Process, method, catalyst, and use

Abstract

The present invention relates to a process for producing hydrogen from the catalytic cracking of ammonia using a catalyst. The catalyst comprises nickel supported on a metal element modified alumina support, the nickel having a particle size of from 0.5 nm to 10 nm, the metal element of the metal element modified alumina support being selected from the group comprising the rare-earth metals, titanium (Ti), zirconium (Zr), molybdenum (Mo), and zinc (Zn).

Description

[0001] P102343

[0002] PROCESS, METHOD, CATALYST, AND USE

[0003] Field of the Invention

[0004] The present invention relates to a process for producing hydrogen from ammonia. More specifically, the present invention relates to a process for producing hydrogen from the catalytic cracking of ammonia using a catalyst. In other aspects, the invention includes a method of producing the catalyst used in the process, the catalyst produced by the method, and use of the catalyst in the catalytic cracking of ammonia.

[0005] Background of the Invention

[0006] There is renewed interest in using hydrogen as a green, carbon free, fuel in a variety of industrial settings. Hydrogen may be combusted to produce heat energy or electricity. Alternatively, hydrogen may be used to produce electrochemical energy in, for example, a fuel cell.

[0007] Ammonia has received interest as a possible compound to enable the storage and transport of hydrogen. Liquid ammonia has a higher hydrogen density than liquid hydrogen, and may be transported using existing infrastructure which is already in use for this purpose, such as that used for the transportation of ammonia in the agrochemical fertiliser industry.

[0008] Once the liquid ammonia has been transported it may be combusted directly or converted to hydrogen by the process of cracking.

[0009] The catalytic cracking of ammonia into hydrogen and nitrogen has been known for many years. The reaction may be depicted as follows:

[0010] 2 NH3N2+ 3 H2

[0011] The ammonia cracking reaction is endothermic and may usefully be achieved by passing ammonia over a suitable catalyst in externally heated catalyst-containing reaction tubes disposed in a furnace. Such furnaces are known, for example, for the steam reforming of natural gas or naphtha feedstocks and are referred to herein as fired ammonia cracking reactors.

[0012] In industrial processes used for the catalytic cracking of ammonia, a fuel is combusted in the fired ammonia cracking reactor to provide heat energy to the catalyst containing reaction tubes. The fuel may be a hydrocarbon fuel, however, typically, the fuel may compriseP102343

[0013] ammonia and / or hydrogen. For instance, the fuel may be a portion of the ammonia which is to be cracked, or a waste gas stream. Waste gas streams are typically produced from the purification of the hydrogen stream (e.g. by pressure swing adsorption) following the ammonia cracking reaction. In certain cases, nitrogen gas (N2) may also be present in the fuel.

[0014] Due to the endothermic nature of the ammonia cracking reaction, the effective utilisation of heat and the fuel used to generate said heat are important considerations. In some processes for ammonia cracking, process gases (e.g. ammonia or hydrogen) may be used to as a fuel to sustain the ammonia cracking reaction. This has the disadvantage of decreasing the hydrogen yield of the ammonia cracking process by consuming reactant and / or product. One way to reduce the energy intensity of the ammonia cracking process is through selection of a suitable catalyst.

[0015] Known catalysts for the cracking of ammonia include nickel supported on a metal oxide support, such as alumina or silica. Example of such catalysts are KATALCO™ 27-2 and KATALCO™ 27-200MQ, available from Johnson Matthey PLC. However, the temperature required to catalyse and sustain the ammonia cracking reaction using nickel catalysts is typically in the range of from 650 °C to 950 °C.

[0016] Catalysts comprising platinum group metals, such as ruthenium, have been found to catalyse the cracking of ammonia at lower temperature. For example, the ruthenium-based catalyst KATALCO™ 27-612, available from Johnson Matthey PLC, shows excellent activity for the cracking of ammonia at temperatures as low as 400 °C. However, catalysts containing platinum group metals are typically more expensive than those which contain base metals.

[0017] There is a need for improved processes for the cracking of ammonia, in particular those with improved utilisation of heat and fuel.

[0018] Summary of the Invention

[0019] Accordingly, the present invention provides a process for the catalytic cracking of ammonia which may be operated at lower temperatures than traditional supported nickel catalysts, and without the increased cost of platinum group metal catalysts.

[0020] In a first aspect of the present invention there is provided a process for the catalytic cracking of ammonia to produce hydrogen and nitrogen, the process comprising the steps of passingP102343

[0021] an ammonia stream over a catalyst in an ammonia cracking reactor and converting ammonia in the ammonia stream into a cracked gas stream comprising hydrogen and nitrogen, wherein the catalyst comprises nickel supported on a metal element modified alumina support, the nickel having a particle size of from 0.5 nm to 10 nm, and wherein the metal element of the metal element modified alumina support is selected from the group comprising the rare-earth metals, titanium (Ti), zirconium (Zr), molybdenum (Mo), and zinc (Zn).

[0022] It has surprisingly been found that the catalyst of the process of the first aspect of the invention is able to crack ammonia to hydrogen (H2) and nitrogen (N2) at a reduced temperature as compared to nickel catalysts of the prior art comprising the same nickel loadings. For example, the catalyst of the process of the first aspect of the invention shows the same rate of ammonia conversion at temperatures 50-70 °C lower than nickel catalysts of the prior art comprising the same nickel loadings. More surprisingly, the catalyst of the process of the first aspect of the invention may provide the same activity for the cracking of ammonia as catalysts of the prior art at the same temperature whilst having half the nickel loading. More surprisingly still, the catalyst of the first aspect of the invention has greater thermal stability, despite its low nickel particle size, and retains high activity for the cracking of ammonia for longer than nickel-based catalysts of the prior art.

[0023] Without being bound by any sort of theory it is believed that the combination of the metal element of the metal element modified alumina support and the nickel particle size increases the activity and stability of the catalyst and allows conversion of ammonia to hydrogen and nitrogen at a lower temperature. Consequently, the amount of fuel required in the ammonia cracking reactor may be significantly reduced.

[0024] In a second aspect, the invention includes a method for preparing the catalyst of the process of the first aspect of the invention, the method comprising the steps of:

[0025] providing an alumina support material;

[0026] impregnating the alumina support material with a metal element compound to provide a metal element modified alumina support;

[0027] impregnating the metal element modified alumina support with a nickel ammine carbonate solution having a pH in the range of 7.5 to 12 to provide a nickel impregnated metal element modified alumina support; and

[0028] drying and calcining the nickel impregnated metal element modified alumina support to produce the catalyst comprising nickel supported on the metal element modified alumina support.P102343

[0029] In a third aspect, the invention includes a catalyst obtained or obtainable from the method of the second aspect of the invention.

[0030] In a fourth aspect, the invention includes a use of the catalyst as defined in the first aspect of the invention as a catalyst to crack ammonia and produce hydrogen and nitrogen.

[0031] In a fifth aspect, the invention includes a use of the catalyst obtained or obtainable from the method of the second aspect of the invention as a catalyst to crack ammonia and produce hydrogen and nitrogen.

[0032] Brief Description of the Drawings

[0033] The invention will be further described by reference to the drawings in which:

[0034] Figure 1 is a chart depicting NH3conversion versus temperature for a catalyst according to the invention and a comparative catalyst, and;

[0035] Figure 2 is a chart depicting relative activity of a catalyst according to the invention to comparative catalyst 1 , versus hours aged at 800 °C.

[0036] Detailed Description

[0037] Preferred and / or optional features of the invention will now be set out. Any aspect of the invention may be combined with any other aspect of the invention unless the context demands otherwise. Any of the preferred and / or optional features of any aspect may be combined, either singly or in combination, with any aspect of the invention unless the context demands otherwise. Lower and / or upper limits of any ranges disclosed herein are envisaged to be combinable with one another to provide new ranges, whether explicitly stated or not.

[0038] The first aspect of the present invention provides a process for the catalytic cracking of ammonia to produce hydrogen and nitrogen and comprises the step of passing an ammonia stream over a catalyst in an ammonia cracking reactor and converting ammonia in the ammonia stream into a cracked gas stream comprising hydrogen and nitrogen.

[0039] The catalytic cracking of ammonia to produce hydrogen and nitrogen is carried out in an ammonia cracking reactor.

[0040] Suitable ammonia cracking reactors are known and may comprise a fuel combustion zone having a radiant section comprising one or more burners to which one or more fuel streams and an oxygen feed gas, such as air, oxygen enriched air, or oxygen, are fed. The radiantP102343

[0041] section may comprise the one or more catalyst containing reaction tubes though which the ammonia stream is passed. Combustion of one or more fuel streams in the one or more burners of the fuel combustion zone, creates heat energy (e.g. radiant heat) for heating the one or more catalyst containing reaction tubes. There may be tens, hundreds, or thousands of catalyst containing reaction tubes in the radiant section. If desired, downstream of the radiant section, a flue gas from the combustion of the one or more fuel streams may be used to pre-heat one or more feed streams in a convection section. Ammonia cracking reactors comprising a radiant section containing catalyst containing reaction tubes and a convection section for preheating feeds are known in steam methane reforming and may be applied to the present invention. Such reactors may be referred to as fired ammonia cracking reactors. Accordingly, the ammonia cracking reactor may be a fired ammonia cracking reactor.

[0042] Where the ammonia cracking reactor is a fired ammonia cracking reactor, the steps of passing the ammonia stream over the catalyst in the ammonia cracking reactor and converting the ammonia in the ammonia stream into the cracked gas stream comprising hydrogen and nitrogen may comprise the steps of:

[0043] i) providing an ammonia stream to an inlet of one or more catalyst containing reaction tubes disposed within a radiant section of a fired ammonia cracking reactor;

[0044] ii) passing the ammonia stream over the catalyst of the one or more catalyst containing reaction tubes and converting ammonia in the ammonia stream into a cracked gas stream comprising hydrogen and nitrogen;

[0045] iii) obtaining the cracked gas stream from the outlet of the one or more catalyst containing reaction tubes.

[0046] Alternatively, the fired ammonia cracking reactor may be of a design where the combustion of the one or more fuel streams in a fuel combustion zone is separate to the reactor comprising the catalyst containing reaction tubes. Such a reactor is the compact reformer available from Johnson Matthey Davy Technologies Limited.

[0047] Alternatively, the ammonia cracking reactor may be a packed bed reactor or a membrane reactor. The packed bed reactor may be adiabatic, heated by combustion of a fuel (e.g. ammonia, hydrogen, or a fossil fuel such as natural gas), or may be electrically heated (e.g. by resistive heating or induction heating). Where an adiabatic packed bed reactor may be used, it will be understood that no heat may be transferred from the reactor to the ammonia stream being fed to it, and that the heat required to catalyse the ammonia cracking reaction may be derived from the ammonia stream itself.P102343

[0048] It has surprisingly been found that the catalyst of the process of the first aspect of the invention is particularly suited for use in packed bed reactors and / or membrane reactors which may be smaller and less complicated than fired ammonia cracking reactors. Packed bed reactors and / or membrane reactors may be used in so called “decentralised” applications where ammonia may be transported to a site where hydrogen fuel is required and the ammonia cracked at the point of need. Because the catalyst of the process of the first aspect of the invention has activity for the cracking of ammonia at lower temperatures it may advantageously be used, and suited for use, in decentralised applications where the supply of energy to the packed bed reactor and / or membrane reactor may be limited. For instance, it may be preferred to use electrical heating in decentralised applications.

[0049] The ammonia stream may comprise 90 mol% ammonia or more, 95 mol% ammonia or more, 97 mol% ammonia or more, or 99 mol% ammonia or more. The ammonia stream may be substantially 100 mol% ammonia. By “substantially 100 mol% ammonia” it is meant that any other component that may be present as an incidental impurity and may be present at an amount of less than 1 mol%, less than 0.5 mol%, or less than 0.1 mol% of the ammonia stream.

[0050] The cracked gas stream contains hydrogen (H2). The cracked gas stream also contains nitrogen (N2), and may further contain residual ammonia (e.g. unreacted ammonia).

[0051] The cracked gas stream may comprise 60 mol% or more H2, 65 mol% or more H2, 70 mol% or more H2, 72 mol% or more H2, or 73 mol% or more H2. The cracked gas stream may comprise up to 75 mol% or less H2. For example, the cracked gas stream may comprise from 60 mol% to 75 mol% H2. Preferably, the cracked gas stream comprises from 70 mol% to 75 mol% H2, such as 72 mol% to 75 mol% H2.

[0052] The cracked gas stream may comprise 20 mol% or more N2, 21 mol% or more N2, 22 mol% or more N2, or 23 mol% N2or more. The cracked gas stream may comprise up to 25 mol% or less N2. For example, the cracked gas stream may comprise from 20 mol% to 25 mol% N2. Preferably, the cracked gas stream comprises from 22 mol% to 25 mol% N2, such as from 23 mol% to 25 mol% N2.

[0053] The cracked gas stream may comprise less than 20 mol% NH3, less than 15 mol% NH3, less than 10 mol% NH3, less than 5 mol% NH3, less than 1 mol% NH3, or less than 0.1 mol%P102343

[0054] NH3. Preferably, the cracked gas stream comprises less than 4 mol% NH3, less than 2 mol% NH3, less than 1 mol% NH3, or less than 0.1 mol% NH3.

[0055] The cracked gas stream may comprise an equilibrium mixture of ammonia, hydrogen, and nitrogen. In other words, the cracked gas stream may comprise a mixture of ammonia, hydrogen, and nitrogen at partial pressures such that no further hydrogen and nitrogen may be produced from further cracking reaction. An equilibrium mixture may comprise from 72 mol% to 75 mol% H2, from 23 mol% to 25 mol% N2, and less than 4 mol% NH3(e.g. less than 1 mol% or less than 0.1 mol% NH3).

[0056] The ammonia stream may be passed over the catalyst at a temperature in the range of 300 °C to 650 °C, from 350 °C to 625 °C, from 400 °C to 600 °C, or from 450 °C to 550 °C, such as from 475 °C to 525 °C. That is, the ammonia stream may have a temperature in the range of 300 °C to 650 °C, from 350 °C to 625 °C, from 400 °C to 600 °C, or from 450 °C to 550 °C, such as from 475 °C to 525 °C as it is passed over the catalyst. The temperature at which the ammonia stream may be passed over the catalyst may be recorded at an inlet or an outlet to the ammonia cracking reactor, such as at the inlet to or the outlet from the one or more catalyst containing reaction tubes of a fired ammonia cracking reactor.

[0057] It is a surprising advantage of the process of the present invention that the temperatures at which the cracking of ammonia to produce hydrogen and nitrogen is performed may be lower than when traditional nickel-based ammonia cracking catalysts are used. Typically, where traditional nickel-based ammonia cracking catalysts are used, an ammonia stream may be passed over a catalyst in a temperature range of from 650 °C to 950 °C.

[0058] The pressure at which the ammonia stream may be passed over the catalyst will be set by the flowsheet design and may be in the range 1 to 100 bar absolute, preferably 10 to 90 bar absolute, such as 31 to 51 bar absolute.

[0059] The process of the first aspect of the invention comprises a catalyst. The catalyst comprises nickel supported on a metal element modified alumina support, the nickel having a particle size of from 0.5 nm to 10 nm.

[0060] The metal element modified alumina support may be in the form of a shaped pellet (such as a sphere, a cylinder, a quadralobe, or a trilobe), an extrudate, a granule, or may be coated as a wash-coat onto a suitable structured substrate such as a monolith honeycomb catalyst support.P102343

[0061] The alumina of the alumina support material may be present in any one of a number of phases. For example, the alumina of the alumina support material may be an alpha alumina, a beta alumina, a delta alumina, a gamma alumina, a theta alumina, or a mixture of these phases. Additionally or alternatively, the alumina of the alumina support material may be an alumina modified with an alkali metal (e.g. Li, Na, K, or Ba) or alkali earth metal (e.g. Mg or Ca). For instance, the alumina of the alumina support material may be a lithium, sodium, potassium, or barium modified alumina, a magnesium aluminate, or a calcium aluminate. Preferably, the alumina of the alumina support material may be a delta-theta alumina, optionally modified with an alkali metal or an alkali earth metal. The alumina of the alumina support may consist of, or consist essentially of, alumina. For the avoidance of doubt, where the alumina is an alumina modified by an alkali metal or an alkali earth metal, the alumina support may also be modified with the metal element, as defined hereinbelow.

[0062] It has surprisingly been found that delta-theta alumina possesses a combination of high surface area, allowing a high dispersion of both metal element and nickel on the surface of the alumina support, and high thermal stability, making it resistant to temperatures typically employed for the cracking of ammonia. Whilst other alumina phases may have a higher surface area or a higher thermal stability, it has surprisingly been found that delta-theta alumina possesses an ideal combination thermal stability and surface area.

[0063] The catalyst of the process of the first aspect of the invention comprises an alumina support which is a metal element modified alumina support. The metal element of the metal element modified alumina support is selected from the group comprising the rare-earth metals, titanium (Ti), zirconium (Zr), molybdenum (Mo), and zinc (Zn). The metal element of the metal element modified alumina support may be selected from the group comprising cerium (Ce), yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), scandium (Sc), titanium (Ti), zirconium (Zr), molybdenum (Mo), and zinc (Zn). The metal element of the metal element modified alumina support may preferably be selected from the group comprising cerium (Ce), yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), and titanium (Ti). The metal element of the metal element modified alumina support may more preferably be selected from the group comprising cerium (Ce), yttrium (Y), and lanthanum (La), and titanium (Ti), most preferably cerium (Ce). The metal element may be present in the alumina support as an oxide. For example, the metal element may be present as CeC>2, Y2O3, La2Os, Nd2C>3, S1TI2O3, SC2O3, TiC>2, ZrC>2, M0O2, M0O3, or ZnO. Preferably, the rare-earth metal may be cerium and may be present in the metal element modified alumina support as CeC>2.P102343

[0064] It will be understood that the term “rare-earth metals” includes the group of elements having atomic numbers 57 to 71 , scandium, and yttrium.

[0065] The alumina support may be modified with the metal element throughout the entire alumina support, that is the metal element modified alumina support may comprise a homogeneous distribution of the metal element throughout its structure. Alternative, the alumina support may be modified on one or more surfaces of the alumina support, and may have an eggshell structure. The term “egg-shell” will be understood to include a metal element modification at or from the surface of the alumina support extending a distance in to the alumina support to form a layer. The layer may have a homogenous distribution of metal element through the layer. The layer may have an inhomogeneous distribution through the layer, such as a gradient through the thickness of the layer in a direction perpendicular to the surface of the alumina support.

[0066] The catalyst may comprise the metal element in an amount of 1 wt% or more, 2 wt% or more, or 3 wt% or more, expressed on an oxide basis and relative to the total weight of the catalyst. The catalyst may comprise the metal element in an amount of 10 wt% or less, 7 wt% or less, or 5 wt% or less, expressed on an oxide basis and relative to the total weight of the catalyst. For example, the catalyst may comprise the metal element in an amount of from 1 wt% 10 wt%, from 2 wt% to 7 wt%, or from 3 wt% to 5 wt%, expressed on an oxide basis and relative to the total weight of the catalyst.

[0067] The concentration and / or distribution of the metal element in the metal element modified alumina support can be determined using analytical techniques known in the art such as X-ray fluorescence (XRF) spectroscopy, scanning electron microscopy (SEM), and / or electron probe micro-analysis (EPMA).

[0068] The nickel may be dispersed on the surface of the metal element modified alumina support as particles or crystallites. The particle size of the particles or crystallites may be measured using transmission electron microscopy, for example by measuring the particle size of a selection (e.g. 100) particles on the support and taking the mean average.

[0069] The nickel may be present in the catalyst as metallic nickel or as a nickel oxide (e.g. NiO). As will be understood, the catalyst as freshly prepared may comprise predominantly nickel as nickel oxide, whilst the active phase of the catalyst during the ammonia cracking reaction may be predominantly metallic nickel.P102343

[0070] The nickel has a particle size of from 0.5 nm to 10 nm. The nickel may have a particle size of 1 nm or more, 1.2 nm or more, or 1.5 nm or more. The nickel may have a particle size of 8 nm or less, 6 nm or less, or 4 nm or less. For example, the nickel may have a particle size of from 1 nm to 8 nm, from 1.2 nm to 6 nm, or from 1.5 nm to 4 nm, such as from 2 nm to 3 nm or from 6 nm to 8 nm.

[0071] The catalyst may comprise nickel in an amount of 5 wt% of greater, 7 wt% or greater, 8 wt% or greater, or 10 wt% or greater, expressed on a NiO basis and relative to the total weight of the catalyst. The catalyst may comprise nickel in an amount of 35 wt% or less, 30 wt% or less, 27 wt% or less, or 25 wt% or less, expressed on a NiO basis and relative to the total weight of the catalyst. A suitable range for the nickel content is in the range of from 5 wt% to 35 wt%, or 10 wt% to 30 wt%. For example, the catalyst may comprise nickel in an amount of 5 wt% to 35 wt%, 7 wt% to 30 wt%, 8 wt% to 27 wt%, or 10 wt% to 25 wt%, such as 12 wt%, 15 wt% or 20 wt%, expressed on a NiO basis and relative to the total weight of the catalyst.

[0072] The BET surface area of the catalyst may be 80 m2 / g or more, 100 m2 / g or more, or 120 m2 / g or more. The BET surface area of the catalyst may be 160 m2 / g or less, 140 m2 / g or less, or 130 m2 / g or less. For example, the BET surface area of the catalyst may be from 80 m2 / g to 160 m2 / g, from 100 m2 / g to 140 m2 / g, or from 120 m2 / g to 130 m2 / g. BET surface area may be determined according to ASTM D3663-20 or the method of Brunauer, S.;

[0073] Emmett, P. H.; Teller, E. (February 1938). "Adsorption of Gases in Multimolecular Layers". Journal of the American Chemical Society. 60 (2): 309-319.

[0074] In preferred processes of the first aspect of the present invention, the catalytic cracking of ammonia may be carried out in more than one reactor. The process of the invention may comprise the step of passing the ammonia stream to a pre-cracker comprising a precracking catalyst and cracking at least a part of the ammonia in the ammonia stream to produce a partially cracked ammonia stream. The process of the invention may comprise the step of passing the partially cracked ammonia stream to the ammonia cracking reactor.

[0075] The pre-cracker may be an adiabatic reactor, a packed bed reactor, an electrically heated reactor, and / or a gas fired reactor. The pre-cracker may derive the heat required for the endothermic ammonia cracking reaction from any source, such as by heat recovery from the cracked gas stream produced by the ammonia cracking reactor, and / or a flue gas derived from the burning of a fuel in the ammonia cracking reactor.P102343

[0076] The ammonia stream may be at least partially cracked in the pre-cracker at a temperature of 500 °C to 800 °C, such as from 600 °C to 700 °C.

[0077] In preferred process of the invention, the pre-cracker catalyst may be the catalyst of the first aspect of the invention.

[0078] It is a surprising advantage of the catalyst of the process of the first aspect of the invention that it may catalyse the cracking of ammonia to form hydrogen and nitrogen at lower temperatures than traditional nickel catalysts. Accordingly, the catalyst is ideally suited for use in a pre-cracker where lower grade or latent heat may be used to support a portion of the ammonia cracking reaction in the ammonia stream before the partially cracked ammonia stream is fed to the ammonia cracking reactor. For example, heat recovered from flue gas from a fired ammonia cracking reactor and / or heat recovered from the cracked gas stream may be used to support the ammonia cracking reaction in the pre-cracker.

[0079] In a second aspect of the invention there is provided a method for preparing the catalyst comprising nickel supported on the metal element modified alumina support of the process of the first aspect of the invention.

[0080] The method of the second aspect of the invention may comprise the steps of:

[0081] providing an alumina support material;

[0082] impregnating the alumina support material with a metal element compound to provide a metal element modified alumina support;

[0083] impregnating the metal element modified alumina support with a nickel ammine carbonate solution having a pH in the range of 7.5 to 12 to provide a nickel impregnated metal element modified alumina support; and

[0084] drying and calcining the nickel impregnated metal element modified alumina support to produce the catalyst comprising nickel supported on the metal element modified alumina support.

[0085] The alumina support material may suitably be in the form of a powder with a D50 average particle size in the range 1-200 pm or in the form of a pellet, extrudate or granule with a smallest dimension in the range 1-25 mm. The alumina supports are commercially available or may be produced using conventional shaping techniques. Where the alumina support material may be in the form of a powder, the resulting alumina support powder may, before or after treatment with a catalytic metal compound, be coated as a wash-coat onto a suitableP102343

[0086] structured substrate such as a monolith or honeycomb catalyst support, including stackable structured catalysts supports, which may be metal or ceramic.

[0087] The step of impregnating the alumina support material with a metal element compound may be achieved by contacting the alumina support material with an aqueous solution containing the metal element compound, such as a metal element nitrate, hydroxide, or carboxylate (e.g. acetate). The aqueous solution of the metal element compound may comprise cerium nitrate, lanthanum nitrate, yttrium nitrate, or niobium nitrate. The metal element may be present in the aqueous solution containing the metal element compound in an amount of from 10 to 60 g / litre on a metal basis.

[0088] The alumina support may be suspended in water and the aqueous solution of the metal element compound added. Alternatively, the alumina support may be suspended in the aqueous solution of the metal element compound. It may be preferred that the alumina support may be subjected to so called incipient-wetness impregnation or “dry impregnation” in which the volume of impregnation solution is similar to the pore volume of the alumina support. Thus, the alumina support may be treated with a volume of the aqueous solution containing the metal element compound equivalent to about the total pore volume of the alumina support. This improves the control of the amount of metal element compound on the alumina support.

[0089] Optionally, following the step of impregnating the alumina support with the metal element compound, the method of the second aspect of the invention may comprise the step of drying the metal element modified alumina support. The step of drying the metal element modified alumina support may be carried out by heating the metal element modified alumina support to a temperature of from 60 °C to 120 °C, such as 100 °C to 120 °C.

[0090] Optionally, following the step of impregnating the alumina support with the metal element compound, the method of the second aspect of the invention may comprise the step of calcining the metal element modified alumina support. The step of calcining the metal element modified alumina support may be carried out at a temperature of from 200 to 800 °C, preferably from 200 °C to 500 °C. The step of calcining the metal element modified alumina support may be carried out in an atmosphere of air. The step of calcining the metal element modified alumina support may be carried out for a period of 0.5 hours to 24 hours, such as 0.5 to 16 hours.P102343

[0091] The method of the second aspect of the invention comprises the step of impregnating the metal element modified alumina support with a nickel ammine carbonate solution having a pH in the range of 7.5 to 12 to provide a nickel impregnated metal element modified alumina support.

[0092] The nickel ammine carbonate solution may be prepared by reacting nickel or nickel carbonate with ammonia and ammonium carbonate in water. The relative amounts should be such that the pH of the solution is in the range 7.5 to 12, preferably 9 to 12. The solution preferably contains 0.1 to 2.5 moles of the nickel complex per litre.

[0093] The step of impregnating the metal element modified alumina support with the nickel ammine carbonate solution may preferably be carried out by deposition-precipitation.

[0094] Deposition-precipitation provides a high nickel dispersion compared to conventional impregnation methods. In deposition-precipitation, the nickel ammine carbonate solution is applied to the surface of the metal element modified alumina support and heated to decompose the nickel complex and deposit insoluble nickel compounds on the support to form a supported nickel precursor. The method may therefore comprise combining the metal element modified alumina support with a nickel ammine carbonate solution and heating the resulting combination to deposit insoluble nickel compounds on the surface of the metal element modified alumina support. The step of heating the combination may be carried out as part of, or in addition to, the steps of drying and calcining the nickel impregnated metal element modified support.

[0095] Deposition-precipitation may involve treating the metal element modified alumina support with the nickel ammine carbonate solution by forming a slurry of the metal element modified alumina support in the nickel ammine carbonate solution and heating the slurry to deposit insoluble nickel compounds on the metal element modified alumina support. The heating step causes the decomposition of the nickel ammine carbonate and may be performed at temperatures in the range 60-120 °C, preferably 100-120 °C. The insoluble nickel compounds may comprise nickel hydroxycarbonate and / or hydroxide.

[0096] Alternatively, the nickel ammine carbonate solution may be used to impregnate the metal element modified alumina support by incipient wetness methods, as described above, to fill the pores of the metal element modified alumina support. The impregnated metal element modified alumina support may then be heated to deposit the insoluble nickel compounds. The heating step causes the decomposition of the nickel ammine carbonate and may beP102343

[0097] performed at temperatures in the range 60-120 °C, preferably 100-120 °C. The insoluble nickel compounds may comprise nickel hydroxycarbonate and / or hydroxide.

[0098] The step of impregnating the metal element modified alumina support with the nickel ammine carbonate solution may be repeated. For example, the step of impregnating the metal element modified alumina support with a nickel ammine carbonate solution may be carried out two times, three times, or four times. Optionally, following each repeat impregnation the nickel impregnated metal element modified alumina support may be heated to cause the decomposition of the nickel ammine carbonate, as described above. As will be understood, repeating the step of impregnating the metal element modified alumina support with a nickel ammine carbonate solution may be used to increase the total nickel loading of the catalyst.

[0099] The step of drying the nickel impregnated metal element modified alumina support may be carried out separately to or at the same time as the step of calcining the nickel impregnated metal element modified alumina support.

[0100] The step of calcining the nickel impregnated metal element modified alumina support may be carried out at a temperature of from 200 to 800 °C, preferably from 200 °C to 500 °C. The step of calcining the nickel impregnated metal element modified alumina support may be carried out in an atmosphere of air. The step of calcining the nickel impregnated metal element modified alumina support may be carried out for a period of 0.5 hours to 24 hours, such as 0.5 to 16 hours.

[0101] In a third aspect of the invention there is provided the catalyst obtained or obtainable from the method of the second aspect of the invention.

[0102] In a fourth aspect of the invention there is provided the use of the catalyst obtained or obtainable from the method of the second aspect of the invention as a catalyst to crack ammonia and produce hydrogen and nitrogen.

[0103] Examples

[0104] All reagents and materials are commercially available and may be obtained from sources such as Merck-Sigma Aldrich.P102343

[0105] Preparation of a catalyst according to the first aspect of the invention (Catalyst 1)

[0106] A delta-theta alumina support with a pore volume of 1.0 ml / g was used for the preparation of 5 wt% CeC^-AhOs. 40.0 g alumina support was impregnated with 40 ml of a solution of 5.32 g (12.2 mmol) cerium nitrate hexahydrate in water. The material was dried at 110 °C for 12 h and then calcined at 450 °C for 6 h (heating ramp rate: 5 °C / min). A solution of 250 g ammonium carbonate and 350 g basic nickel carbonate in 1 litre of 28 wt% ammonium hydroxide was prepared. This solution was used to impregnate the 5 wt% CeC^-AhOs support with nickel using a volume equal to the pore volume (incipient wetness impregnation). The material was subsequently dried at 110 °C for 12 h after which the material was impregnated with nickel a second time. The material was then dried at 110 °C for 12 h and finally calcined at 350 °C for 2 h (heating ramp rate: 5 °C / min).

[0107] Weight % Ni: 18.62 (23.70 wt% NiO).

[0108] Weight % Ce: 3.50 (4.30 wt% CeO2).

[0109] Ni metal surface area: 18.20 m2 / g.

[0110] Preparation of a comparative nickel catalyst (Comparative Catalyst 1)

[0111] Comparative Catalyst 1 was a nickel catalyst, representative of nickel catalysts of the prior art, and comprises nickel on a pelletised calcium aluminate support and had a comparable nickel loading to that of Catalyst 1.

[0112] A calcium aluminate (CaAI2O4) support was impregnated using a nickel nitrate solution (46 g / L on a Ni basis) for 20 minutes. The impregnated support was air dried at 100 °C for 4 hours and calcined at 640 °C for 4 hours. The steps of impregnation, drying, and calcining were repeated until a nickel loading of 18.15 wt% (23.10 wt% NiO) was obtained.

[0113] Weight % Ni: 18.15 (23.10 wt% NiO)

[0114] Ni metal surface area: 4.15 m2 / g.

[0115] Preparation of a comparative nickel catalyst (Comparative Catalyst 2)

[0116] A second comparative nickel catalyst was prepared using a nickel ammine carbonate solution and an unmodified alumina support. The method described above for preparing catalyst 1 (according to the invention) was used, except that the steps to modify the alumina support material with cerium were omitted.

[0117] Weight % Ni: 17.05 (21.70 wt% NiO).

[0118] Ni metal surface area: 17.70 m2 / g.P102343

[0119] Ammonia conversion test

[0120] The ammonia conversion as a function of temperature was investigated for Catalyst 1, and Comparative Catalyst 1. The results from this test are shown in Figure 1.

[0121] It can be seen that Catalyst 1 has a higher activity than the nickel-based Comparative Catalyst 1.

[0122] Moreover, this experiment shows that at the same nickel loading, catalysts of the present invention have an operating temperature window below that of Comparative Catalyst 1: the same ammonia conversion is provided at temperatures 50 °C to 70 °C lower than Comparative Catalyst 1. For example, Catalyst 1 achieves 10 % NH3 conversion at a temperature of ~430 °C whereas Comparative Catalyst 1 achieves this conversion at a temperature of ~480 °C.

[0123] It is therefore a clear advantage of the catalyst according to the invention that lower temperatures may be used compared to traditional nickel ammonia cracking catalysts. Accordingly, lower quantities of fuel are required to sustain the cracking reaction.

[0124] Alternatively, catalysts with lower nickel loadings may be used at the elevated temperatures typical of traditional nickel-based ammonia cracking catalysts.

[0125] Aging test

[0126] Catalyst 1 and Comparative Catalyst 1 were artificially aged in a 100 % NH3atmosphere at 800 °C in a reactor.

[0127] At timed intervals the temperature of the reactor was lowered to 500 °C and the catalyst’s activity determined. The temperature was then returned to 800 °C to continue the aging process.

[0128] Figure 2 shows the relative activity of Catalyst 1 and Comparative Catalyst 1 for the cracking of ammonia as a function of the numbers of hours aged.

[0129] Figure 2 shows that catalysts of the invention have greater stability than nickel catalysts of the prior art, and retain activity for the cracking of ammonia for longer.

[0130] Without wishing to be bound by any sort of theory, the improved stability is believed to be due to a combination of the use of the nickel ammine carbonate solution providing nickelP102343

[0131] particles on the support with an optimum size in combination with the metal element modification of the alumina support material.

[0132] Effect of metal element modification

[0133] The activity of Catalyst 1 and Comparative Catalyst 2 for the cracking of ammonia at 500 °C were investigated before and after ageing.

[0134] Catalyst 1 and Comparative Catalyst 2 were artificially aged in a 100 % NH3atmosphere at 800 °C for 320 hours.

[0135] Prior to ageing, Catalyst 1 demonstrated an activity 43 % higher than that of Comparative Catalyst 2. Following ageing, it was found that the activity of Catalyst 1 was over three times higher than that of Comparative Catalyst 2.

[0136] This test shows that the metal element modification of the alumina support not only provided an increase in initial activity but also improved the stability of the catalyst and its resistance to thermal ageing.

Claims

1. P102343Claims1. A process for the catalytic cracking of ammonia to produce hydrogen and nitrogen, the process comprising the steps of passing an ammonia stream over a catalyst in an ammonia cracking reactor and converting ammonia in the ammonia stream into a cracked gas stream comprising hydrogen and nitrogen, wherein the catalyst comprises nickel supported on a metal element modified alumina support, the nickel having a particle size of from 0.5 nm to 10 nm, and wherein the metal element of the metal element modified alumina support is selected from the group comprising the rare-earth metals, titanium (Ti), zirconium (Zr), molybdenum (Mo), and zinc (Zn).

2. A process according to claim 1 , wherein the alumina of the alumina support is an alpha alumina, a beta alumina, a delta alumina, a gamma alumina, a theta alumina, or a mixture thereof.

3. A process according to claim 1 or claim 2, wherein the alumina of the alumina support material is an alumina modified with an alkali metal or an alkali earth metal.

4. A process according to any one of the preceding claims, wherein the alumina of the alumina support is a delta-theta alumina.

5. A process according to any one of the preceding claims, wherein the metal element of the metal element modified alumina support is selected from the group comprising cerium (Ce), yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), scandium (Sc), titanium (Ti), zirconium (Zr), molybdenum (Mo), and zinc (Zn).

6. A process according to any one of the preceding claims, wherein the metal element of the metal element modified alumina support is selected from the group comprising cerium (Ce), yttrium (Y), and lanthanum (La), and titanium (Ti).

7. A process according to any one of the preceding claims, wherein the metal element of the metal element modified alumina support is present as an oxide.

8. A process according to any one of the preceding claims, wherein the catalyst comprises the metal element in an amount of from 1 wt% to 10 wt%, from 2 wt% to 7 wt%, or from 3 wt% to 5 wt, expressed on an oxide basis and relative to the total weight of the catalyst.P1023439. A process according to any one of the preceding claims, wherein the nickel is dispersed on a surface of the support as particles or crystallites.

10. A process according to any one of the preceding claims, wherein the nickel has a particle size of from 1 nm to 8 nm, from or from 6 nm to 8 nm.

11. A process according to any one of the preceding claims, wherein the catalyst comprises nickel in an amount of 5 wt% to 35 wt%, 7 wt% to 30 wt%, 8 wt% to 27 wt%, 10 wt% to 25 wt%, or 10 wt% to 30 wt%, such as 12 wt%, 15 wt% or 20 wt%, expressed on a NiO basis and relative to the total weight of the catalyst.

12. A process according to any one of the preceding claims, wherein the BET surface area of the catalyst is from 80 m2 / g to 160 m2 / g, from 100 m2 / g to 140 m2 / g, or from 120 m2 / g to 130 m2 / g.

13. A process according to any one of the preceding claims, wherein the catalytic cracking of ammonia is carried out in more than one reactor.

14. A process according to claim 13, wherein the process comprises the step of passing the ammonia stream to a pre-cracker comprising a pre-cracking catalyst and cracking at least a part of the ammonia in the ammonia stream to produce a partially cracked ammonia stream.

15. A process according to claim 14, wherein the process comprises the step of passing the partially cracked ammonia stream to the ammonia cracking reactor.

16. A process according to claim 15, wherein the pre-cracker derives the heat required for the endothermic ammonia cracking reaction by heat recovery from the cracked gas stream produced by the ammonia cracking reactor, and / or a flue gas derived from the burning of a fuel in the ammonia cracking reactor.

17. A process according to any one of claims 14 to 16, wherein the pre-cracker catalyst is the catalyst defined in any one of claims 1 to 12.

18. A process according to any one of the preceding claims, wherein the ammonia cracking reactor is a fired ammonia cracking reactor, and the steps of passing the ammonia stream over the catalyst in the ammonia cracking reactor and converting the ammonia in the ammonia stream into the cracked gas stream comprising hydrogen and nitrogen comprises the steps of:P102343i) providing the ammonia stream to an inlet of one or more catalyst containing reaction tubes disposed within a radiant section of the fired ammonia cracking reactor;ii) passing the ammonia stream over the catalyst of the one or more catalyst containing reaction tubes and converting the ammonia in the ammonia stream into a cracked gas stream comprising hydrogen and nitrogen;iii) obtaining the cracked gas stream from the outlet of the one or more catalyst containing reaction tubes.

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