Process for removal of NH 3 from a gas stream

Abstract

The present invention relates to a method of producing a fuel gas composition. The method comprises providing a feed gas composition comprising H2 and NH3, monitoring the concentration of NH3 in the feed gas composition; providing an oxidising gas comprising NO and at least one of: O2, NO2, and NO2 + O2; mixing the feed gas composition with the oxidising gas to provide a catalysis gas composition; providing a NOx reducing reactor having a catalysis gas inlet and a fuel outlet, and a selective reduction catalyst between the catalysis gas inlet and the fuel outlet; applying the catalysis gas composition to the catalysis gas inlet and passing the catalysis gas composition through the selective reduction catalyst; obtaining the fuel gas composition at the fuel outlet. The method can remove NH3 to improve an H2-based fuel.

Description

[0001] PROCESS FOR REMOVAL OF NH3FROM A GAS STREAM

[0002] Field of the invention

[0003] The present invention relates to the removal of ammonia from a gas stream containing hydrogen. In particular, when ammonia is used as a hydrogen carrier, hydrogen gas may be released from ammonia via cracking of ammonia. The product gas may still contain smaller amounts of ammonia. The method allows for selective conversion of the ammonia to nitrogen and water, with minor loss of hydrogen. The method is of particular interest for, but not limited to, the application of ammonia cracking to produce hydrogen feeds for fuel cells.

[0004] Background

[0005] Ammonia (NH3) is an interesting carbon-free compound for energy storage and fuel for power production. For example, NH3 is regarded as an alternative fuel for combustion engines, in particular in maritime applications, but NH3 has also been considered as a fuel for fuel cells. In some types of fuel cell, e.g. Polymer Electrolyte Membrane (PEM), Anion-Exchange Membrane (AEM), Alkaline fuel cells, it is necessary to convert NH3 to H2 and N2 before using it as a fuel in a fuel cell. The thermal cracking (Reaction 1 ) of NH3 to H2 and N2 occurs spontaneously above 500°C and is practically complete at 1100°C. The cracking reaction is often performed in the presence of a catalyst, which allows for the reaction to take place more efficiently at lower temperatures. The H2 formed by cracking is then converted to H2O and electricity in a fuel cell according to Reaction 2.

[0006] Reaction 1 2 NH3 < - N2 + 3 H2

[0007] Reaction 2 H2 + O2 - H2O

[0008] An example of the application of NH3 as a carrier for H2 is described in Fraunhofer Research News, 1 March 2021 , pp. 1 -4. In this example, a high- temperature ammonia-powered fuel cell for maritime applications is presented, in which NH3 is first converted to H2 and N2 with a residual 100 ppm NH3, via cracking of NH3. The H2 / N2 / NH3 containing cracking product is then passed to a fuel cell, in which the H2 reacts with O2 to produce electrical power. The exhaust gas from the fuel cell contains some H2 due to incomplete conversion, and some NH3. To avoid unwanted emissions of NH3, the exhaust gas is then passed to a Pt based oxidation catalyst, to oxidise the NH3 to nitrogen and water. Because a Pt catalyst also oxidises H2, this approach to reduce NH3 emission implies a significant loss of H2, and therefore also a loss of efficiency of the energy system.

[0009] An approach to abate NH3 is to remove residual NH3 from a fuel stream led to a fuel cell. For example, JP2014123468 describes how a hydrocarbon gas is used for providing H2 as a fuel for a fuel cell, and the catalytic conversion of the hydrocarbon gas can produce ammonia, which is removed by absorption in water before leading the H2 to the fuel cell.

[0010] Other examples exist where NH3 is converted to H2 and N2 and led to a fuel cell, but as the conversion is rarely 100%, removal of residual NH3 has been suggested. US 2020 / 403258 describes a system with a decomposition reaction device for producing H2 by decomposing NH3 and a hydrogen fuel cell, and the system includes removing residual NH3 in an adsorption method, a complexing method or a selective catalytic oxidation method. The adsorption method uses a zeolite molecular sieve as an adsorbent or an activated carbon to adsorb ammonia gas; and the complexing method uses MgCl2 or CuCl2 for a complex reaction with ammonia gas to remove the ammonia gas; and the selective catalytic oxidation method oxidises ammonia gas using a transition metal oxide as a catalyst to remove the ammonia gas.

[0011] Tuna et al (Fuel, vol. 105, 2013, pages 331 -337) concerns selective catalytic oxidation of ammonia by nitrogen oxides in a model synthesis gas and disclose a study of the selective oxidation of ammonia in reducing environments, where NOx are removed from flue gas by reaction with injected ammonia over a catalyst.

[0012] US5906803 discloses a process for removing, by selective oxidation in the presence of a solid catalyst, ammonia from gasification gas obtained from fuel and aims to substantially oxidise ammonia without affecting hydrogen, methane or other oxidizing components of the gasification gas, and by means of which the ammonia can be decomposed more completely and / or at a substantially lower temperature than by means of previously used catalysts.

[0013] US8337793 concerns a method and equipment for the removal of ammonia from oxygen-comprising fluids, such as effluent, flue or waste fluids where an NHs-bearing fluid mixture is conveyed through two functional units, where the NH3 effluents can be converted into nitrogen at a high selectivity, and firstly NH3 is decomposed into nitrogen and partly converted catalytically or thermally into nitrogen oxides NO and NO2 in an oxidation / decomposition unit of NH3, through which all of the fluid goes, or part of the fluid can bypass this unit through a by-pass, where the fluid streams may combine after the bypass and be allowed to mix together in a mixing space, where the fluids comprising NH3 and nitrogen oxides mix well with each other.

[0014] KR20240010242 discloses a method for producing hydrogen from ammonia comprising a step of producing hydrogen and nitrogen by decomposing ammonia through an ammonia decomposition reaction followed by a step of removing unreacted ammonia. The hydrogen production system has an ammonia decomposition reactor containing a catalyst to produce hydrogen and nitrogen through ammonia decomposition, and a selective oxidation catalyst-containing unreacted ammonia removal reactor for oxidizing and removing unreacted ammonia, and an injection nozzle is installed on the exhaust gas flow between the ammonia decomposition hydrogen production system and the selective ammonia oxidation catalytic reactor.

[0015] KR20230083367 discloses an ammonia decomposition system and a method for ships, which comprises a vaporizer which receives liquid ammonia and vaporizes it; a decomposition unit which receives the ammonia vaporized in the vaporizer and thermally decomposes it to produce decomposition gas containing hydrogen, nitrogen, and undecomposed ammonia; an undecomposed ammonia removal unit which collects undecomposed ammonia from the decomposed gas; a hydrogen purifier which receives the decomposed gas that has passed through the undecomposed ammonia removal unit, removes nitrogen, and purifies it into hydrogen; and a selective catalytic reduction unit which denitrifies combustion gas generated by thermal decomposition of ammonia in the decomposition unit. There is a need for an improved procedure to remove residual NH3 from a stream of decomposed NH3 and the present invention aims to address this need.

[0016] Summary

[0017] The present invention relates to a method of producing a fuel gas composition. In its broadest terms, the method comprises the steps of: providing a feed gas composition comprising H2 and NH3, monitoring the concentration of NH3 in the feed gas composition; providing an oxidising gas comprising NO and at least one of: O2, NO2, and NO2 + O2; mixing the feed gas composition with the oxidising gas to provide a catalysis gas composition; providing a NOx reducing reactor having a catalysis gas inlet and a fuel outlet, and a selective reduction catalyst between the catalysis gas inlet and the fuel outlet; applying the catalysis gas composition to the catalysis gas inlet and passing the catalysis gas composition through the selective reduction catalyst; obtaining the fuel gas composition at the fuel outlet. The method is useful in the removal of ammonia from a gas stream containing hydrogen, where the hydrogen is intended to be used as a fuel, and the feed gas composition may be provided from cracking ammonia, or the feed gas composition may be a gas stream, e.g. an exhaust gas stream, from a fuel cell, which gas stream contains hydrogen that has not been converted in the fuel cell, so that removal of ammonia allows recycling the provided fuel gas composition back to the fuel cell. In general terms, the concentration of NH3 may be up to 10% of the feed gas composition, e.g. when the feed gas composition is provided from cracking ammonia. The concentration of H2 is generally at least 1% of the feed gas composition. For example, the concentration of H2 in the feed gas composition may be in the range of 1 % to 99%, e.g. in the range of 2% to 95%.

[0018] In an example, the feed gas composition has a molar content of H2 of at least 50% of the gas feed gas composition and a ratio of H2 to NH3 of at least 6. For example, when the feed gas composition is a stream of cracked ammonia, the feed gas composition should contain of at least 50% H2 and have a ratio of H2 to NH3 of at least 6. In another example, the feed gas composition has a molar content of H2 of up to 50% of the feed gas composition and a ratio of H2 to NH3 of up to 10. This example is relevant, when the feed gas composition is an exhaust gas stream from a fuel cell, especially a solid oxide fuel cell (SOFC). In an example, the feed gas composition is an exhaust gas from a fuel cell, and the concentration of H2 in the feed gas composition is in the range of 1 % to 30%.

[0019] A catalysis gas composition is provided in the present method, specifically by mixing the oxidising gas and the feed gas composition. The catalysis gas composition may also be referred to as a gas composition for the selective catalytic reduction of NO, an SCR gas composition, or a selective catalytic reduction gas composition.

[0020] The present method allows the removal of ammonia, especially of smaller amounts of ammonia, from a gas stream containing hydrogen. In particular, when ammonia is used as a hydrogen carrier, hydrogen gas is released from ammonia via cracking of ammonia. The product gas may still contain smaller amounts of ammonia. The method of the invention allows for selective conversion of the ammonia to nitrogen and water, with minor loss of hydrogen. The application of the invention is of particular interest for, but not limited to, the application of ammonia cracking to produce hydrogen feeds for fuel cells.

[0021] The fuel gas composition produced in the method may also be described as NH3 depleted. In the present context, NH3 depleted means that NH3 has been removed from the treated feed gas composition, and “NH3 depleted” may for example indicate that the fuel gas composition comprises up to 100 ppm NH3, although it is preferred that the concentration of NH3 in the fuel gas composition is even lower, e.g. up to 50 ppm or up to 10 ppm. The low level of NH3 in the fuel gas composition allows that the fuel gas composition is used as a fuel in a fuel cell regardless of the sensitivity to NH3 of the fuel cell. For example, the fuel gas composition may be used in a Polymer Electrolyte Membrane (PEM), an Anion-Exchange Membrane (AEM), or an Alkaline fuel cell.

[0022] Selective catalytic reduction reactions (NH3-SCR) are commonly applied for removing NOx gasses from exhausts from fuel lean combustion processes, i.e. combustion processes with excess air present, such as in diesel engines, power plants, and chemical plants. In the present context, the abbreviation “NH3-SCR” generally refers to selective reduction reactions as used for removing NOx gasses from exhaust gasses, although it may also be relevant in the context of the present method. The NH3-SCR technology is based on Reaction 3 and Reaction 4 that convert NOx to nitrogen and water via reduction by ammonia in the presence of oxygen

[0023] Reaction 3 4 NO + 4 NH3 + O2 < - 4 N2 + 6 H2O

[0024] Reaction 4 2 NO + 4 NH3 + 2 NO2 4 N2 + 6 H2O

[0025] The method employs an oxidising gas comprising NO and at least one of: O2, NO2, and NO2 + O2. In the present context, NO and NO2 may be referred to collectively as “NOx”. Thus, when the present disclosure mentions NOx, this may be NO, NO2, or a mixture of NO and NO2 at any proportion of the individual gasses.

[0026] NH3-SCR technology is referred to using the term “reduction” and involves reducing a NOx gas, but the reactions necessarily also involve an oxidation, i.e. of NH3 using the NOx gas. However, the present inventors have now surprisingly found that NH3-SCR catalysts used for the removal of NOx gasses from the exhaust from the combustion of fossil fuels can be used to remove NH3, i.e. convert the NH3 to N2 and H2O with the aid of NO, O2 and NO2, without excessively oxidising H2 present in the gas. Reaction 3 and Reaction 4 are thus also relevant in the present method. Thereby, an NH3-SCR catalyst can be used to selectively remove NH3 from a feed gas with H2 to provide an H2-based fuel gas. Any NH3-SCR catalyst that can be used for treating an exhaust gas functions equally in the present method. In the context of the present method, the NH3-SCR catalyst is generally referred to as a “selective reduction catalyst”, although the selective reduction catalyst may also be referred to as a catalyst that is active for the selective catalytic reduction of NO, or for the selective catalytic reduction of NOx. Correspondingly, the reactor having the catalyst is generally referred to as the NOx reducing reactor, although the reactor may also be referred to as an SCR reactor. In combustion processes where the combustion of a fossil fuel takes place in excess air, the exhaust gas still contains some oxygen, typically in the range of 2-15%, dependent on the chosen conditions in the combustion process. The aspect that the reduction of NOx by ammonia can take place in the presence of oxygen motivates the choice for the NH3-SCR technology, and it is therefore commonly applied for removing NOx gasses from exhausts from fuel lean combustion processes. When a concentration in a gas is provided as a percentage in the present context, it is understood to be a molar content, unless noted otherwise. Correspondingly, unless noted otherwise, contents are on a molar basis in the present context.

[0027] When used for the removal of NOx from an exhaust gas, the NH3-SCR reaction uses the presence of ammonia. As the exhaust gases do not contain ammonia, the ammonia used to convert the NOx in the exhaust gas is added to the exhaust gas stream. The technology can be executed in different ways. In diesel combustion engines on vehicles, the concentration of NOx in the exhaust gas is measured, and an appropriate amount of urea is sprayed in the gas stream. At sufficiently high temperatures, which usually are present in the exhaust system of vehicles, the urea decomposes to release the required ammonia for the NH3-SCR reaction.

[0028] Another way of performing the NH3-SCR technology is to inject the appropriate amount of ammonia as a gas in the exhaust gas stream. This is typically the approach if ammonia is available, which can be the case at chemical plants and power plants. Yet another way of performing the NH3-SCR technology is to inject the appropriate amount of ammonia, whereby the ammonia is released by decomposing salts of formula Ma(NH3)nXz, wherein M represents one or more cations selected from alkaline earth metals and transition metals, X represents one or more anions (see e.g. US7964163, US9889403). Common for all these methods is that the concentration of NOx in the exhaust gas is measured, and the amount of ammonia that is injected is determined from that measured amount of NO.

[0029] Evidently, in the field of internal combustion engines, the term “reduction” refers to the fact that NOx gasses are reduced with the aid of NH3 and an appropriate catalyst, whereas for the present invention, the reaction of interest may be described as a selective oxidation reaction where NH3 is oxidised. However, as the reaction of interest involves both a reduction and an oxidation, the catalyst employed in the present method is referred to as a “selective reduction catalyst”. In the context of the present disclosure, the selective reduction catalyst may also be referred to as an “SCR catalyst” and the two terms may be used interchangeably.

[0030] The present method employs an oxidising gas comprising NO and at least one of: O2, NO2, and NO2 + O2. In general terms, NO must be present in the oxidising gas, and a combination of NO2 and / or O2 is also present. Without being bound by any particular theory, the present inventors consider that NO and O2 may react to form NO2. The reactions between the oxidising gas and NH3 generally take place in a combination of Reaction 3 and Reaction 4. Correspondingly, the optimal composition of the oxidising gas may be based on the stoichiometries of Reaction 3 and Reaction 4, and the oxidising gas may be described in terms of the atoms of the molecules of the oxidising gas relative to the atoms of the molecules of the feed gas composition. In an example, the oxidising gas comprises NO and at least one of: O2, NO2, and NO2 + O2, wherein the ratio of oxygen atoms to nitrogen atoms of the NH3 is at least 1 .5, the ratio of nitrogen atoms to nitrogen atoms of the NH3 is in the range of 0.8 to 1 .2, and the ratio of oxygen atoms of NO2 to nitrogen atoms of the NH3 is up to 1 . The oxidising gas may include further atmospheric components, e.g. when O2 is provided from ambient air. In the present context, the further atmospheric components may include noble gases, e.g. argon, neon, and helium, CO2, and H2O, although the further atmospheric components are not limited to these species. Moreover, when present, the further atmospheric components are present in such low amounts that oxygen atoms included in individual further atmospheric components can be ignored in the calculations of the ratio of oxygen atoms to nitrogen atoms of the NH3 of the feed gas composition. The ratio of oxygen atoms to nitrogen atoms of the NH3 may be at least 1.5, although it is preferred that the ratio of oxygen atoms to nitrogen atoms of the NH3 is up to 10. In an example, the ratio of oxygen atoms to nitrogen atoms of the NH3 is selected from the stoichiometries of Reaction 3 and Reaction 4. The present method employs an oxidising gas containing NO, and the oxidising gas may further employ O2. The presence of O2 in the oxidising gas generally does not negatively influence the catalytic removal of NH3 and as such there is no upper limit to O2 allowed to be present in the oxidising gas. As used in the context of the combustion of fossil fuels, conventional NH3-SCR technology commonly involves an oxygen concentration typically between 2 and 15%, which represent conditions at which the NH3-SCR reaction proceeds efficiently, although the general behaviour of NH3-SCR catalysts is that the activity decreases rapidly when the oxygen concentration approaches zero. However, the present inventors have surprisingly found that in the present method, a conventional NH3-SCR catalyst operates at a sufficient velocity for the selective oxidation of NH3 to take place even at a content of O2 below 2% in the catalysis gas composition. Thus, in an example, the oxidising gas contains O2 to provide a concentration of O2 in the catalysis gas composition of up to 2%. The NH3-SCR activity is sufficiently high at reasonable conditions for effective removal of NH3, even at oxygen concentration on the order of a 100-1000 ppm, which makes the method of the invention a viable way to remove ammonia from a gas stream containing hydrogen. For example, NH3 may be in the range of 0.1 % to 2%, e.g. 0.1 % to 1 %. Regardless of the concentration of O2 in the catalysis gas composition, the ratio of oxygen atoms to nitrogen atoms of the NH3 of the feed gas composition may be in the range of 1 .5 to 50, e.g. in the range of 1 .5 to 20 or 1 .5 to 10.

[0031] As used for the removal of NOx from an exhaust gas, the NH3-SCR reaction employs a catalyst. Any catalyst known from NH3-SCR treatment of an exhaust gas may be used as the selective reduction catalyst in the present method. In general, an appropriate SCR catalyst includes a catalytically active compound on a carrier material. Commonly applied catalysts are based on vanadium oxide supported on anatase TiO2, Cu zeolites or Fe zeolites, see e.g. T.V. Johnson, Review of Selective Catalytic Reduction (SCR) and Related Technologies for Mobile Applications, in: Urea-SCR Technology for deNOx After Treatment of Diesel Exhausts. Eds. E. Tronconi, I. Nova., Springer Science+Business Media, New York, 2014: pp. 3-32, which is included herein by reference. Thus, the selective reduction catalyst is selected from the list consisting of V-oxide / TiO2, V2Os / TiO2, Cu-zeolite, and Fe-zeolite or a combination thereof. Other known types of catalyst consist of one or more transition metal oxides, such as manganese oxide, tungsten oxide, iron oxide, or rare earth metal oxides, such as cerium oxide, Mn-Fe spinel, Ni-Mn-spinel, which can be supported on an oxidic support, such as titania, vanadia, ceria, silica, manganese oxide, carbon nanotubes, or the material known as Santa Barbara Amorphous-15 (SBA-15), as explained by L. Han, et al., Selective Catalytic Reduction of NOx with NH3 by Using Novel Catalysts: State of the Art and Future Prospects, Chem. Rev. 119 (2019) 10916-10976, which is included herein by reference. Thus, the selective reduction catalyst may be vanadium oxide supported on anatase TiO2, Cu zeolites or Fe zeolites, a transition metal oxide, such as manganese oxide, tungsten oxide, iron oxide, a rare earth metal oxides, such as cerium oxide, Mn-Fe spinel, Ni-Mn-spinel, which can be supported on an oxidic support, such as titania, vanadia, ceria, silica, manganese oxide, carbon nanotubes, or SBA-15. The selective reduction catalyst may also be a combination of several catalytic compounds or materials.

[0032] Other relevant selective reduction catalysts are described in WO 2018 / 197176, which discloses a filter bag house with one or more fabric filter bags comprising an SCR catalyst for reducing NOx gasses in presence of ammonia at a relatively low temperature, and WO 2018 / 184921 which discloses a system and a corresponding method for the removal of nitrogen oxides, volatile organic compounds and particulate matter from engine exhaust gas with a focus on an improved reduction of NOx during cold start of the engine. The method involves forming NO2 externally to an exhaust gas cleaning system in an exhaust gas channel and injecting the prepared NO2 into the engine exhaust gas in an amount that promotes the fast SCR reaction.

[0033] Exemplary selective reduction catalysts are provided as powders that may be processed to catalyst products of different forms, such as pellets, rings, extrudates like e.g. flow-through or wall-flow monoliths, spheres, hollow spheres, granulates. The sizes of these products typically vary from approximately 1 mm to 5 cm. Such catalyst products may contain holes (see e.g. Synthesis of Solid Catalysts; de Jong, K. P. (Ed.), Ed.; Wiley-VCH: Weinheim, 2009, Chapter 9, which is included herein by reference). The powder support materials may be processed before adding the active components or promoters for the NH3-SCR catalysts. In such cases, the selected active compounds or promoters or both are deposited on such preformed solid support material by methods known to the skilled person (Heterogeneous Catalysis and Solid Catalysts, Ullmann Encyclopedia 2009, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, p. 47 et seq; Synthesis of Solid Catalysts; de Jong, K. P. (Ed.), Ed.; Wiley-VCH: Weinheim, 2009, Chapters 3-8, which is included herein by reference). In a second procedure, the powders are processed to catalyst products after the active compounds or promoters are deposited by methods known to the skilled person (Synthesis of Solid Catalysts; de Jong, K. P. (Ed.), Ed.; Wiley-VCH: Weinheim, 2009, Chapters 3-9, which is included herein by reference). The catalyst powders can also be processed to catalytic products like ceramic foams, 3D-printed forms, porous ceramic filters, in the size range 1 -500 cm (S. Govender and H. B. Friedrich, Monoliths: A Review of the Basics, Preparation Methods and Their Relevance to Oxidation, Catalysts (2017), 7, 62, which is included herein by reference). In a third procedure, the procedures mentioned here are combined, such that a solid support material in the form of a powder having activity for NH3-SCR are processed to catalytic products, followed by deposition of a second portion of the same or a different powder with NH3-SCR activity by methods known to the skilled person (Synthesis of Solid Catalysts; de Jong, K. P. (Ed.), Ed.; Wiley-VCH: Weinheim, 2009, Chapters 3-9, which is included herein by reference).

[0034] In another embodiment, powder having NH3-SCR activity is processed to a catalytic article by applying it to the accessible surface of pre-shaped articles, such as flow-through monoliths, wall-flow filters or corrugated monoliths as known from exhaust treatment catalysts in automotive applications, plates, mesh, wires, other preformed bodies, glass wool, metal wool, by e.g. wash coating, deposition methods, or any other method designed to fix the solid support material to the outer surface of solid bodies (Avila et al., Chem. Eng. J. (2005), 109, 11 - 36, which is included herein by reference). The pre-shaped articles can in principle be of any solid material, such as metals, oxidic materials, ceramic materials, fibre glass, polymers. Such articles are often based on fibre materials or powder materials that are pre-shaped in a solid body by using appropriate binders, coatings, glues (S. Govender and H. B. Friedrich, Monoliths: A Review of the Basics, Preparation Methods and Their Relevance to Oxidation, Catalysts (2017), 7, 62, which is included herein by reference).

[0035] Flow-through monoliths have fine, parallel gas flow passages extending from an inlet to an outlet face of the substrate, such that passages are open for fluid flow. The passages, which are essentially straight paths from their fluid inlet to their fluid outlet, are defined by walls. The catalytic material can be coated as a wash-coat, so that the gases flowing through the passages come in contact with the catalytic material. The flow passages of the monolithic substrate are generally thin-walled channels, which can be of any suitable cross-sectional shape and size such as trapezoidal, rectangular, square, sinusoidal, hexagonal, oval, circular, etc. Such structures may contain from about 20 - 900 or more gas inlet openings (e.g., cells) per square inch of cross section (3 - 140 cells / cm2). The wall thicknesses, e.g. the thickness of the walls which separate the channels of the substrate from one another, are usually from about 0.005 cm to about 0.3 cm. Flow-through monoliths typically have a porosity of more than 20%, generally from 20% to 70%, in particular from 35% to 65% [measured according to DIN 66133], The mean pore size is normally at least 1 pm, e.g. from 1 .5 pm to 25 pm, preferably more than 3 pm, in particular from 5 pm to 18 pm, e.g. measured according to DIN 66134.

[0036] A corrugated monolith may consist of alternating layers of flat and wavy sheets with regular curved folds or grooves. Through winding or stacking of the combined flat and wavy sheets to a desired form, channels may be created in the wavy layer of the article. In principle, such a structure can be made of any material that can be formed, combined to, and retain such a structure, e.g. metal, ceramics, paper sheets, polymers, glass fibre sheets. To stabilise the structure, one or more further processing steps may be necessary, such as welding, soldering, glue, coating, heating. Such corrugated substrates and their manufacture are disclosed in WO 2010 / 066345, which is included herein by reference, and the teaching thereof can be applied to the present invention. By applying a catalytically active material on the surface of the channels or in the porous structure of these materials, a corrugated catalytic article can be obtained.

[0037] A preferred embodiment of a corrugated catalytic article is a corrugated article based on a glass fibre substrate. The glass fibre substrate should have a wall density of at least 50 g / l but not more than 150 g / l and a porosity of at least 50%. The substrate monolith may consist of sheets of high silica content glass or a sheet of E-glass fibre. High silica content glass sheets may optionally comprise a layer of a metal oxide, such as alumina, silica, TiO2 or diatomaceous earth to stabilise the structure. In the present invention, a catalyst powder having NH3-SCR activity support may be applied on the surface of the wavy and flat sheets of the article, for example by wash-coating. In another embodiment, a catalyst powder having NH3-SCR activity, may be applied inside the porous structure of the glass fibre material that constitutes the wavy and flat sheets of the article. In yet another embodiment, the compounds active for NH3-SCR are applied directly on the wavy and flat sheets. In a typical method to produce such glass fibre articles, these articles are contacted with e.g. solutions of appropriate precursors, according to processes known to the skilled worker (Heterogeneous Catalysis and Solid Catalysts, Ullmann Encyclopedia 2009,Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, p. 47 et seq; Synthesis of Solid Catalysts; de Jong, K. P. (Ed.), Ed.; Wiley-VCH: Weinheim, 2009, Chapters 3-8, which is included herein by reference). By this measure the compounds having NH3-SCR activity may be deposited onto the article in small clusters. The clusters can be fixed to the outer surface of the glass fibre walls, or inside the porous structure of the glass fibre walls, by appropriate drying and calcining procedures known to a skilled person.

[0038] A preferred selective reduction catalyst contains a vanadium oxide on an appropriate carrier material. A particularly preferred reduction catalyst contains a vanadium oxide and a tungsten oxide on an appropriate carrier material, e.g. a transition metal oxide, such as TiO2, or aluminium oxide.

[0039] The temperature employed while passing the catalysis gas composition through the selective reduction catalyst may be selected freely, but it is preferred that the temperature is controlled. For example, the method may further comprise the step of controlling the temperature of the catalysis gas composition to be in the range of 100°C to 600°C while passing the catalysis gas composition through the selective reduction catalyst. The temperature while passing the catalysis gas composition through the selective reduction catalyst may also be referred to as the operating temperature. In broad terms, the reaction proceeds more efficiently, the higher the temperature, but the selective reduction catalyst may be selected based on its optimal operating temperature. For example, the method may further comprise the step of controlling the temperature of the catalysis gas composition to be in the range of 150°C to 350°C while passing the catalysis gas composition through the selective reduction catalyst. In a specific example, the reduction catalyst contains a vanadium oxide or a vanadium oxide and a tungsten oxide on an appropriate carrier material, e.g. TiO2, and the operating temperature is in the range of 250°C to 350°C.

[0040] The present method includes the step of monitoring the concentration of NH3 in the feed gas composition. In general, any gas may be monitored in the method, and the gasses may be monitored at any stage, e.g. before or after mixing the relevant gasses and / or before or after conducting catalytic reactions. The gasses may be monitored using any available technology. For example, an FTIR spectrometer may be employed to monitor concentrations of NO, NO2, NH3, and H2O.

[0041] The feed gas composition may be provided as a gas stream from an NH3 cracking reactor to contain H2 and N2 and residual NH3, which gas steam is intended to be used as an H2 containing fuel gas. Thus, the feed gas composition may be provided in the steps of: providing a stream of gaseous NH3; providing an ammonia cracking reactor having an NH3 inlet and a cracked gas outlet, which ammonia cracking reactor comprises an NHs-decomposition catalyst between the NH3 inlet and the cracked gas outlet; applying the stream of gaseous NH3 at the NH3 inlet and passing the stream of gaseous NH3 through the decomposition catalyst to obtain the feed gas composition at the cracked gas outlet, the feed gas composition comprising H2, N2, and NH3. In general, any decomposition catalyst may be used in the present method. Relevant catalysts include commercial Haber-Bosch catalysts. An exemplary NHs-decomposition catalyst is an iron-based NHs-synthesis catalyst. Ironbased NHs-synthesis catalyst are well-known to the skilled person and commercially readily available.

[0042] When the feed gas composition is from an NH3 cracking reactor and contains H2, N2 and NH3, the feed gas composition generally has a molar content of H2 of at least 50% of the gas feed gas composition and the ratio of H2 to NH3 is at least 6. In general terms, an NH3 cracking process may be described in terms of a conversion factor x, where x is the fraction of NH3 decomposed. Correspondingly, x can have a value of up to 1. When the decomposition is performed at a value of x of 1 , no residual NH3 is present in the gas stream from the cracking reactor. When the feed gas composition is provided as a gas stream from an NH3 cracking reactor, the value of x should be as high as possible in order to minimise the content of NH3 in the gas stream leaving the cracking reactor. However, while x can be set as desired for a cracking process by appropriate setting the parameters of the process, high values of x are technically cumbersome to obtain and a cracking process is rarely planned for complete cracking, i.e. x =1 , but by combining the present method with the use of an NH3 cracking reactor to obtain an H2-based fuel gas stream, NH3 can be removed selectively from the fuel gas stream, and thereby an H2-based fuel gas substantially free from NH3 can be provided even when x in the cracking is below 1. Thereby, an overall more efficient process is provided. Thus, the present invention solves the problem of obtaining an H2- based fuel gas substantially free from NH3 from cracking NH3 at less than perfect conditions. In general terms, the ratio of H2 to NH3 may be determined from the value of x in the cracking process. For example, when x = 0.8, the ratio of H2 to NH3 is about 6. Thus, x should be at least 0.8. However, it is preferred that x is >0.8, and the ratio of H2 to NH3 may be up to 100. The ratio of H2 to NH3 may also be higher than 100. For example, the ratio of H2 to NH3 may be in the range of 6 to 100, e.g. in the range of 8 to 50, or 10 to 20. When the method includes obtaining the feed gas composition as a gas stream from an NH3 cracking reactor, the ammonia cracking reactor may be configured to have a value of x in the range of 0.8 to 0.98. Alternatively, the feed gas composition may be provided as a gas stream from a fuel cell containing NH3 and N2 and residual H2, and optionally also H2O. For example, the feed gas composition may be an exhaust gas from a fuel cell or a gas containing unreacted H2 from a fuel cell, in particular a SOFC. When the feed gas composition is an exhaust gas stream from a fuel cell, the molar content of H2 is up to 50%, e.g. up to 40%, up to 30%, up to 20%, up to 10%, up to 5%, up to 3%, or up to 2%, of the gas feed gas composition and the ratio of H2 to NH3 is up to 10. The ratio of H2 to NH3 in a gas stream from a fuel cell is generally determined by the efficiency of the fuel cell, e.g. with respect to the conversion of H2, but with due consideration of the value of x when the fuel gas to the fuel cell is provided from the cracking of NH3. For example, the ratio of H2 to NH3 in the feed gas composition may be in the range of 0.05 to 10. Selective removal of NH3 allows the thus provided fuel gas to be recycled to the fuel cell so that the residual H2 can be burned in the fuel cell. Thereby, a more efficient utilisation of the fuel gas, especially a fuel gas provided from cracking NH3, is obtained.

[0043] The oxidising gas, e.g. the oxidising gas to be used in the SCR reaction, may be provided freely, e.g. by mixing NO with O2 and / or NO2, in particular to that the ratio of oxygen atoms to nitrogen atoms of the NH3 of the feed gas composition is at least 1.5, the ratio of nitrogen atoms to nitrogen atoms of the NH3 of the feed gas composition is in the range of 0.8 to 1 .2, and the ratio of oxygen atoms of NO2 to nitrogen atoms of the NH3 of the feed gas composition is up to 1 . In an example, the oxidising gas is provided in the steps of: providing a stream of gaseous NH3; providing an NH3 oxidising reactor having an NH3 inlet, an oxidant inlet and an outlet, and an NH3 oxidation catalyst between the NH3 inlet and the outlet; and applying the stream of gaseous NH3 at the NH3 inlet of the NH3 oxidising reactor and a stream of an oxidant at the oxidant inlet and passing the stream of gaseous NH3 through the NH3 oxidation catalyst to obtain the oxidising gas at the outlet of the NH3 oxidising reactor. The oxidant comprises an oxidising species but may also comprise further species. The oxidising species is preferably O2, e.g. the oxidant may be atmospheric air. It is especially preferred that the oxidising species is O2, and that the amount of O2 is chosen based on the intended ratio of oxygen atoms to nitrogen atoms of the NH3 of the feed gas composition. It is generally preferred that the composition of the gas at the outlet is monitored. For example, the concentrations of NO, NO2, and O2, and optionally also H2O, may be monitored, e.g. using an FTIR spectrometer.

[0044] It is especially preferred that the stream of gaseous NH3 is split into a stream that is led to the NH3 oxidising reactor and another stream that is led to an ammonia cracking reactor, so that the same supply of NH3 provides NH3 for both cracking and oxidising to provide the oxidising gas. The concentration of NH3 in the gas stream leaving the ammonia cracking reactor, i.e. being representative of the feed gas composition, may be monitored, and an amount of NH3 may be provided based on the observed concentration of NH3, from the stream of gaseous NH3 to provide an appropriate amount of oxidising gas from the NH3 oxidising reactor to match the method of the invention.

[0045] In general, any gas stream at any stage in the method may be monitored to determine the concentration of any component that may be present in a process stream. The process streams may for example monitored using an FTIR spectrometer. The present method produces a fuel gas composition, especially an H2-based fuel gas composition. The fuel gas composition may be intended for any use where H2 is appropriate as a fuel. For example, the H2 may be burned or the H2 may be converted to H2O and electricity in a fuel cell. The method may further comprise the step of removing at least one of O2, NO2, NO and H2O at any stage in the method, although especially from the fuel gas composition. In an example, H2O is removed from the fuel gas composition. H2O may be removed. For example, a condenser and / or an adsorbent may be used to remove H2O. Removal of H2O may for example be used, when the feed gas composition is an exhaust gas from a fuel cell. In general, the exhaust gas from a fuel cell may contain, especially when the fuel cell is an SOFC fuel cell, H2O from the conversion of H2 so that removal of H2O can prevent accumulation of H2O. In another example, a gas stream, e.g. the feed gas composition or a stream of cracked NH3, is passed through a separator, e.g. a membrane separator, to remove unwanted components.

[0046] The NH3 oxidation catalyst may be selected freely from appropriate catalysts known to the skilled person. In an example, the NH3 oxidation catalyst comprises a platinum group metal. NH3 oxidation catalysts are used commonly used for making nitric acid (HNO3) in the process known as the Ostwald process, and any variant, e.g. any known variant, of the Ostwald process may be used in the present method. In the present context, the platinum group metal may be at least one of Pt, Pd, Rh, Ru, and lr. The platinum group metal may be supported on a carrier material, e.g. an oxidic carrier material. In the present context, the oxidic carrier material may be alumina, silica, titania, ceria, zeolite, silicalite, or a combination thereof. In an example, the platinum group metal comprises, or is, a fibrous material. For example, the platinum group metal may have a fibrous form, or the platinum group metal may be carried on a material having a fibrous form. For example, the NH3 oxidation catalyst may comprise a catalytic metal, e.g. a platinum group metal, as filaments, e.g. “catalytic filaments”, with a diameter in the range of 0.01 mm to 0.1 mm, or the NH3 oxidation catalyst may comprise a supportive metal as wires with the platinum group metal being carried on the metal wires. In both cases, the metal wires may be referred to as “catalytic wires”. The catalytic wires may have a diameter in the range of 0.1 mm to 1 mm. Catalytic wires may be bundled together in an ordered or a random form. For example, catalytic wires may be knitted together or form a structured net, or the catalytic wires may be assembled in the form of a mesh of catalytic wires. The catalytic wires may be provided in sheets or layers, and a sheet may have any thickness, as appropriate, e.g. in the range of 10 pm to 1 mm, such as 50 pm to 200 pm.

[0047] In an aspect, the invention relates to a catalysis gas composition. Thus, the invention relates to a catalysis gas composition comprising N2, NH3, H2, NO and at least one of: O2, NO2, and NO2 + O2, wherein the molar content of H2 is at least 50% of the catalysis gas composition and a ratio of H2 to NH3 is at least 6, and wherein the ratio of oxygen atoms to nitrogen atoms of the NH3 is at least 1 .5, the ratio of nitrogen atoms to nitrogen atoms of the NH3 is in the range of 0.8 to 1 .2, and the ratio of oxygen atoms of NO2 to nitrogen atoms of the NH3 is up to 1. Specifically, the catalysis gas composition is available from the method of the invention. For example, the feed gas composition may be provided from cracking ammonia so that the cracked ammonia has a molar content of H2 of at least 50% of the catalysis gas composition and a ratio of H2 to NH3 is at least 6, e.g. in the range of 6 to 100, e.g. in the range of 8 to 50, or 10 to 20.

[0048] The present method may be performed in a system comprising appropriate unit operations in fluid communication as relevant. In another aspect, the invention relates to a system comprising unit operations for conducting the steps of the method. The system of the invention may be configured to perform any example of the disclosure. Any example of the system may comprise an NH3 supply, and the system may further be configured to be provided with air containing an oxidant, e.g. atmospheric air with O2 as the oxidant.

[0049] Relevant unit operations include a NOx reducing reactor having a catalysis gas inlet and a fuel outlet, and a selective reduction catalyst between the catalysis gas inlet and the fuel outlet, an ammonia cracking reactor having an ammonia entrance ammonia entrance and a cracked gas outlet, which ammonia cracking reactor comprises an NHs-decomposition catalyst between the ammonia entrance and the cracked gas outlet, and an NH3 oxidising reactor having an NH3 inlet, an oxidant inlet and an outlet, and an NH3 oxidation catalyst between the NH3 inlet and the outlet, and a fuel cell having a fuel cell inlet and a fuel cell outlet

[0050] In an example, the system comprises an NH3 oxidising reactor having an NH3 inlet, an oxidant inlet and an outlet, and an NH3 oxidation catalyst between the NH3 inlet and the outlet, a NOx reducing reactor having a catalysis gas inlet and a fuel outlet and a selective reduction catalyst between the catalysis gas inlet and the fuel outlet; an oxygen inlet; a feed gas mixing site in fluid communication with the outlet of the NH3 oxidising reactor, the catalysis gas inlet and the oxygen inlet; and an NH3 sensor for measuring the NH3 concentration of a gas entering the feed gas mixing site. The system typically comprises a pipe network to provide useful connections between the unit operations. The pipes of the pipe network may be selected freely based on the specific gases, temperatures, and pressures, but in general pipes made from steel or stainless steel can be used for any pipe in the pipe network. The pipes in the pipe network may be connected to each other and to relevant unit operations using any type of connection available in the field.

[0051] The system may comprise mixing sites where different gas streams are mixed. In general, mixing sites may be referred to by indicating specific functions, e.g. with respect to what gasses are mixed or what gas is provided by mixing, and a mixing site may have several functions, especially mixing functions. For example, the oxidising gas comprises NO and at least one of: O2, NO2, and NO2 + O2, and the system may comprise one or more mixing sites where the individual components are mixed. In a specific example, NOx is provided by oxidising NH3, and the NOx may be mixed with O2 to provide the oxidising gas as relevant for the specific embodiment.

[0052] The system may comprise any number of sensors useful for analysing a gas stream at any step or stage in the method. For example, the system may comprise sensor for specific components, e.g. in addition to the NH3 sensor. The system may also comprise one or more sensors for temperature, pressure and / or flowrate.

[0053] In general, steps in the method may involve controlling a temperature. In the present context, the term “controlling” may mean that the temperature is increased or decreased, as appropriate, to reach a target temperature, and the temperature may be maintained at the target temperature, once this has been reached. Furthermore, the unit operations and the pipes of the pipe network may include thermal insulation to minimise loss of heat from a thermally insulated unit operations or pipes. Any unit operation may be integrated with another unit operation or otherwise set up so as to transfer heat, e.g. heat considered to be waste heat, from a unit operation where the heat is generated to a unit operation where the heat can be utilised.

[0054] The method of the invention is generally based on gaseous streams, and the pressures of the gasses in the different steps can be selected freely as appropriate for the specific reaction. The method, and also the system, may include compressors or decompressors to modify the pressure of a gaseous stream to have an appropriate value. However, when NH3 is decomposed, NH3 can be supplied as liquid NH3, e.g. from a storage tank. The liquid NH3 is then converted to gaseous form before being decomposed.

[0055] The system may further comprise an NH3 supply; and an ammonia cracking reactor having ammonia entrance and a cracked gas outlet, which ammonia cracking reactor comprises an NHs-decomposition catalyst between the ammonia entrance and the cracked gas outlet, with the NH3 supply being in fluid communication with the ammonia entrance and the cracked gas outlet being in fluid communication with the connection pipe; wherein the NH3 supply is in fluid communication with the NH3 inlet and the ammonia entrance.

[0056] In yet another example, the system comprises a fuel cell having a fuel cell inlet and a fuel cell outlet, wherein the fuel outlet is in fluid communication with the fuel cell inlet, and the fuel cell outlet is in fluid communication with the feed gas mixing site.

[0057] The system may in particular comprise a heating arrangement configured to adjust the temperature of the NOx reducing reactor to a temperature in the range of 100°C to 600°C. In a specific example, the selective reduction catalyst comprises vanadium oxide on a carrier material. In another example, the NH3 oxidation catalyst comprises a platinum group metal on carrier material.

[0058] Any embodiment of the invention may be used in any aspect of the invention, and any advantage for a specific embodiment applies equally when an embodiment is used in a specific aspect.

[0059] Brief description of the drawings

[0060] In the following the invention will be explained in greater detail with the aid of an example and with reference to the schematic drawings, in which Figure 1 shows a system of the invention;

[0061] Figure 2 shows a system of the invention;

[0062] Figure 3 shows a system of the invention; Figure 4 shows the effect of temperature on the removal of NH3 in the method of the invention;

[0063] Figure 5 shows the effect of temperature on the removal of NH3 in the method of the invention.

[0064] The invention is not limited to the embodiment / s illustrated in the drawings. Accordingly, it should be understood that where features mentioned in the appended claims are followed by reference signs, such signs are included solely for the purpose of enhancing the intelligibility of the claims and are in no way limiting on the scope of the claims.

[0065] The term “comprising” as used in this specification and claims means “consisting at least in part of”. When interpreting statements in this specification and claims which include the term “comprising”, other features besides the features prefaced by this term in each statement can also be present. Related terms such as “comprise” and “comprised” are to be interpreted in a similar manner.

[0066] Detailed Description

[0067] The present invention relates to a method of producing a fuel gas composition

[0068] 1 and to a system 100 for carrying out the method. The method involves selectively oxidising NH3 in a feed gas composition 2 to provide an H2-based fuel gas 1 depleted in NH3. An example of the system 100 is depicted in Figure 1 , in which a feed gas composition 2 is provided from cracking a stream of gaseous NH3 5 in an ammonia cracking reactor 20, before monitoring NH3 in the feed gas composition 2 using an NH3 sensor 103. The feed gas composition

[0069] 2 is then mixed with an oxidising gas 3. Specifically, the oxidising gas 3 is provided by oxidising a stream of NH3 5 in an NH3 oxidising reactor 30. The feed gas composition 2 and the oxidising gas 3 are mixed at a feed gas mixing site 102. As shown in Figure 1 , the system 100 is equipped with an oxygen inlet 101 allowing addition of further O2 gas 8 to the feed gas composition 4. Further O2 gas 8 may be added to provide a specific ratio of oxygen atoms to nitrogen atoms of the NH3 of the feed gas composition 2. As shown in Figure 1 , the system 100 includes an NH storage tank 24. The NH storage tank 24 provides liquid NH3 that is converted to gaseous NH3 5, which is led to an ammonia cracking reactor 20 for providing the feed gas composition 2 and to the NH3 oxidising reactor 30 for providing the oxidising gas 3. The system 100 has an NH3 sensor 103, which monitors the NH3 concentration of the feed gas composition 2, and based on the recorded NH3 concentration, a proportion of the stream of NH3 5 is directed to the NH3 oxidising reactor 30 to match the need for oxidising gas 3 of the feed gas composition 2.

[0070] The ammonia cracking reactor 20 contains an NHs-decomposition catalyst 23 between an ammonia entrance 21 and a cracked gas outlet 22. The NHs-decom position catalyst 23 is a commercial Haber-Bosch catalyst. Atmospheric air with O2 as an oxidant 7 is mixed with the NH3 from the NH3 storage 24 at an oxidant inlet 32, before leading the mixture through the NH3 oxidising reactor 30.

[0071] The NH3 oxidising reactor 30 has an NH3 inlet 31 , an oxidant inlet 32 and an outlet, and an NH3 oxidation catalyst 34 is located between the NH3 inlet 31 and the outlet 33. The NH3 oxidation catalyst 34 comprises platinum on an alumina carrier. The reaction in the NH3 oxidising reactor 30 takes place according to the Ostwald process, which may also be viewed as the standard technology for the production of nitric acid.

[0072] The system 100 comprises a NOx reducing reactor 10. The feed gas composition 2 is mixed with the oxidising gas 3 to provide the catalysis gas composition 4, which via the catalysis gas inlet 11 is led through the NOx reducing reactor 10 to obtain the fuel gas composition 1 at the fuel outlet 12 of the NOx reducing reactor 10. The NOx reducing reactor 10 comprises a selective reduction catalyst 13 between the catalysis gas inlet 11 and the fuel outlet 12. The selective reduction catalyst 13 of the system 100 of Figure 1 is a V-oxide on a carrier of TiO2, although the NHs-decomposition catalyst 23 may be any catalytic material applicable to, e.g. known from, SCR treatment of exhaust gasses.

[0073] The fuel gas composition 1 may be led from the fuel outlet 12 to any operation where the NH3 depleted H2 containing fuel gas composition 1 can be used. The operation may in particular be a fuel cell. As the fuel gas composition 1 is NH3 depleted, the fuel cell may be selected freely.

[0074] In another example, as depicted in Figure 2, the system 100 includes an ammonia cracking reactor 20 containing an NHs-decomposition catalyst 23 between an ammonia entrance 21 and a cracked gas outlet 22. The NH3- decomposition catalyst 23 is a commercial Haber-Bosch catalyst, and the system 100 is configured to produce hydrogen and N2 in a 3:1 ratio. The system 100 further comprises a solid oxide fuel cell (SOFC) 50 where the cracked gas outlet 22 is in fluid communication with the fuel cell inlet 51 allowing that the cracked NH3 from the cracked gas outlet 22 is used as the fuel for the fuel cell 50. The exhaust gas 6 from the fuel cell outlet 52 is then used as the feed gas composition 2, which is mixed with the oxidising gas 3 and optionally also O2 gas 8 to provide the catalysis gas composition 4. The catalysis gas composition 4 is treated in a NOx reducing reactor 10 having a selective reduction catalyst 13 of a V-oxide on a carrier of TiO2 between the catalysis gas inlet 11 and the fuel outlet 12. The fuel gas composition 1 produced in the NOx reducing reactor 10 is then recycled to be mixed with the cracked NH3 from the cracked gas outlet 22. The system 100 comprises a condenser 105 after the fuel outlet 12 to remove H2O from the fuel gas composition 1. Thereby, unreacted H2 from the fuel cell 50 can be recycled to the fuel cell 50 to thereby increase the utilisation of H2.

[0075] In a further example, as depicted in Figure 3, the stream from the ammonia cracking reactor 20 via the cracked gas outlet 22 is led to a membrane separator 104 for H2 purification.

[0076] Examples

[0077] Several experiments were conducted to illustrate the present invention, and two SCR catalyst types were selected: a Cu-exchanged chabazite zeolites (or Cu-CHA) catalyst and a V-oxide / TiO2 catalyst. Specifically, the Cu-CHA catalyst included 3.2 wt% Cu and Si / AI=6.7, and the oxide / TiO2 catalyst was 5.3 wt% V2O5 / 3.5 wt% WO3 / TiO2. The catalysts employed in the examples were commercially available catalysts. Example 1

[0078] A 50 mg sample of a Cu-CHA catalyst, 3.2 wt% Cu, Si / AI=6.7, was placed in a quartz ll-tube reactor (6 mm inner diameter). The catalyst was exposed to a gas consisting of 396 ppm NO, 429 ppm NH3, 1 % O2, approximately 24% N2, and approximately 75% H2 at temperatures between 180 and 200°C, at a flow rate of 9 N L / h. An FTIR spectrometer was connected to the reactor system, allowing for measurement of the concentrations of NO, NO2, NH3, and H2O at the inlet and outlet of the reactor. Thus, the ratio of NO to NH3 at the inlet, i.e. in the feed gas, was 0.923, and the ratio of O2 to NH3 at the inlet was 23.3.

[0079] The measured outlet concentrations of NH3, NO and water are summarised in Table 1 , which also shows the NH3 and NO at the inlet.

[0080] Table 1

[0081] The concentrations of ammonia in the outlet measured under these conditions correspond to a conversion of 99%. The measured concentrations of H2O are about 2000 ppm. With a large excess of 1 % O2 in the feed (i.e. a ratio of O2 to NH3 of 23), a full oxidation of hydrogen would result in a concentration of 20,000 ppm water, and correspondingly the amount of NH3 at the inlet would provide about 640 ppm H2O at the outlet if no H2 were oxidised. Therefore, the concentration of water in the outlet is an order of magnitude lower, indicating that no significant oxidation of H2 has taken place.

[0082] Example 2

[0083] This example explores the effect of low concentrations of oxygen on the removal of NH3. A 50 mg sample of a Cu-CHA catalyst, 3.2 wt% Cu, S i / AI=6.7, was placed in a quartz ll-tube reactor (6 mm inner diameter). The catalyst was exposed to a gas consisting of 416 ppm NO, 484 ppm NH3, 1000 ppm O2, approximately 20% N2, and approximately 80% H2 at temperatures between 180 and 220°C, at a flow rate of 9 N L / h. An FTIR spectrometer was connected to the reactor system, allowing for measurement of the concentrations of NO, NO2, NH3, and H2O at the inlet and outlet of the reactor. Thus, the ratio of NO to NH3 at the inlet, i.e. in the feed gas, was 0.86, and the ratio of O2 to NH3 at the inlet was 2.07.

[0084] The measured outlet concentrations of NH3, NO and water are summarised in Table 2, which also shows the NH3 and NO at the inlet.

[0085] Table 2

[0086] The results show that the ammonia is removed from the stream containing hydrogen at an oxygen concentration as low as 1000 ppm. This means that the removal of ammonia still is effective, even at such low concentrations of oxygen. At low concentrations of oxygen, it is possible to increase the temperature to compensate for a less effective removal of NH3.

[0087] Example 3

[0088] This example examines the effect of the O2 concentration and indicates the relevance of oxygen for the removal of NH3. A 50 mg sample of a Cu-CHA catalyst, 3.2 wt% Cu, Si / AI=6.7, was placed in a quartz ll-tube reactor (6 mm inner diameter). The catalyst was exposed to a gas consisting of 412 ppm NO, 429 ppm NH3, 1000 ppm O2, approximately 20% N2, and approximately 80% H2 at 180°C, at a flow rate of 9 N L / h. An FTIR spectrometer was connected to the reactor system, allowing for measurement of the concentrations of NO, NO2, NH3, and H2O at the inlet and outlet of the reactor. Thus, the ratio of NO to NH3 at the inlet, i.e. in the feed gas, was 0.96, and the ratio of O2 to NH3 at the inlet varied between 0.58 and 2.33.

[0089] Table 3

[0090] Example 4

[0091] This example shows that a higher temperature is required for oxidation of H2 over Cu-CHA. A 50 mg sample of a Cu-CHA catalyst, 3.2 wt% Cu, Si / AI=6.7, was placed in a quartz ll-tube reactor (6 mm inner diameter). The catalyst was exposed to a gas consisting of 1 % O2, 20% N2, and 80% H2, balance N2 at a flow 9 N L / h, and heated to 500°C at a rate of 2°C / min. The concentration of water was then tracked as a function of temperature. Figure 4 shows that the increase in H2O concentration in the outlet first becomes significant in the range 350-500°C, which was clearly higher than 180-220°C, where the removal of NH3 takes place in the system of the invention. At 500°C, the measured water concentration was higher than 1.5%, which was close to 2%, the expected value when all oxygen was used for oxidation of H2. This is a direct indication that the removal of ammonia around 200°C was selective, without a major loss of oxygen to the oxidation of hydrogen.

[0092] Example 5

[0093] This example shows that the presence of NO is necessary for the removal of NH3 at around 200°C. A 50 mg sample of a Cu-CHA catalyst, 3.2 wt% Cu, Si / AI=6.7, was placed in a quartz ll-tube reactor (6 mm inner diameter). The catalyst was exposed to a gas without NO, further consisting of 401 ppm NH3, 1 % O2, approximately 24% N2, and approximately 75% H2 at temperatures between 180 and 200°C, at a flow rate of 9 N L / h. An FTIR spectrometer was connected to the reactor system, allowing for measurement of the concentrations of NO, NO2, NH3, and H2O at the inlet and outlet of the reactor.

[0094] The measured outlet concentrations of NH3, NO and water are summarised in Table 4, which also shows the NH3 and NO at the inlet.

[0095] Table 4

[0096] These values indicate that the NH3 is not removed in the absence of NO.

[0097] Example 6

[0098] This example shows that a catalyst based on vanadium oxide, another known type of SCR catalyst, can be used as well to remove NH3 from a stream containing hydrogen. A 103 mg sample of a catalyst consisting of 5.3 wt% V2O5 / 3.5 wt% W0s / Ti02 was placed in a quartz ll-tube reactor (6 mm inner diameter). The catalyst was exposed to a gas consisting of 491 ppm NO, 417 ppm NH3, 1 % O2, approximately 24% N2, and approximately 75% H2 at temperatures between 200 and 240°C, at a flow rate of 9 N L / h. An FTIR spectrometer was connected to the reactor system, allowing for measurement of the concentrations of NO, NO2, NH3, and H2O at the inlet and outlet of the reactor.

[0099] The measured outlet concentrations of NH3, NO and water are summarised in the table below.

[0100] Table 5

[0101] The low concentrations of NH3 and H2O in the outlet shows the effective removal of NH3 from the gas stream, without oxidation of hydrogen taking place.

[0102] Example 7

[0103] This example shows the performance of a catalyst based on vanadium oxide at very low concentrations of oxygen. A 103 mg sample of a catalyst consisting of 5.3 wt% V2O5 / 3.5 wt% W0s / Ti02 was placed in a quartz ll-tube reactor (6 mm inner diameter). The catalyst was exposed to a gas consisting of 383 ppm NO, 458 ppm NH3, 200 ppm O2, approximately 24% N2, and approximately 75% H2 at temperatures between 270 and 300°C, at a flow rate of 9 N L / h. An FTIR spectrometer was connected to the reactor system, allowing for measurement of the concentrations of NO, NO2, NH3, and H2O at the inlet and outlet of the reactor.

[0104] The measured outlet concentrations of NH3, NO and water are summarised in the table below. Table 6

[0105] The low concentrations of NH3 and H2O show the effective removal of NH3 from the gas stream without oxidation of hydrogen taking place. The temperature has been increased to 270-300°C in order to compensate for the lower rate of NH3 removal, due to the low concentration of oxygen.

[0106] Example 8

[0107] This example shows that a vanadium-oxide based catalyst does not oxidise hydrogen, even at high temperatures. A 103 mg sample of a catalyst consisting of 5.3 wt% V2O5 / 3.5 wt% W0s / Ti02 was placed in a quartz ll-tube reactor (6 mm inner diameter). The catalyst was exposed to a gas consisting of 1 % O2, 80% H2, balance N2 at a flow 9 N L / h, and heated to 500°C at a rate of 2°C / min. The concentration of water was then tracked as a function of temperature. Figure 5 shows that the concentration of H2O in the outlet of the reactor remained below 0.1 %, indicating that no hydrogen oxidation occurs, even at high temperatures.

[0108] Reference signs list

[0109] 1 Fuel gas composition

[0110] 2 Feed gas composition

[0111] 3 Oxidising gas

[0112] 4 catalysis gas composition

[0113] 5 Gaseous NH3 Exhaust gas

[0114] Oxidant

[0115] Oxygen (O2)

[0116] System

[0117] NOx reducing reactor catalysis gas inlet Fuel outlet

[0118] Selective reduction catalyst

[0119] Ammonia cracking reactor

[0120] Ammonia entrance

[0121] Cracked gas outlet NHs-decomposition catalyst NH3 storage

[0122] NH3 oxidising reactor

[0123] NH3 inlet

[0124] Oxidant inlet

[0125] Outlet

[0126] NH3 oxidation catalyst

[0127] Oxygen inlet

[0128] Feed gas mixing site

[0129] NH3 sensor

[0130] Membrane separator

[0131] Condenser

[0132] NH3 supply

[0133] Fuel cell

[0134] Fuel cell inlet

[0135] Fuel cell outlet

[0136] Heating arrangement

Claims

P A T E N T C L A I M S1. A method of producing a fuel gas composition (1 ), the method comprising the steps of: providing a feed gas composition (2) comprising H2 and NH3,; monitoring the concentration of NH3 in the feed gas composition (2); providing an oxidising gas (3) comprising NO and at least one of: O2, NO2, and NO2 + O2; mixing the feed gas composition (2) with the oxidising gas (3) to provide a catalysis gas composition (4); providing a NOx reducing reactor (10) having a catalysis gas inlet (11 ) and a fuel outlet (12), and a selective reduction catalyst (13) between the catalysis gas inlet (11 ) and the fuel outlet (12); applying the catalysis gas composition (4) to the catalysis gas inlet (11 ) and passing the catalysis gas composition (4) through the selective reduction catalyst (13); obtaining the fuel gas composition (1 ) at the fuel outlet (12) characterised in that the feed gas composition (2) has a molar content of H2 of at least 50% of the gas feed gas composition (2) and a ratio of H2 to NH3 of at least 6, or in that the feed gas composition (2) has a molar content of H2 of up to 50% of the gas feed gas composition (2) and a ratio of H2 to NH3 of up to 10.

2. The method of producing a fuel gas composition (1 ) according to claim 1 , wherein the feed gas composition (2) is provided in the steps of: providing a stream of gaseous NH3 (5); providing an ammonia cracking reactor (20) having an ammonia entrance (21 ) and a cracked gas outlet (22), which ammonia cracking reactor (20) comprises an NHs-decomposition catalyst (23) between the ammonia entrance (21 ) and the cracked gas outlet (22); applying the stream of gaseous NH3 (5) at the ammonia entrance (21 ) and passing the stream of gaseous NH3 (5) through the decomposition catalyst to obtain the feed gas composition (2) at the cracked gas outlet (22), the feed gas composition (2) comprising H2, N2, and NH3.

3. The method of producing a fuel gas composition (1 ) according to claim1 , wherein the feed gas composition (2) is an exhaust gas (6) from a fuel cell.

4. The method of producing a fuel gas composition (1 ) according to according to any one of claims 1 to 3, wherein in the oxidising gas (3), the ratio of oxygen atoms to nitrogen atoms of the NH3 of the feed gas composition (2) is at least 1.5, the ratio of nitrogen atoms to nitrogen atoms of the NH3 of the feed gas composition (2) is in the range of 0.8 to 1.2, and the ratio of oxygen atoms of NO2 to nitrogen atoms of the NH3 of the feed gas composition (2) is up to 1 .

5. The method of producing a fuel gas composition (1 ) according to according to any one of claims 1 to 4, wherein the catalysis gas composition (4) has a concentration of O2 of up to 2%.

6. The method of producing a fuel gas composition (1 ) according to any one of claims 1 to 5 further comprising the step of controlling the temperature of the catalysis gas composition (4) to be in the range of 100°C to 600°C while passing the catalysis gas composition (4) through the selective reduction catalyst (13).

7. The method of producing a fuel gas composition (1 ) according to any one of claims 1 to 6, wherein the oxidising gas (3) is provided in the steps of: providing a stream of gaseous NH3 (5); providing an NH3 oxidising reactor (30) having an NH3 inlet (31 ), an oxidant inlet (32) and an outlet (33), and an NH3 oxidation catalyst (34) between the NH3 inlet (31 ) and the outlet (33); and applying the stream of gaseous NH3 (5) at the NH3 inlet (31 ) of the NH3 oxidising reactor (30) and a stream of an oxidant (7) at the oxidant inlet (32) and passing the stream of gaseous NH3 (5) through the NH3 oxidation catalyst (34) to obtain the oxidising gas (3) at the outlet of the NH3 oxidising reactor (30).

8. A catalysis gas composition (4) comprising N2, NH3, H2, NO and at least one of: O2, NO2, and NO2 + O2, characterised in that the molar content of H2 is at least 50% of the catalysis gas composition (4) and a ratio of H2 to NH3 is at least 6, and wherein the ratio of oxygen atoms to nitrogen atoms of the NH3 is at least 1 .5, the ratio of nitrogen atoms to nitrogen atoms of the NH3 is in the range of 0.8 to 1.2, and the ratio of oxygen atoms of NO2 to nitrogen atoms of the NH3 is up to 1 .

9. A system (100) comprising: an NH3 oxidising reactor (30) having an NH3 inlet (31 ), an oxidant inlet (32) and an outlet (33), and an NH3 oxidation catalyst (34) between the NH3 inlet (31 ) and the outlet (33), a NOx reducing reactor (10) having a catalysis gas inlet (11 ) and a fuel outlet (12) and a selective reduction catalyst (13) between the catalysis gas inlet (11 ) and the fuel outlet (12); an oxygen inlet (101 ); a feed gas mixing site (102) in fluid communication with the outlet (33) of the NH3 oxidising reactor (30), the catalysis gas inlet (11 ) and the oxygen inlet (101 ); and an NH3 sensor (103), characterised in that the NH3 sensor (103) is configured to measure the NH3 concentration of a gas entering the feed gas mixing site (102).

10. The system (100) according to claim 9, wherein the system (100) further comprises: an NH3 supply (40); and an ammonia cracking reactor (20) having ammonia entrance (21 ) and a cracked gas outlet (22), which ammonia cracking reactor (20) comprises an NHs-decomposition catalyst (23) between the ammonia entrance (21 ) and the cracked gas outlet (22), with the NH3 supply (40) being in fluid communication with the ammonia entrance (21 ) and the cracked gas outlet (22) being in fluid communication with the feed gas mixing site (102); whereinthe NH3 supply (40) is in fluid communication with the NH3 inlet (31 ) and the ammonia entrance (21 ).

11. The system (100) according to claim 9 or 10 further comprising a fuel cell (50) having a fuel cell inlet (51 ) and a fuel cell outlet (52), wherein the fuel outlet (52) is in fluid communication with the fuel cell inlet (51 ), and the fuel cell outlet (52) is in fluid communication with the feed gas mixing site (102).

12. The system (100) according to any one of claims 9 to 11 , wherein the system (100) comprises a heating arrangement configured to adjust the temperature of the NOx reducing reactor (10) to a temperature in the range of 100°C to 600°C.

13. The system (100) according to any one of claims 9 to 12, wherein the selective reduction catalyst (13) comprises vanadium oxide on a carrier material.

14. The system (100) according to any one of claims 9 to 13, wherein the NH3 oxidation catalyst (34) comprises a platinum group metal.

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