Hydrogen promoted SCR catalyst desulphation

Abstract

The invention provides an apparatus comprising an internal combustion engine (14) configured to run on a mixture of air and a gaseous fuel comprising at least 70 vol% hydrogen gas (H2), a source of the gaseous fuel that supplies hydrogen to a combustion chamber of the internal combustion engine and an exhaust gas treatment system (12) for treating an exhaust gas stream produced by the engine (14). The system comprises a substrate comprising a SCR catalyst (16) comprising a copper-promoted zeolite, an iron-promoted zeolite, a manganese-promoted zeolite, or a combination of two or more of the promoter metals: copper, iron and manganese that is located to receive and thus be contacted with an exhaust gas stream produced by the engine (14), thereby to treat the exhaust gas stream by promoting reduction of NOx to N2 in the exhaust gas using a nitrogenous reductant. The SCR catalyst is liable to become sulphated in use. The system (12) also comprises a controller (26) that is configured, when in use, e.g. pre-programmed, to apply a desulphation treatment to the SCR catalyst (16) when it is determined that the SCR catalyst (16) is sulphated, thereby to increase NOx conversion activity of a sulphated SCR catalyst (16). The desulphation treatment comprises providing hydrogen gas in the exhaust gas stream upstream of the sulphated SCR catalyst (16), in a predetermined concentration sufficient to promote removal of sulphur from the sulphated SCR catalyst at a predetermined contact temperature.

Description

[0001] HYDROGEN PROMOTED SCR CATALYST DESULPHATION

[0002] Field of the invention

[0003] This invention relates to selective catalytic reduction (SCR) exhaust gas treatment systems that use SCR catalysts to promote catalytic reduction of nitrogen oxides (NOx) in exhaust gas streams of internal combustion engines. More specifically, the invention relates to a desulphation method of sulphated SCR catalysts.

[0004] Background to the Invention

[0005] Selective catalytic reduction, or SCR, is applied to exhaust gas streams of inter alia internal combustion engines to abate the emission of harmful nitrogen oxides, or NOx, that are contained in such exhaust gas streams. This involves contacting an exhaust gas stream with a SCR catalyst in the presence of a nitrogenous reductant, such as urea or ammonia, such that the catalyst catalyses reductive conversion of the NOx to dinitrogen (N2) and water.

[0006] SCR catalysts should ideally be able to retain good catalytic activity over a wide range of temperature conditions of use, for example from 200°C to 600 °C or higher, under hydrothermal conditions, i.e. in exhaust gas containing water, as steam, in addition to NOx.

[0007] Sulphur species in internal combustion engine fuel and / or lubricant can generate sulphur oxides (SOx) as combustion byproducts and are therefore present in the exhaust gas in addition to other components, including NOx. Sulphur species, including SOx, can interfere with the catalytic function of SCR catalysts, degrading or "poisoning" their catalytic activity through sulphation of catalyst promoter metals of the catalysts, i.e., sulphur species can react with the catalyst promoter metals of the SCR catalyst.

[0008] The mechanism through which SCR catalysts get poisoned by sulphur species is believed to involve the formation of complexes between sulphur species and the catalyst promoter metals of the catalysts. For example, in the case of copper-promoted zeolite catalysts, copper sulphate may be formed.

[0009] Despite the introduction of lower sulphur diesel fuels, even those having a sulphur concentration as low as 15 ppmw (parts per million by weight), such fuels can still poison and thus deactivate SCR catalysts because, according to Euro 6 stage emission standards, the exhaust system components should last the service life of a vehicle being the earlier of 160,000 km or 5 years, rising to 160,000 km or 8 years main lifetime under Euro 7 stage legislation.

[0010] In the case of hydrogen gas-fuelled IC engines, depending on the source of hydrogen, the hydrogen fuel can be relatively sulphur-free, e.g. green hydrogen. Nonetheless, sulphur species derived from the hydrogen fuel used can also be present in the exhaust gas streams of such engines. For example, black / grey / blue hydrogen is produced from fossil fuels, black hydrogen being produced from coal and grey and blue hydrogen being produced from natural gas using steam reformation of methane Another potential source of sulphur species in exhaust gas of hydrogen gas-fuelled IC engines is from lubricating oil leakages into the combustion chamber and incidental combustion of such lubricating oil in the combustion chamber.

[0011] To restore the performance of poisoned, or sulphated, SCR catalysts, the removal of sulphur species from catalyst promoter metal surfaces of such catalysts is periodically beneficial. This process is known as “desulphation”.

[0012] In the case of hydrogen gas-fuelled engines, the need for desuiphation is amplified due to the water content of the exhaust gas streams of such engines, which is significantly higher than that of diesel engine exhaust gas streams. Water promotes the sulphation of SCR catalysts by various mechanisms, including by increasing sulphur mobility and by reacting with less harmful sulphur dioxide (SO2) in the exhaust gas stream to form, for example, more detrimental sulphuric acid (H2SO4).

[0013] Desulphation of SCR catalysts to regenerate their catalytic activity conventionally requires high energy, e.g. heat (typically temperatures in excess of 600°C), due to a relatively strong bond energy that exists between sulphated catalyst promoter metals and the relevant sulphur species.

[0014] However, exposing SCR catalysts to high temperatures can result in thermal degradation of the catalyst, thus also having a negative effect on activity and longer-term durability. Many lean-burn vehicles using SCR catalysts in their exhaust aftertreatment systems also have difficulty in attaining high desulphation temperatures during normal operation, thus potentially requiring a disproportionate amount of energy input to obtain desuiphation, which can impact overall vehicle fuel economy.

[0015] Conventional approaches to SCR catalyst desulphation also include exposing the catalyst to an ammonia-based reductant that promotes ion exchange of catalyst promoter metal sulphates with the ammonia, or a precursor thereof, to form an ammonium sulphate species, which can more easily dissociate from the catalyst.

[0016] WO 2017 / 168327 discloses a method of desulphating a SCR catalyst, specifically in the context of diesel-fuelled internal combustion engines. The method involves treating the catalyst with an exhaust gas stream that comprises a reductant. The reductant is ammonia or an ammonia precursor. The treatment is performed at first and second temperatures, wherein the second temperature is higher than the first temperature and both temperatures are preferably below 600°C.

[0017] US patent publication no. 2023 / 287822A1 discloses an emission treatment system comprising an oxidation catalyst composition in fluid communication with an exhaust gas stream emitted from an engine that combusts both hydrocarbon fuel and hydrogen; and optionally, at least one selective catalytic reduction (SCR) composition and / or at least one three-way conversion (TWC) catalyst composition, and a method of treating an exhaust gas stream produced by combusting hydrogen fuel during a cold-start period using the emission treatment system.

[0018] JP H06 307232 A discloses an apparatus for recovering operation of a SOx poisoned alkali metal or alkaline earth metal NOx absorbent comprising a hydrogen gas supply device to supply hydrogen gas in the exhaust passage of an internal combustion engine to the NOx absorbent at the same time that the exhaust air-fuel ratio of the engine is made rich. The age of the document (1994) is before the development of H2-IC engines.

[0019] There is a constant need to improve SCR catalyst desulphation in the treatment of exhaust gas streams of internal combustion engines, and to do so using available engine resources. Hydrogen gas-fuelled engines are of particular interest in this regard.

[0020] Summary of the invention

[0021] Broadly, the present invention provides for the exploitation of hydrogen gas (H2) in desulphating a sulphated SCR catalyst of an SCR exhaust gas treatment system that is located downstream of an internal combustion engine that produces an exhaust gas stream that is treated by the SCR catalyst.

[0022] The invention comprises exposing the catalyst, at a predetermined contact temperature, to a gas stream comprising hydrogen gas in a predetermined concentration that is sufficient to promote removal of sulphur species from the sulphated SCR catalyst at the predetermined contact temperature.

[0023] Conveniently, the gas stream comprising the hydrogen gas may be the exhaust gas stream as emitted by the engine and that is treated by the catalyst. For the purpose of desulphation, the exhaust gas stream may be enriched with hydrogen gas, compared to the concentration of hydrogen gas in the exhaust gas stream under normal operation of the engine that produces the exhaust gas stream. Enrichment can be done by adjusting fuel-injection timing in-cylinder or via a dedicated injector for injecting hydrogen into exhaust gas downstream from the engine, e.g. downstream from an engine manifold.

[0024] Exhaust gas streams to which the present invention can apply are exhaust gas streams that are produced by internal combustion engines and that contain sufficient sulphur for SCR catalysts of exhaust gas treatment systems of such engines to become sulphated over time. Such internal combustion engines include both hydrocarbon fuel-burning internal combustion engines, such as diesel fuel-burning internal combustion engines, and hydrogen gas fuelburning internal combustion engines (as defined hereinbelow), preferably hydrogen gas burning internal combustion engines.

[0025] When the internal combustion engine is a hydrogen gas fuelled internal combustion engine (as defined hereinbelow), both the operability of the engine to adjust the concentration of hydrogen gas in the exhaust gas stream and the ready availability of hydrogen gas as a fuel gas can be advantageously exploited in the invention to supply hydrogen gas for desulphation to be performed. That is, when the internal combustion engine is a hydrocarbon fuelled internal combustion engine, particularly a diesel fuel-burning combustion engine, a dedicated source of hydrogen gas would need to be carried on a vehicle for supply, e.g. a hydrogen tank or a hydrogen generator.

[0026] More specifically, according to one aspect of the invention, there is provided an exhaust gas treatment system for treating an exhaust gas stream produced by an internal combustion engine, to reduce NOx in the exhaust gas stream, the system comprising - a substrate comprising a SCR catalyst that is disposed to receive and thus be contacted with an exhaust gas stream produced by an internal combustion engine, thereby to treat the exhaust gas by promoting reduction of NOx in the exhaust gas stream with a nitrogenous reductant; and

[0027] a controller that is configured to apply a desulphation treatment to the SCR catalyst when it is determined that the SCR catalyst is sulphated, thereby to recover NOx conversion activity of the sulphated SCR catalyst,

[0028] wherein the desulphation treatment comprises providing hydrogen gas in the exhaust gas stream upstream of the SCR catalyst, in a predetermined concentration sufficient to promote removal of sulphur from the sulphated SCR catalyst at a predetermined contact temperature.

[0029] As mentioned hereinabove, the exhaust gas stream is an exhaust gas stream that contains sulphur species in a concentration sufficient to cause sulphation of the SCR catalyst and thus impact the catalyst’s catalytic activity over time during use, giving rise to a requirement for desulphation of the catalyst to remove such sulphur species from the catalyst and recover some lost catalytic activity.

[0030] The sulphur species (hereinafter “sulphur”) that is comprised in the sulphated SCR catalyst can exist as elemental sulphur or can be present in an oxidation state of -2, +2, +4, +6, or a combination thereof depending on the counter ion that the sulphur associates with. Typical sulphur species include sulphur (S2~), elemental sulphur (S°), sulphite (SO?2), and sulphate (SO42.

[0031] Likewise, the sulphur that is removed from the catalyst through desulphation can also exist as elemental sulphur or can be present in an oxidation state of -2, +2, +4, +6, or a combination thereof depending on counter ion that the relevant sulphur species associates with. As mentioned earlier, typical sulphur species include sulphur dioxide (SO2), sulphur trioxide (SO3), and sulfuric acid (H2SO4). Most typically, in the present invention, sulphur species on the sulphated catalyst is desorbed, through desulphation according to the invention, as gaseous SO2.

[0032] The engine that produces the exhaust gas stream may be a hydrocarbon-, e.g. diesel- or methane- (natural gas) fuelled engine. Most preferably, however, the engine that produces the exhaust gas stream is a hydrogen-fuelled internal combustion engine (as defined hereinbelow). By providing hydrogen gas in the exhaust gas stream sufficient to promote removal of sulphur from the sulphated SCR catalyst at the predetermined contact temperature, a hydrogen enriched exhaust gas stream may thus be produced.

[0033] The controller is configured, when in use, e.g. as a pre-programmed computer processor, to apply a desulphation treatment to the SCR catalyst when it is determined that the SCR catalyst is sulphated thereby to recover NOx conversion activity of the sulphated SCR catalyst. The controller may be operatively connected to the engine, e.g. as a component part of an engine control unit (ECU), to directoperation of the engine to provide the predetermined concentration of hydrogen gas in the exhaust gas stream. Such direction of engine operation may, for example, be in respect of late-stage, e.g. post-injection or after- injection (as defined hereinbelow) of hydrogen gas injection into the cylinders of the engine. Determination of a SCR catalyst sulphation state may be done, e.g. by appropriate sensor inputs, such as a current NOx conversion relative to a stored “fresh” catalyst NOx conversion.

[0034] Thus, operating the engine to provide the predetermined concentration of hydrogen gas in the exhaust gas stream may include adjusting the air-to-hydrogen ratio of an air and hydrogen gas mixture that is combusted in the engine.

[0035] For example, whereas a hydrogen fuelled engine would typically operate under normal lean burn conditions, the controller would, to apply the desulphation treatment, operate the engine with a hydrogen and air gas mixture that is richer in hydrogen gas than under normal lean burn conditions.

[0036] Operation of the engine to provide the predetermined concentration of hydrogen gas in the exhaust gas stream would most typically find application in the case of the engine being a hydrogen fuelled internal combustion engine.

[0037] Alternatively, or in addition to operating the engine to provide the predetermined concentration of hydrogen gas in the in the exhaust gas stream, the system may include a hydrogen gas injector that is located to inject hydrogen gas directly into the exhaust gas stream. Typically, such a hydrogen gas injector would be located downstream of an internal combustion chamber of the engine, e.g. downstream of an engine manifold and / or turbo, and upstream of the SCR catalyst. When such a hydrogen gas injector is provided, the controller is operatively connected to the hydrogen gas injector in addition to being operatively connected to the engine to direct operation of the engine as hereinbefore described, whereby to control the injection of hydrogen gas directly into the exhaust gas stream, thereby to provide the predetermined concentration of hydrogen gas in the exhaust gas stream.

[0038] In this embodiment, the system is configured to supply hydrogen gas to the hydrogen gas injector, for injection thereof into the exhaust gas stream. When the engine is a hydrogen-fuelled internal combustion engine, the hydrogen injector may be connected to and supplied with hydrogen from a source of hydrogen that also supplies hydrogen to the internal combustion chamber, e.g. cylinder, of the engine.

[0039] When the engine is a hydrocarbon-fuelled internal combustion engine, the engine may be an engine that produces a methane containing exhaust gas stream, e.g. from a natural gas fuel. The downstream hydrogen injector may then be connected to and supplied with hydrogen from a hydrogen generator that generates hydrogen from methane, e.g. methane that is contained in the exhaust gas stream that is produced by the engine or that is supplied from a methane tank. Alternatively, a dedicated tank of hydrogen gas may be provided.

[0040] The predetermined concentration may be about 1000ppm to about 20,000ppm, preferably about 1000ppm to about 5000ppm, for example in a range of from about 1000ppm to about 4500ppm, more preferably in a range of from about 2500ppm to about 4500ppm.

[0041] Considering the typical operating temperatures of internal combustion engines and, more specifically, the temperatures of exhaust gas streams thereof, it is unlikely that the exhaust gas stream would be produced at the predetermined contact temperature, although such an embodiment is not excluded from the invention.

[0042] More typically, however, the system would be configured to provide the predetermined contact temperature.

[0043] In one embodiment of the invention, the predetermined contact temperature may be provided by temperature treatment of the exhaust gas stream. Thus, the system, and more particularly the controller, may be configured to apply a temperature treatment to the exhaust gas stream to provide the predetermined contact temperature, e.g. to increase the heat of combusted exhaust gas at engine outlet to the predetermined contact temperature. Alternatively, or additionally, the predetermined contact temperature may be provided by the catalyst, more specifically by temperature treatment of the catalyst, e.g. by use of an electrically heated catalyst (EHC) substrate. Thus, the system, and more particularly the controller, may be configured to apply a temperature treatment to the catalyst to provide the predetermined contact temperature, e.g. to heat the catalyst from a normal operating temperature thereof to the predetermined contact temperature.

[0044] The predetermined contact temperature may be 500°C or less, preferably 450°C or less, more preferably in a range of from about 360°C to about 425°C.

[0045] The controller may further be configured to determine that the SCR catalyst has become sulphated.

[0046] In one embodiment of the invention, the controller may be configured, when in use, e.g. by pre-programming, to determine that the catalyst has become sulphated based, e.g. on the passage of a predetermined period of contact time between the exhaust gas stream and the catalyst and / or by comparing a current NOx conversion activity with an activity of a “fresh” SCR catalyst by suitable sensor input.

[0047] In another embodiment of the invention, the controller may be configured to determine that the catalyst has become sulphated based thereon that a concentration of NOx detected downstream of the catalyst has exceeded a predetermined threshold value, e.g. by suitable sensor input.

[0048] In another embodiment of the invention, the controller may be configured to determine that the catalyst has become sulphated based on a concentration of SOx detected downstream of the catalyst has exceeded a predetermined threshold value.

[0049] The controller may be configured to apply the desulphation treatment when it has determined that the catalyst has become sulphated. In accordance with the invention, this may include operating the engine such that the predetermined concentration of hydrogen gas is provided in the exhaust gas stream upstream of the SCR catalyst substrate and / or injecting hydrogen gas directly into the exhaust gas stream upstream of the SCR catalyst substrate and downstream of the engine, while also providing the predetermined contact temperature, if not provided by the exhaust gas stream under normal operation of the engine, by heating the exhaust gas stream and / or heating the SCR catalyst and / or SCR catalyst substrate.

[0050] The catalyst would, as is conventional in the art in question, typically comprise a catalyst support supporting a catalyst promoter metal capable of promoting reduction of NOx in the exhaust gas stream.

[0051] In this context, “catalyst support” refers to a material, usually a solid material in particulate format, that supports a catalyst promoter metal thereon. The catalyst promoter metal may be provided on the catalyst support by ion exchange and, thus, the catalyst would typically be a catalyst promoter metal ion-exchanged SCR catalyst, as is conventional in the art. Such a support would typically comprise a porous refractory material, such as a molecular sieve. Most suitably, the catalyst support may be a zeolite, preferably an aluminosilicate zeolite. A zeolite is a microporous aluminosilicate having any one of the framework structures listed in the Database of Zeolite Structures published by the International Zeolite Association (IZA). The framework structures include, but are not limited to those of the CHA, FAU, BEA, MFI, MOR types. Non-limiting examples of zeolites having these structures include chabazite, faujasite, zeolite Y, ultrastable zeolite Y, beta zeolite, mordenite, silicalite, zeolite X, and ZSM-5. Aluminosilicate zeolites can have a silica / alumina molar ratio (SAR) defined as SIOa / AlsOa) from at least about 5, preferably at least about 20, with useful ranges of from about 10 to 200. Higher SAR zeolites are preferred because the zeolites are more hydrothermally durable to the relatively high volumetric water concentrations in Ha-ICE exhaust gas. However, relatively high SAR zeolites have fewer exchange sites for exchange with promoter metals, including copper and / or manganese. Accordingly there is a balance between catalytic activity and catalyst durability. For example, it may be necessary to use higher loadings of higher SAR zeolites at lower promoter-exchanged loadings.

[0052] Typically, the catalyst promoter metal would be selected from transition metals or rare earth metals. The catalyst promoter metal may therefore, for example, be selected from copper (Cu), cobalt (Co), nickel (Ni), lanthanum (La), manganese (Mn), iron (Fe), vanadium (V), silver (Ag), and cerium (Ce), neodymium (Nd), praseodymium (Pr), titanium (Ti), chromium (Cr), zinc (Zn), tin (Sn), niobium (Nb), molybdenum (Mo), hafnium (Hf), yttrium (Y), and tungsten (W).

[0053] Preferably the metal-exchanged zeolite is a small pore zeolite, preferably having a CHA framework structure. Small-pore zeolites are framework type codes (according to the IZA) comprising a maximum pore ring size of eight tetrahedral atoms. Preferably the zeolite is exchanged with Cu, Fe or both Cu and Mn. Preferably the zeolite is copper-promoted and has a CHA framework. Preferably the copper is present in an amount of from 0.1 to 5 wt% and most preferably from 2 to 4 wt%, by weight of the copper-promoted zeolite.

[0054] Preferably the SCR catalyst for use in the invention comprises a copper-promoted zeolite, an iron-promoted zeolite, a manganese-promoted zeolite, or a combination of two or more of these promoter metals, e.g. CuMn or CuFe. The total amount of Cu, Mn and Fe is preferably present in an amount of from 0.1 to 5 wt% and most preferably from 1 to 3 wt%, by weight of the promoted zeolite.

[0055] The catalyst promoter metal would, as alluded to above, be a metal that catalyses the reduction of nitrogen (NOx) to dinitrogen (N2) using a reductant, which is typically ammonia or urea.

[0056] In the catalyst, the catalyst promoter metal supported on the support, may be carried on a substrate. Typically, the support supporting the catalyst promoter metal would be coated, e.g. washcoated in the form of a slurry, onto a substrate or incorporated within a substrate, e.g. as an extrudate. In this context, the term "substrate" refers to a monolithic structure.

[0057] A washcoat is a thin, adherent coating carrying the catalyst support supporting the catalyst promoter metal, applied to a substrate. A washcoat is formed by preparing a slurry containing a certain solid content (e.g. 10-60% by weight) of support particles, supporting catalyst promoter metal, in a liquid vehicle typically water, which is then coated onto a substrate and dried and calcined to provide a washcoat layer on the substrate. Methods of applying a washcoat to a substrate are known from the art, e.g. Applicant’s WO99 / 47260.

[0058] An example of a suitable monolith substrate for use in the context of the present invention is a flow-through substrate, e.g. comprising a metal or ceramic material having a honeycomb structure. Cordierite is one example of a suitable ceramic material. Alternatively, the monolith substrate can be a filter substrate, preferably a wall-flow filter substrate.

[0059] Provision may also be made for a nitrogenous reductant, such as ammonia or urea, to be injected into the exhaust gas stream upstream of the SCR catalyst. In accordance with conventional practice in the art of the invention, urea or ammonia can be used as a nitrogenous reductant for the SCR catalyst promoter metal catalysed reduction of NOx in the exhaust gas stream, to produce N2and water.

[0060] According to another aspect of the invention, there is provided a method of desulphating a sulphated SCR catalyst of an exhaust gas treatment system for treating an exhaust gas stream produced by an internal combustion engine to reduce NOx with a nitrogenous reductant in the exhaust gas stream, the method comprising – producing a hydrogen enriched exhaust gas stream by introducing hydrogen gas into the exhaust gas stream in a predetermined concentration sufficient to promote removal of sulphur from the sulphated SCR catalyst at a predetermined contact temperature; and contacting the sulphated SCR catalyst with the hydrogen enriched exhaust gas stream at the predetermined contact temperature.

[0061] The method may be a method performed by the system described according to the invention and, accordingly, features of the method of the invention would correspond to features of the system of the invention.

[0062] More specifically, the SCR catalyst, the exhaust gas stream, the hydrogen enriched exhaust gas stream, the exhaust gas treatment system, the internal combustion engine, the introduction of hydrogen gas into the exhaust gas stream, the sulphation of the SCR catalyst, the predetermined concentration, and the predetermined contact temperature, may all be as described in accordance with the system of the invention.

[0063] Brief description of the drawing

[0064] In order to provide an understanding of the invention, reference is made to the appended diagrammatic drawing, in which reference numerals refer to components of an exemplary embodiment of the invention. The drawings are exemplary only and should not be construed as limiting the invention.

[0065] Figure 1 is a schematic depiction of an embodiment of an exhaust gas treatment system according to the invention.

[0066] Detailed description of an embodiment Features of an embodiment of the invention as characterised herein will now be described without limitation by way of illustrative example only, with reference to the accompanying diagrammatic drawing in Figure 1.

[0067] It will be understood that the invention may embody the described features thereof in many different forms within the scope of the characterisation of the invention. The invention should therefore not be construed as limited to any specific embodiments set forth therein. Such specific embodiments are provided by way of non-limiting example only.

[0068] Referring to the drawing, reference numeral 10 generally indicates an assembly of an exhaust gas treatment system 12 according to the invention and a hydrogen gas fuelled internal combustion engine 14, wherein the exhaust treatment system 12 is located downstream of the engine 14.

[0069] The system 12 includes a SCR catalyst housing 15, inside of which an SCR catalyst 16 is located.

[0070] The SCR catalyst 16 is washcoated onto a monolithic flow-through cordierite substrate and comprises a particulate aluminosilicate CHA zeolite catalyst support ion-exchanged with copper.

[0071] The system 12 further includes an exhaust gas stream transfer line 18 that leads from the engine 14 to the catalyst housing 15, such that an exhaust gas stream produced by the engine 14 is, in use, supplied to the SCR catalyst 16, thus being contacted with the SCR catalyst 16 in the presence of an ammonia or urea nitrogenous reductant, which is supplied along reductant feed line 19.

[0072] The SCR catalyst 16 catalyses reductive conversion of NOx in the exhaust gas stream to N2and H2O by reaction with the ammonia or urea nitrogenous reductant inside the catalyst housing 15 and thus abates NOx emissions from the engine 14.

[0073] A treated exhaust gas stream is discharged from the catalyst housing 15 along discharge line 17, which is typically provided by a tailpipe of a vehicle operated by the engine 14 and comprising the system 12. The discharge line, or tail pipe, 17 is provided with a sensor or gas analyser 20 that in use analyses, or provides sensor input to an engine control unit of, the composition of the treated exhaust gas stream, specifically, for the purposes of the present invention, in respect of the concentration of unreduced NOx and the concentration of SOx, most prominently SO2.

[0074] The engine 14 is supplied with a hydrogen gas fuel stream from a hydrogen tank 22 along hydrogen gas supply line 24. The hydrogen gas fuel stream is supplied to the engine 14 as a hydrogen and air mixture and hydrogen gas from the tank 22 is thus mixed with air upstream of the engine 14 (not illustrated).

[0075] Hydrogen gas fuel stream that is supplied to the engine 14 is combusted in a combustion chamber of the engine 14, typically being provided by a plurality of piston cylinders, e.g. to power a vehicle of which the engine 14 forms part, thus producing the exhaust gas stream which is then passed along line 18 to the exhaust gas treatment system 12 to be treated as hereinbefore described.

[0076] The system 12 further includes an electronic controller 26.

[0077] The electronic controller 26 is in communication with the sensor or gas analyser 20 along communication line 28, to receive treated exhaust gas stream composition information from the sensor or gas analyser 20.

[0078] The electronic controller 26 is configured to determine, on the basis of the treated exhaust gas stream composition information, whether catalytic NOx conversion is above a predetermined required level or has dropped to below the predetermined required level, with reference to whether or not the NOx concentration in the treated exhaust gas stream exceeds the predetermined required level thereof.

[0079] The controller 26 is further configured, when in use, e.g. by pre-programming, to draw a conclusion that the SCR catalyst 16 has been sulphated if the treated exhaust gas stream composition information indicates that catalytic NOx conversion has dropped to below the predetermined required level, and to apply a desulphation treatment to the catalyst 16 based on such a conclusion.

[0080] In accordance with the invention, the desulphation treatment that the electronic controller 26 is configured to apply, comprises providing hydrogen gas in the exhaust gas stream in line 18 upstream of the SCR catalyst 16, in a predetermined concentration sufficient to promote removal of sulphur from the sulphated SCR catalyst 16 at a predetermined contact temperature. In other words, the desulphation treatment comprises producing a hydrogen enriched exhaust gas stream that has been enriched with hydrogen to the predetermined concentration and contacting the SCR catalyst 16 with the hydrogen enriched exhaust gas stream at the predetermined contact temperature.

[0081] In one embodiment of the invention, the electronic controller 26 is operatively connected to the engine 14 by control and communication line 27, to direct operation of the engine 14 to apply the desulphation treatment.

[0082] More specifically, in such an embodiment of the invention, the electronic controller 26 is configured to direct operation of the engine 14 to increase the hydrogen-to-air ratio of the hydrogen and air mixture that is supplied to the engine 14 as fuel, thus supplying a hydrogen and air gas mixture to the engine 14 that is richer in hydrogen gas than under normal, conventional engine operation and thus also increasing the concentration of non-combusted hydrogen gas in the exhaust gas stream that is supplied to the SCR catalyst 16 along transfer line 18.

[0083] A further sensor or gas analyser 30 in the transfer line 18 analyses the composition of the exhaust gas stream discharged from the engine, specifically in respect of hydrogen gas concentration. The sensor or gas analyser 30 is in communication with the electronic controller 26 along communication line 32, to communicate exhaust gas stream composition information, comprising hydrogen gas concentration information, to the electronic controller 26.

[0084] Receiving the hydrogen gas concentration information from the sensor or gas analyser 30 allows the electronic controller 26 to determine whether the exhaust gas stream that is supplied to the SCR catalyst 16 along transfer line 18 has the predetermined concentration of hydrogen required for the catalyst desulphation treatment, i.e. has been sufficiently enriched with hydrogen.

[0085] In another embodiment of the invention, the electronic controller 26 is configured to inject hydrogen gas directly into the exhaust gas stream in line 18, upstream of the catalyst housing 15, thereby to provide the predetermined concentration of hydrogen gas in the exhaust gas stream. For this purpose, the system 12 includes an engine bypass hydrogen gas supply line 34 that leads from the hydrogen gas tank 22 to a hydrogen gas injector 36 that is located to inject hydrogen gas that is fed to it along the bypass line 34 into the exhaust gas stream in line 18 downstream of the engine 14 and upstream of the catalyst housing 15, thus bypassing the engine 14.

[0086] The supply line 34 is provided with a valve 38 selectively to allow and disallow supply of hydrogen gas from the hydrogen tank 14 along the supply line 34.

[0087] The electronic controller 26 is in electronic controlling communication with the valve 38 along communication and control line 40 and with the hydrogen gas injector 36 along communication and control line 42, in order to open the valve 38 and operate the injector 36 to inject sufficient hydrogen gas into the exhaust gas stream in line 18 to provide the predetermined hydrogen gas concentration in the exhaust gas stream in line 18 for the desulphation treatment to be performed.

[0088] Also in such an embodiment, receiving the hydrogen gas concentration information from the sensor or gas analyser 30 allows the controller 26 to determine whether the exhaust gas stream that is supplied to the SCR catalyst 16 along transfer line 18 has the predetermined concentration of hydrogen required for the catalyst desulphation treatment, i.e. has been sufficiently enriched with hydrogen.

[0089] In accordance with the invention, applying the desulphation treatment also requires contacting the exhaust gas stream, enriched with hydrogen to the predetermined concentration, with the SCR catalyst 16 at a predetermined contact temperature, which contact temperature would be higher than the temperature at which the exhaust gas is produced by the engine 14 if the exhaust gas produced by the engine 14 is not at the predetermined contact temperature.

[0090] To provide the predetermined contact temperature, the system 12 is configured for one or both of two approaches to be followed.

[0091] The first approach is to heat the SCR catalyst 16 to the predetermined temperature. For this purpose, the system 12 includes an electric heater 44 that is located to heat the SCR catalyst 16 in the catalyst housing 15, to the predetermined temperature. The second approach is to heat the hydrogen enriched exhaust gas in transfer line 18 to the predetermined temperature, upstream of the catalyst housing 15 and therefore also upstream of the SCR catalyst 16. For this purpose, the system 12 includes a gas heater 46 upstream of the catalyst housing 15 and downstream of the engine 14.

[0092] The electronic controller 26 is in electronic controlling communication with the heater 44 along communication and control line 48 and / or with the heater 46 along communication and control line 50, whichever one or both is / are provided.

[0093] The electronic controller 26 is also in electronic communication with a hydrogen enriched exhaust gas feed temperature sensor 52 along communication line 54. The sensor 52 communicates a temperature of the hydrogen enriched exhaust gas stream to the electronic controller 26, on the basis of which the controller selectively exercises control over the heater 44 and / or the heater 46 to provide the predetermined contact temperature between the hydrogen enriched exhaust gas stream and the SCR catalyst 16.

[0094] By such application of the desulphation treatment by the electronic controller 26, the SCR catalyst 16 is desulphated, which desulphation is monitored by the gas composition sensor or gas analyser 20 in respect of SO2 and NOx concentration in the treated exhaust gas stream.

[0095] More specifically, a decrease in NOx concentration in the treated exhaust gas stream and a periodic increase followed by a decrease of SO2 concentration in the treated exhaust gas stream, as determined by the sensor or gas analyser 20, would input to the electronic controller 26 that desulphation has been effected, thus causing the electronic controller 26 to discontinue such treatment.

[0096] A discontinuation of the desulphation treatment would include discontinuing supply of (excess) hydrogen to the exhaust gas stream at the predetermined concentration and to discontinue temperature treatment to provide the predetermined contact temperature, thus returning the engine 14 and the system 12 to conventional operating conditions that existed before desulphation treatment was applied.

[0097] Definitions As defined herein, H2-ICE engines are internal combustion engines configured to run on a mixture of air and fuel, wherein the fuel of the mixture of air and fuel is a gaseous fuel comprising a majority fuel mass of hydrogen.

[0098] A “majority fuel mass” can be at least 70 vol% hydrogen gas (H2), e.g. of one of the colour sources discussed above or a mixture of two or more thereof. Exhaust gas of ICE engines powered wholly or in part by H2 include H2 itself and oxides of nitrogen (NO and NO2, collectively NOX). To compare to the redox composition of prior art diesel and gasoline exhaust gas, the lambda value of exhaust gases emitted by internal combustion engines configured to run on a mixture of air and fuel, wherein the fuel of the mixture of air and fuel is a gaseous fuel comprising a majority fuel mass of H2, can vary widely, e.g. from 1 to 30, which can make catalytic aftertreatment difficult. Lambda can be calculated using the Brettschneider Equation.

[0099] Although emission standards similar to e.g., the so-called Euro 7 emission standard, have yet to be set for internal combustion engines powered by H2 fuel, Applicant believes that treatment of emissions from on-road vehicles and non-road vehicles with a power rating >56 kW will require treatment of both uncombusted H2 and oxides of nitrogen (NOX), whereas non-road vehicles power rated <56 kW may require treatment only of uncombusted H2. H2 emissions can be treated by oxidation to H2O, whereas NOXcan be treated by a range of possible reactions, but one preferred reaction is the selective reduction of NOXwith a nitrogenous reductant, particularly ammonia which may - according to common general knowledge - be derived from a urea precursor. NOXreduction using NH3 - and urea as a precursor thereof -has already been applied to current Diesel vehicles.

[0100] It is anticipated that vehicular H2-ICE will include electronically controlled fuel injection systems, such as common rail fuel injection, and central processing units of engine control units pre-programmed, when in use, variably to control fuel injection timing for, among other reasons, emissions control. These arrangements allow for the application of such processes as multiple injections during one engine cycle of a cylinder, wherein one engine cycle comprises a number of strokes. For example, a four-stroke engine requires four piston strokes per cylinder for each full combustion process engine cycle. As the name suggests, multiple injections can replace a single injection event with multiple discrete injection events.

[0101] Injection events that occur after a main injection, often referred to as post-injections or afterinjections, can be used to control to manage exhaust aftertreatment systems. The following definitions are used herein: (i) Post-injections occur very shortly after the main injection event while the process of combusting the main fuel injection is still underway and are intended to burn in-cylinder; and

[0102] (ii) After-injections occur much later after the combustion process is complete and are not intended to bum in-cylinder.

[0103] The invention may also be defined according to one or more of the following statements:

[0104] 1. An exhaust gas treatment system for treating an exhaust gas stream produced by an internal combustion engine, to reduce NOx in the exhaust gas stream, the system comprising

[0105] a substrate comprising a SCR catalyst that is disposed to receive and thus be contacted with an exhaust gas stream produced by an internal combustion engine, thereby to treat the exhaust gas by promoting reduction of NOx in the exhaust gas stream with a nitrogenous reductant; and

[0106] a controller that is configured to apply a desulphation treatment to the SCR catalyst when it is determined that the SCR catalyst is sulphated, thereby to recover NOx conversion activity of the sulphated SCR catalyst,

[0107] wherein the desulphation treatment comprises providing hydrogen gas in the exhaust gas stream upstream of the SCR catalyst, in a predetermined concentration sufficient to promote removal of sulphur from the sulphated SCR catalyst at a predetermined contact temperature.

[0108] 2. The system according to 1, wherein the internal combustion engine is an engine configured to run on a mixture of air and fuel, wherein the fuel of the mixture of air and fuel is a gaseous fuel comprising a majority fuel mass of hydrogen, the system comprising a source of gaseous fuel comprising a majority fuel mass of hydrogen and the controller is operatively connected to the engine, being configured to operate the engine to provide the predetermined concentration of hydrogen gas in the exhaust gas stream.

[0109] 3. The system according to 2, wherein operating the engine to provide the predetermined concentration of hydrogen gas in the exhaust gas stream includes adjusting the air-to-fuel ratio of a mixture of air and fuel comprising a majority fuel mass of hydrogen that is combusted in the engine. 4. The system according to 1, which comprises a hydrogen gas injector that is iocated downstream of an internal combustion chamber of the engine and upstream of the SCR catalyst substrate, being operatively connected to the controller and adapted to be operated by the controller to control a feed of hydrogen gas directly into the exhaust gas stream, thereby to provide the predetermined concentration of hydrogen gas in the exhaust gas stream.

[0110] 5. The system according to 4, wherein ~

[0111] the internal combustion engine is an engine configured to run on a mixture of air and fuel, wherein the fuel of the mixture of air and fuel is a gaseous fuel comprising a majority fuel mass of hydrogen, the system comprising a source of gaseous fuel comprising a majority fuel mass of hydrogen, and the hydrogen injector is connected to and supplied with hydrogen from a source of hydrogen that also supplies hydrogen to the internal combustion chamber of the engine; or

[0112] the internal combustion engine is an engine that produces a methane-containing exhaust gas stream, and the hydrogen injector is connected to and supplied with hydrogen from a hydrogen generator that generates hydrogen from methane contained in exhaust gas stream produced by the engine.

[0113] 6. The system according to any one of 1 to 5, wherein the predetermined contact temperature is 500°C or less, more preferably 450°C or less, more preferably in a range of from about 360°C to about 425°C.

[0114] 7. The system according to any one of 1 to 6, wherein:

[0115] the predetermined contact temperature is a temperature of the exhaust gas stream, and the controller is configured to apply a temperature treatment to the exhaust gas stream to provide the predetermined contact temperature; and / or

[0116] the predetermined contact temperature is a temperature of the catalyst, and the controller is configured to apply a temperature treatment to the catalyst to provide the predetermined contact temperature.

[0117] 8. The system according to any one of 1 to 7, wherein the predetermined concentration of hydrogen gas is about 1000ppm to about 20,000ppm, preferably about 1000ppm to about 5000ppm. 9. The system according to any one of 1 to 8, wherein the controiier is configured, when in use and via suitable sensor inputs, to determine that the SCR catalyst has become sulphated, whereby to trigger the desulphation treatment, with reference to any one or more of —

[0118] that a predetermined period of contact time between the exhaust gas stream and the catalyst has elapsed;

[0119] that a concentration of NOx downstream of the SCR catalyst substrate has exceeded a predetermined threshold value; and

[0120] that the SCR catalyst is at or above a pre-determined temperature.

[0121] 10. The system according to any one of 1 to 9, wherein the SCR catalyst comprises a catalyst support supporting a catalyst promoter metal capable of promoting reduction of NOx in the exhaust gas stream.

[0122] 11. The system according to 10, wherein the catalyst promoter metal is copper ion-exchanged in a zeolite catalyst support.

[0123] 12. The system according to any one of 1 to 11, including apparatus for injecting a nitrogenous reductant, preferably urea, into the exhaust gas stream upstream of the SCR catalyst

[0124] 13. A method of desulphating a sulphated SCR catalyst of an exhaust gas treatment system for treating an exhaust gas stream produced by an internal combustion engine to reduce NOx in the exhaust gas stream with a nitrogenous reductant, the method comprising

[0125] producing a hydrogen enriched exhaust gas stream by introducing hydrogen gas into an exhaust gas stream produced by an internal combustion engine, in a predetermined concentration sufficient to promote removal of sulphur from the sulphated SCR catalyst at a predetermined contact temperature; and

[0126] contacting the sulphated SCR catalyst with the hydrogen enriched exhaust gas stream at the predetermined contact temperature.

[0127] 14. The method according to 13, wherein the predetermined contact temperature is 500°C or less, more preferably 450°C or less, more preferably in a range of from about 360°C to about 425°C; and

[0128] the predetermined concentration of hydrogen gas is about 1000ppm to about 20,000ppm, preferably about 1000ppm to about 5000ppm.

[0129] 15. The method according to 13 or 14, wherein sulphur on the sulphated SCR catalyst is desorbed as gaseous SO2.

[0130] EXAMPLES

[0131] The following non-limiting Examples are provided by way of illustration only.

[0132] Example 1 - De-greened “fresh” SCR Catalyst Preparation

[0133] A 4wt% Cu ion-exchanged synthetic aluminosilicate AEI zeolite (silica-to-alumina ratio = 20:1) SCR catalyst was prepared by washcoating a suitable flow-through monolith substrate and drying and calcining the washcoated part. The “as calcined” part is referred to as a “fresh” catalyst. A cylindrical core of 15 x 20mm was cut from the substrate. The SCR catalyst of the cylindrical core was de-greened in a flowing gas mixture in a synthetic catalytic activity test (SCAT) apparatus (de-greening conditions performed on a: 550°C for 30 minutes in 10vol% O2, 25vol% H2O, balance N2, 3 litres per minute gas flow rate, 51,000 hr-1space velocity).

[0134] Example 2 - SCR catalyst activity analysis conditions

[0135] The steady state synthetic gas compositions and temperatures set out in Table 1 were used in the SCAT apparatus to assess SCR catalyst activity of 15 x 20 mm catalysed monolith substrate cores. The gas flow rate used was 3 litres per minute, corresponding to a swept volume of 51,000 hr-1. This test was performed on: (i) the degreened SCR catalyst of Example 1 prior to any sulphation or desulphation; and (ii) the sulphated SCR catalyst that had been subsequently desulphated (of Example 4 below). It will be noted that, for the purposes of further comparison, the SCR catalyst activity of (i) and (ii) were separately tested in (a) a synthetic diesel; and (b) a synthetic H2-ICE exhaust gas. Attention is drawn to the significantly higher water content of the synthetic H2-ICE exhaust gas, which is typical of H2-ICE exhaust gases, relative to diesel engine exhaust gases.

[0136] Table 1: Synthetic exhaust gas compositions (balance: N2) and temperatures

[0137]

[0138] “Outlet temperature” is steady state sample core outlet temperature.

[0139] Example 3 - Sulphation conditions

[0140] The de-greened “fresh” catalyst monolith substrate cores of Example 1 were subjected to an accelerated sulphation ageing treatment in a SCAT apparatus with a synthetic internal combustion engine exhaust gas having an enriched sulphur content and using the conditions described in Table 2, thereby to provide a realistically aged and sulphated SCR catalyst comparable to a SCR catalyst aged through use on a vehicle for the purposes of performance and desulphation analysis. The gas flow rate used was 3 litres per minute, corresponding to a swept volume of 51,000 hr-1.

[0141] Table 2: SCR catalyst sulphation conditions (balance: N2)

[0142]

[0143] Steady state sample core outlet temperature.

[0144] Example 4 - Desulphation conditions

[0145] The de-greened SCAT -sulphated SCR catalysts of Example 3 were then subjected to a range of desulphation treatments in the SCAT apparatus based on the synthetic diesel or H2-ICE exhaust gas conditions set out in Table 3 below, further modified as described in the Key to Tables 4 and 5 hereinbelow, by using, respectively (a) an increased gas temperature only; (b) an increased gas temperature and ammonia combined; and (c) for the synthetic H2-ICE exhaust gas, all three of an increased gas temperature, ammonia and hydrogen.

[0146] Table 3: SCR catalyst desulphation conditions (balance: N2)

[0147]

[0148] As also explained in Example 2 hereinabove, following the selected desulphation conditions, the SCR catalyst activity of the desulfated sample was re-tested for comparison with the degreened activity in both the synthetic H2-ICE and, for comparison, the diesel synthetic exhaust gases at 200°C and 250°C as described in Example 2 / Table 1.

[0149] Table 4: Desulphation effect on ammonia concentration and temperature in terms of NOx conversion %

[0150]

[0151] All temperatures indicated are steady state sample core outlet temperature. Temperature control was performed by heating the SCR catalyst monolith substrate core.

[0152] Key to Table 4: “De-greened” - NOx conversion % of de-greened catalyst of Example 1 tested in the relevant synthetic exhaust gas mixture (i.e. diesel or H2-ICE) of Example 2, Table 1 at steady-state temperatures of 200°C or 250°C.

[0153] “DeSOx 425°C” - NOx conversion % of sulphated catalyst of Example 3 after desulphation using the conditions described in the heading of Example 4, Table 3, wherein the NO used was 0 ppm, the NH3 used was 0 ppm and the H2 used was 0 ppm, ramping the temperature of the catalyst up from the steady state temperature of 275°C to a holding temperature of 425°C, over 30 minutes at a ramp rate of 10°C per minute.

[0154] “DeSOx 450°C” - NOx conversion % of sulphated catalyst of Example 3 after desulphation using the conditions described as for “DeSOx 425°C” above, ramping the temperature of the catalyst up from the steady state temperature of 275°C to a holding temperature of 450°C, over 30 minutes at a ramp rate of 10°C per minute.

[0155] “DeSOx 475°C” - NOx conversion % of sulphated catalyst of Example 3 after desulphation using the conditions described as for “DeSOx 425°C” above, ramping the temperature of the catalyst up from the steady state temperature of 275°C to a holding temperature of 475°C, over 30 minutes at a ramp rate of 10°C per minute.

[0156] “DeSOx 450°C + 350ppm NH3” - NOx conversion % of sulphated catalyst of Example 3 after desulphation using the conditions described in the heading of Example 4, Table 3, wherein the NO used was 0 ppm, the NH3 used was 350 ppm and the H2 used was 0 ppm, ramping the temperature of the catalyst up from the steady state temperature of 275°C to a holding temperature of 450°C, over 30 minutes at a ramp rate of 10°C per minute.

[0157] “DeSOx 450°C + 1000ppm NH3 (Hot)” - NOx conversion % of sulphated catalyst of Example 3 after desulphation using the conditions described in the heading of Example 4, Table 3, wherein the NO used was 0 ppm, the NH3 used was 1000 ppm and the H2 used was 0 ppm, ramping the temperature of the catalyst up from the steady state temperature of 275°C to a holding temperature of 450°C, over 30 minutes at a ramp rate of 10°C per minute.

[0158] “DeSOx 450°C + 1000ppm NH3 (Cold)” - NOx conversion % of sulphated catalyst of Example 3 to which the following NH3 “pre-loading” step was performed immediately following sulphation and prior to desulphation: a steady state sample core outlet temperature of 275°C for 30 minutes: SO2 0 ppm, NO 350 ppm, NH3 1000 ppm, O2 10%, CO2 0%, H2O 25%, balance: N2. Desulphation was then done using the conditions described in the heading of Example 4, Table 3, wherein the NO used was 0 ppm, the NH3 used was 0 ppm and the H2 used was 0 ppm, ramping the temperature of the catalyst up from the steady state temperature of 275°C to a holding temperature of 450°C, over 30 minutes at a ramp rate of 10°C per minute.

[0159] From the results presented in Table 4, it will be seen that, in the case of using an ammonia

[0160] reductant in the desulphation process, improvement in catalyst activity is comparatively poor

[0161] in the case of H2-ICE exhaust gases, as compared to diesel exhaust gases. It is believed that, using the methodology described, some of the sulphur species resulting from the sulphation conditions of Example 3 / Table 2 form ammonium sulphate when ammonia is used jn the desulphation conditions set out in the he ading of Table 4.

[0162] Further desulphation conditions were tested using a similar methodology to those explained in connection with Example 4, Table 4, as set out in Table 5 below and explained in greater detail in the Key below Table 5, in which the desulphation effect of hydrogen was tested compared to the performance of de-greened catalyst of Table 4.

[0163] Table 5: Desulphation effect on hydrogen concentration and temperature in terms of NOx conversion %

[0164]

[0165]

[0166] Key to Table 5:

[0167] “De-greened” - Conditions and methodology identical to Table 4 and the accompanying “Key” thereto, for the purposes of comparison.

[0168] “DeSOx 425°C + 1500ppm H - NOx conversion % of sulphated catalyst of Example 3 after desulphation using the conditions described in the heading of Example 4, Table 5, wherein the NO used was 0 ppm, the NH3 used was 0 ppm and the H2 used was 1500 ppm, ramping the temperature of the catalyst up from the steady state temperature of 275°C to a holding temperature of 425°, over 30 minutes at a ramp rate of 10°C per minute.

[0169] “DeSOx 425°C + 3000ppm H2” - NOx conversion % of sulphated catalyst of Example 3 after desulphation using the conditions described in the heading of Example 4, Table 5, wherein the NO used was 0 ppm, the NH3 used was 0 ppm and the H2 used was 3000 ppm, ramping the temperature of the catalyst up from the steady state temperature of 275°C to a holding temperature of 425°C, over 30 minutes at a ramp rate of 10°C per minute.

[0170] “DeSOx 450°C + 1500ppm H2” - NOx conversion % of sulphated catalyst of Example 3 after desulphation using the conditions described in the heading of Example 4, Table 5, wherein the NO used was 0 ppm, the NH3 used was 0 ppm and the H2 used was 1500 ppm, ramping the temperature of the catalyst up from the steady state temperature of 275°C to a holding temperature of 450°C, over 30 minutes at a ramp rate of 10°C per minute.

[0171] “DeSOx 450°C + 3000ppm H2” - NOx conversion % of sulphated catalyst of Example 3 after desulphation using the conditions described in the heading of Example 4, Table 5, wherein the NO used was 0 ppm, the NH3 used was 0 ppm and the H2 used was 3000 ppm, ramping the temperature of the catalyst up from the steady state temperature of 275°C to a holding temperature of 450°C, over 30 minutes at a ramp rate of 10°C per minute. “DeSOx 375°C + 20,000ppm H2” - NOx conversion % of sulphated catalyst of Example 3 after desulphation using the conditions described in the heading of Example 4, Table 5, wherein the NO used was 0 ppm, the NH3 used was 0 ppm and the H2 used was 20,000 ppm (2.0 vol%), ramping the temperature of the catalyst up from the steady state temperature of 275°C to a holding temperature of 375°C, over 30 minutes at a ramp rate of 10°C per minute.

[0172] “DeSOx 400°C + 20,000ppm H2” - NOx conversion % of sulphated catalyst of Example 3 after desulphation using the conditions described in the heading of Example 4, Table 5, wherein the NO used was 0 ppm, the NH3 used was 0 ppm and the H2 used was 20,000 ppm (2.0 vol%), ramping the temperature of the catalyst up from the steady state temperature of 275°C to a holding temperature of 400°C, over 30 minutes at a ramp rate of 10°C per minute.

[0173] “DeSOx 425°C + 20,000ppm H2” - NOx conversion % of sulphated catalyst of Example 3 after desulphation using the conditions described in the heading of Example 4, Table 5, wherein the NO used was 0 ppm, the NH3 used was 0 ppm and the H2 used was 20,000 ppm (2.0 vol%), ramping the temperature of the catalyst up from the steady state temperature of 275°C to a holding temperature of 425°C, over 30 minutes at a ramp rate of 10°C per minute.

[0174] From the results shown in Table 5 compared with those in Table 4, it can be seen that significantly more SCR catalyst activity is recovered in H2-ICE exhaust gas conditions when H2 is used in the desulphation process than when NH3 is used in the desulphation process. As sulphation causes a loss of SCR catalyst activity, a higher post-sulphation recovery of SCR catalyst activity implies that more sulphur has been driven off the catalyst. Comparing the results from Tables 4 and 5, the use of hydrogen gas as desulphation agent in treating an exhaust gas stream of a hydrogen gas-fuelled internal combustion engine achieves significantly higher removal of sulphur from the catalyst, particularly at a higher hydrogen gas enrichment, and does so at significantly lower temperatures than ammonia.

[0175] Table 6 hereinbelow provides further details from the results set out in Tables 4 and 5, in particular the temperature at which SO2 is detected at the sample core outlet for the relevant desulphation test conditions using Fourier-transform infrared spectroscopy (FTIR) (NB: FTIR detects SO2 only and not SO3). Table 6: Lowest temperature at which SO2 is detected by FTIR

[0176]

[0177] It will be noted that the temperature at which SO2 is detected for both the “DeSOx 425°C + 3000ppm H2” and “DeSOx 450°C + 3000p pm H2” conditions was the same. This was because the temperature ramp began at 275°C for both sets of conditions and then ramped up to hold at the maximum temperature indi c ated at a ramp rate of 10°C per minute. Therefore, despite the ultimate final hold tempera ture for these two tests being different, the conditions at the lower end of the ramp wer e identical, so - as would be expected for identical gas mixtures -the temperature at which the SO2 was first detected at the bottom of the temperature ramp was the same. However, what was observed was that the “DeSOx 450°C + 3000ppm H2” conditions generated a larger integrated peak of detected SO2 - as indicated by the area under the peak - compared with the “DeSOx 425°C + 3000ppm H2” conditions (results not shown).

[0178] As is evident from Table 6, the use of hydrogen gas as desulphation agent in treating an exhaust gas stream of a hydrogen gas-fuelled internal combustion engine achieves significantly lower temperature removal of sulphur from the SCR catalyst, particularly at a higher hydrogen gas enrichment, than ammonia.

[0179] For the avoidance of doubt, the entire contents of all documents acknowledged herein are incorporated herein by reference.

Claims

CLAIMS:

1. An apparatus comprising an internal combustion engine configured to run on a mixture of air and a gaseous fuel comprising at least 70 vol% hydrogen gas (H2), a source of the gaseous fuel that supplies hydrogen to a combustion chamber of the internal combustion engine and an exhaust gas treatment system for treating an exhaust gas stream produced by the internal combustion engine, to reduce NOx in the exhaust gas stream to N2, the system comprising - a substrate comprising a SCR catalyst that is disposed to receive and thus be contacted with an exhaust gas stream produced by an internal combustion engine, thereby to treat the exhaust gas by promoting reduction of NOx in the exhaust gas stream with a nitrogenous reductant, wherein the SCR catalyst comprises a copper-promoted zeolite, an iron-promoted zeolite, a manganese-promoted zeolite, or a combination of two or more of the promoter metals: copper, iron and manganese;apparatus for injecting a nitrogenous reductant, preferably urea, into the exhaust gas stream upstream of the SCR catalyst; anda controller that is configured to apply a desulphation treatment to the SCR catalyst when it is determined that the SCR catalyst is sulphated, thereby to recover NOx conversion activity of the sulphated SCR catalyst,wherein the desulphation treatment comprises providing hydrogen gas in the exhaust gas stream upstream of the SCR catalyst, in a predetermined concentration sufficient to promote removal of sulphur from the sulphated SCR catalyst at a predetermined contact temperature.

2. The apparatus according to claim 1, wherein the controller is operatively connected to the engine, being configured to operate the engine to provide the predetermined concentration of hydrogen gas in the exhaust gas stream.

3. The apparatus according to claim 2, wherein operating the engine to provide the predetermined concentration of hydrogen gas in the exhaust gas stream includes adjusting the air-to-fuel ratio of a mixture of air and fuel comprising at least 70 vol% hydrogen gas (H2) that is combusted in the engine.

4. The apparatus according to claim 1, which comprises a hydrogen gas injector that is located downstream of an internal combustion chamber of the engine and upstream of the SCR catalyst substrate, being operatively connected to the controller and adapted to beoperated by the controller to control a feed of hydrogen gas directly into the exhaust gas stream, thereby to provide the predetermined concentration of hydrogen gas in the exhaust gas stream.

5. The apparatus according to claim 4, wherein - the hydrogen injector is connected to and supplied with hydrogen from the source of hydrogen that also supplies hydrogen to the internal combustion chamber of the engine.

6. The apparatus according to any one of claims 1 to 5, wherein the predetermined contact temperature is 500°C or less, more preferably 450°C or less, more preferably in a range of from about 360°C to about 425°C.

7. The apparatus according to any one of claims 1 to 6, wherein:the predetermined contact temperature is a temperature of the exhaust gas stream, and the controller is configured to apply a temperature treatment to the exhaust gas stream to provide the predetermined contact temperature; and / orthe predetermined contact temperature is a temperature of the catalyst, and the controller is configured to apply a temperature treatment to the catalyst to provide the predetermined contact temperature.

8. The apparatus according to any one of claims 1 to 7, wherein the predetermined concentration of hydrogen gas is about 1000ppm to about 20,000ppm, preferably about 1000ppm to about 5000ppm.

9. The apparatus according to any one of claims 1 to 8, wherein the controller is configured, when in use and via suitable sensor inputs, to determine that the SCR catalyst has become sulphated, whereby to trigger the desulphation treatment, with reference to any one or more of - that a predetermined period of contact time between the exhaust gas stream and the catalyst has elapsed;that a concentration of NOx downstream of the SCR catalyst substrate has exceeded a predetermined threshold value; andthat the SCR catalyst is at or above a pre-determined temperature.

11. A method of desulphating a sulphated SCR catalyst in an exhaust system of an apparatus comprising an internal combustion engine configured to run on a mixture of air anda gaseous fuel comprising at least 70 vol% hydrogen gas (H2), a source of the gaseous fuel that supplies hydrogen to a combustion chamber of the internal combustion engine and the exhaust gas treatment system for treating an exhaust gas stream produced by the internal combustion engine, which SCR catalyst comprises a copper-promoted zeolite, an iron-promoted zeolite, a manganese-promoted zeolite, or a combination of two or more of the promoter metals: copper, iron and manganese and is adapted to reduce NOx in the exhaust gas stream to N2with a nitrogenous reductant, the method comprising – producing a hydrogen enriched exhaust gas stream by introducing hydrogen gas into the exhaust gas stream produced by the internal combustion engine, in a predetermined concentration sufficient to promote removal of sulphur from the sulphated SCR catalyst at a predetermined contact temperature; andcontacting the sulphated SCR catalyst with the hydrogen enriched exhaust gas stream at the predetermined contact temperature.

12. The method according to claim 11, whereinthe predetermined contact temperature is 500°C or less, more preferably 450°C or less, more preferably in a range of from about 360°C to about 425°C; andthe predetermined concentration of hydrogen gas is about 1000ppm to about 20,000ppm, preferably about 1000ppm to about 5000ppm.

13. The method according to claim 11 or claim 12, wherein sulphur on the sulphated SCR catalyst is desorbed as gaseous SO2.

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