Catalyst, in particular for cracking ammonia, method for preparing the catalyst and method for synthesising hydrogen

Abstract

The invention relates to a catalyst for the decomposition of ammonia into hydrogen and nitrogen, wherein the catalyst comprises at least ruthenium, mesoporous cerium oxide and at least one oxide selected from among cobalt, nickel and iron oxides, preferably nickel oxide, and to a method for producing hydrogen from ammonia comprising the following steps in this order: activating at least one catalyst according to the invention at a temperature ranging from 300°C to 600°C under a stream of a reducing gas; bringing the activated catalyst into contact with a gas to be treated comprising ammonia at a temperature ranging from 200°C to 800°C, and at a pressure ranging from atmospheric pressure to 100 bar.

Description

[0001] CATALYST, IN PARTICULAR FOR AMMONIA CRACKING, PROCESS FOR PREPARING THE CATALYST AND PROCESS FOR SYNTHESIZING HYDROGEN

[0002] Field of invention

[0003] The present invention relates to the field of catalysts suitable for the cracking of ammonia to obtain hydrogen and, accordingly, it also relates to the field of hydrogen synthesis processes.

[0004] State of the art

[0005] In recent years, climate change has intensified, and hydrogen has gained popularity worldwide as an environmentally friendly alternative to fossil fuels. Hydrogen makes it possible to generate "cleaner" energy, i.e., using more environmentally friendly technologies: less polluting and less impactful on the greenhouse effect.

[0006] However, in order to use hydrogen, it is essential to have infrastructure available to transport and store it safely and efficiently.

[0007] There are several methods of storing hydrogen, however not all of them are suitable for the end use of this hydrogen.

[0008] Hydrogen is known to be an environmentally friendly energy carrier, as it has a high energy density (between 120 MJ / kg and 144 MJ / kg) and generates very few polluting by-products during combustion.

[0009] As such, it is notably used as an alternative to fossil fuels in proton exchange membrane fuel cells and water electrolysis cells to generate environmentally friendly energy.

[0010] However, the major problem with this technology is that hydrogen must be stored at a very high pressure, greater than 300 bar, which makes it a difficult gas to transport. In addition, compressing this gas requires a very high amount of energy.

[0011] Faced with this problem, one of the proposed solutions is to use ammonia, that is to say to transport and store ammonia, and to transform it into hydrogen at the place of use of said hydrogen. Ammonia has many advantages, such as a high hydrogen density (the hydrogen content is 17.6% by mass in ammonia), a decomposition energy lower than that of the electrolysis of water and simpler conditions of use and transport, largely mastered at the industrial level.

[0012] Ammonia can be decomposed into hydrogen and nitrogen according to the following reaction: 2 NH3 — 3 H2+ N2.

[0013] This decomposition reaction, also called ammonia cracking, is an endothermic reaction generally carried out in a fixed-bed tubular reactor. This reaction takes place without carbon emissions.

[0014] The decomposition of ammonia is usually carried out in a reactor containing a catalyst at temperatures between 550 and 750°C.

[0015] The conversion rate of ammonia during this reaction depends on several parameters, including the nature of the catalyst used, the temperature, the pressure and the ratio between the gas flow rate to be treated and the volume of catalyst used (i.e. the WH: Hourly Volume Velocity).

[0016] Depending on the desired uses, it may be interesting to produce hydrogen containing a significant quantity of ammonia or very little ammonia.

[0017] In particular, when hydrogen is intended to be used in fuel cells, achieving very high conversion is particularly important, as this technology requires a high degree of hydrogen purity, greater than 99%.

[0018] However, this high degree of purity cannot be achieved with all known ammonia cracking catalysts. Indeed, achieving such a high level of conversion requires very severe operating conditions, including very high temperatures, which often lead to rapid degradation of catalyst performance.

[0019] Catalysts used for the decomposition of ammonia are generally made of a metal, typically iron, cobalt, nickel, ruthenium, rhodium, platinum, palladium, iridium deposited on a support which is a metal oxide such as alumina (AI2O3) or carbon nanotubes (CNT). Catalysts not containing noble metals exhibit good catalytic activity at a temperature above 550°C but their catalytic activity at lower temperatures is average or even low.

[0020] On the other hand, catalysts based on noble metals such as ruthenium and platinum are generally preferred because they exhibit satisfactory catalytic activity for the decomposition of ammonia at lower temperatures, but these catalysts often contain a high quantity of noble metals, which can represent several percent of the final formulation, which makes them particularly expensive.

[0021] Furthermore, their activity is closely linked to other parameters such as the nature of the support used as well as the presence of specific dopants in the formulation.

[0022] As a result, manufacturers continue to seek satisfactory alternatives to these catalysts, offering the best compromise between performance, cost and durability.

[0023] These technical problems have been solved by the catalyst according to the present invention.

[0024] Summary of the invention

[0025] The invention aims to overcome the drawbacks of the prior art by proposing an ammonia cracking catalyst which is efficient, durable, competitive in terms of cost and which makes it possible to significantly reduce the energy requirements associated with the ammonia cracking process by reducing in particular the temperature at which the process is carried out.

[0026] Surprisingly and advantageously, the inventors have solved this technical problem by proposing a catalyst, preferably for the decomposition of ammonia into hydrogen and nitrogen, said catalyst comprising at least ruthenium, mesoporous cerium oxide (CeCh) and at least one oxide chosen from cobalt (CoO), nickel (NiO) and iron (Fe2O3) oxides, preferably nickel oxide (NiO).

[0027] In the following text, the expressions "ammonia cracking" and "ammonia decomposition" are used interchangeably.

[0028] The catalysts according to the invention are particularly stable; in fact, no deactivation has been observed over a time scale over which commercial catalysts show definite deactivation. Consequently, the catalysts according to the invention do not require a particularly high replacement frequency, which is advantageous for the maintenance of ammonia cracking units.

[0029] The cracking catalysts according to the invention generally contain fewer noble metals in their formulation than conventional catalysts, and they allow the cracking of ammonia under less energy-intensive operating conditions than the catalysts of the prior art: in fact, at iso-conversion to ammonia, the catalysts of the invention operate at lower temperatures than the catalysts of the prior art.

[0030] Consequently, a first advantage of the present invention is that it makes it possible to have catalysts with a reduced ruthenium content which exhibit satisfactory or even better performance than the noble metal-based catalysts of the prior art, particularly in terms of ammonia conversion.

[0031] The present invention also makes it possible to obtain catalysts comprising a quantity of ruthenium of the order of that of the noble metal-based catalysts of the prior art, these catalysts according to the invention then have the advantage of allowing decomposition of ammonia at a significantly lower temperature.

[0032] As a result, the invention allows the conduct of an industrial process aimed at producing hydrogen from ammonia with a favorable energy balance and high sustainability.

[0033] According to a first aspect, the invention relates to a catalyst, preferably for the decomposition of ammonia into hydrogen and nitrogen, comprising at least ruthenium (Ru), mesoporous cerium oxide (CeCh) and at least one oxide chosen from cobalt (CoO), nickel (NiO) and iron (Fe2O3) oxides, preferably nickel oxide (NiO).

[0034] According to one variant, the catalyst comprises mesoporous cerium oxide as a support on which are impregnated at least ruthenium and at least one oxide chosen from cobalt, nickel and iron oxides, preferably at least ruthenium and nickel oxide.

[0035] According to another variant, the catalyst comprises at least ruthenium impregnated on a mesoporous mixed oxide comprising at least one mesoporous cerium oxide and at least one oxide of an element chosen from cobalt, nickel and iron, preferably ruthenium impregnated on a mesoporous mixed oxide of cerium and nickel.

[0036] By "mixed oxide" is meant a mixture of several oxides. In particular, the catalyst according to the invention has a ruthenium content ranging from 0.1 to 10.0%, preferably from 0.2 to 5.0% by weight, preferably from 0.2 to 2.0% and more preferably from 0.2 to 1.0% relative to the total weight of the catalyst.

[0037] Ruthenium is not in alloy form.

[0038] Preferably, the catalyst according to the invention is in a form chosen from granules, beads, cylinders or honeycombs.

[0039] According to a second aspect, the invention relates to a process for preparing this catalyst.

[0040] According to a third aspect, the invention also aims at the use of the catalyst according to the invention or prepared according to the process according to the invention to produce hydrogen and nitrogen from ammonia.

[0041] According to a fourth aspect, the invention relates to a process for producing hydrogen from ammonia using a catalyst according to the invention previously activated.

[0042] Brief description of the figures

[0043] Other characteristics and advantages of the invention will emerge from reading the detailed description which follows, with reference to the appended figures, which illustrate:

[0044] [Fig. 1]: Ammonia conversion rate as a function of temperature, measured on 3 catalysts: a catalyst according to the invention (1% Ru / NiO - CeCh) and two comparative catalysts C1 (5% Ru / CeCh) and C2 (5% Ru / AI2O3).

[0045] [Fig. 2]: Ammonia conversion rate as a function of temperature, measured on 2 catalysts: a catalyst according to the invention (1% Ru -10% NiO / CeO2) and a comparative catalyst (2% Ru / CeO2).

[0046] [Fig. 3]: Ammonia conversion rate as a function of temperature, measured on 4 catalysts: three catalysts in accordance with the invention and comparative catalyst C1.

[0047] [Fig. 4]: Ammonia conversion rate as a function of temperature, measured on 2 catalysts: a catalyst according to the invention and a comparative catalyst with an alumina support.

[0048] [Fig. 5]: Monitoring of activity as a function of time measured on 2 catalysts, one in accordance with the invention and the other being a comparative - Method for analyzing the kinetics of deactivation of catalysts. Description of the invention

[0049] Catalyst

[0050] Ru

[0051] The catalyst according to the present invention comprises at least ruthenium as catalytically active metal.

[0052] The ruthenium content in the catalyst according to the invention ranges from 0.1 to 10.0%, preferably from 0.2 to 5.0%, preferably from 0.2 to 2.0% and more preferably from 0.2 to 1.0% by weight relative to the total weight of the catalyst.

[0053] The catalysts according to the present invention, even with reduced ruthenium content, exhibit good activity, in particular a particularly high ammonia conversion rate, comparable or even higher than that of the catalysts of the prior art comprising higher ruthenium contents.

[0054] Indeed, it has been observed in the examples which follow that a catalyst having only 1% by weight of Ru has better performances than a conventional catalyst comprising 5% by weight of Ru, in addition a catalyst having only 0.5% by weight of Ru has performances comparable or even significantly better than those of the conventional catalyst.

[0055] This reduction in the amount of ruthenium in the catalyst allows for savings in natural resources and also savings in catalyst manufacturing costs.

[0056] Furthermore, the activity of the catalysts according to the invention is high even at low temperature, in particular when the reaction temperature is below 500°C.

[0057] It has thus been observed that the catalysts according to the present invention comprising a greater quantity of ruthenium, of the order of 5%, operate at significantly lower temperatures than the catalysts of the prior art.

[0058] The catalysts according to the present invention therefore operate at lower temperatures, which is particularly advantageous in view of the endothermic nature, and therefore particularly energy-consuming, of the ammonia cracking reaction. CeO2

[0059] The catalyst according to the present invention comprises at least one mesoporous cerium oxide (CeCh).

[0060] For the purposes of the present invention, the term “mesoporous” means a material in which the majority of pores; i.e. more than 50%; have a diameter between 2 and 50 nm. This definition corresponds to that of the IUPAC.

[0061] Cerium oxide is present in the catalyst as a support.

[0062] The cerium oxide content in the catalyst according to the invention ranges from 50.0% to 95.0%, preferably from 70.0% to 90.0% by weight relative to the total weight of the catalyst.

[0063] Oxide of an element in group VIII of the periodic table

[0064] The catalyst according to the present invention also comprises at least one oxide of a group VIII element chosen from cobalt (CoO), nickel (NiO) and iron (Fe2O3) oxides.

[0065] The content of cobalt and / or nickel and / or iron oxide(s) ranges from 5.0% to 20.0% by weight, preferably from 10.0% to 20.0% by weight relative to the total weight of the catalyst.

[0066] Preferably, the catalyst according to the present invention comprises at least NiO.

[0067] According to a first variant, the oxide of a group VIII element is NiO.

[0068] According to a second variant, the catalyst according to the present invention comprises NiO and at least one other oxide of a group VIII element chosen from CoO and Fe2O3.

[0069] According to a first embodiment of the invention, this / these oxide(s) of group VIII is / are present in the catalyst according to the invention as metal oxide(s) impregnated on the support.

[0070] According to this first mode, at least one oxide of an element chosen from CoO, NiO and Fe2O3 is impregnated on the support.

[0071] According to a first preference, at least NiO is impregnated on the support.

[0072] According to a second preference, NiO and at least one other oxide chosen from CoO and Fe2O3 are impregnated on the support. According to a second embodiment of the invention, this / these oxide(s) of group VIII is / are in the catalyst support, as constituent(s) of the catalyst support.

[0073] According to this second mode, at least one oxide of an element chosen from CoO, NiO and Fe2O3 is present in the catalyst support.

[0074] According to this second mode, the support comprises, preferably consists of, a mixed oxide comprising at least mesoporous CeCh and at least one oxide chosen from CoO, NiO and Fe2O3.

[0075] The mixed oxide is mesoporous.

[0076] According to a first preference, the support comprises, preferably consists of, a mesoporous mixed oxide comprising at least mesoporous CeO2 and NiO.

[0077] According to a second preference, the support comprises, preferably consists of, a mesoporous mixed oxide comprising at least mesoporous CeO2, NiO and at least one other oxide chosen from CoO and Fe2O3.

[0078] According to a third embodiment of the invention, this / these oxide(s) of group VIII is / are present both as a metal oxide impregnated on the support and as a constituent(s) of the catalyst support.

[0079] This third embodiment of the invention brings together all the variants of the first and second embodiments of the invention described below.

[0080] When the catalyst includes a mixed oxide as a support, then the ruthenium is impregnated onto the mixed oxide.

[0081] Advantageously, the catalyst according to the present invention comprises from 0.1 to 10.0%, preferably from 0.2 to 5.0% by weight, preferably from 0.2 to 2.0% and more preferably from 0.2 to 1.0% of ruthenium; from 50.0% to 95.0%, preferably from 70.0% to 90.0% by weight of mesoporous cerium oxide and from 5.0% to 20.0% by weight, preferably from 10.0% to 20.0% by weight of at least one oxide of a group VIII element chosen from CoO, NiO and Fe2O3 relative to the total weight of the catalyst.

[0082] Doping

[0083] According to a preferred variant, the catalyst according to the present invention further comprises at least one oxide chosen from the oxides of cesium (CS2O), magnesium (MgO), potassium (K2O), lanthanum (La2O3), praseodymium (PreOn), yttrium (Y2O3), neodymium (Nd2O3), barium (BaO) and gadolinium (Gd2O3).

[0084] Advantageously, the content of oxide(s) chosen from cesium, magnesium, potassium, lanthanum, praseodymium, yttrium, neodymium, barium and gadolinium oxides ranges from 1.0 to 10.0% by weight relative to the total weight of the catalyst.

[0085] This oxide, used as a dopant, is added by impregnation onto the support.

[0086] More specifically, the method of introducing dopants during the preparation of catalysts can vary depending on the nature of the dopant:

[0087] • dopants of the oxide type of Cs, Mg, K and Ba are generally added by impregnation of their respective salts on the support;

[0088] • dopants of type La, Pr, Y, Nd, Gd are generally added either by impregnation of their respective salts on the support, or by coprecipitation during the synthesis of the support itself.

[0089] Preparation of catalysts

[0090] According to a second aspect, the invention relates to a process for preparing this catalyst.

[0091] The preparation method according to the invention comprises the following steps in this order: a) providing an oxide comprising at least one mesoporous cerium oxide chosen from mesoporous cerium oxides and mesoporous mixed oxides of cerium and at least one oxide chosen from CoO, NiO and Fe2O3; b) optionally impregnating the oxide comprising at least one mesoporous cerium oxide with at least one precursor of at least one oxide chosen from CoO, NiO and Fe2O3 and then calcining the oxide obtained; c) impregnating the mesoporous mixed oxide of cerium and at least one oxide chosen from CoO, NiO and Fe2O3 provided in step a) or the oxide obtained in step b) with a ruthenium precursor; d) calcining the oxide impregnated with ruthenium obtained in step c).When the support is a mesoporous cerium oxide, the preparation method comprises the following steps in this order: providing a mesoporous cerium oxide; impregnating the mesoporous cerium oxide with at least one precursor of at least one oxide selected from CoO, NiO and Fe2O3; then calcining the mesoporous cerium oxide impregnated with a precursor of at least one oxide selected from CoO, NiO and Fe2O3; impregnating the mesoporous cerium oxide already impregnated with at least one oxide selected from selected from CoO, NiO and Fe2O3 obtained with a ruthenium precursor; calcining the oxide impregnated with an oxide selected from CoO, NiO and Fe2O3 and with ruthenium.

[0092] When the support is a mesoporous mixed oxide of cerium and at least one oxide chosen from CoO, NiO and Fe2O3, the method according to the invention comprises the following steps in this order: providing a mesoporous mixed oxide of cerium and at least one oxide chosen from CoO, NiO and Fe2O3; optionally impregnating the mixed oxide with at least one precursor of at least one oxide chosen from CoO, NiO and Fe2O3; then calcining the oxide comprising at least one mixed oxide impregnated with a precursor of at least one oxide chosen from CoO, NiO and Fe2O3; impregnating the oxide obtained with a ruthenium precursor; calcining the oxide impregnated with ruthenium obtained.

[0093] More particularly, when several oxides chosen from CoO, NiO and Fe2O3 are present in the catalyst support, said support can be obtained by different methods, for example by co-precipitation of the nitrated salts of the chosen elements in the presence of a basic reagent such as sodium hydroxide, ammonia, potash or any other reagent known from the prior art. In this case, the impregnation step with at least one oxide chosen from CoO, NiO and Fe2O3 is optional.

[0094] More particularly, the step of impregnation with a precursor of at least one oxide chosen from CoO, NiO and Fe2O3 is carried out in the following manner: providing a suspension of an oxide comprising at least one mesoporous cerium oxide; providing an aqueous solution of at least one precursor of at least one oxide chosen from CoO, NiO and Fe2O3; mixing the suspension obtained, drying the impregnated oxide obtained; calcining the impregnated oxide obtained at a temperature ranging from 300 to 800°C, preferably ranging from 350 to 700°C and more preferably from 400 to 600°C for a period ranging from 2 to 10 hours and preferably from 3 to 5 hours.

[0095] More particularly, the step of impregnation with a ruthenium precursor is carried out in the following manner: providing a suspension of an oxide comprising at least one mesoporous cerium oxide already impregnated with at least one oxide chosen from CoO, NiO and Fe2O3 or a suspension of at least one mixed oxide of mesoporous cerium and at least one oxide chosen from CoO, NiO and Fe2O3; providing an aqueous solution of at least one ruthenium precursor; mixing the suspension obtained, drying the impregnated oxide obtained; calcining the impregnated oxide obtained at a temperature ranging from 300 to 800°C, preferably ranging from 350 to 700°C and more preferably from 400 to 600°C for a period ranging from 2 to 10 hours and preferably from 3 to 5 hours.

[0096] Generally, the precursors of the oxides selected from CoO, NiO and Fe2O3 are selected from inorganic salts, such as oxides, hydroxides, nitrates, sulfates, and carbonates; organic salts, such as acetates and oxalates; and organometallic complexes.

[0097] Generally, the ruthenium precursors are ruthenium salts, preferably selected from ruthenium chloride, ruthenium nitrate, potassium ruthenate, sodium ruthenate, ruthenium acetylacetonate and ruthenium nitrosyl nitrate.

[0098] The catalysts according to the invention or obtained by the preparation process according to the invention are in the form of powders.

[0099] Advantageously, the catalyst according to the present invention has the following specificities: a particle size measured by laser diffraction of between 2 and 50 10' 6m (pm) (d50 value, i.e. median size); a pore distribution between 1 and 100 10' 9 m (nm) with a majority, i.e. more than 50%, of pores between 2 and 50 10' 9 m (nm); a specific surface area, measured by the BET method, between 30 and 200 m 2 / g, preferably between 50 and 150 m 2 / g. a pore volume between 0.1 and 0.8 10' 6 m 3 / g (cm 3 / g) and preferably between 0.1 and 0.5 10' 6 m 3 / g (cm 3 / g) .

[0100] The specific surface area, pore volume, and pore size distribution are measured by a gas adsorption / desorption analyzer (N2) according to the BET / BJH method.

[0101] Advantageously, to facilitate the use of the catalyst on an industrial scale, the catalyst in powder form is shaped or deposited on an inert substrate.

[0102] Catalyst shape

[0103] The catalysts according to the invention obtained in the form of powders can then optionally be shaped to appear in a form chosen from granules, beads, cylinders or honeycombs.

[0104] The dimensions of these catalysts vary.

[0105] These catalysts can also be applied to any substrate usually used in the field of catalysis. Substrates are mineral forms based on alumina, titanium oxide, cerium oxide, etc., ceramic materials such as zirconia and cordierite. The substrates can also be metallic in nature, such as NiCrAlloy, FeCrAlloy, aluminum, etc.

[0106] Catalysts can also be used in catalytic systems. These catalytic systems can comprise a coating (called a "wash coat") with catalytic properties and based on these catalyst compositions, on a substrate such as, for example, a metal monolith or a ceramic one, in particular cordierite. They can also be incorporated into the porosity of a thermally conductive material such as graphene.

[0107] According to a fourth aspect, the invention also relates to a process for producing hydrogen from ammonia comprising at least the following steps in this order:

[0108] - activation of at least one catalyst according to the invention or prepared according to the preparation process according to the invention at a temperature ranging from 300°C to 600°C, preferably ranging from 400°C to 500°C under a flow of a reducing gas chosen from hydrogen, ammonia, carbon monoxide, preferably hydrogen,

[0109] - bringing said activated catalyst into contact with a gas to be treated comprising ammonia at a temperature ranging from 200°C to 800°C, preferably ranging from 350°C and 500°C and at a pressure ranging from atmospheric pressure to 100 bar.

[0110] Preferably, the gas to be treated is generally pure ammonia, however the catalysts of the invention are also active for the decomposition of NH3 in a mixture containing an inert gas, in particular nitrogen. In this case the concentration of NHs can vary from 1 to 99%. In other cases the catalytic systems of the invention are compatible with the presence of other gaseous species such as H2, H2S, H2O, CH4, saturated and unsaturated hydrocarbons, cyclic or linear, ...

[0111] These catalytic systems and more particularly the catalysts of the invention can find many applications. They are thus well suited to, and therefore usable in, the catalysis of various reactions such as, for example, reforming, steam reforming, cracking, hydrocracking, hydrogenation, dehydrogenation, isomerization, dehydrocyclization of hydrocarbons or other organic compounds, oxidation and / or reduction reactions, water gas reactions also called shift reactions, carbon monoxide and dioxide hydrogenation reactions, the Fisher-Tropsch reaction and the synthesis of ammonia.

[0112] This method and various modes of execution are now described below with reference to Figures 1 to 5.

[0113] The following examples illustrate the invention without limiting its scope.

[0114] EXAMPLES

[0115] In the following examples the following products were used:

[0116] - mesoporous cerium oxide CeCh, in the form of powder with a particle size d50 equal to 7 10' 6 m, synthesized by precipitation of a nitro salt of cerium (IV) and an ammonia base, followed by an autoclave curing step carried out between 100 and 150°C for 2 hours. At the end of these steps, the precipitated material obtained is washed with demineralized water with a ratio of volume of water: volume of precipitate equal to 1.5. It is then dried for 12 hours at 120°C in a ventilated oven, before being calcined in air in a muffle furnace, at 500°C for a 4-hour period,

[0117] - nickel nitrate hexahydrate: Ni(NOs)2, 6H2O;

[0118] - iron nitrate nonahydrate: Fe(NO3)3, 9H2O;

[0119] - cobalt nitrate hexahydrate: Co(NO3)2, 6H2O;

[0120] - hydrated Ruthenium chloride: RuCh, XH2O.

[0121] A. CeC Support Catalysts

[0122] Example 1.1: Catalyst 1%Ru +10%NiQ / CeO2

[0123] 100 g of a Ru - NiO / CeCh catalyst containing 1% Ru and 10% NiO were prepared according to the following protocol:

[0124] NiO impregnation

[0125] The impregnation of NiO on CeO2 was carried out by implementing the following steps: o 38.9 g of nickel nitrate were dissolved in 150 mL of water at room temperature with stirring; o 88.7 g of mesoporous CeO2 were suspended in 150 mL of water with stirring at room temperature; o Then the pH of the CeO2 suspension was adjusted to 4 by adding a 70% HNO3 solution, o the nickel nitrate solution and the CeO2 suspension were mixed and then the mixture was stirred for 10 min at 60°C on a rotary evaporator; o The suspension obtained was evaporated under vacuum; o The product obtained - comprising nickel nitrate impregnated on mesoporous CeO2 - was dried at 80°C for 10 hours o Then calcined at 500°C for 4 hours.

[0126] Ru impregnation

[0127] The impregnation of Ru on CeO2 was carried out by implementing the following steps: o 2.2 g of Ruthenium chloride (45% Ru salt) were dissolved in 100 mL of water at room temperature with stirring; o The NiO / CeCh product obtained in the previous paragraph, i.e. 98.7 g, was suspended in 200 mL of water with stirring at room temperature; o Then the pH of the NiO / CeO2 suspension was adjusted to 4 by adding a 70% HNO3 solution, o the Ru solution and the NiO / CeO2 suspension were mixed and then the mixture was stirred for 10 min at 60°C on a rotary evaporator; o The suspension obtained was evaporated under vacuum; o The product obtained was dried at 80°C for 10 hours o Then calcined at 400°C for 4 hours.

[0128] Using the same method and adapting the amount of ruthenium, the following catalysts were prepared:

[0129] Example 1.2: 5%Ru +10% NiO / CeO2;

[0130] Example 1.3: 2%Ru +10% NiO / CeO2; And

[0131] Example 1.4: 0.5%Ru +10% NiO / CeO2.

[0132] 100 g of a Ru - NiO -CoO / CeO2 catalyst containing 1% Ru, 10% CoO and 10% NiO were prepared according to the following protocol:

[0133] Co-impregnation of NiO and CoO

[0134] The co-impregnation of NiO and CoO on CeO2 was carried out by implementing the following steps: o 38.9 g of nickel nitrate and 38.8 g of cobalt nitrate were dissolved in 200 mL of water at room temperature with stirring; o 78.7 g of mesoporous CeO2 were suspended in 100 mL of water with stirring at room temperature; o Then the pH of the CeO2 suspension was adjusted to 4 by adding a 70% HNO3 solution, o the nickel nitrate and cobalt nitrate solution and the CeO2 suspension were mixed and then the mixture was stirred for 10 min at 60°C on a rotary evaporator; o The obtained suspension was evaporated under vacuum; o The product obtained - comprising nickel nitrate and cobalt nitrate impregnated on mesoporous CeCh - was dried at 80°C for 10 hours o Then calcined at 500°C for 4 hours.

[0135] Ru impregnation

[0136] The impregnation of Ru on the CeCh previously impregnated with CoO and NiO was carried out by implementing the following steps: o 2.2 g of Ruthenium chloride (45% Ru salt) was dissolved in 100 mL of water at room temperature with stirring; o The NiO-CoO / CeCh product obtained in the previous paragraph, i.e. 98.7 g, was suspended in 200 mL of water with stirring at room temperature; o Then the pH of the NiO-CoO / CeCh suspension was adjusted to 4 by adding a 70% HNO3 solution, o the Ru solution and the NiO-CoO / CeCh suspension were mixed and then the mixture was stirred for 10 min at 60°C on a rotary evaporator; o The suspension obtained was evaporated under vacuum; o The product obtained was dried at 80°C for 10 hours; o Then calcined at 400°C for 4 hours.

[0137] B Catalysts: NiO + CeO2 support

[0138] Example 3.1: Catalyst 0.5%Ru / NiO + CeO?

[0139] 100 g of a Ru / NiO-CeCh catalyst containing 0.5% Ru and 10% NiO were prepared according to the following protocol:

[0140] Mesoporous mixed oxide of CeO2 and NiO, in the form of powder with a particle size d50 equal to 7 10' 6 m, is synthesized by precipitation of a nitrated salt of cerium (IV) and nickel with an ammonia base, followed by an autoclave maturing step carried out between 100 and 150°C for 2 hours. At the end of these steps, the precipitated material obtained is washed with demineralized water with a ratio of volume of water: volume of precipitate equal to 1.5. It is then dried for 12 hours at 120°C in a ventilated oven, before being calcined in air in a muffle furnace, at 500°C for a 4-hour stage.

[0141] Ru impregnation

[0142] The impregnation of Ru on the NiO-CeO2 mixed oxide was carried out by implementing the following steps: o 1.1 g of Ruthenium chloride (45% Ru salt) was dissolved in 100 mL of water at room temperature with stirring; o 99.3 g of the mesoporous mixed oxide of CeO2 and NiO were suspended in 200 mL of water with stirring at room temperature; o Then the pH of the mixed oxide suspension was adjusted to 4 by adding a 70% HNO3 solution, o the Ru solution and the mixed oxide suspension were mixed and then the mixture was stirred for 10 min at 60°C in a rotary evaporator; o The obtained suspension was evaporated under vacuum; o The product obtained was dried at 80°C for 10 hours o Then calcined at 400°C for 4 hours.

[0143] Using the same method and adapting the amount of ruthenium, the following catalysts were prepared:

[0144] Example 3.2: 1%Ru / NiO + CeO2,

[0145] Example 3.3: 5%Ru / NiO + CeO2.

[0146] C. Comparative Catalysts

[0147] C.1: 5% Ru / CeO2

[0148] 100 g of a Ru / CeO2 catalyst containing 5% Ru was prepared according to the following protocol;

[0149] Ru impregnation

[0150] The impregnation of Ru on CeO2 was carried out by implementing the following steps: o 11.1 g of Ruthenium chloride (45% Ru salt) were dissolved in 100 mL of water at room temperature with stirring; o 93.4 g of mesoporous CeCh were suspended in 100 mL of water with stirring at room temperature; o Then the pH of the CeCh suspension was adjusted to 4 by adding a 70% HNO3 solution, o the Ru solution and the CeCh suspension were mixed and then the mixture was stirred for 10 min at 60°C on a rotary evaporator; o The suspension obtained was evaporated under vacuum; o The product obtained was dried at 80°C for 10 hours o Then calcined at 400°C for 4 hours.

[0151] Using the same method and adapting the amount of ruthenium, the catalyst CT: 2% Ru / CeCh was prepared.

[0152] C.2: 5% Ru / AI2O3

[0153] 100 g of a RU / AI2O3 catalyst containing 5% Ru were prepared according to the following protocol:

[0154] Ru impregnation

[0155] The impregnation of Ru on alumina was carried out by implementing the following steps: o 11.1 g of Ruthenium chloride (45% Ru salt) were dissolved in 100 mL of water at room temperature with stirring; o 93.4 g of AI2O3 were suspended in 100 mL of water with stirring at room temperature; o Then the pH of the A^Os suspension was adjusted to 4 by adding a 70% HNO3 solution, o the Ru solution and the A^Os suspension were mixed and then the mixture was stirred for 10 min at 60°C in a rotary evaporator; o The suspension obtained was evaporated under vacuum; o The product obtained was dried at 80°C for 10 hours o Then calcined at 400°C for 4 hours. C.3: 1%Ru +10%NiQ / AI2O3

[0156] Catalyst C3 was prepared using the same method as the preparation method of catalyst 1.1 by replacing CeCh with AI2O3.

[0157] Table 1 lists the characteristics of the prepared materials.

[0158] The specific surface area, pore volume, and pore size distribution are measured by a gas adsorption / desorption analyzer (N2) according to the BET / BJH method. [Table 1] Decomposition of ammonia

[0159] Ammonia decomposition was carried out in a fixed-bed tubular reactor under the following conditions:

[0160] - Atmospheric pressure;

[0161] - hourly volumetric speed (WH): 10,000 h -1 -5,000 h -1 ;

[0162] - Temperature: 350-550°C

[0163] - NH3: 10%

[0164] - presence of N2.

[0165] Measurement of the results of ammonia decomposition reactions

[0166] Ammonia decomposition reactions were carried out using the catalysts prepared as described above and comparative catalysts to determine the ammonia conversion rates.

[0167] The ammonia decomposition capacity was measured under the operating conditions presented above. The NH3 contents at the reactor inlet [NH3] en reactor inlet and outlet [NH3] SO rtie were measured by gas chromatography, thus allowing the ammonia conversion rate to be calculated using the following formula:

[0168] NH3 conversion (%) = ([NH3] en tree - [NH3] SO rtie) *100 / [NH3] en tree

[0169] Figure 1

[0170] Figure 1 shows the ammonia conversion rate, in %, as a function of temperature, in °C, of ​​3 catalysts: a catalyst according to the invention (example 3.2) and two comparative catalysts C1 and C2 comprising 5 times more ruthenium.

[0171] Figure 1 shows that the catalyst of example 3.2 according to the invention (at 1% Ru, NiO + CeCh support) allows a better conversion of NH3 (of the order of 15%) from 350°C than the two comparative catalysts.

[0172] Furthermore, the conversion of NH3 between 35% and 90% is obtained at a lower temperature with the catalyst according to the invention: the catalyst according to the invention allows the same conversion percentage to be obtained at a temperature 10 to 20°C lower than the comparative catalysts.

[0173] Figure 2 Figure 2 shows the ammonia conversion rate, in %, as a function of temperature, in °C, of ​​2 catalysts: a catalyst according to the invention (example 1.1) and the comparative catalyst CT (2% Ru / CeCh).

[0174] Figure 2 shows that the catalyst of example 1.1 according to the invention (at 1% Ru+10% NiO ZCeCh) allows a better conversion (of the order of 10%) of NH3 at iso temperature from 350°C than the comparative catalyst comprising 2% ruthenium.

[0175] Furthermore, the conversion of NH3 between 30% and 90% is obtained at a lower temperature with the catalyst according to the invention: the catalyst according to the invention allows the same conversion percentage to be obtained at a temperature approximately 20°C lower.

[0176] Figure 3

[0177] Figure 3 shows the ammonia conversion rate in %, as a function of temperature, in °C, of ​​4 catalysts: three catalysts in accordance with the invention (examples 3.3, 3.2 and 3.1) and comparative catalyst C1.

[0178] Figure 3 shows that the catalysts of Examples 3.3 and 3.2 according to the invention (comprising 5% and 1% Ru respectively) allow a conversion of NH3 significantly better than that of the comparative catalyst C1 comprising 5% ruthenium from 350°C. In addition, the catalyst of Example 3.1 according to the invention comprising 0.5% ruthenium allows a conversion of NH3 of the order of that of catalyst C1 or even slightly higher.

[0179] Figures 1-3 show that the use of the catalysts according to the invention is doubly advantageous: these catalysts contain less ruthenium, which is a noble, expensive metal, and they allow the conversion of NH3 to be carried out at lower temperatures. At iso-conversion to ammonia, the catalysts of the invention operate at lower temperatures than the catalysts of the prior art.

[0180] Figure 4

[0181] Figure 4 shows the ammonia conversion rate, in %, as a function of temperature, in °C, of ​​2 catalysts: a catalyst according to the invention (example 1.1) and the comparative catalyst C3 based on alumina. Figure 4 shows that the catalyst of example 1.1 according to the invention allows a better conversion of NH3 at iso temperature from 350°C than the comparative catalyst. Figure 5

[0182] Figure 5 shows the activity, i.e. the percentage of ammonia conversion, of two catalysts as a function of time.

[0183] The activity of catalyst 3.2 was measured at 450°C (top curve) and 400°C (bottom curve). At these two temperatures, no deactivation was observed after 30 hours of operation.

[0184] On the other hand, for the comparative catalyst C1, a progressive deactivation is observed from the start and throughout the operating time.

Claims

CLAIMS 1. Catalyst, preferably for the decomposition of ammonia into hydrogen and nitrogen, said catalyst comprising at least ruthenium, mesoporous cerium oxide and at least one oxide chosen from cobalt, nickel and iron oxides, preferably nickel oxide.

2. Catalyst according to claim 1 comprising mesoporous cerium oxide as support on which are impregnated at least ruthenium and at least one oxide chosen from cobalt, nickel and iron oxides, preferably at least ruthenium and nickel oxide.

3. Catalyst according to claim 1 comprising at least ruthenium impregnated on a mesoporous mixed oxide comprising at least one mesoporous cerium oxide and at least one oxide of an element chosen from cobalt, nickel and iron, preferably ruthenium impregnated on a mixed oxide of cerium and nickel.

4. Catalyst according to any one of claims 1 to 3, characterized in that the cerium oxide content ranges from 50.0% to 95.0%, preferably from 70.0% to 90.0% by weight relative to the total weight of the catalyst.

5. Catalyst according to any one of claims 1 to 4, characterized in that the ruthenium content ranges from 0.1 to 10.0%, preferably from 0.2 to 5.0%, preferably from 0.2 to 2.0% and more preferably from 0.2 to 1.0% by weight relative to the total weight of the catalyst.

6. Catalyst according to any one of claims 1 to 5, characterized in that the content of cobalt and / or nickel and / or iron oxide(s) ranges from 5.0% to 20.0%, preferably from 10.0% to 20.0% by weight relative to the total weight of the catalyst.

7. Catalyst according to any one of claims 1 to 6, characterized in that it further comprises at least one oxide chosen from the oxides of cesium, magnesium, potassium, lanthanum, praseodymium, yttrium and neodymium, barium and gadolinium.

8. Catalyst according to the preceding claim, characterized in that the content of oxide(s) chosen from oxides of cesium, magnesium, potassium, lanthanum, praseodymium, yttrium, neodymium, barium and gadolinium ranges from 1.0 to 10.0% by weight relative to the total weight of the catalyst.

9. Catalyst according to any one of the preceding claims, characterized in that the catalyst is in a form chosen from granules, beads, cylinders or honeycombs.

10. A process for preparing the catalyst according to any one of claims 1 to 9 comprising the following steps in this order: a) providing an oxide comprising at least one mesoporous cerium oxide chosen from mesoporous cerium oxides and mesoporous mixed oxides of cerium and at least one oxide chosen from CoO, NiO and Fe2O3; b) optionally impregnating the oxide comprising at least one mesoporous cerium oxide with at least one precursor of at least one oxide chosen from CoO, NiO and Fe2O3 and then calcining the oxide obtained; c) impregnating the mesoporous mixed oxide of cerium and at least one oxide chosen from CoO, NiO and Fe2O3 provided in step a) or the oxide obtained in step b) with a ruthenium precursor; d) calcining the ruthenium-impregnated oxide obtained in step c).

11. Use of the catalyst according to any one of claims 1 to 9 or prepared according to claim 10 for producing hydrogen and nitrogen from ammonia.

12. Process for producing hydrogen from ammonia comprising at least the following steps in this order: - activation of at least one catalyst according to any one of claims 1 to 9 or prepared by the process of claim 10 at a temperature ranging from 300°C to 600°C, preferably ranging from 400°C to 500°C under a flow of a reducing gas chosen from hydrogen, ammonia, carbon monoxide, preferably hydrogen; - bringing said activated catalyst into contact with a gas to be treated comprising ammonia, at a temperature ranging from 200°C to 800°C, preferably ranging from 350°C to 500°C and at a pressure ranging from atmospheric pressure to 100 bar.

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