least one borane compound, such as L*BH3, L*BY3, L*BHY2 and L*BH2Y, contained in the solid phase be in solution in the solvent L,

- separate the remaining solid phase, which notably comprises the halide acid complex L*HY, from the liquid phase of the second composition, and recover said liquid phase of the second composition,

- performing a second hydrodehalogenation reaction starting from the liquid phase recovered from the first and second compositions, in the hydrogen gas atmosphere in the presence of the catalyst,

- separating the liquid phase containing L*BH3 and the solid phase both resulting from the second hydrodehalogenation reaction, and

- optionally, recovering the solid phase resulting from the second reaction, and notably evaporating the excess solvent L contained therein.

Said solid and liquid phases can be separated with a centrifuge apparatus.

Embodiments of the process according to the invention are illustrated hereafter with the non-limitative following examples and accompanying figures.

Figure 1 represents the 7Li NMR liquid spectroscopy diagrams of commercial LiAlH4 (upper diagram) and of hydrogenation solid products dissolved in THF and in CDCI3 (lower diagram) as presented in example 2;

Figure 2 represents the 7Ei NMR liquid spectroscopy diagrams of commercial Li AIH4 (upper diagram line) and hydrogenation solid products (middle and lower diagram) dissolved directly in deuterium oxide (D2O) as presented in example 2;

Figure 3 represents the 11B NMR liquid spectroscopy diagrams of TEA-BH3, TEA-BCI3, liquid phase obtained after a hydrodehalogenation reaction of TEA-BCI3 (test 1) and after a second (test 2) hydrodehalogenation test, in solution in CDCI3 as presented in example 2;

Figure 4 represents the XRD analysis of the solid phase obtained after tests 1 and 2 of figure 3 as presented in example 2; the diamond dots correspond to TEA-HC1 diffraction peaks;

Figure 5 represents the 11B NMR liquid spectroscopy diagrams of TEA-BH3, TEA-BBr3, liquid phase obtained after a hydrodehalogenation reaction of TEA-BBn (test 1) and after a second (test 2) hydrodehalogenation test, in solution in CDCI3 as presented in example 2; Figure 6 represents the XRD analysis of the solid phase obtained after tests 1 and 2 of figure 5 as presented in example 2; the diamond dots correspond to TEA-HBr diffraction peaks;

Figure 7 represents the XRD analysis of the dehydrogenated product of LiAl(BH4)4(NH3)e presented in example 1;

Figure 8 represents the Raman spectrum of the dehydrogenated product of LiAl(BH4)4(NH3)e presented in example 1;

Figure 9 represents the XPS spectrum for a) boron and b) nitrogen of the dehydrogenated product of LiAl(BH4)4(NH3)e presented in example 1;

Figure 10 represents the 11B NMR MAS (acronym of Nuclear Magnetic Resonance Magic Angle Spinning) of the dehydrogenated product of LiAl(BH4)4(NH3)e presented in example 1.

Example 1

LiAl(BH4)4(NH3)e is dehydrogenated by heating from room temperature to 200°C. The solid product obtained is then characterized by different techniques.

It appears from the XRD pattern represented on figure 7 that this solid product is poorly crystallized and mainly amorphous. The four peaks of the XRD pattern correspond either to metallic Al or to Al _x Li _y alloy (Alo.gLio.i, Alo.89Lio.11, Alo.955Lio.o45).

The dehydrogenated product is dissolved by the acid mixture of HC1 and HNO3 to proceed to its elementary analysis for Li, Al and B by ICP-OES. The molar ratio obtained for Li:Al:B is l:0.9:3.5.

It can be deduced from the Raman spectrum represented on figure 8 that B-H, N-H and B-H bonds are present in the dehydrogenated product.

The solid product was also analyzed by XPS spectroscopy, as represented on figure 9. The XPS spectra of figures 9a and 9b, measured at three different points of the dehydrogenated product for boron and nitrogen respectively, confirm the presence of amorphous BN and are similar to the dehydrogenated product of ammonia borane NH3BH3 and of Mg(BH4 (NH3)6. The quantitative analysis of XPS gives a molar ratio Li:Al:B:N of l:0.9:4.3:4.6.

The 11B RMN MAS spectrum of the dehydrogenated product is presented on figure 10. The peaks at 24.6, 19.8 and 10.6 ppm correspond to tricoordinate B atoms such as BN2H and/or BN3. The peaks at -1.14 and -21.9 ppm correspond to fourcoordinate B atoms such as BNH3 and/or BN2H2 and/or BN3H. The peak at -40.4 ppm corresponds to the BH4 group. The possible BNH-based polymers obtained are BN3, BN2H, BNH3, BN2H2, BN3H, the ratio of B :N being greater than 1 : 1 (except BNH3). This result is consistent with the result of quantitative XPS analysis. The dehydrogenated product contains thus several kinds of B product, which are mainly BNH-based polymers in amorphous form.

Example 2

0.05 g of LiAl(BNH)4, 0.007 g of TiCh and 2 ml of tetrahydrofuran have been introduced in an autoclave at a temperature of 25 °C. The autoclave has been sealed and H2 has been introduced therein at a pressure of 5 MPa. The temperature of the autoclave has been increased up to 100°C and maintained for 72 hours.

Then, the pressure has been lowered back to atmospheric pressure, and BNH particles as well as a product of formula LiAlH4 were extracted as a solute in THF, as observed in Figure 1. A liquid-solid separation was performed in a centrifuge apparatus and a liquid phase comprising THF and LiAlH4 was allowed to recover. The solvent THF was then evaporated under dynamic vacuum at 60°C for 4h. Figure 2 presents the 7Li NMR liquid spectroscopy diagram of the corresponding LiAlH4.

The digestion of BNH has been done by mixing the BNH compound with CS2 and AICI3 and submitting the obtained solution in anhydrous HC1 gas at a temperature of 80°C and at a pressure of 40 bar.

Further, boron trichloride has been mixed with TEA for 60 minutes at 0°C. Hydrodechlorination of TEA*BC13 has been conducted by loading a vessel with TEA*BC13, NiB and TEA. Then the mixture is submitted to a pressure of 67 bar with H2 gas at a temperature of 130 °C. Once pressure has been lowered to atmospheric pressure and temperature has been lowered to room temperature, TEA*BH3 and TEA*HC1 have been obtained, present in a composition comprising a solid phase and a liquid phase. The liquid phase and the solid phase were separated by centrifugation. The liquid phase was recovered, and the solid phase was dissolved in TEA to put the boron contained in the solid phase in solution such a to prepare a second solution. The TEA*HC1 was then eliminated from the thus dissolved solid phase. Then another hydrodechlorination of TEA*BC13 has been conducted by loading a vessel with the remaining liquid phase, NiB and TEA in the conditions described here above. Finally, after this another hydrodechlorination, a composition has been obtained which comprises:

- a liquid phase comprising a content of TEA*BH3 of 21.6 % higher than the one of 7 % in the liquid phase obtained after the first hydrodechlorination, as it can be observed in figure 3, and

- a solid phase comprising TEA*HC1, as evidenced by the XRD analysis of figure 4.

The same hydrodehalogenation procedure was also employed starting from TEA-BBrs. As it can be observed on figures 5 and 6, TEA-BH3 can be obtained with sensibly 100% yield after performing two hydrodehalogenation reaction tests. Thus, the process has successfully provided a metal hydride LiAIFU, and

TEA*BH3 which can be used for preparing Al(BH4)3(NH3)e and Li2Al(BH4)s(NH3)6.

Of course, the present invention is not limited to the experiments presented therein for illustrative purpose.