Catalyst composition for decomposing ammonia

Abstract

A catalyst composition for decomposing ammonia (NH3) into nitrogen (N2) and hydrogen (H2) comprises (i) a platinum group metal (PGM) and / or a base metal; and (ii) an alkali or alkaline earth metal promoter as catalytically active material. The catalytically active material is supported on a catalyst support material. The catalyst support material is mesoporous and has a total pore volume of at least 0.35ml / g and an average pore width of at least 15 nm.

Description

[0001]P102268 Catalyst composition for decomposing ammonia Field of the inventionThis invention relates to the decomposition of ammonia (NH3) for the production of hydrogen(H2). The invention provides a catalyst composition for decomposing ammonia. The inventionalso provides a process of decomposing ammonia to produce hydrogen and nitrogen (N2) anda process and system for the generation of power. Background to the inventionAmmonia decomposition, or cracking, involves the catalytic decomposition of ammonia intohydrogen and nitrogen. Exploiting such decomposition in the production of hydrogen as a fuelfor use in a fuel cell system or in a hydrogen fuelled internal combustion engine is attractive,considering that ammonia has a high energy density and a high hydrogen storage capacity. Moreover, no carbon dioxide (CO2) is produced in the decomposition. Techniques for producing hydrogen by ammonia decomposition are well-known. These techniques are generally not commercially feasible at fuel cell operating conditions, however,due to poor catalyst performance. Furthermore, the decomposition of ammonia to hydrogenis an endothermic process. As such, a high degree of conversion requires high reaction temperatures and low partial pressures of the reactants. Catalytic ammonia decomposition may also be useful in the treatment of ammonia emissions, in applications where oxygen is absent or not present in sufficient quantities to employ ammonia oxidation. For example, exhaust gas from an ammonia-fuelled internal combustion engine may comprise slipped ammonia which should be treated before emission to the atmosphere.Ammonia decomposition occurs in the presence of a metal catalyst. Generally, ammoniadecomposition systems focus on ruthenium-based supported catalysts. Other platinum groupmetals and Group VIII metals (nickel, iridium, iron, cobalt and rhodium), as well as metalcarbides and metal nitrides, have also been proven to catalyse the ammonia decomposition process. P102268 Ammonia decomposition proceeds with high velocity on ruthenium, cobalt, nickel, and iron metal supported catalysts. The overall number of metal active sites in supported catalysts primarily depends on metal dispersion, which directly affects catalyst performance. Metaldispersion with adequate metal-support interaction is therefore a key parameter in design ofactive catalysts for ammonia decomposition. To improve the metal dispersion and interaction of the metal with the support material, promotors such as alkali or alkaline earth metal promoters are known to be used. Forexample, Han (Han, Wenfeng et al., Effect of activated carbon on the dispersion of Ru and Kover supported Ru-based catalyst for ammonia synthesis, Catalyst Communications 8 (2007), 351-354, Elsevier) discloses the use of potassium (K) as a promoter for a supported ruthenium (Ru) ammonia synthesis catalyst.Obtaining a high degree conversion of ammonia to hydrogen with minimum energy input, forexample at working temperatures of fuel cells, is a significant challenge to future practicalapplications. Therefore, the development of efficient and stable ammonia catalysts operableat lower temperatures is of great importance. Summary of the inventionBroadly speaking, the inventors have surprisingly found that a marked improvement inammonia (NH3) decomposition into nitrogen (N2) and hydrogen (H2) can be achieved using anammonia decomposition catalyst composition comprising an alkali or alkaline earth metalpromoted platinum group metal (PGM) or base metal supported on a large pore catalystsupport material.The increase that can be achieved conveniently allows for the platinum group metal or basemetal loadings to be reduced, or at least limited, thereby also to achieve a reduction in thecost of the catalyst composition. Put differently, higher conversions can be achieved at lowercatalytic metal (e.g. platinum group metal) loadings.Accordingly, the invention provides, as one aspect thereof, a catalyst composition fordecomposing ammonia into nitrogen and hydrogen, the catalyst composition comprising acatalyst support material supporting a catalytically active material, wherein the catalyticallyactive material comprises (i) a platinum group metal and / or a base metal and (ii) an alkali or P102268alkaline earth metal promoter, and wherein the catalyst support material is mesoporous andhas a total pore volume of at least 0.35 ml / g and an average pore width of at least 15 nm.In this specification, a mesoporous catalyst support material with a total pore volume of atleast 0.35 ml / g and an average pore width of at least 15 nm is from time to time referred to asa “large pore catalyst support material”.The mesoporous catalyst support material may have a total pore volume of from 0.35 ml / g to1.30 ml / g and an average pore width of from 15 to 40 nm. The total pore volume of themesoporous catalyst support material may be in the range 0.4 to 1.3 ml / g, for example 0.45to 1.30 ml / g, 0.48 to 1.30 ml / g, 0.5 to 0.9 ml / g, 0.5 to 0.8 ml / g. 0.6 to 0.9 ml / g or 0.6 to 0.8ml / g. The average pore width of the mesoporous catalyst support material may be in the range20 to 40 nm, for example, 20 to 30 nm or 25 to 30 nm.As used herein, the term “mesoporous” indicates that a material comprises pores that rangein width from 2 to 50 nanometres (nm).As used herein the term “total pore volume” is the total pore volume as measured by Barrett-Joyner-Halenda (BJH) methodology, specifically BJH desorption cumulative volume of pores in the range between 17 Å and 3,000 Å width.As used herein, the term “average pore width” means the BJH desorption average pore widthas determined by N2 physisorption according to the Barrett-Joyner-Halenda (BJH)methodology. The average pore width is equal to 4*V / A, the where V is pore volume and Aarea.Preferably, at least 30% of the total pore volume (BJH) of the mesoporous catalyst supportmaterial consists of pores having an average pore width (BJH) in the mesoporous range (20to 50nm), more preferably 50 to 90% of the total pore volume.The support material is preferably a mesoporous refractory oxide support material.The refractory oxide support material may be selected from the group consisting of alumina, silica, titania, zirconia, ceria, zinc oxide, tin oxide, magnesium oxide, yttrium oxide, tantalumoxide, hafnium oxide, lanthanum oxide and a mixed or composite oxide thereof, e.g. a mixedoxide or a composite oxide of two or more thereof. P102268Preferably, the refractory oxide support material is alumina. The alumina may be gammaphase alumina, theta phase alumina, alpha phase alumina, delta (δ), eta (η) and kappa (κ) or a mixture thereof.Alternatively, the support material may be a molecular sieve. In such a case, the molecularsieve would typically be an aluminosilicate, e.g. a mesoporous zeolite. A mesoporous zeolitemay have both micropores and mesopores, for example, mesoporosity may be introduced into the into the microporous crystallite structure of the zeolite by a post-synthesis treatmentapplied to the zeolite. Zeolites may be categorised according to their microporosity by, e.g. amaximum number of tetrahedral atoms present in a zeolite’s framework. As defined herein, a “small pore” zeolite, such as CHA, contains a maximum ring size of eight tetrahedral atoms, whereas a “medium pore” zeolite, e.g. MFI, contains a maximum ring size of ten tetrahedral atoms; and a “large pore” zeolite, such as BEA, contains a maximum ring size of twelvetetrahedral atoms. The mesoporous zeolite may be a small, medium or large pore zeolite thathas had mesoporosity introduced, in which the zeolitic framework of the underlying zeolite intowhich mesoporosity has been introduced still has the defined maximum ring size. Themesoporous zeolite may preferably be a medium pore zeolite, for example having a frameworktype selected from FER, MEL, MFI, STI and STT, or a large pore zeolite, for example havinga framework type selected from AFI, BEA, MAZ, MOR and OFF.Where the catalytically active material comprises PGM, the PGM may be selected fromruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt) ormixtures thereof. Most typically, the PGM would be ruthenium. Where the catalytically activematerial comprises a base metal, the base metal may be selected from nickel (Ni), iron (Fe),cobalt (Co) or mixtures thereof. The PGM and / or base metal may be present in the catalystcomposition as oxides or in metallic form.Where the catalytically active material comprises ruthenium, the catalyst composition maycomprise, by mass, from 0.5% to 10%, such as 0.5% to 3%, e.g.1%, ruthenium based on themass of the composition.When the PGM is ruthenium, the ruthenium may be present in the catalyst composition as anoxide or in metallic form. P102268 The promoter would most typically be an alkali or alkaline earth metal. Preferably, thepromoter is selected from potassium (K) and caesium (Cs) or a mixture thereof.The catalyst composition may comprise, by mass, from 1% to 10%, more preferably from 2%to 6%, e.g. 2%, of the promoter metal based on the mass of the composition.The promoter would typically be present in the catalyst composition as an oxide, but mayalternatively or additionally be present in the form of a hydroxide, nitrate or carbonate.The catalytically active material is supported by the support material, that is, the catalyticallyactive material may be disposed on or within the support material. The catalytically activematerial may be disposed directly onto or is directly supported on the support material (e.g.there is no intervening material between the catalytically active material and the supportmaterial). The catalytically active material may be dispersed on the support material (e.g.particles of the catalytically active material are dispersed over the surface of a particulaterefractory oxide). Alternatively, the catalytically active material may be present within the poresof the support material, for example, the support material is impregnated with the catalytically active material.The catalyst support material may be loaded with the catalytically active material by any knownmeans, for example by means of precipitation or ion exchange. The PGM or base metal andthe promoter may be loaded separately or at the same time. For example, the catalyst supportmaterial in powder form may be combined with an aqueous solution comprising a salt of a PGM and a salt of the promoter metal, such as nitrate, acetate, hydroxide, chloride or oxalatesalts thereof.The catalyst composition may be disposed on a substrate. The substrate may be a flow-through substrate or a filter substrate.The term “disposed on” in this context may encompass both having the composition directlydisposed on the substrate, i.e. with no intervening material, and / or indirectly disposed on the substrate, i.e. with intervening material. If the substrate is porous, then the term “disposed on” may also encompass having the composition disposed therein, for example within the poresof the substrate, i.e. wherein the composition is disposed thereon and / or therein. The catalyticcomposition is typically disposed on the substrate in the form of a washcoat. The term P102268 “washcoat” as used herein is well-known in the field and refers to an adherent coating that is applied to a substrate usually during the production of a catalyst.The substrate is preferably a ceramic substrate, a metallic substrate or a carbon-basedsubstrate.When the substrate is a ceramic substrate, the ceramic substrate may be made of any suitablerefractory material, e.g., alumina, silica, titania, ceria, zirconia, magnesia, zeolites, silicon nitride, silicon carbide, zirconium silicates, magnesium silicates, aluminosilicates, metallo aluminosilicates (such as cordierite and spudomene), or a mixture or mixed oxide of any two or more thereof. Cordierite, a magnesium aluminosilicate, and silicon carbide are particularly preferred. When the substrate is a metallic substrate, the metallic substrate may be made of any suitable metal, and in particular heat-resistant metals and metal alloys such as titanium and stainless steel as well as ferritic alloys containing iron, nickel, chromium, and / or aluminum in addition to other trace metals.When the substrate is carbon-based, the substrate may be activated carbon, charcoal,lampblack, carbon nanofiber carbon nanotubes. When the substrate is a flow-through substrate, the flow-through substrate is preferably a flow- through monolith having a honeycomb structure with many small, parallel thin-walled channels running axially through the substrate and extending throughout from an inlet or an outlet of the substrate. The channel cross-section of the substrate may be any shape, but is preferably square, sinusoidal, triangular, rectangular, hexagonal, trapezoidal, circular, or oval. The flow-through substrate may also be of high porosity which allows the catalyst to penetrate into thesubstrate walls. When the substrate is a filter substrate, the filter substrate is preferably a wall-flow monolithfilter. The channels of a wall-flow filter are alternately blocked, which allow a gas stream toenter a channel from the inlet, then flow through the channel walls, and exit the filter from a different channel leading to the outlet. Particulates in the gas stream are thus trapped in the filter. P102268The catalyst composition may be added to the substrate by any known means, such as awashcoating procedure, wherein a solution, slurry or suspension of the catalyst compositionin a solvent is coated onto the substrate. The coated substrate then typically undergoes a calcination step, to remove solvent and to fix the catalytically active material to the substrate.Alternatively, the catalyst composition may be pelletised. In other words, the catalystcomposition, typically including a suitable binder in such a case, may be formed into pelletsusing a suitable pelletising process.Alternatively, the catalyst composition may be in the form of an “all-active extrudate” whereina substrate comprises an extrusion of the catalyst composition, i.e. the substrate itself is catalytically active.As another aspect of the invention, there is provided a process for converting ammonia intonitrogen and hydrogen, the process including contacting a gaseous stream that comprisesammonia with a catalyst composition according to the invention at a temperature above 200°C.The temperature at which the gaseous stream comprising ammonia is contacted with thecatalyst composition may be in the range > 200°C to 700°C, preferably > 200°C to 600°C,more preferably > 200°C to 500°C, even more preferably in the range 300 to 500°C, most preferably >350 to 500°C. A further aspect of the invention provides a process for generating power comprising: (a) converting ammonia into nitrogen and hydrogen by contacting a gaseous stream comprising ammonia with a catalyst composition according to the invention at a temperature above 200°C; and (b) feeding hydrogen produced by step (a) to a hydrogen-fuelled internal combustion engine or fuel cell. A further aspect of the invention provides a power generation system comprising: -an ammonia source;- an ammonia cracking unit; and- a hydrogen-fuelled internal combustion engine or fuel cell;wherein the ammonia cracking unit comprises the catalyst composition according to the invention. A further aspect of the invention provides a fuel combustion and exhaust system comprising a fuel combustor and an exhaust gas treatment system, wherein the fuel combustor is in fluid P102268 communication with the exhaust gas treatment system and is an ammonia-containing-fuel- combustor, and wherein the exhaust gas treatment system comprises the catalyst composition according to the invention. The term “ammonia-containing-fuel-combustor” as used herein may encompass a fuel combustor that is designed to burn a fuel that comprises ammonia. The ammonia-containing-fuel-combustor may be an ammonia-fuelled internal combustion engine. The invention will now be described with reference to examples and to the accompanying drawings, in which:Figure 1 shows the average pore width vs total pore volume for the support materials used inthe examples described herein.Figure 2 shows a plot of ammonia conversion % against catalyst bed temperature for non-promoted comparative catalyst compositions; andFigure 3 shows a plot of ammonia conversion % against catalyst bed temperature for a non-promoted reference catalyst composition and promoted catalyst compositions, both according to the invention and for comparison.Figure 4 shows the results of NH3 temperature programmed desorption analysis ofcomparative catalyst compositions and a catalyst composition according to the invention.Each aspect / embodiment so defined herein may be combined with any otheraspect / embodiment or aspects / embodiments unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined withany other feature or features indicated as being preferred or advantageous.Further, the term “comprising” as used herein can be exchanged for the definitions “consisting essentially of” or “consisting of”. The term “comprising” is intended to mean that the named elements are essential, but other elements may be added and still form a construct within the scope of the claim. The term “consisting essentially of” limits the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s) of the claimed invention. The term “consisting of” closes the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith P102268 ExamplesThe performance of catalyst compositions according to the invention (inv.) in thedecomposition of ammonia was tested and compared to the performance of comparative(comp.) catalyst compositions, in each case both for non-promoted and for promoted catalystcompositions.Catalyst compositions were pre-treated by exposing them to an ammonia stream for 15minutes at 400°C. Ammonia decomposition was observed by passing a gaseous ammoniastream, comprising 1% NH3 / Ar at 400 ml / min, through a packed bed reactor comprising 0.2gof the pre-treated catalyst composition in particulate form, at bed temperatures ranging from150°C to 400°C to generate a light-off curve.The catalyst compositions were prepared by dispersing the support material and salts of Ruand, where applicable, potassium in water to form a slurry with a solids content of less than50%. The slurry had a pH of <7 and was agitated for at least an hour. The slurry was thendried at 80°C and then calcined at 250-300°C.Pore volume and width information derived via BJH methodology for the support materialsemployed in the examples is shown in Figure 1. The catalyst compositions that were testedare set out in Table 1. The catalyst compositions of examples 4, 5 and 6 were equivalent tothose of examples 1, 2 and 3 respectively, except for the inclusion of potassium promoter.Table 1 Example Ru Catalyst Total Average Percentage of total K metal number metal support Pore pore pore volume of loading loading material Volumewidth of support material(wt%) (wt%) of support having average pore support materialwidth in the rangematerial (nm) 20-50 nm (ml / g) 1 Gamma 1% Ru0.47 9.6(comp.) Al2O31.8% 0 P102268 2 Theta 1% Ru0.91 30(comp.) Al2O389% 03 Gamma 1% Ru0.61 23.4(c61% 0omp.) Al2O3 4 Gamma 1% Ru0.47 9.6 2(comp) Al2O31.8%5 Theta 1% Ru0.91 30Al289% 2O3 6 Gamma 1% Ru0.61 23.4 2Al2O361%As can be seen from Figure 2, the catalyst compositions of comparative examples1, 2 and 3only achieved 13%, 19% and 25% NH3 conversion respectively at 300°C. This shows that theselection of the support itself does not significantly improve the performance of Ru catalyst,even though the support material of example 2 has larger pore width than the support materialof example 1.However, as seen from Figure 3, after adding 2% K metal to the catalyst of example 2, theresulting catalyst composition (example 5) achieved nearly 50% NH3 conversion at 300°Cwhile after adding 2% K to the catalyst of example 1, the resulting catalyst (example 4) canonly achieve 30% NH3 conversion at 300°C. After adding the same amount of K to the catalystof example 3, the resulting catalyst (example 6) shows similar performance as the catalyst ofexample 5.Additionally, the effect of alkali and alkaline earth metal promoters was investigated. Table 2shows the ammonia conversion results at 300 °C for different metal promoters. As shown inFigure 3 and Table 2, alkali metal promoters (K and Cs), used in examples 5-7, deliver higherammonia conversion rates compared to alkaline earth metal promoters (Ba and Sr), used inexamples 8 and 9. These findings indicate that alkali metal promoters enhance the low- temperature activity of PGM catalysts more effectively than alkaline earth metal promoters. P102268 Table 2 Example Ru Catalyst Total Average Percentage Alkali / Ammonia number metal support Pore pore of total pore alkaline Conversion loading material Volume width of volume of earth at 300 °C (wt%) of support support metal and support material material loading material (nm) having (wt%) (ml / g) average pore width in the range 20-50 nm 7 Gamma 1% Ru0.61 23.4 2%Cs 45%Al2O3 61% 8 Gamma 1% Ru0.61 23.4 2%Ba 29%Al2O3 61% 9 Gamma 1% Ru0.61 23.4 2%Sr 29%Al2O3 61%The result indicates that the use of a large pore support for a promoted PGM catalyst producesa superior effect in ammonia decomposition reactions at lower temperatures.NH3 temperature programmed desorption analysis was also performed on comparativeexamples 1 and 5 and example 6. Samples of all three catalyst compositions were pre-treatedwith H2 at 300°C for 0.5 hour and then saturated in NH3 gas at 100oC for 1 hour. The sampleswere then heated to 400°C at a ramp rate of 10C / min in helium. Desorption of the N2 species(mass 28 signal) due to the ammonia decomposition was observed on all three samples. Theresults are shown in Figure 4. The peak temperature for the N2 desorption for example 6 is at196oC while the peak temperatures for comparative examples 5 and 1 are at 220oC and 270oCrespectively. This trend suggests that using support with higher mesoporosity can result inammonia decomposition and N2 desorption from catalyst surface at lower temperatures. SinceN2 desorption step is a rate-limiting step for ammonia decomposition over Ru catalysts, fasterN2 desorption can lead to higher overall rate for ammonia decomposition.Further aspects and embodiments of the present disclosure are set out in the following numbered clauses: P1022681. A catalyst composition for decomposing ammonia (NH3) into nitrogen (N2) and hydrogen(H2), the catalyst composition comprising catalyst support material supporting a catalytically active material, wherein the catalytically active material comprises (i) a platinum group metal (PGM) and / or a base metal; and (ii) an alkali or alkaline earth metal promoter, and wherein the catalyst support material is mesoporous and has a total pore volume of at least 0.35ml / g and an average pore width of at least 15 nm.2. A catalyst composition as disclosed in clause 1, wherein the catalytically active materialcomprises a PGM selected from platinum (Pt), palladium (Pd), ruthenium (Ru) or mixtures thereof.3. The catalyst composition according to clause 2, wherein the PGM is ruthenium (Ru).4. A catalyst composition as disclosed in clause 1, 2 or 3 wherein the catalytically activematerial comprises a base metal selected from nickel (Ni), iron (Fe), cobalt (Co) or mixtures thereof.5. The catalyst composition according to any preceding clause, wherein the catalystsupport material has a total pore volume of from 0.35 mg / l to 1.30 mg / l and a pore widthof from 15 to 40 nm.6. The catalyst composition according to any preceding clause wherein the catalyst supportmaterial has a total pore volume of from 0.4 to 1.3 ml / g, for example, 0.45 to 1.30 ml / g, 0.48 to 1.30 ml / g, 0.5 to 0.9 ml / g, 0.5 to 0.8 ml / g.0.6 to 0.9 ml / g or 0.6 to 0.8 ml / g.7. The catalyst composition according to any preceding clause, wherein the supportmaterial is a refractory oxide support material.8. The catalyst composition according to clause 6, wherein the refractory oxide material isselected from the group consisting of alumina, silica, titania, zirconia, ceria and a mixed or composite oxide thereof, e.g. a mixed oxide or a composite oxide of two or more thereof.9. The catalyst composition according to any one of clauses 1 to 8, which comprises, bymass, from 0.5 to 3%, preferably 0.75 to 2 %, more preferably 0.75 to 1.25 %, most preferably about 1%, Ru based on the mass of the composition. P10226810. The catalyst composition according to any one of clauses 1 to 9, wherein the promoteris selected from potassium (K), caesium (Cs), lithium (Li), sodium (Na) or a mixture thereof.11. The catalyst composition according to any one of clauses 1 to 10, which comprises, bymass, from 1% to 10%, more preferably from 2% to 6%, most preferably about 2%, promoter based on the mass of the composition.12. The catalyst composition according to any one of clauses 1 to 10 wherein the catalystcomposition is coated on a flow-through substrate or a filter substrate.13. A process for converting ammonia into nitrogen and hydrogen, the process includingcontacting a gaseous stream that comprises ammonia with a catalyst composition according to any one of clauses 1 to 12 at a temperature above 200°C, preferably at atemperatures in the range 350-500°C.14. A power generation system comprising:- an ammonia source;- an ammonia cracking unit; and- a hydrogen-fuelled internal combustion engine or fuel cell;wherein the ammonia cracking unit comprises the catalyst composition as disclosed in any ofclauses 1 to 12.15. A fuel combustion and exhaust system comprising a fuel combustor and an exhaust gastreatment system, wherein the fuel combustor is an ammonia-containing-fuel-combustor and is in fluid communication with the exhaust gas treatment system, and wherein the exhaust gas treatment system comprises the catalyst composition as disclosed in anyof clauses 1 to 12.

Claims

P102268 Claims1. A catalyst composition for decomposing ammonia (NH3) into nitrogen (N2) and hydrogen(H2), the catalyst composition comprising catalyst support material supporting acatalytically active material, wherein the catalytically active material comprises (i) aplatinum group metal (PGM); and (ii) an alkali metal promoter, and wherein the catalystsupport material is mesoporous and has a total pore volume of at least 0.35ml / g and anaverage pore width of at least 15 nm.

2. A catalyst composition as claimed in claim 1, wherein the catalytically active materialcomprises a PGM selected from platinum (Pt), palladium (Pd), ruthenium (Ru) ormixtures thereof.

3. The catalyst composition according to claim 2, wherein the PGM is ruthenium (Ru).

4. The catalyst composition according to any preceding claim, wherein the catalyst supportmaterial has a total pore volume of from 0.35 mg / l to 1.30 mg / l and a pore width of from15 to 40 nm.

5. The catalyst composition according to any preceding claim, wherein the catalyst supportmaterial has a total pore volume of from 0.4 to 1.3 ml / g, for example, 0.45 to 1.30 ml / g,0.48 to 1.30 ml / g, 0.5 to 0.9 ml / g, 0.5 to 0.8 ml / g.0.6 to 0.9 ml / g or 0.6 to 0.8 ml / g.

6. The catalyst composition according to any preceding claim, wherein the support materialis a refractory oxide support material.

7. The catalyst composition according to claim 6, wherein the refractory oxide material isselected from the group consisting of alumina, silica, titania, zirconia, ceria and a mixed or composite oxide thereof, e.g. a mixed oxide or a composite oxide of two or morethereof.

8. The catalyst composition according to any one of claims 1 to 8, which comprises, bymass, from 0.5 to 3%, preferably 0.75 to 2 %, more preferably 0.75 to 1.25 %, mostpreferably about 1%, Ru based on the mass of the composition.P1022689. The catalyst composition according to any one of claims 1 to 9, wherein the promoter isselected from potassium (K), caesium (Cs), lithium (Li), sodium (Na) or a mixture thereof.

10. The catalyst composition according to any one of claims 1 to 10, which comprises, bymass, from 1% to 10%, more preferably from 2% to 6%, most preferably about 2%,promoter based on the mass of the composition.

11. The catalyst composition according to any one of claims 1 to 10 wherein the catalystcomposition is coated on a flow-through substrate or a filter substrate.

12. A process for converting ammonia into nitrogen and hydrogen, the process includingcontacting a gaseous stream that comprises ammonia with a catalyst compositionaccording to any one of claims 1 to 12 at a temperature above 200°C, preferably at atemperature in the range 350-500°C.

13. A power generation system comprising:- an ammonia source;- an ammonia cracking unit; and- a hydrogen-fuelled internal combustion engine or fuel cell;wherein the ammonia cracking unit comprises the catalyst composition as claimed in any of claims 1 to 12.

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