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EP-4066923-B1 - CATALYST FOR THE ABATEMENT OF AMMONIA FROM THE EXHAUST OF GASOLINE INTERNAL COMBUSTION ENGINES

EP4066923B1EP 4066923 B1EP4066923 B1EP 4066923B1EP-4066923-B1

Inventors

  • COLOMBO, MASSIMO
  • BRAUN, Carolin
  • SCHMIDT, MARCUS
  • SEYLER, MICHAEL
  • Servais, Philippe

Dates

Publication Date
20260506
Application Date
20210330

Claims (12)

  1. Catalyst comprising a carrier body having a length L extending between a first end face and a second end face, and differently composed material zones A, B and C arranged on the carrier body, wherein - material zone A comprises rhodium and/or nickel and/or cerium, - material zone B comprises platinum, and - material zone C comprises a zeolite which is able to store ammonia and to catalyze the selective catalytic reduction of NOx, and optionally a material zone D which comprises a zeolite which is able to store ammonia and to catalyze the selective catalytic reduction of NOx, characterized in that , material zones A, B, C and if present material zone D are present in the form of coatings on the carrier body; andmaterial zone A extends starting from the first end face of the carrier body over 10 to 90 % of the length L, material zone B extends starting from the second end face of the carrier body over 10 to 90 % of the length L and material zone C extends starting from the second end face of the carrier body over 10 to 90 % of the length L, wherein L = LA + LB, wherein LA is the length of material zone A and LB is the length of the material zone B and wherein material zone C is located on top of material zone B.
  2. Catalyst according to claim 1, characterized in that material zone A comprises rhodium in an amount of 0.01 to 1 g/l, based on the volume of the carrier body and calculated as rhodium metal.
  3. Catalyst according to claim 1 and/or 2, characterized in that material zone A comprises nickel in an amount of 1 to 100 g/l, based on the volume of the carrier body and calculated as NiO.
  4. Catalyst according to one or more of claims 1 to 3, characterized in that material zone A comprises cerium in an amount of 1 to 100 g/l, based on the volume of the carrier body and calculated as CeO2.
  5. Catalyst according to one or more of claims 1 to 4, characterized in that material zone B comprises platinum supported on aluminum oxide.
  6. Catalyst according to one or more of claims 1 to 5, characterized in that material zone C comprises Cu-AEI, Cu-CHA or Fe-BEA.
  7. Catalyst according to one or more of claims 1 to 6, characterized in that it comprises a material zone D which comprises a zeolite which is able to store ammonia and to catalyze the selective catalytic reduction of NOx.
  8. Catalyst according to claim 7, characterized in that material zones C and D contain the identical components in the identical amounts.
  9. Catalyst according to claim 1, characterized in that material zone A extends starting from the first end face of the carrier body over 10 to 90 % of the length L, material zone B extends starting from the second end face of the carrier body over 10 to 90 % of the length L material zone C extends starting from the second end face of the carrier body over 10 to 90 % of the length L, and material zone D extends starting from the first end face of the carrier body over 10 to 90 % of the length L, wherein L = LA + LB = LC + LD, wherein LA is the length of material zone A, LB is the length of the material zone B, LC is the length of material zone C and LD is the length of material zone D and wherein material zone C is located on top of material zone B and material zone D is located on top of material zone A.
  10. Catalyst according to claim 9, characterized in that material zones A, B, C and D all extend over 50 % of the length L and material zones C and D are identical.
  11. Method for eliminating ammonia from gasoline exhaust gases, characterized in that the gasoline exhaust gas is conducted through a catalyst according to one or more of claims 1 to 9.
  12. Exhaust gas purification system which comprises a three-way catalyst and a catalyst according to one or more of claims 1 to 9.

Description

The present invention relates to a catalyst for the abatement of ammonia from the exhaust of gasoline internal combustion engines which comprises several material zones. It is well known in the field of combustion engines that fuel combustion is not complete and yield emissions of pollutants like unburned hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx) and particulate matter (PM). In order to improve air quality, emission limits legislations are in place to achieve lower emissions of pollutants from stationary applications and from mobile sources. For mobile sources like passenger cars, primary measures enabled achieving decrease in the emission of pollutants. Improvement of fuel-air mixing as primary measure yielded considerable diminution of pollutants. However, due to more stringent legislations over the years, the use of heterogeneous catalysts has been made inevitable. For gasoline engines, the so-called three-way catalyst (TWC) enables the elimination of HC, CO and NOx. Optimal use of the TWC is around Lambda = 1 +/-0.005 where the air/fuel ratio is equal to 14.56. Above these values, the exhaust gas is said lean, and CO and HC are catalytically oxidized to carbon dioxide and water. Below this value, the exhaust gas is said rich and mainly NOx is reduced to nitrogen N2 using e.g. CO as reducing agent. Optimal conversion of HC, CO and NOx is achieved at Lambda = 1. However, gasoline engines operate under oscillating conditions between slightly lean and slightly rich conditions. Under purely rich conditions, the conversion of hydrocarbon drops rapidly. In order to broaden the optimal operation of a TWC, oxygen storage material (OSM) in the form of Ce-mixed oxides were included in the formulation of the TWC. Under certain operating conditions ammonia can be formed on TWC catalysts, resulting in ammonia being present in the exhaust stream. This is undesirable in view of its toxic effects and consequently ammonia emissions are increasingly limited in the exhaust gas legislation. To avoid ammonia emissions, so called ammonia slip catalysts (ASC) have been developed and are mainly used in the exhaust gas of modern Diesel engines. ASC catalysts normally contain a platinum group metal (PGM) component, in particular platinum, to carry out the oxidation of ammonia at temperatures as low as possible. However, PGM based materials do not only oxidize ammonia to nitrogen, but can as well form nitrogen oxides, in particular N2O, NO and NO2. To improve the selectivity of the ammonia oxidation component, it is usually combined with an SCR catalyst which is to re-reduce the nitrogen oxides formed. SCR catalyst which can be used are for example zeolite based or vanadium based in different spatial arrangements. In case of a layered arrangement the SCR layer is normally overcoating the PGM containing layer. This concept cannot easily be exceeded on the exhaust of gasoline engines, because ammonia cannot be oxidized in rich exhaust gas exhausted by the gasoline engine. Consequently, a different working mode is needed in case of the application of an ASC catalyst to the exhaust gas of gasoline engines. During rich phase operation, the SCR layer acts as a buffer, storing the ammonia that is produced by the upstream TWC. During lean phase operations when oxygen is present in the exhaust stream, ammonia can be oxidized by the PGM layer. Such an operating mode has the following limitations. First, the amount of ammonia that can be stored is limited to the ammonia storage capacity of the SCR layer. Once the capacity is reached, ammonia emissions will occur. This problem might be even more severe after catalyst ageing, which typically results in a loss of ammonia storage capacity. Second, the ammonia stored on the SCR layer at a given temperature can desorb at any time following a temperature increase. If such a temperature increase occurs during rich operation, the ammonia will not be converted by the ASC catalyst, resulting in ammonia emissions. Therefore, a solution is needed to overcome these limitations and further reduce the possibility of ammonia emissions in the exhausts of gasoline engines. GB1453456A discloses catalysts which decompose ammonia to nitrogen and hydrogen. Such catalysts include NiO and NiO containing materials. It is said that catalysts which contain large amounts of NiO (approximately over 50 Mol%) exhibit a substantial catalytic action for the decomposition of ammonia. EP0723805A2 describes a process which comprises converting NOx components to ammonia in a reducing atmosphere (e.g. via a three-way catalyst) and resolving the ammonia via an NH3 decomposing catalyst in an oxidizing atmosphere when the temperature of the catalyst is in a predetermined temperature range. EP3782726A1 discloses a catalyst for ammonia conversion according to the prior art, comprising a carrier substrate on which are arranged two differently composed material zones. It has now been found that the catalyst describe