A system and method for treating an exhaust gas comprising hydrogen

Abstract

There is provided a system comprising: (i) an internal combustion 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 (H2); (ii) a source of gaseous fuel comprising a majority fuel mass of hydrogen (H2); and (iii) an exhaust system for the internal combustion engine comprising an oxidation catalyst for oxidising H2 in an exhaust gas of the engine to H2O; wherein the oxidation catalyst comprises a washcoat coated on a monolith substrate, the washcoat comprising a platinum group metal consisting essentially of platinum, the platinum group metal supported on a particulate support material which is titanium oxide doped with a mixture of silicon oxide and tungsten oxide.

Description

[0001] A SYSTEM AND METHOD FOR TREATING AN EXHAUST GAS COMPRISING HYDROGEN

[0002] Field of the Invention

[0003] The present invention relates to a system and method for treating an exhaust gas comprising hydrogen. More particularly, the present invention relates to treating a system comprising and internal combustion 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 and an exhaust system comprising an oxidation catalyst for converting H2 and optionally also NO in the exhaust to H2O and NO2. The oxidation catalyst comprises a platinum group metal supported on a titanium oxide-based particulate support material.

[0004] Background to the Invention

[0005] Hydrogen has been receiving significant attention as a potential future alternative fuel for powering internal combustion engines (ICEs). It is envisioned that low-carbon hydrogen could be produced via hydrolysis of water using renewable electricity supplied by wind and solar powerplants. This produces so-called “green hydrogen” with essentially zero greenhouse gas (GHG) emissions. Different “types” of hydrogen are commonly referred to using a colour scheme that reflects the degree of upstream GHG emissions. For example, black / grey hydrogen is produced from fossil fuels, black hydrogen being produced from coal and grey hydrogen being produced from natural gas using steam reformation of methane; blue hydrogen is essentially the same as grey hydrogen, but with its CO2 sequestered or repurposed; turquoise hydrogen is produced from natural gas via pyrolysis (with solid carbon as a by-product); pink / red / purple hydrogen is produced using nuclear power though electrolysis, thermolysis or a combination thereof; white hydrogen is produced as a byproduct of industrial processes such as fracking; and yellow hydrogen produced by electrolysis of water using grid electricity, typically derived from a mixture of renewable energies and fossil fuels.

[0006] It is known to fuel a compression ignition engine with a fuel mixture comprising diesel fuel and a minority fuel mass of hydrogen (see e.g. K.S. Varde et al, International Journal of Hydrogen Energy, 7, 549-555 (1983)). It is also known to fuel a spark-ignition engine with a fuel mixture comprising gasoline (petrol) and a minority fuel mass of hydrogen (see M. Al -Baghdadi et al, Energy Conversion and Management, 41, 77-91 (2000)). Hydrogen may be derived on the vehicle by an on-board fuel reformer (see e.g. Applicant’s WO2014 / 118574A1; and W02012 / 063082A1). For further information, Applicant refers to DieselNet Technology Guide » Alternative Fuels » “Hydrogen” particularly section “5. Hydrogen Fueled Engines”, Author: H. Jaaskelainen, Revision 2023.07 available at https: / / dieselnet.com / tech / fuel_hydrogen.php.

[0007] In contrast to prior art disclosures of a minority fuel mass of hydrogen, the present invention is directed to systems comprising 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 and an exhaust system comprising an oxidation catalyst for converting H2 and optionally also NO in the exhaust to H2O and NO2. 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). Combustion of lubricating oil can generate CO, hydrocarbons, and particulate matter, as well as urea-generated particles where selective catalytic reduction is used to reduce NOX. Particulates derived from these sources may require filtration. Ammonia emissions could also be possible under conditions that generate rich combustion. 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.

[0008] 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. In this regard, several chemical reactions occur in an NH3selective catalytic reduction (SCR) process, all of which represent desirable reactions that reduce NOXto nitrogen. Specifically:

[0009] (1) 4NH3+ 4NO + O24N2+ 6H2O (i.e. 1 : 1 NH3:N0)

[0010] (2) 4NH3+ 2NO + 2NO24N2+ 6H2O (i.e. 1 : 1 NH3:NOX)

[0011] (3) 8NH3+ 6NO2 7N2+ 12H2O (i.e. 4:3 NH3:NO2)

[0012] The dominant reaction is reaction (1). However, reaction (2) is kinetically faster than either reactions (1) and (3) and can be desirably promoted by oxidising NO in exhaust gas to NO2 upstream from the SCR catalyst so that exhaust gas entering the SCR catalyst has an approximately 1 : 1 volume ratio of NO to NO2. A relevant undesirable, non-selective sidereaction is:

[0013] (4) 2NH3+ 2NO2N2O + 3H2O + N2.

[0014] Suitable catalysts active for reactions (1), (2) and (3) are known, and include aluminosilicate zeolites, particularly those known as “small pore zeolites”, i.e. containing a maximum ring size of eight tetrahedral atoms, including zeolites of the framework type code CHA and AEI, promoted, e.g. ion-exchanged, with copper and / or iron; and vanadia supported on titania or titania optionally doped with silica. The titania can also be promoted with oxides of tungsten.

[0015] Applicant has investigated how to treat greenhouse gas components of exhaust gas of 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. In this regard, nitrous oxide (N2O) has a global warming potential (GWP) 265-289 times that of CO2 for a 100-year timescale, i.e., N2O emitted today remains in the atmosphere more than 100 years, on average (CO2, by definition, has a GWP of 1 regardless of the time period used, because it is the gas being used as the reference). Accordingly, it is hugely desirable to limit the quantity of N2O emitted to atmosphere by exhaust gas aftertreatment processes.

[0016] WO2023 / 222715A1 discloses an emission treatment system comprising a hydrogen oxidation catalyst, the use of said catalyst for oxidizing hydrogen gas in an emission treatment system, and a method for heat generation in an engine exhaust system. Following research, Applicant has identified a specific oxidation catalyst that is active for oxidising hydrogen to H2O, and also for oxidising NO to NO2 for promoting reaction (2) on a downstream SCR catalyst and at the same time having relatively low N2O formation.

[0017] Summary of the Invention

[0018] According to a first aspect, the invention provides a system comprising:

[0019] (i) an internal combustion 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 (H2);

[0020] (ii) a source of gaseous fuel comprising a majority fuel mass of hydrogen (H2); and

[0021] (iii) an exhaust system for the internal combustion engine comprising an oxidation catalyst for oxidising H2 in an exhaust gas of the engine to H2O; wherein the oxidation catalyst comprises a washcoat coated on a monolith substrate, the washcoat comprising a platinum group metal consisting essentially of platinum, the platinum group metal supported on a particulate support material which is titanium oxide doped with a mixture of silicon oxide and tungsten oxide.

[0022] The present disclosure will now be described further. In the following passages, different aspects / embodiments of the disclosure are defined in more detail. Each aspect / embodiment so defined may be combined with any other aspect / embodiment or aspects / embodiments unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

[0023] As such, a second aspect of the present invention provides a method of treating an exhaust gas from an internal combustion engine running on a mixture of air and fuel, wherein the fuel is a gaseous fuel comprising a majority fuel mass of hydrogen (H2), the method comprising contacting the exhaust gas with an oxidation catalyst, wherein the oxidation catalyst comprises a washcoat coated on a monolith substrate, the washcoat comprising a platinum group metal consisting essentially of platinum, the platinum group metal supported on a particulate support material which is titanium oxide doped with a mixture of silicon oxide and tungsten oxide. That is, the method of treating an exhaust gas comprises contacting the exhaust gas with the oxidation catalyst as described in respect of the system of the first aspect.

[0024] A further aspect of the present invention therefore provides the use of an oxidation catalyst comprising a platinum group metal consisting essentially of platinum, the platinum group metal supported on a particulate support material which is titanium oxide doped with a mixture of silicon oxide and tungsten oxide, to oxidise H2 to H2O, and optionally NO to NO2, in exhaust gas emitted from an internal combustion engine running on a mixture of air and fuel, wherein the fuel is a gaseous fuel comprising a majority fuel mass of hydrogen (H2).

[0025] The system comprises an internal combustion 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 (H2), and a source of gaseous fuel comprising a majority fuel mass of hydrogen (H2). Preferably the internal combustion engine configured to run on a majority fuel mass of hydrogen (H2) is configured to run on a fuel comprising >70 vol% H2, such as >90 vol% H2, >95 vol% H2, >99 vol% H2, and more preferably, a fuel consisting essentially of H2. The balance of the fuel mass may consist of hydrocarbons such as methane, diesel and / or gasoline.

[0026] A hydrogen internal combustion engine is well-known to those skilled in the art and, unlike a hydrogen fuel cell, is simply a modified version of a traditional gasoline (petrol) or diesel powered internal combustion engines. A hydrogen internal combustion engine can therefore operate essentially free of carbon-based emissions in the exhaust gases (e.g. CO or CO2) or unbumed hydrocarbons (HCs), though some trace emissions may still exist due to combustion of engine additives, such as lubricating oil. Additionally, unbumed hydrogen is nevertheless a problem for hydrogen internal combustion engines, as are oxides of nitrogen which arise from the combustion of the fuel in air (which is approximately 78 vol% nitrogen) as is known in respect of traditional combustion engines.

[0027] As such, the system further comprises an exhaust system for the internal combustion engine, the exhaust system comprising an oxidation catalyst suitable for oxidising H2 contained in the exhaust gas of the engine to H2O. Specifically, the oxidation catalyst comprises a washcoat coated on a monolith substrate, the washcoat comprising a platinum group metal consisting essentially of platinum, the platinum group metal supported on a particulate support material which is titanium oxide doped with a mixture of silicon oxide and tungsten oxide.

[0028] As is known in the art for automotive catalysts, the oxidation catalyst article comprises a substrate having an inlet end and an outlet end and a longitudinal (axial) length extending therebetween. The monolith substrate has a plurality of channels extending between the inlet end and the outlet end. The plurality of channels extends in the longitudinal direction and provide a plurality of inner surfaces (e.g. the surfaces of the walls defining each channel). For a flow-through substrate, each of the plurality of channels has an opening at the inlet end and an opening at the outlet end.

[0029] For a wall-flow filter adjacent channels are alternatively plugged at each end of the monolith article such that, in use, the exhaust gas passes along an inlet channel (i.e. a channel open at an inlet end of the monolith article for receiving an exhaust gas) and is forced to pass through the channel walls an into an adjacent outlet channel (i.e. a channel open at an outlet end of the monolith article). The channel walls have a distribution of fine pores providing the monolith article with the required porosity, the average dimensions of the pores in the channel walls, e.g. the filter walls, are typically in the range from 5 to 50 pm.

[0030] The channels may be of a constant width and each plurality of channels may have a uniform channel width. Preferably within a plane orthogonal to the longitudinal direction, the monolith substrate has from 300 to 900 channels per square inch, preferably from 400 to 800, such as from 600 to 700 channels per square inch. The channels can have cross sections that are rectangular, square, circular, oval, triangular, hexagonal, or other polygonal shapes.

[0031] The monolith substrate acts as a support for holding catalytic material. Suitable materials for forming the monolith substrate include ceramic-like materials such as cordierite, silicon carbide, silicon nitride, zirconia, mullite, spodumene, alumina-silica magnesia or zirconium silicate, or of porous, refractory metal. Such materials and their use in the manufacture of porous monolith substrates are well known in the art.

[0032] It should be noted that the monolith substrate is a single component (i.e. a single brick), nonetheless, when forming an exhaust system, the substrate used may be formed by adhering together a plurality of channels or by adhering together a plurality of smaller substrates. Such techniques are well known in the art, as well as suitable casings and configurations of the emission treatment system. In embodiments wherein the catalyst article of the present comprises a ceramic substrate, the ceramic substrate may be made of any suitable refractory material, e.g., alumina, silica, ceria, zirconia, magnesia, zeolites, silicon nitride, silicon carbide, zirconium silicates, magnesium silicates, aluminosilicates and metallo-aluminosilicates (such as cordierite and spodumene), or a mixture or mixed oxide of any two or more thereof. Cordierite, a magnesium aluminosilicate, and silicon carbide are particularly preferred.

[0033] In embodiments wherein the catalyst article of the present invention comprises a metallic substrate, the metallic substrate may be made of any suitable metal, and in particular heat-resistant metals and metal alloys such as titanium and stainless steel as well as ferritic alloys containing iron, nickel, chromium, and / or aluminium in addition to other trace metals.

[0034] The channel walls of the monolith substrate are coated with a washcoat, and preferably the coating consists of the single washcoat formulation as described herein. The washcoat loading of the particulate support material on the monolith substrate may be from 0.2 to 2.0 g / in3, preferably from 0.8 to 1.8 g / in3.

[0035] The washcoat comprises a platinum group metal (PGM) supported on a particulate support material, the PGM consisting essentially of platinum (Pt). As such, the washcoat is rhodium-free. Preferably the oxidation catalyst is not a three-way catalyst (TWC) and / or the particulate support material does not include cerium (cerium oxide - ceria). The definition “rhodium-free” in the aspects of the present invention are adopted to avoid accidental anticipation by prior art wherein the internal combustion engine uses spark ignition, similarly to a gasoline (petrol) engine. For similar reasons, the oxidation catalyst can be defined as being “not a three-way catalyst”, which is a catalyst technology which typically also includes in the three-way catalyst formulation a ceria-containing mixed oxide as an oxygen storage component.

[0036] A TWC is configured to remove all three major exhaust pollutants from traditional combustion engine exhausts, including oxidation of carbon monoxide and hydrocarbons and the simultaneously the reduction of nitrogen oxides to nitrogen. On the contrary, the oxidation catalyst for use in the present invention can also, advantageously, oxidise NO in the exhaust gas from the hydrogen internal combustion engine to NO2.

[0037] Preferably the platinum concentration in the oxidation catalyst on the monolith substrate is from 2 to 120 g / ft3, preferably 5 to 50 g / ft3. As shown in the Examples provided herein, effective H2 and NO oxidation has been demonstrated with as little as about 10 g / ft3Pt. Reduced PGM content reduces the overall cost of the oxidation catalyst article. More particularly, the present inventors have found that a platinum-only formulation is unexpectedly more effective than comparisons with a small quantity of palladium (Pd), such PGMs being common in the oxidation catalysts for exhausts from traditional combustion engines in the combustion of unbumt hydrocarbons. Even more particularly, the platinum is provided on a particulate support material which is titanium oxide doped with a mixture of silicon oxide and tungsten oxide. This combination has been found to provide an ideal balance for highly effective H2 oxidation (as evidenced by the lower light-off temperatures) and increased NCh / NOx conversion rates when compared to PGM on an undoped alumina or undoped titania support. The formulation of the washcoat has also been found to mitigate formation of nitrous oxide (N2O) during exhaust gas treatment which is an undesirable byproduct with a relatively high global warming potential.

[0038] Preferably the particulate support material comprises at least 80 wt% titanium oxide, preferably from 80 wt% to 90 wt% titanium oxide. Preferably, the particulate support material comprises at least 3 wt% silicon oxide and / or at most 10 wt% silicon oxide. Additionally, the particulate support material may preferably comprise at least 3 wt% tungsten oxide and / or at most 10 wt% tungsten oxide, more preferably from 6 wt% to 10 wt% tungsten oxide since tungsten oxide was found to be particularly effective at mitigating N2O formation resulting from the presence of silicon oxide whilst also improving NCh / NOx conversion under conventional hydrogen slip concentrations in exhaust gases (e.g. from 1,000 ppm to 5,000 ppm, though it will be appreciated that there may be spikes in concentration during operation, such as up to 25,000 ppm). It is believed that with future improvements in engine calibration and design, hydrogen combustion will improve and hydrogen slip will reduce accordingly. The inventors have advantageously found that for low hydrogen slip concentrations in exhaust gases (e.g. from 100 ppm to 1,000 ppm, or from 150 ppm to 500 ppm), the oxidation catalyst can exhibit minimal formation of N2O as a byproduct, preferably less than 10 ppm, N2O, more preferably less than 5 ppm N2O.

[0039] Preferably the particulate support material comprises silicon oxide and tungsten oxide in a total amount of from 10 wt% to 15 wt%. In some preferred embodiments, the particulate support material comprises from 4 wt% to 6 wt% silicon oxide, and from 7 wt% to 9 wt% tungsten oxide. The washcoat of the oxidation catalyst article may preferably consist essentially of titanium oxide, silicon oxide and tungsten oxide. Preferably the particulate support material comprises silicon oxide and tungsten oxide in a weight ratio (SiC^WCh) of from 0.5: 1 to 1.5: 1, preferably from 0.5: 1 to 1 : 1, more preferably from 0.5: 1 to 0.8: 1.

[0040] It is well known that when preparing a washcoat it is possible to include further ingredients which are conventional in forming washcoat slurries. These include one or more of a binder and a thickening agent. Binders may include, for example, an oxide material with small particle size to bind the individual insoluble particles together in washcoat slurry. The use of binders in washcoats is well known in the art. Thickening agents may include, for example, a natural polymer with functional hydroxyl groups that interacts with insoluble particles in washcoat slurry. It serves the purpose of thickening washcoat slurry for the improvement of coating profile during washcoat coating onto substrate. It is usually burned off during washcoat calcination. Examples of specific thickening agents / rheology modifiers for washcoats include galactomannan gum, guar gum, xanthan gum, curdlan schizophyllan, scleroglucan, diutan gum, Whelan gum, hydroxymethyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose and hydroxyethyl cellulose.

[0041] Methods of washcoating are well known in the art. The method typically involves a step of applying the washcoat slurry to at least a portion of the substrate to form a washcoated substrate. Disposing the slurry on a substrate may be carried out using techniques known in the art. Typically, the slurry may be poured into the inlet of the substrate using a specific moulding tool in a predetermined amount, thereby disposing the loaded support material on the substrate. Subsequent vacuum and / or air knife and / or and drying steps may be employed during the disposition step. When the support is a filter block, the loaded support material may be disposed on the filter walls, within the filter walls (if porous) or both. A preferred coating method is disclosed in Applicant’s WO 1999 / 047260A1.

[0042] Production of oxidation catalyst article further comprises calcining the washcoated substrate. The term "calcine", or "calcination", means heating the material in air or oxygen. This definition is consistent with the IUPAC definition of calcination. (IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http: / / goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi: 10.1351 / goldbook). The temperatures used in calcination depend upon the components in the material to be calcined and generally are between about 400°C to about 900°C for approximately 1 to 8 hours. In some cases, calcination can be performed up to a temperature of about 1200°C. In applications involving the processes described herein, calcinations are generally performed at temperatures from about 400°C to about 700°C for approximately 1 to 8 hours, preferably at temperatures from about 400°C to about 650°C for approximately 1 to 4 hours.

[0043] Calcining is typically carried out in an oven or furnace, more typically a belt or static oven or furnace, typically in hot air at a specific flow from one direction. The calcining may also comprise an initial drying step. The drying and calcination steps may be continuous or sequential. For example, a separate washcoat may be applied after the substrate is already washcoated and dried with a previous washcoat. A washcoated substrate can also be dried and calcined using one continuous heating program if coating is completed. As a result of the heating (calcination), the substrate is typically substantially free of organic compounds, more typically completely free of organic compounds (such as thickeners).

[0044] Following the heating step, the substrate is typically cooled, more typically to room temperature. The cooling is typically carried out in air with or without cooling agent / media, typically without cooling agent.

[0045] As described herein, the method of treating an exhaust gas from an internal combustion engine running on a mixture of air and hydrogen comprises contacting the exhaust gas from the internal combustion engine with the oxidation catalyst. The oxidation catalyst is highly effective for the oxidation of unbumt H2 in the exhaust gas of the engine to H2O. Additionally, the oxidation catalyst can oxidise NO to NO2, such NOXconversion being particularly advantageous where the method further comprises mixing the exhaust gas from the oxidation catalyst with a nitrogenous reductant and passing the exhaust gas mixture over a catalyst for selectively reducing a mixture of NO and NO2 to N2. A preferred nitrogenous reductant is ammonia (NH3), and optionally, the ammonia reductant may be derived from an ammonia precursor such as urea. Such a method may be referred to as the selective catalytic reduction of NOX, said reduction being promoted by the upstream oxidation of NO to NO2.

[0046] Thus, in preferred embodiments of the system described herein, the exhaust system further comprises: an SCR catalyst for selectively reducing NOXin exhaust gas to N2 with a nitrogenous reducing agent, the SCR catalyst being disposed downstream from the oxidation catalyst; an injector for injecting a nitrogenous reducing agent, or a precursor of a nitrogenous reducing agent, into a flowing exhaust gas between the oxidation catalyst and the SCR catalyst; and a reservoir of the nitrogenous reductant or precursor thereto. Such exhaust system configurations are known in the art for treating Diesel engine exhaust gas (see, e.g., WO99 / 39809A1). The preferred system can also comprise an ammonia slip catalyst disposed downstream from the catalyst for selectively reducing NO and NO2 to N2 for oxidizing NH3 to N2. This ammonia slip catalyst can be coated on the same monolith substrate as the SCR catalyst (see, e.g., W02010 / 062730A2) or on a separate monolith substrate disposed downstream from the SCR monolith substrate.

[0047] Preferably, the exhaust system further comprises: a filter substrate for filtering ash from the exhaust gas, especially PM10 particulates. Ash may be present in the exhaust gas due to combustion of organic engine additives such as engine oil / lubricant. In some embodiments, the filter may be disposed downstream of the oxidation catalyst, preferably between the oxidation catalyst and the injector for injecting a nitrogenous reducing agent (which is itself provided upstream of the SCR catalyst).

[0048] The fuel, and therefore the exhaust gas, may comprise sulphur impurities derived from the hydrogen source, e.g. black / grey hydrogen and / or the engine lubricant, whereby the step of contacting the exhaust gas from the internal combustion engine with the oxidation catalyst results in the formation of a sulphated catalyst.

[0049] In such embodiments, it is preferred that the system further comprises: an engine control unit including a pre-programmed processor unit for periodically controlling fuel delivery to the engine so that the exhaust gas contains an increased vol% of H2 gas relative to normal operating conditions. As such, the method preferably further comprises periodically controlling fuel delivery to the engine so that the exhaust gas contains an increased vol% of H2 gas relative to normal operating conditions thereby contacting the sulphated catalyst with an exhaust gas enriched with hydrogen gas in order to desulphate the catalyst. The method may alternatively, or preferably additionally, comprise periodically heating the oxidation catalyst to a temperature of up to 450°C, preferably from 350°C to 450°C, in order to desulphate the catalyst. The present inventors were surprised to find that the oxidation catalyst described herein is particularly sulphur tolerant, and may be easily regenerated under relatively low temperatures which otherwise typically require greater than 500°C in order to effect desulphation and regeneration of the catalytic activity. EXAMPLES

[0050] The “established coating techniques” used to coat all catalysts in these Examples was the method and apparatus disclosed in WO99 / 47260A1, i.e. a method of coating a monolithic support, comprising the steps of (a) locating a containment means on top of a support, (b) dosing a pre-determined quantity of a liquid component into said containment means, either in the order (a) then (b) or (b) then (a), and (c) by applying vacuum, drawing the entirety of said quantity of liquid component into at least a portion of the support, and retaining substantially all of said quantity within the support, without recycle. Where a 100% axial length coating of the same washcoat is applied, a washcoat is applied from a first end of the substrate to less than the total axial length of the substrate, which is then dried in air at about 120°C before the same washcoat is applied from a second end to coat the remainder of the axial length of the substrate. A small amount of overlap at a join between the two washcoat dose applications may be expected.

[0051] Example 1 - Comparative Sample 1 preparation

[0052] A washcoat slurry was prepared by dispersing 5 wt% silica-doped alumina powder in water and milling it to a d90 < 20 micron. Soluble platinum salts or both soluble platinum and palladium salts were added to the slurry. The mixture was stirred to homogenise. The resulting washcoat was applied to the full axial length of a 1.4 litre volume cordierite flow- through (honeycomb) monolith substrate with 62 cells per square centimetre (400 cells per square inch) using the established coating techniques. The coated part was dried at about 120°C in air and calcined in air at 500°C. The washcoat composition and washcoat loading (g / L) was formulated to obtain a total PGM loading on the substrate of 0.353 g / L (10 g / ft3) at the Pt:Pd weight ratios shown in Table 2 hereinbelow, with the PGM supported on the 5 wt% silica-doped alumina. The total washcoat loading, i.e. the combination of the supported PGM and the 5 wt% silica-doped alumina, on the substrate was 85.4 g / L (1.4 g / in3).

[0053] Core samples were taken from the coated substrates. The cores were hydrothermally aged in an oven at 550°C for 50 hours in an oven box. A constantly replenished gas mixture of compressed air / 20% H2O (water) (equivalent to 20% O2) controlled by mass flow and liquid flow controllers respectively was pumped into the oven box at a flow rate of 5 litres per minute. The honeycomb substrate cores were arranged within the oven box so that the channels extended vertically and the flowing gas mixture was forced to enter the channels of each core disposed within the oven box from a lower end thereof.

[0054] Example 2 - Preparation of Samples

[0055] A number of aged samples according to the invention were prepared similarly to the method disclosed in Comparative Example 1 but using commercially available particulate titania (TiCh) powder or particulate titania doped with silica and / or tungstate instead of the 5 wt% silica-doped alumina powder of Comparative Sample 1. The particulate titania powder supports tested are set out in Table 1 hereinbelow:

[0056] Table 1

[0057] Example 3 - Oxidation activity testing

[0058] The catalytic activity for each core was determined using a synthetic gas laboratory catalytic activity test (SCAT) apparatus. The aged cores were tested using a temperature ramp 80°C to 500°C at 20°C per minute in one of the simulated exhaust gas mixtures shown in Table 2 below, staring with gas mix 1. In each of the gas mixtures, the water (H2O) content was 13 vol%, the oxygen (O2) content was 14 vol%, and the balance nitrogen (N2). The swept volume was 80,000 hr-1. Two successive ramp tests were conducted in each gas mix and the catalyst activity on the second “ramp” is reported hereinbelow. Between each ramp test, the catalyst core sample was allowed to cool to 80°C. Following the second ramp, the catalyst was immediately tested in the next gas mix to be used, starting at 80°C. Table 2

[0059] Example 4 - Results for Pt:Pd weight ratio study using Gas Mix 1 (5,000 ppm H2, 500 ppm

[0060] NO) Table 3

[0061] Example 5 - Results for Pt:Pd weight ratio study using Gas Mix 2 (200 ppm H2, 100 ppm

[0062] NO)

[0063] Table 4 N2O (ppm) emission for all samples was negligible (2.0 ppm maximum).

[0064] In general, it was found that the more NO is present in the exhaust gas, the more H2 oxidation is suppressed. So, for Gas Mix 2 (100 ppm NO), maximal H2 oxidation at temperatures above T50 can be close to 100 vol%, whereas in Gas Mix 1 (500 ppm NO), maximal H2 oxidation may be as low at 20 vol%. Additionally, from the results presented in Examples 4 and 5, it can be seen that, for Pt-only, the doped titania support gave better hydrogen oxidation activity than the Comparative sample with better selectivity for NO oxidation, i.e. comparatively higher NO oxidation at comparatively lower N2O generation. The addition of relatively small amounts of Pd (Pt:Pd weight ratio of 5:1) decreased H2 conversion for Sample 2 relative to Comparative Example 1 and with greater NO selectivity (lower N2O generation).

[0065] Example 6 - Effect of sulphation on oxidation activity and recovery following desulphation

[0066] Aged cores of Comparative Sample 1 and Sample 2 were subjected to a sulphur ageing and testing protocol set out in Table 5. The sulphur ageing steps 2 and 6 were carried out in a separate synthetic catalytic activity test (SCAT) apparatus “off-line” from the SCAT apparatus used to test the H2 oxidation light-off (T50) (steps 1, 3, 5, 7 and 9), and regeneration steps 4 and 8.

[0067] Table 5

[0068] The results for the second “run” of steps 1-9 inclusive for H2 T50 light-off are presented in Table 6, and the results for first “run” NCh / NOx conversion @ 250°C (%) are presented in Table 7. The reason why the second “run” light-off is reported for the H2 oxidation is that it was found that the results for the first “run” showed some activation effect. Only after the second “run” did reproduceable H2 oxidation activity results emerge.

[0069] Table 6 - H2 light-off temperature (T50) From the results presented, it can be seen that the silicon oxide and tungsten oxide doped titania-based Samples (Sample 2) exhibit an unexpectedly large activation of oxidation activity following the initial sulphation through a reduction in the observed T50 light-off temperature. Though there is little onward change in the activity for the Pt-only (1 :0) embodiment of Sample 2, the T50 light-off temperature remains significantly lower that the Comparative Samples, including the Pt:Pd 5:1 example of Sample 2 whose oxidation activity is generally much poorer and broadly similar to the activity of the silicon oxide doped alumina-based Samples.

[0070] Table 7 - Gas Mix 2 NCh / NOx conversion @ 250°C (%)

[0071] From the results presented, it can be seen that Sample 2 shows some sulphur deactivation in NO oxidation. Recovery of activity following regeneration (step 8) occurs with temperatures from 400°C. Greater recovery of activity could be expected at higher temperatures than 400°C as sulphur is driven off the sample, but at an increased energy demand and the potential for TiO2 sintering. It can also be seen that the Pt-only (1 :0) embodiment of Sample 2 is significantly more sulphur tolerant than the Pt:Pd 5: 1 Sample.

[0072] Example 7 - H2 oxidation activity for Sample Nos. 2 to 8

[0073] Newly prepared aged Pt-only samples of Comparative Sample 1 and Sample 2 and Samples 3 to 8 were prepared according to Examples 1 and 2 and tested for hydrogen oxidation activity according to Example 3 using Gas Mixes 1 and 2. The temperature at 50% H2 conversion (T50) (°C) are reported in Table 8 hereinbelow. It will be noted that the comparison H2 T50 results for Comparative Sample 1 and Sample 2 presented in Table 8 show some slight variation with those in Tables 3 and 4 because the comparison presented in Example 6 is of a different - but identically formulated - sample to those in Examples 3, 4 and 5. That is, a fresh comparison of Comparative Sample 1 and Sample 2 was done so that the results in Example 6 are a self-contained, directly comparable data set to remove other variables in testing.

[0074] Table 8

[0075] From the above results, there appears to be a trend for improved H2 oxidation in relatively high H2-, relatively high NO-containing exhaust gas for increased quantities of silica dopant. The presence of tungsten also appears to improve H2 oxidation in exhaust gases containing relatively low H2 and NO concentrations.

[0076] • Under high H2 levels (5,000 ppm H2 and 500 ppm NO) and low H2 levels (200 ppm H2 and 100 ppm NO), alternative titania supports showed a similar H2 conversion to Sample 2. The increased SiCh content in Samples 4 and 5 provide and 5 or 6°C boost under high H2 levels and at least a 6°C boost at low H2 levels.

[0077] • SiCh and WO3 addition to pure titania increased NCh / NOx conversion. SiCh addition however increased the N2O formation whereas WO3 addition decreased it. SiCh WCh ratio around 1 : 1, or WO3 rich, seems to give the best NO2 make.

[0078] • Like Sample 2, the Inventive Samples showed some SOXdeactivation in NO2 and H2 conversion and a good recovery with a 400°C regeneration.

[0079] As used herein, the singular form of “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. The use of the term “comprising” is intended to be interpreted as including such features but not excluding other features and is also intended to include the option of the features necessarily being limited to those described. In other words, the term also includes the limitations of “consisting essentially of’ (intended to mean that specific further components can be present provided they do not materially affect the essential characteristic of the described feature) and “consisting of’ (intended to mean that no other feature may be included such that if the components were expressed as percentages by their proportions, these would add up to 100%, whilst accounting for any unavoidable impurities), unless the context clearly dictates otherwise.

[0080] It will be understood that, although the terms "first", "second", etc. may be used herein to describe, for example, various elements, layers and / or portions, the elements, layers and / or portions should not be limited by these terms. These terms are only used to distinguish one element, layer or portion from another, or a further, element, layer or portion. Spatially relative terms, such as “under”, "below", "beneath", "lower", “over”, "above", "upper" and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s). It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if an article as described herein is turned over, elements described as "under” or “below" other elements or features would then be oriented “over” or "above" the other elements or features. Thus, the example term "under" can encompass both an orientation of over and under. The article may be otherwise oriented and the spatially relative descriptors used herein interpreted accordingly. Numerical lower and upper limits of features described herein may preferably be combined to provide a closed range.

[0081] The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.

[0082] For the avoidance of doubt, the entire contents of all documents acknowledged herein are incorporated herein by reference.

[0083] The present invention will be described further with reference to the following nonlimiting clauses:

[0084] 1. A system comprising:

[0085] (i) an internal combustion 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 (H2);

[0086] (ii) a source of gaseous fuel comprising a majority fuel mass of hydrogen (H2); and

[0087] (iii) an exhaust system for the internal combustion engine comprising an oxidation catalyst for oxidising H2 in an exhaust gas of the engine to H2O; wherein the oxidation catalyst comprises a washcoat coated on a monolith substrate, the washcoat comprising a platinum group metal consisting essentially of platinum, the platinum group metal supported on a particulate support material which is titanium oxide doped with a mixture of silicon oxide and tungsten oxide.

[0088] 2. The system according to clause 1, wherein the monolith substrate is a flow-through monolith.

[0089] 3. The system according to clause 1, wherein the monolith substrate is a wall-flow filter monolith.

[0090] 4. The system according to any one of the preceding clauses, wherein the platinum concentration in the oxidation catalyst on the monolith substrate is from 2 to 120 g / ft3, preferably 5 to 50 g / ft3. 5. The system according to any one of the preceding clauses, wherein the washcoat loading of the particulate support material on the monolith substrate is from 0.2 to 2.0 g / in3, preferably from 0.8 to 1.8 g / in3.

[0091] 6. The system according to any one of the preceding clauses, wherein the particulate support material comprises at least 3 wt% silicon oxide and / or at most 10 wt% silicon oxide.

[0092] 7. The system according to any one of the preceding clauses, wherein the particulate support material comprises at least 3 wt% tungsten oxide and / or at most 10 wt% tungsten oxide.

[0093] 8. The system according to any one of the preceding clauses, wherein the particulate support material comprises at least 80 wt% titanium oxide, preferably from 80 wt% to 90 wt% titanium oxide.

[0094] 9. The system according to any one of the preceding clauses, wherein the particulate support material comprises silicon oxide and tungsten oxide in a weight ratio of from 0.5: 1 to 1.5: 1, preferably from 0.5: 1 to 1 : 1, more preferably from 0.5: 1 to 0.8: 1.

[0095] 10. The system according to any one of the preceding clauses, wherein the particulate support material comprises silicon oxide and tungsten oxide in a total amount of from

[0096] 10 wt% to 15 wt%.

[0097] 11. The system according to any one of the preceding clauses, wherein the particulate support material comprises from 4 wt% to 6 wt% silicon oxide, and from 7 wt% to 9 wt% tungsten oxide.

[0098] 12. The system according to any one of the preceding clauses, wherein the oxidation catalyst is not a three-way catalyst.

[0099] 13. The system according to any one of the preceding clauses, wherein the system further comprises: an engine control unit including a pre-programmed processor unit for periodically controlling fuel delivery to the engine so that the exhaust gas contains an increased vol% of H2 gas relative to normal operating conditions.

[0100] 14. The system according to any one of the preceding clauses, wherein the exhaust system further comprises: an SCR catalyst for selectively reducing NOXin exhaust gas to N2 with a nitrogenous reducing agent, the SCR catalyst being disposed downstream from the oxidation catalyst; an injector for injecting a nitrogenous reducing agent, or a precursor of a nitrogenous reducing agent, into a flowing exhaust gas between the oxidation catalyst and the SCR catalyst; and a reservoir of the nitrogenous reductant or precursor thereto.

[0101] 15. The system according to clause 14, wherein the exhaust system further comprises: an ammonia slip catalyst disposed downstream from the SCR catalyst.

[0102] 16. The system according to any one of the preceding clauses, wherein the internal combustion engine configured to run on a majority fuel mass of hydrogen (H2) is configured to run on a fuel comprising >70 vol% H2, and preferably consisting essentially of H2.

[0103] 17. The system according to any one of the preceding clauses, wherein the exhaust system further comprises: a filter substrate for filtering ash from the exhaust gas.

[0104] 18. The system according to clause 17, wherein the filter substrate is disposed between the oxidation catalyst and the injector.

[0105] 19. A method of treating an exhaust gas from an internal combustion engine running on a mixture of air and fuel, wherein the fuel is a gaseous fuel comprising a majority fuel mass of hydrogen (H2), the method comprising contacting the exhaust gas with an oxidation catalyst as defined in any one of clauses 1 to 18.

[0106] 20. The method according to clause 19, further comprising mixing the exhaust gas from the oxidation catalyst which further comprises NO2 with a nitrogenous reductant and passing the exhaust gas mixture over a catalyst for selectively reducing a mixture of NO and NO2 to N2.

[0107] 21. The method according to clause 19 or clause 20, wherein the nitrogenous reductant is ammonia (NH3), optionally ammonia derived from an ammonia precursor, preferably urea.

[0108] 22. The method according to any one of clauses 19 to 21, wherein the fuel comprises sulphur impurities whereby the step of contacting the exhaust gas with the oxidation catalyst results in a sulphated catalyst, the method further comprising: periodically controlling fuel delivery to the engine so that the exhaust gas contains an increased vol% of H2 gas relative to normal operating conditions thereby contacting the sulphated catalyst with an exhaust gas enriched with hydrogen gas in order to desulphate the catalyst. 23. The method according to any one of clauses 19 to 22, wherein the fuel comprises sulphur impurities whereby the step of contacting the exhaust gas with the oxidation catalyst results in a sulphated catalyst, the method further comprising: periodically heating the oxidation catalyst to a temperature of up to 450°C, preferably from 350°C to 450°C, in order to desulphate the catalyst.

[0109] 24. Use of an oxidation catalyst comprising a platinum group metal consisting essentially of platinum, the platinum group metal supported on a particulate support material which is titanium oxide doped with a mixture of silicon oxide and tungsten oxide, to oxidise H2 to H2O, and optionally NO to NO2, in exhaust gas emitted from an internal combustion engine running on a mixture of air and fuel, wherein the fuel is a gaseous fuel comprising a majority fuel mass of hydrogen (H2).

Claims

CLAIMS:

1. A system comprising:(i) an internal combustion 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 (H2);(ii) a source of gaseous fuel comprising a majority fuel mass of hydrogen (H2); and(iii) an exhaust system for the internal combustion engine comprising an oxidation catalyst for oxidising H2 in an exhaust gas of the engine to H2O; wherein the oxidation catalyst comprises a washcoat coated on a monolith substrate, the washcoat comprising a platinum group metal consisting essentially of platinum, the platinum group metal supported on a particulate support material which is titanium oxide doped with a mixture of silicon oxide and tungsten oxide.

2. The system according to any one of the preceding claims, wherein the platinum concentration in the oxidation catalyst on the monolith substrate is from 2 to 120 g / ft3, preferably 5 to 50 g / ft3.

3. The system according to any one of the preceding claims, wherein the particulate support material comprises from 3 wt% to 10 wt% silicon oxide, and / or from 3 wt% to 10 wt% tungsten oxide.

4. The system according to any one of the preceding claims, wherein the particulate support material comprises at least 80 wt% titanium oxide, preferably from 80 wt% to 90 wt% titanium oxide.

5. The system according to any one of the preceding claims, wherein the particulate support material comprises silicon oxide and tungsten oxide in a weight ratio of from 0.5: 1 to 1.5: 1, preferably from 0.5: 1 to 1 : 1, more preferably from 0.5: 1 to 0.8: 1.

6. The system according to any one of the preceding claims, wherein the particulate support material comprises silicon oxide and tungsten oxide in a total amount of from 10 wt% to 15 wt%.

7. The system according to any one of the preceding claims, wherein the particulate support material comprises from 4 wt% to 6 wt% silicon oxide, and from 7 wt% to 9 wt% tungsten oxide.

8. The system according to any one of the preceding claims, wherein the exhaust system further comprises: an SCR catalyst for selectively reducing NOXin exhaust gas to N2 with a nitrogenous reducing agent, the SCR catalyst being disposed downstream from the oxidation catalyst; an injector for injecting a nitrogenous reducing agent, or a precursor of a nitrogenous reducing agent, into a flowing exhaust gas between the oxidation catalyst and the SCR catalyst; and a reservoir of the nitrogenous reductant or precursor thereto.

9. The system according to claim 8, wherein the exhaust system further comprises: an ammonia slip catalyst disposed downstream from the SCR catalyst.

10. A method of treating an exhaust gas from an internal combustion engine running on a mixture of air and fuel, wherein the fuel is a gaseous fuel comprising a majority fuel mass of hydrogen (H2), the method comprising contacting the exhaust gas with an oxidation catalyst as defined in any one of claims 1 to 9.

11. The method according to claim 10, further comprising mixing the exhaust gas from the oxidation catalyst which further comprises NO2 with a nitrogenous reductant and passing the exhaust gas mixture over a catalyst for selectively reducing a mixture of NO and NO2 to N2.

12. The method according to claim 10 or claim 11, wherein the nitrogenous reductant is ammonia (NH3), optionally ammonia derived from an ammonia precursor, preferably urea.

13. The method according to any one of claims 10 to 12, wherein the fuel comprises sulphur impurities whereby the step of contacting the exhaust gas with the oxidation catalyst results in a sulphated catalyst, the method further comprising: periodically controlling fuel delivery to the engine so that the exhaust gas contains an increased vol% of H2 gas relative to normal operating conditions thereby contacting the sulphated catalyst with an exhaust gas enriched with hydrogen gas in order to desulphate the catalyst.

14. The method according to any one of claims 10 to 13, wherein the fuel comprises sulphur impurities whereby the step of contacting the exhaust gas with the oxidation catalyst results in a sulphated catalyst, the method further comprising: periodically heating the oxidation catalyst to a temperature of up to 450°C, preferably from 350°C to 450°C, in order to desulphate the catalyst.

15. Use of an oxidation catalyst comprising a platinum group metal consisting essentially of platinum, the platinum group metal supported on a particulate support material which is titanium oxide doped with a mixture of silicon oxide and tungsten oxide, to oxidise H2 to H2O, and optionally NO to NO2, in exhaust gas emitted from an internal combustion engine running on a mixture of air and fuel, wherein the fuel is a gaseous fuel comprising a majority fuel mass of hydrogen (H2).

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