Device and method for removing nitrogen oxides from the exhaust gas of lean-burn hydrogen combustion engines

Abstract

A device (1) for removing nitrogen oxides from the exhaust gas of lean-burn hydrogen combustion engines (2) comprises a first catalyst (3) which has a base body (5), a carrier layer (6) made of a metal oxide applied to the base body (5) and an active component (7) made of gold and / or rhodium applied to the carrier layer (6), and in which the nitrogen oxides are converted with hydrogen to ammonia, and a second SCR catalyst (4) arranged downstream of the first catalyst (3) in the flow direction (x) of the exhaust gas, in which nitrogen oxides not converted in the first catalyst (3) are converted with the ammonia produced in the first catalyst (3).

Description

The invention relates to an apparatus and a method for removing nitrogen oxides from the exhaust gas of lean-burn hydrogen combustion engines.A wide variety of devices and methods for removing nitrogen oxides from internal combustion engines are known from the prior art. The known solutions are designed for internal combustion engines operating on the diesel or Otto principle. Noble metal-based three-way catalysts for spark-ignition engines require a combustion process control close to lambda 1 and diesel engines require a combustion process control > lambda 1. hydrogen engines are distinguished by a particularly lean combustion process control of lambda > >1. In addition, the exhaust gas temperature band differs from classic engines by a smaller band width in the engine characteristic map. Due to the significantly larger oxygen excess in hydrogen engines, the use of typical three-way catalysts is not possible. Only NH 3- SCR catalysts are suitable for reducing the nitrogen oxide emissions which occur from hydrogen engines. However, the complexity, installation space and system costs are considerable in this case.At temperatures of more than 250° C., the NO x- emission in lean, i.e. oxygen-rich, combustion exhaust gases is generally reduced by means of selective catalytic reduction, which is also referred to as SCR technology. In the SCR technique, the nitrogen oxides are reduced by ammonia on a V 2 O 5 / WO 3 TO 2- or Fe- or Cu-containing zeolite catalyst. A disadvantage here is the space requirement of the additional tank for the aqueous urea solution, from which ammonia is generated on board the vehicle. Furthermore, it is necessary to re-tank the aqueous urea solution at regular intervals, which means increased effort for users to operate the vehicle.Alternatively, in lean-burn engines of motor vehicles, NO x- storage catalysts which contain platinum, palladium and rhodium and basic NO x- adsorbents, such as Ba(OH) 2, are also used. This so-called NSK technique is based on a cyclical operation in which nitrogen is adsorbed on the storage components. For the regeneration or reduction of the nitrogen oxides, short, rich operating phases (lambda <1) are induced. The NSK technique is, due to the cost intensity of the noble metals and the characteristic intermittent operating mode, suitable for use in mobile applications. The catalysts used are optimized for operation of the internal combustion engine with hydrocarbon-based fuels with regard to function and durability.Furthermore, it is fundamentally known that NO x- reduction with hydrogen as reducing agent (also referred to as H 2- DeNO x ) is an effective method for the removal of nitrogen oxides at low exhaust gas temperatures (<250° C.). The thermodynamically preferred products N 2 and H 2 O are predominantly formed.Such a reaction has been successfully demonstrated, for example, in Esser, E., Kureti, S., Heckemmuller, L., Todt, A. et al., "Low-Temperature NOx Reduction by H2 in Diesel Engine Exhaust," SAE Technical Paper 2022-01-0538, 2022, doi:10.4271 / 2022-01-0538 for a passenger car diesel engine. In this case, the H 2- DeNO x- conversion was developed exclusively for low exhaust gas temperatures of less than 250° C., since the SCR and NSK technologies described above cannot be used there or cannot be used effectively there. In the H 2- DeNO x- catalyst used in this process, platinum was used as the active component.It has already been known for the 1970's that Pt-Al x O 3- catalysts are very efficient and provide high conversions even below 150° C., see, for example, J. H. Jones, J. T. Kummer, K. Otto, M. Sheelef, E. E. Weaver, "Selective catalytic reaction of hydrogen with nitrous oxide in the presence of oxygen", Env. Science & Technology vol. 5, pp. 790-798, 1971; A. Wildermann, "Development of a hydrogen-SCR catalyst for NO x- Reduction in Smoke and Exhaust Gases", Ph.D. Dissertation, University of Erlangen, 1994; E. Frank, H. Oguz, W. Weisweller, "Modeling of kinetic pressures for reduction of NO x by hydrogen in oxygenrich exhausts using a gradient-free loop reactor", Chem. Eng. Technol., vol. 26, no. 6, pp. 679-683, 2003; F. J. P. Schott, P. Balle, J. Adler, and S. Kureti, "Reduction of NO x by H 2 on Pt / WO 3 / ZrO 2 catalysts in oxygenrich exhaust", Appl. Catal. B Environ., vol. 87, no. 1, pp. 18-29, 2009. However, considerable amounts of N 2 O are formed, sometimes even with selectivities of up to 90%. Owing to the high propellant gas potential of N 2 O, this is to be regarded as extremely critical.Significant improvements in activity and especially N 2- selectivity have been made with the methods described in C.N. Costa and A.M. Efstathiou, "Mechanistic aspects often he H 2- SCR of NO on a novel Pt / MgO-CeO 2 catalyst", J. Phys. Chem. C., vol. 111, no. 7, pp. 3010-3020, 2007 and C. N. Costa, P. G. Savva, C. Andronikou, P. S. Lanbrou, K. Polychronopoulou, V. C. Blessi, A. M. Erstathiou, "An Investigation of the NO / H 2 / O 2( lean deNO x) reaction on a highly active and selective Pt / La 0.7 Sr 0.2 Ce 0.1 FeO 3 catalyst at low temperatures", J. Catal., vol. 209. Pp. 456-471, 2002.Furthermore, various metal oxides based on molybdenum, cobalt, sodium or tungsten have been described as effective promoters, for example in Z. Liu, J. Wu, C. Hardace, "Research progress in the selective catalytic reduction of NO x by H 2 in the presence of O 2", Catal. Surv. Asia, vol. 22, pp. 146-155, 2018; Z. Hu, R. T. Yang, "110th An: Recent progress and future challenges in selective catalytic reduction of NO by H 2 in the presence of O 2 ", Ind. Eng. Chem. Res., vol. 58, pp. 10140-10153, 2019, B. France, G. Emig, A. Renken, "Kinetics and mechanism of the reduction of nitrous oxides by H 2 under lean-burn conditions on a Pt-Mo-Co / α-Al 2 O 3 catalyst", Appl. Catal. B: Environ., vol. 19, pp. 45-57, 1998; R. Burch, M. D. Coleman, "An Investigation of Promoter Effects in the Reduction of NO by H 2 under Lean-Burn Conditions", J. Catal., vol. 208, pp. 435-447, 2002; M. Machida, T. Watanabe, "Effect of Na-addition on Catalytic Activity of Pt-ZSM-5 for Low-temperature NO-H 2- O 2 reactions", Appl. Catal. B: Environ., vol. 52, pp. 281-286, 2004. In this context, high DeNO x- conversions and N 2- selectivities of up to 90% have been found, in particular for Pt-WO 3 / ZrO 2- catalysts, see also C. Hahn, M. Endisch, F. J. P. Schott, S. Kureti, "Kinetic modelling often he NO x reduction by H 2 on Pt / WO 3 / ZrO 2 catalyst in success of O 2 ", Appl. Catal. B: Environ., vol. 168, pp. 429-440, 2015.In D.T. Koch, E. Eβer, S. Kureti, and A. Sousa, "H 2- DeNO x catalyst for H 2 combustion engines", MTZ Worldw., vol. 81, no. 6, pp. 30-35, 2002, the current state of the art of H 2- DeNO x- catalysis in lean exhaust gas for hydrogen combustion engines and in E. Eβer, L. Heckemller, A. Todt, T. Morahitz, W. Waiblinger, S. Hossiany, D. Barbarossa, "H 2- DeNO x- Low-temperature NO x reduction by H 2 in the exhaust of diesel engines", FVV Project no. 1319, 2021 for diesel engines is described. The H 2- DeNO x- catalyst used there has a platinum-coated honeycomb body whose noble metal loading is less than 10 g / ft 3. For both the hydrogen and the diesel internal combustion engine, the catalyst has a high efficiency with a relatively low N 2 O selectivity of about 20%. Furthermore, this catalyst is hydrothermally stable and stable to SO x.However, in view of the practical use of the H 2- DeNO x- technique, it is necessary to further reduce the formation of N 2 O and to increase the efficiency of hydrogen for the NO x- reduction, in particular since about 15 to 90% of the hydrogen reacts with the oxygen present in excess and are therefore not available to the H 2- DeNO x- reaction.As described in M. Weich, F. J. P. Schott, M. Bruns, S. Kureti, "NO x reduction by H 2 on WO x / ZrO 2- supported Pd catalysts under lean conditions", Appl. Catal. B: Environ., vol. 275, pp. 117-118, 2012; N. Macleod, R. M. Lambert, "Selective NO x reduction during the H x- NO-O 2 reaction under oxygen-rich conditions over Pd / V 2 O 5 / Al 2 O 3: evidence for in situ ammonia generation", Catal. Lett., vol. 990, no. 3-4, pp. 111-115, 2003; K. Duan, B. Chen, T. Zhu, Z. Liu, "Novel Pd-Au / TiO 2 catalyst for the selective catalytic reduction of NO x by H 2", Appl. Catal. B: Environ., vol. 176-177, pp. 618-626, 2015, palladium was also investigated as an active component for the H 2- DeNO x- reaction in addition to platinum. It has been found that catalysts in which palladium is used as active component on the one hand have a lower activity, but on the other hand have an improved N 2- selectivity than catalysts in which platinum is used as active component. Furthermore, it was observed that the operating window shifts to higher temperatures of up to 250° C.Against the background of the high reactivity of the hydrogen, the H 2- DeNO x- technique therefore addresses almost exclusively the low-temperature range of less than 220° C., which cannot be achieved with the SCR technique. However, the H 2- DeNO x- catalysts equipped with platinum and palladium as active component are not suitable for temperatures of more than 220° C. because of their high H 2- oxidation activity.In J.P. Breen, R. Burch, C. Hardace, C.J. Hill, B. Krutzsch, B. Bandl-Konrad, E. Jobson, L. Cider, P.G. Blakeman, L.J. Peace, "An investigation of the thermal stability and sulphur tolerance of Ag / γ-Al 2 O 3 catalysts for the SCR of NO x with hydrocarbons and hydrogen", Appl. Catal. B: Environ., vol. 70, pp. 36-44, 2007; R. Burch, M. D. Coleman, "An investigation of the NO / H 2 / O 2 reaction on noble-metal catalysts at low temperatures under lean-burn conditions", Appl. Catal. B: Environ., vo. 23, pp. 115-121, 1999; H. Hamada, M. Haneda, "A review of selective catalytic reduction of nitrogen oxides with hydrogen and carbon monoxide", Appl. Catal. A: Gen., vol. 421-422, pp. 1-13, 2012, have described noble metals with lower oxidation efficiency, namely rhodium, iridium and gold, in X. Wang, W. Wen, Y. Su, R. Wang, "Influence of transition metals (M=Co, Fe and Mn) on ordered mesoporous CuM / Ce 2 catalysts and applications in selective catalytic reduction of NO x with H 2 "RSC Adv., vol. 5, pp. 63135-63141, oxides of the transition metals iron, cobalt, copper and manganese, in A. Mahata, K. S. Rawat, I. Choudhuri, B. Pathak "Octahedral Ni nanoclusters (Ni 85) for efficient and selective reduction of nitrous oxide to nitrogen (N 2) ", Sci. Rep., vol. 6, pp. 25590, 2016 nickel and zinc in A. Valiheikki, K. C. Pelliidou, C. M. Kalamaras, T. Koli, M. Huuhtanen, T. Maunula, R. L. Keiski, A. M. Ustathiou "Selective catalytic reduction of (NO x by hydrogen (H 2- SCR) on WO x- promoted Ce z Zr 1-z O 2 solids", Appl. Catal. B: Environ., vol. 156-157, pp. 72-83, 2014 5 zinc. Some of the catalysts show high NO x- conversions of up to 90%, but the catalysts were only tested in the laboratory under conditions which are not very practical, i.e. with low O 2- and H 2 O contents in the gas stream.The most effective catalysts hitherto at temperatures above 200° C. are Cu / CeO 2, partly with Co, Mn and Fe additions, and also Ir / SiO 2 with alkali additions. However, it is to be noted that the range of temperatures above 250° C. in the region of the lean H 2- DeNO x- reaction has not yet been concluded.It is therefore an object of the present invention to provide an apparatus and a method for removing nitrogen oxides from the exhaust gas of lean-burn hydrogen combustion engines, which have a greater efficiency than the known solutions.According to the invention, this object is achieved by the features mentioned in claim 1.The device according to the invention for removing nitrogen oxides from the exhaust gas of lean-burn hydrogen internal combustion engines accordingly has a first catalyst and a second SCR catalyst connected downstream of the first catalyst in the flow direction of the exhaust gas. The first catalyst has a main body, a carrier layer made of a metal oxide applied to the main body and an active component made of gold and / or rhodium applied to the carrier layer. The SCR catalyst can be implemented in a manner known per se and not described in more detail here.While in the first catalyst, among other reactions, the nitrogen oxides are reacted with hydrogen to form ammonia, in the SCR catalyst those nitrogen oxides are reacted with the ammonia generated in the first catalyst that could not be reacted in the first catalyst. The first catalytic converter is thus bifunctional, i.e. it reduces NO x and produces NH 3, which, by the downstream conversion at the second SCR catalytic converter, brings about an additional and thus very efficient NO x- conversion. The first catalyst is accordingly an H 2- DeNO x- catalyst.In this way, particularly at higher exhaust gas temperatures of 200° C. to 500° C., very high NO x- conversions and thus very low NO x- emissions can be achieved downstream of the novel catalyst system formed from the first and the second catalyst connected downstream thereof. The first catalyst of the apparatus according to the invention has good H 2- DeNO x- performance with high NH 3- selectivity and low N 2 O selectivity at the abovementioned high temperatures.The device according to the invention accordingly shows a high and virtually selective NO x- conversion to N 2 without the addition of an additional operating substance (reducing agent NH 3). at temperatures relevant to practice and under oxygen-rich conditions.A further considerable advantage of the solution according to the invention is that, by using the second catalyst operating on the SCR principle, the entrainment of a urea solution in a vehicle using the device can be dispensed with. The installation space thereby released and the weight saving can be used for the transport task in mobile applications.In a very advantageous development of the invention, a hydrogen feed device for feeding hydrogen to the first catalyst can be provided. By means of such a hydrogen supply device, the hydrogen used for the reaction on the first catalyst can be brought very easily to the desired location, namely into the region of the first catalyst. The supply of hydrogen upstream of the catalyst system can thus be realized with the hydrogen supply device. The hydrogen supply device can be formed, for example, by a line extending from a hydrogen tank and opening into the region of the catalyst. However, the hydrogen supply means may be formed by supplying a larger amount of hydrogen than used for the actual combustion to the hydrogen internal combustion engine and supplying this surplus hydrogen to the first catalyst as a slip.According to a further advantageous embodiment of the device according to the invention, a nitrogen oxide sensor arranged upstream of the first catalytic converter in the flow direction of the exhaust gas can be provided. By means of such a nitrogen oxide sensor, the content of nitrogen oxides in the exhaust gas upstream of the first catalytic converter can be measured and the amount of hydrogen to be supplied to the first catalytic converter can be adjusted from the measured result.In order to prevent ammonia which may not be used for reducing nitrogen oxides from leaving the device according to the invention, an ammonia removal catalyst downstream of the second catalyst in the flow direction of the exhaust gas may furthermore be provided.A further advantageous embodiment of the invention provides an H 2- DeNO x- catalyst downstream of the ammonia elimination catalyst in the flow direction of the exhaust gas. Such an H 2- DeNO x- catalyst can remove from the exhaust gas those nitrogen oxides that were not removed by the upstream catalysts at possibly lower exhaust gas temperatures.In order to achieve a compact construction of the device according to the invention, it can furthermore be provided that the first catalytic converter and the second catalytic converter are arranged in a common housing. In such a housing, the ammonia elimination catalyst and / or the H 2- DeNO x- catalyst downstream thereof can also be accommodated, if appropriate. Alternatively, however, it is also possible to accommodate one or more of the catalytic converters in respective separate housings.For the desired conversion of the nitrogen oxides, it has proven to be particularly effective if the metal oxide of the carrier layer of the first catalyst comprises titanium dioxide, silicon dioxide, aluminum dioxide, zirconium oxide, cerium oxide or mixtures thereof, and if the proportion of gold and / or rhodium in the carrier layer is 0.1 to 15 mass %, preferably 0.2 to 9 mass %. For cost reasons, it is expedient here to keep the proportion of rhodium and / or gold as low.A method for removing nitrogen oxides from the exhaust gas of lean-burn hydrogen combustion engines is set forth in claim 8.In this case, the nitrogen oxides are reacted with hydrogen to form ammonia in the first catalyst, and unreacted nitrogen oxides are reacted with the ammonia generated in the first catalyst in the first catalyst in the second catalyst, so that very high NO x- conversions, combined with correspondingly low NO x- emissions, can be achieved, it being possible to dispense with feeding NH 3 and therefore also carrying a urea solution.In an advantageous development of the method, it can be provided that hydrogen is supplied to the first catalyst by means of a hydrogen supply device. By means of such a hydrogen supply device, the hydrogen used for the reaction on the first catalyst can be brought very easily to the desired location, namely into the region of the first catalyst. The hydrogen supply device can be formed, for example, by a line extending from a hydrogen tank and opening into the region of the catalyst. However, it is also possible to supply a larger amount of hydrogen to the hydrogen combustion engine than is used for the actual combustion and to supply this excess hydrogen to the first catalytic converter as a slip.The process according to the invention can be used particularly effectively if the temperature of the exhaust gas is 200° C. to 500° C.An exemplary embodiment of the invention is illustrated in principle below with reference to the drawing.It shows: FIG. 1 shows a schematic illustration of an apparatus according to the invention for removing nitrogen oxides from the exhaust gas of lean-burn hydrogen internal combustion engines; FIG. 2 is a detailed view of the first catalytic converter of the device according to the invention; FIG. 3 shows an enlarged illustration of the first catalytic converter from FIG. 2 ; FIG. 4 shows a diagram in which the NO x- conversion versus temperature is shown when carrying out the process according to the invention; and FIG. 5 shows a graph in which the selectivities of N 2, N 2 O and NH 3 when using the process according to the invention are shown over temperature.FIG. 1 shows an apparatus 1 for removing nitrogen oxides from the exhaust gas of a lean-burn hydrogen internal combustion engine 2, and the hydrogen internal combustion engine 2 is therefore operated with hydrogen as fuel in a manner known per se. The term "lean-burn" means that more combustion air is present than is required for stoichiometric combustion of the fuel in the cylinder. The combustion air ratio λ is therefore >1. The device 1 has a first catalytic converter 3 and a second catalytic converter, which is designed as an SCR catalytic converter 4 and is connected downstream of the first catalytic converter 3 in a flow direction of the exhaust gas denoted by "x".FIGS. 2 and 3 show a more detailed representation of the first catalyst 3. this catalyst has a base body 5, a carrier layer 6 made of a metal oxide applied to the base body 5, and an active component 7 made of gold and / or rhodium applied to the carrier layer 6 or dispersed therein.The main body 5 of the first catalytic converter 3 is preferably designed in honeycomb form, so that the exhaust gas can flow through the holes or channels present in this honeycomb form. The base body 5 can consist of ceramic, metal or another suitable material.The metal oxide of the carrier layer 6 of the first catalyst 3 preferably comprises titanium dioxide, silicon dioxide, aluminum dioxide, zirconium oxide, cerium oxide or mixtures thereof.In the case of the use of titanium dioxide, a mixture of titanium dioxide in the rutile modification and the anatase modification of titanium dioxide is preferably used. The ratio between the rutile modification and the anatase modification is preferably about 50:50.The active component 7 is usually located in the pores of the comparatively porous metal oxide of the carrier layer 6.The second catalytic converter, which is designed as an SCR catalytic converter 4, can have a construction known per se, which is therefore not described in more detail herein. In this context, it is possible to integrate the SCR catalytic converter 4 into a particle filter, i.e. to coat the particle filter with the catalytic converter material. Furthermore, it is possible to arrange a particle filter at a suitable location within the device 1.In the first catalyst 3, the nitrogen oxides present in the exhaust gas of the hydrogen internal combustion engine 2 are reacted with hydrogen to form ammonia (NH 3). The off-gas also contains water (H 2 O), oxygen (O 2) and optionally hydrogen (H 2). The first catalyst 3 converts these substances, in addition to the reaction described in ammonia, also in water, nitrogen and oxygen. Since not all nitrogen oxides are converted in the first catalytic converter 3, nitrogen oxides are also present in the exhaust gas exiting from the first catalytic converter 3, in addition to the reaction products mentioned. These are then reacted in the SCR catalyst 4 with the ammonia generated in the first catalyst 3. Since the reactions taking place in the SCR catalytic converter 4 are known per se, they are not described in any more detail here. By combining the first catalytic converter 3 with the SCR catalytic converter 4 connected downstream thereof, an approximately complete conversion of the nitrogen oxides in the two catalytic converters 3 and 4 can be achieved.In a manner not shown, the device 1 can have an NO x- storage component in which nitrogen oxides can be stored at least temporarily. The NO x- storage component can be formed, for example, by the carrier layer 6, so that nitrogen oxides could also be stored in the first catalytic converter, in addition to the above-described function of the same.In order to ensure that a sufficient amount of hydrogen necessary for the reactions described is present in the region of the first catalyst 3, the apparatus 1 furthermore has a hydrogen feed device 8 for feeding hydrogen to the first catalyst 3. The hydrogen supply device 8 in the present case has a line 8 a lead from a tank 9 to the first catalytic converter 3. If necessary, the pipe 8 acan be omitted, and the hydrogen supply device 8 can be formed by supplying a larger amount of hydrogen to the hydrogen internal combustion engine 2 than is required for the actual combustion. This excess hydrogen can then be fed as a slip to the first catalytic converter 3. For example, the additional hydrogen can also be injected only into a combustion chamber of the hydrogen combustion engine 2. By supplying the hydrogen into the first catalytic converter 3, the amount of ammonia generated in the first catalytic converter 3 and used in the SCR catalytic converter 4 is accordingly also controlled, wherein the ammonia is generated from the nitrogen oxides emitted by the hydrogen internal combustion engine 2 and the supplied hydrogen.The device 1 furthermore has a nitrogen oxide sensor 10 arranged upstream of the first catalytic converter 3 in the flow direction x of the exhaust gas. The latter measures the proportion of the nitrogen oxides contained in the exhaust gas and can thus control the amount of hydrogen supplied to the first catalytic converter 3 via the hydrogen supply device 8, for example via a control device, not shown, to which the nitrogen oxide sensor 10 and the hydrogen supply device 8 are connected.In a manner not shown, the device 1 can have an NH 3- sensor which would be arranged after the first catalyst 3 in the flow direction x and with which the amount of NH 3 flowing through the first catalyst 3 could be measured in order to optimally adapt the above-described H 2- metering. This NH 3- sensor could also be connected to the above-mentioned control device.Downstream of the second catalytic converter 4 in the flow direction x of the exhaust gas is an ammonia removal catalyst 11, which can also be referred to as ammonia slip catalyst. An H 2- DeNO x- catalyst 12 is again connected downstream of this ammonia removal catalyst 11 in the flow direction x of the exhaust gas. Since the structure and operation of the ammonia elimination catalyst 11 and the H 2- DeNO x- catalyst 12 are known per se, they are not described in detail herein.In the illustrated embodiment of the device 1, the first catalyst 3, the second catalyst 4 and in this case also the ammonia removal catalyst 11 and the H 2- DeNO x- catalyst 12 are arranged in a common housing 13. In an embodiment which is not shown, it would also be possible to arrange one or more of the catalytic converters 3 and 4 and optionally 11 and 12 in respective separate housings. These housings would then be connected to suitable leads.With the above-described apparatus 1, a method for removing nitrogen oxides from the exhaust gas of the lean-burn hydrogen internal combustion engine 2 can be performed. In this case, in the first catalytic converter 3, the nitrogen oxides contained in the exhaust gas are reacted with hydrogen to form ammonia. In the SCR catalyst 4, unreacted nitrogen oxides are reacted with the ammonia generated in the first catalyst 3 in the first catalyst 3. Hydrogen is supplied to the first catalyst 3 by the hydrogen supply device 8. The temperature of the exhaust gas is 200° C. to 500° C., preferably 250° C. to 450° C.It can be seen from the two diagrams according to FIGS. 4 and 5 that the apparatus 1 with the two catalysts 3 and 4 exhibits a nitrogen oxide conversion of 98% at about 300° C. at selectivities for N 2 at 91%, NH 3 at 6% and N 2 O at 3%. For the laboratory tests on which the two diagrams are based, 300 mg of granulated catalyst powder (125-250 μm) were fixed in a quartz glass reactor with quartz wool and tested in a temperature range from 200° C. to 450° C. The synthetic exhaust gas with which the studies were carried out was composed as follows: y (O 2): 14 v-v%, y (H 2 O): 16 v-v%, y (NO): 200 ppm, y (H 2): 1 v-v%, y (N 2): balance. The space velocity or reciprocal residence time was virtually 120,000 h -1. Each test point was held constant for at least 20 minutes so that steady-state temperatures and outlet concentrations were established.After passing through the first catalyst 3, a maximum NO x- conversion of 55% was achieved at 300° C. Selectivities were 87% for NH 3, 10 % for N 2 and only 3% for N 2 O. However, the values shown in the diagrams of FIGS. 3 and 4 have been measured after passing through the two catalysts 3 and 4, as already mentioned. As a result, by using the SCR catalyst 4, the NO x unreacted in the first catalyst 3 reacted with the NH 3 formed in the first catalyst 3.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Cited Non-Patent LiteratureEsser, E., Kureti, S., Heckemmuller, L., Todt, A. et al., "Low-Temperature NOx Reduction by H2 in Diesel Engine Exhaust," SAE Technical Paper 2022-01-0538, 2022, doi:10.4271 / 2022-01-0538

[0006] J.H. Jones, J.T. Kummer, K. Otto, M. Sheelef, E.E. Weaver, "Selective catalytic reaction of hydrogen with nitrous oxide in the presence of oxygen", Env. Science & Technology vol. 5, pp. 790-798, 1971

[0007] A. Wildermann, "Development of a hydrogen SCR catalyst for NO x- Reduction in Smoke and Exhaust Gases", PhD. Thesis, University of Erlangen, 1994

[0007] E. France, H. Oguz, W. Weisweller, "Modeling of kinetic expressions for reduction of NO x by hydrogen in oxygen rich exhausts using a gradient-free loop reactor", Chem. Eng. Technol., vol. 26, no. 6, pp. 679-683, 2003

[0007] F. J. P. Schott, P. Balle, J. Adler, and S. Kureti, "Reduction of NO x by H 2 on Pt / WO 3 / ZrO 2 catalysts in oxygen rich exhaust", Appl. Catal. B Environ., vol. 87, no. 1, pp. 18-29, 2009

[0007] C.N. Costa and A.M. Efstathiou, "Mechanistic aspects often he H 2- SCR of NO on a novel Pt / MgO-CeO 2 catalyst", J. Phys. Chem. C., vol. 111, no. 7, pp. 3010-3020, 2007

[0008] C.N. Costa, P.G. Savva, C. Andronikou, P.S. Lanbrou, K. Poly chronopoulou, V.C. Blessi, A.M. Efstathiou, "An Investigation of the NO / H 2 / O 2( lean deNO x) reaction on a highly active and selective Pt / La 0.7 Sr 0.2 Ce 0.1 FeO 3 catalyst at low temperatures", J. Catal., vol. 209. Pp. 456-471, 2002

[0008] Z. Liu, J. Wu, C. Hardace, "Research progress in the selective catalytic reduction of NO x by H 2 in the presence of O 2", Catal. Surv. Asia, vol. 22, pp. 146-155, 2018

[0009] Z. Hu, R.T. Yang, "110th An: Recent progress and future challenges in selective catalytic reduction of NO by H 2 in the presence of O 2 ", Ind. Eng. Chem. Res., vol. 58, pp. 10130-10153, 2019

[0009] B. France, G. Emig, A. Renken, "Kinetics and mechanism of the reduction of nitrous oxides by H 2 under lean-burn conditions on a Pt-Mo-Co / α-Al 2 O 3 catalyst", Appl. Catal. B: Environ., vol. 19, pp. 45-57, 1998

[0009] R. Burch, M. D. Coleman, "An Investigation of promoter effects in the reduction of NO by H 2 under lean-burn conditions", J. Catal., vol. 208, pp. 435-447, 2002

[0009] M. Machida, T. Watanabe, "Effect of Na-addition on catalytic activity of Pt-ZSM-5 for low-temperature NO-H 2- O 2 reactions", Appl. Catal. B: Environ., vol. 52, pp. 281-286, 2004

[0009] C. Hahn, M. Endisch, F. J. P. Schott, S. Kureti, "Kinetic modelling often he NO x reduction by H 2 on Pt / WO 3 / ZrO 2 catalyst in success of O 2 ", Appl. Catal. B: Environ., vol. 168, pp. 429-440, 2015

[0009] D.T. Koch, E. Eβer, S. Kureti, and A. Sousa, "H 2- DeNO x catalyst for H 2 combustion engines", MTZ Worldw., vol. 81, no. 6, pp. 30-35, 2002

[0010] E. Eβer, L. Heckemulller, A. Todt, T. Morahitz, W. Waiblinger, S. Hossey, D. Barbarossa, "H 2- DeNO x- Low-temperature NO x reduction by H 2 in the exhaust of diesel engines", FVV Project no. 1319, 2021

[0010] M. Weich, F. J. P. Schott, M. Bruns, S. Kureti, "NO x reduction by H 2 on WO x / ZrO 2- supported Pd catalysts under lean conditions", Appl. Catal. B: Environ., vol. 275, pp. 117-118, 2012

[0012] Macleod, N., Lambert, R.M., "Selective NO x reduction during the H x- NO-O 2 reaction under oxygen-rich conditions over Pd / V 2 O 5 / Al 2 O 3: evidence for in situ ammonia generation", Catal. Lett., vol. 990, no. 3-4, pp. 111-115, 2003

[0012] Duan, K., Chen, B., Zhu, Z. Liu, "Novel Pd-Au / TiO 2 catalyst for the selective catalytic reduction of NO x by H 2 ", Appl. Catal. B: Environ., vol. 176-177, pp. 618-626, 2015

[0012] J.P. Breen, R. Burch, C. Hardace, C.J. Hill, B. Krutzsch, B. Bandl-Konrad, E. Jobson, L. Cider, P.G. Blakeman, L.J. Peace, "An investigation of the thermal stability and sulphur tolerance of Ag / γ-Al 2 O 3 catalysts for the SCR of NO x with hydrocarbons and hydrogen", Appl. Catal. B: Environ., vol. 70, pp. 36-44, 2007

[0014] R. Burch, M.D. Coleman, "An investigation of the NO / H 2 / O 2 reaction on noble-metal catalysts at low temperatures under lean-burn conditions", Appl. Catal. B: Environ., vo. 23, pp. 115-121, 1999

[0014] H. Hamada, M. Haneda, "A review of selective catalytic reduction of nitrogen oxides with hydrogen and carbon monoxide", Appl. Catal. A: Gen., vol. 421-422, pp. 1-13, 2012

[0014] X. Wang, W. Wen, Y. Su, R. Wang "Influence of transition metals (M=Co, Fe and Mn) on ordered mesoporous CuM / Ce 2 catalysts and applications in selective catalytic reduction of NO x with H 2 " RSC Adv., vol. 5, pp. 63135-63141

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[0014]

Claims

Device (1) for removing nitrogen oxides from the exhaust gas of lean-burn hydrogen internal combustion engines (2), having a first catalyst (3) which has a base body (5), a support layer (6) made of a metal oxide and applied to the base body (5) and an active component (7) made of gold and / or rhodium applied to the support layer (6) and in which the nitrogen oxides are reacted with hydrogen to form ammonia, and having a second SCR catalyst (4) which is connected downstream of the first catalyst (3) in the flow direction (x) of the exhaust gas and in which nitrogen oxides which are not reacted with the ammonia generated in the first catalyst (3) are reacted in the first catalyst (3).Apparatus according to claim 1, characterized bya hydrogen supply device (8) for supplying hydrogen to the first catalyst (3).Device according to Claim 2, characterized bya nitrogen oxide sensor (10) arranged upstream of the first catalytic converter (3) in the flow direction (x) of the exhaust gas.Device according to Claim 1, 2 or 3, characterized byan ammonia removal catalyst (11) arranged downstream of the second catalyst (4) in the flow direction (x) of the exhaust gas.Device according to Claim 4, characterized byan H 2- DeNO x- catalyst (12) which is connected downstream of the ammonia removal catalyst (11) in the flow direction (x) of the exhaust gas.Device according to one of Claims 1 to 5, characterized in that the first catalytic converter (3) and the second catalytic converter (4) are arranged in a common housing (13).Device according to one of Claims 1 to 6, characterized in that the metal oxide of the carrier layer (6) of the first catalyst (3) comprises titanium dioxide, silicon dioxide, aluminium dioxide, zirconium oxide, cerium oxide or mixtures thereof, and in that the proportion of gold and / or rhodium in the carrier layer (6) is 0.1 to 15% by mass, preferably 0.2 to 9% by mass.Method for removing nitrogen oxides from the exhaust gas of lean-burn hydrogen internal combustion engines, wherein in a first catalyst (3) which has a base body (5), a support layer (6) made of a metal oxide and applied to the base body (5) and an active component (7) made of gold and / or rhodium applied to the support layer (6), the nitrogen oxides are reacted with hydrogen to form ammonia, and wherein in a second SCR catalyst (4) which is arranged downstream of the first catalyst (3) in the flow direction (x) of the exhaust gas, unreacted nitrogen oxides are reacted with the ammonia generated in the first catalyst (3) in the first catalyst (3).Method according to Claim 8, characterized in that hydrogen is supplied to the first catalyst (3) by means of a hydrogen supply device (8).Process according to Claim 8 or 9, characterized in that the temperature of the offgas is 200°C to 500°C.

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