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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
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  • B01J37/024—Multiple impregnation or coating
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  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively
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  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/46—Removing components of defined structure
  • B01D53/54—Nitrogen compounds
  • B01D53/56—Nitrogen oxides
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  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
  • B01D53/9404—Removing only nitrogen compounds
  • B01D53/9409—Nitrogen oxides
  • B01D53/9413—Processes characterised by a specific catalyst
  • B01D53/9422—Processes characterised by a specific catalyst for removing nitrogen oxides by NOx storage or reduction by cyclic switching between lean and rich exhaust gases (LNT, NSC, NSR)
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  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
  • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/024—Multiple impregnation or coating
  • B01J37/0246—Coatings comprising a zeolite
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  • B01D2255/2042—Barium
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  • B01D2255/9022—Two layers
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  • B01D2255/908—O2-storage component incorporated in the catalyst
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/90—Physical characteristics of catalysts
  • B01D2255/91—NOx-storage component incorporated in the catalyst
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/90—Physical characteristics of catalysts
  • B01D2255/912—HC-storage component incorporated in the catalyst
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2258/00—Sources of waste gases
  • B01D2258/01—Engine exhaust gases
  • B01D2258/012—Diesel engines and lean burn gasoline engines
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/70—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65
  • B01J29/72—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65 containing iron group metals, noble metals or copper
  • B01J29/74—Noble metals
  • B01J29/7415—Zeolite Beta

Definitions

• the present invention relates to an NOx storage catalyst with improved hydrocarbon conversion activity, as well as to a method for the treatment of automobile exhaust gas and to a treatment system for an automobile exhaust gas stream.
• JP 1 1226415 A and JP 1130021 1 A respectively disclose a NOx storage catalyst comprising a first layer on a substrate which contains a nitrogen oxide storage material, and a second layer provided on the first layer which contains a hydrocarbon trapping material supporting a selective catalytic reduction catalyst.
• EP 935055 A additionally teaches the introduction of an intermediate layer to these layers, wherein said layer essentially consists of alumina and/or silica and is free of noble metal, for improving the thermal stability of the active components of the first and third layers.
• JP 2005169203 A discloses a multilayer NOx trap containing a hydrocarbon trap layer on a substrate and upper layers disposed on the hydrocarbon trap layer which contain a nitrogen oxide storage material and a selective reduction catalyst. Said NOx traps, however, display a decreased conversion rate with respect to hydrocarbons, NOx and CO during the cold start period of exhaust gas treatment compared to NOx traps devoid of the hydrocarbon trapping functionality.
• the object of the present invention is to provide an improved NOx storage catalyst, as well as an improved method for the treatment of automobile exhaust gas and an improved treatment system for an automobile exhaust gas stream.
• the NOx storage catalyst according to the present invention displays an improved hydrocarbon conversion activity, wherein the catalyst's activity towards the conversion of CO and NOx remains practically unaffected.
• the object of the present invention may be achieved.
• a nitrogen oxide storage catalyst comprising: a substrate;
• a first washcoat layer provided on the subtstrate, the first washcoat layer com- prising a nitrogen oxide storage material
• the second washcoat layer comprising a hydrocarbon trap material
• hydrocarbon trap material comprises substantially no element or compound in a state in which it is capable of catalyzing selective catalytic reduction, pref- erably wherein the hydrocarbon trap material comprises substantially no element or compound in a state in which it is capable of catalyzing a reaction wherein nitrogen oxide is reduced to N 2 ,
• said catalyst further comprising a nitrogen oxide conversion material which is either comprised in the second washcoat layer and/or in a washcoat layer provided between the first washcoat layer and the second washcoat layer.
• the substrate any material may be used provided that it may support the washcoat layers of the nitrogen oxide storage catalyst and that it is resistant to the conditions which reign during the exhaust gas treatment process.
• the substrate according to the present invention may be of any conceivable shape, provided that it allows for the fluid contact with at least a portion of the washcoat layers present thereon.
• the substrate is a monolith, wherein more preferably the monolith is a flow-through monolith.
• Suitable substrates include any of those materials typically used for preparing catalysts, and will usually comprise a ceramic or metal honeycomb structure.
• the monolithic substrate contains fine, parallel gas flow passages extending from an inlet to an outlet face of the substrate, such that passages are open to fluid flow (referred to as honeycomb flow through substrates).
• the passages which are essentially straight paths from their fluid inlet to their fluid outlet, are defined by walls on which the washcoats are disposed, so that the gases flowing through the passages contact the catalytic material.
• the flow passages of the monolithic substrate are thin-walled channels, which can be of any suitable cross-sectional shape and size such as trapezoidal, rectangular, square, sinusoidal, hexagonal, oval, or circular.
• Such structures may contain up to 900 gas inlet openings (i.e., cells) per square inch of cross section, wherein according to the present invention structures preferably have from 50 to 600 openings per square inch, more preferably from 300 to 500, and even more preferably from 350 to 400.
• the nitrogen oxide storage catalyst comprises a substrate which is a monolith, preferably a flow-through monolith, more preferably a flow-through monolith having a honeycomb-structure.
• the nitrogen oxide storage catalyst incorporates the function of a catalyzed soot filter.
• the substrate is preferably a honeycomb wall flow filter, wound or packed fiber filter, open- cell foam, or sintered metal filter, wherein wall flow filters are particularly preferred.
• Useful wall flow substrates have a plurality of fine, substantially parallel gas flow passages extending along the longitudinal axis of the substrate. Typically, each passage is blocked at one end of the substrate body, with alternate passages blocked at opposite end-faces.
• Particularly preferred wall flow substrates for use in the present invention include thin porous walled honeycomb monoliths, through which the fluid stream passes without causing too great an increase in back pressure or pressure across the nitrogen oxide storage catalyst.
• Ceramic wall flow substrates used in the present invention are prefer- ably formed of a material having a porosity of at least 40%, preferably from 40 to 70%, and having a mean pore size of at least 5 microns, preferably from 5 to 30 microns. Further preferred are substrates having a porosity of at least 50% and having a mean pore size of at least 10 microns.
• the substrate can be made from materials commonly known in the art.
• porous materials are preferably used as the substrate material, in particular ceramic and ceramic-like materials such as cordierite, ⁇ -aiumina, an a!uminosi!icate, cordierite-aiumina, silicon carbide, aluminum titanate, silicon nitride, zirconia, muliite, zircon, zircon muliite, zircon silicate, sillimanite, a magnesium silicate, petalite, spodu- mene, alumina-silica-magnesia and zirconium silicate, as well as porous refractory metals and oxides thereof.
• ceramic and ceramic-like materials such as cordierite, ⁇ -aiumina, an a!uminosi!icate, cordierite-aiumina, silicon carbide, aluminum titanate, silicon nitride, zirconia, muliite, zircon, zircon muliite, zircon silicate, sillimanite, a
• refractory metal refers to one or more metals selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Re.
• the substrate may also be formed of ceramic fiber composite materials.
• the substrate is preferably formed from cor- dierite, silicon carbide, and/or from aluminum titanate. In general, materials are preferred which are able to withstand the high temperatures to which a NOx storage catalyst is exposed to, in particular when used in the treatment of automotive exhaust gas.
• the loading of the catalytic composition on a wall flow substrate will depend on substrate properties such as porosity and wall thickness.
• the substrates useful for the catalysts of embodiments of the present invention may also be metallic in nature and be composed of one or more metals or metal alloys.
• the metallic substrates may be employed in various shapes such as corrugated sheet or monolithic form.
• Suitable metallic supports include the heat resistant metals and metal alloys such as titanium and stainless steel as well as other alloys in which iron is a substantial or major component.
• Such alloys may contain one or more of nickel, chromium and/or aluminum, and the total amount of these metals may advantageously comprise at least 15 wt.-% of the alloy, e.g., 10-25 wt.-% of chromium, 3-8 wt.-% of aluminum and up to 20 wt.-% of nickel.
• the alloys may also contain small or trace amounts of one or more other metals such as manganese, copper, vanadium, titanium and the like.
• the surface or the metal substrates may be oxidized at high temperatures, e.g., 1000°C and higher, to improve the resistance to corrosion of the alloys by forming an oxide layer on the surfaces the substrates. Such high temperature-induced oxidation may enhance the subsequent adherence of the washcoat compositions to the sub- strate.
• the first washcoat layer further comprises an oxygen storage component. In principle, any oxygen storage component may be used, provided that it may reversibly store oxygen.
• said oxygen storage component comprises at least one compound selected from the group consisting of zirconia, ceria, baria, !anthana, praseodymia, neodymia, and mixtures thereof.
• the oxygen storage component comprises ceria and/or zirconia, wherein even more preferably the oxygen storage component comprises ceria.
• any possible loading of the oxygen storage component may be chosen in the first washcoat layer, provided that a sufficient amount of oxygen may be stored for the oxidation processes taking place in the NOx storage catalyst and that the function of the remaining components comprised in the NOx storage catalyst is not impaired.
• the loading of an oxygen storage component in the first washcoat layer may range from 0.1 to 3.0 g/in 3 , with respect to the weight of the metal contained in the respective compound, wherein the loading of the oxygen storage component preferably ranges from 0.3 to 2.0 g/in 3 , more preferably from 0.5 to 1.5 g/in 3 , even more preferably from 0.7 to 1.2 g/in 3 , even more preferably from 0.75 to 1.15 g/in 3 , and even more pre- ferably from 0.8 to 0.95 g/in 3 .
• the first washcoat layer comprises at least one platinum group metal, wherein within the meaning of the present invention the platinum group metals are Ru, Rh, Pd, Os, Ir, and Pt.
• the at least one platinum group metal comprised in the first washcoat layer is Pt and/or Pd.
• the one or more platinum group metal will typically be present in the first washcoat layer in an amount of up to 200 g/ft 3 , preferably in an amount of from 10 to 150 g/ft 3 , more preferably from 15 to 100 g/ft 3 , more preferably from 20 to 80 g/ft 3 , more preferably from 30 to 70 g/ft 3 , and even more preferably of from 35 to 65 g/ft 3 .
• the loading thereof in said layer is generally in the range of 10 to 100 g/ft 3 , preferably in the range of from 15 to 80 g/ft 3 , more preferably in the range of from 20 to 70 g/ft 3 , and even more preferably in the range of from 30 to 60 g/ft 3 .
• the loading thereof in said layer is generally in the range of from 1 to 30 g/ft 3 , preferably in the range of from 2 to 15 g/ft 3 , more preferably in the range of from 3 to 10 g/ft 3 , more preferably in the range of from 4 to 8 g/f tt 3 , more preferably in the range of from 5 to 7 g/ft J , and even more preferably in the range of from 6 to 6.5 g/ft 3 .
• a nitrogen oxide conver- sion material is at least comprised in a washcoat layer provided between the first and second washcoat layers
• at least one platinum group metal is present in the first washcoat layer, preferably in an amount of from 15 to 70 g/ft 3 , more preferably from 20 to 50 g/ft 3 , more preferably from 25 to 45g/ft 3 , and even more preferably of from 30 to 40 g/ft 3 .
• the loading thereof in said layer is comprised in the range of from 10 to 50 g/ft 3 , more preferably in the range of from 15 to 45 g/ft 3 , more preferably in the range of from 20 to 40 g/ft 3 , and even more preferably in the range of from 25 to 35 g/ft 3 .
• a " nitrogen oxide conversion material is at least comprised in a washcoat layer provided between the first and second washcoat layers
• at least one platinum group metal is present in the first washcoat layer, preferably in an amount of from 30 to 100 g/ft 3 , more preferably from 50 to 85 g/ft 3 , more preferably from 55 to 80 g/ft 3 , more preferably of from 60 to 75 g/ft 3 , and even more preferably of from 65 to 70 g/ft 3 .
• the loading thereof in said layer is comprised in the range of from 25 to 95 g/ft 3 , more preferably in the range of from 45 to 80 g/ft 3 , more preferably in the range of from 50 to 75 g/ft 3 , more preferably in the range of from 55 to 70 g/ft 3 , and even more preferably in the range of from 60 to 65 g/ft 3 .
• a nitrogen oxide conversion material is at least comprised in the second washcoat layer
• at least one platinum group metal is present in the first washcoat layer, pre- ferably in an amount of from 30 to 100 g/ft 3 , more preferably from 50 to 85 g/ft 3 , more preferably from 55 to 80 g/ft 3 , more preferably of from 60 to 75 g/ft 3 , and even more preferably of from 65 to 70 g/ft 3 .
• the loading thereof in said layer is comprised in the range of from 25 to 95 g/ft 3 , more preferably in the range of from 45 to 80 g/ft 3 , more preferably in the range of from 50 to 75 g/ft 3 , more preferably in the range of from 55 to 70 g/ft 3 , and even more preferably in the range of from 60 to 65 g/ft 3 .
• the first washcoat layer comprises one or more platinum group metals
• said layer further comprises metal oxide support particles, wherein preferably at least part of the metal oxide support particles support at least part of the at least one platinum group metal.
• the first washcoat layer may contain any possible amount of metal oxide support particles, provided that the function of the remaining components comprised in the NOx storage catalyst is not impaired, in general, the loading of the metal oxide component comprised in the first washcoat layer may range from 1.0 to 5.0 g/in 3 , and preferably ranges from 1.5 to 4.5 g/in 3 , more preferably from 2.0 to 4.2 g/in 3 , and even more preferably from 2.2 to 4.0 g/in 3 .
• any metal oxide particles may be used in the first washcoat layer, provided that they may adequately support the at least one platinum group metal and that they can withstand the conditions encountered during the treatment of automotive exhaust gas, in particular with respect to. the temperatures incurred by the NOx storage catalyst.
• high surface area refractory metal oxide supports such as alumina support materials, also referred to as “gamma alumina” or “activated alumina,” are used. Said materials typically exhibit a BET surface area ranging from 60 to 200 m 2 /g or higher.
• Such activated alumina is usually a mixture of the gamma and delta phases of alumina, but may also contain substantial amounts of eta, kappa and theta alumina phases.
• Refractory metal oxides other than activated alumina can be used as a support for at least some of the catalytic components.
• bulk ceria, zirconia, alpha alumina and other materials are known for such use. Although many of these materials suffer from the disadvantage of having a considerably lower BET surface area than activated aiumina, that disadvantage tends to be offset by a greater durability of the resulting catalyst.
• BET surface area has its usual meaning of referring to the Brunauer, Emmett, Teller method for determining surface area by N 2 adsorption. Pore diameter and pore volume can also be determined using BET-type N 2 adsorption.
• the active alumina has a specific surface area comprised in the range of from 60 to 350 m 2 /g, and typically 90 to 250 m 2 /g.
• the metal oxide support particles comprise at least one compound selected from the group consisting of alumina, silica, titania, silica-alumina, titania-alumina, zirconia, zirconia-alumina, ba- ria-alumina, ceria, ceria-alumtna, baria-ceria-alumina, lanthana-alumina, lanthana- zirconia-aiumina, baria-lanthana-alumina, baria-lanthana-neodymia-alumina, zirconia- silica, titania-silica, titania-zirconia, and mixtures thereof, more preferably at least one compound selected from the group consisting of ceria, baria-alumina, ceria-alumina, baria-ceria-alumina, and mixtures thereof, wherein even more preferably at least part of the metal oxide support particles comprise ceria and/or
• the metal oxide support particles comprised in the first washcoat layer may be doped with one or more compounds.
• the metal oxide support, preferably alumina, comprised in the first washcoat layer is preferably doped with ceria and/or baria, preferably with from 5 to 60 wt.-% of at least one of said compounds, more preferably with from 10 to 50 wt.- %, more preferably with from 20 to 40 wt.-%, more preferably with from 25 to 35 wt.-%, and even more preferably from 28 to 32 wt.-%.
• the ratio of baria to ceria generally ranges from 4 : 1 to 1 ; 2, preferably from 3 : 1 to 1 : 1, more preferably from 5 : 2 to 3 : 2, and even more preferably from 2.2 : 1 to 1.8 : 1.
• any conceivable element or compound may be used, either alone or in combination with further elements or compounds, provided that said element or compound is capable of reversib!y fixing nitrogen oxide.
• the nitrogen oxide storage material is chosen such that it is capable of binding nitrogen oxide at lower temperatures and subsequently releasing it at higher temperatures, in particular at temperatures at which effective catalytic conversion thereof may be achieved. More specifically, lower temperatures as used in the present context refer to those encountered in automotive exhaust gas purification during cold start conditions, prior to which the engine is at most at ambient temperature.
• Higher temperatures refer to those temperatures encountered when the exhaust gas system has attained a temperature at which it is fully operative with respect to exhaust gas treatment, in particular with respect to the conversion efficiency of nitrogen oxide emissions.
• conversion is used in the sense that it encompasses both the chemical conversion of emissions to other compounds, as well as the trapping of emissions by chemical and/or adsorptive binding to an appropriate trapping material. This applies in particular to the cold start periods in the treatment of automotive exhaust gas, since the effective trapping of emissions ideally has the effect of temporarily storing them until efficient conversion thereof may be achieved in the hotter phases of exhaust gas treatment.
• Emissions as used in the context of the present invention preferably refers to exhaust gas emissions, more preferably to exhaust gas emissions comprising NOx, CO, and hydrocarbons, and even more preferably to NOx, CO, and hydrocarbons comprised in automotive exhaust gas.
• nitrogen oxide storage materials are preferred which comprise at least one metal compound selected from the group consisting of alkali metal compounds, alkaline earth metal compounds, rare earth metal compounds, and mixtures thereof, preferably from the group consisting of alkaline earth metal compounds, rare earth metal compounds, and mixtures thereof.
• Preferred alkaline earth metal and rare earth metal compounds are the respective oxides of said compounds.
• the preferred nitrogen oxide storage materials of the present invention those are further preferred which comprise at least one element selected from the group consisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Ce, La, Pr, Nd, and mixtures thereof, preferably from the group consisting of Mg, Ba, Ce, and mixtures thereof, wherein the nitrogen oxide storage material preferably comprises Mg and/or Ba.
• the nitrogen oxide storage material preferably comprises Mg and/or Ba.
• the nitrogen oxide storage material thus preferably comprising magnesia and/or baria.
• any possible loading of the nitrogen oxide storage material may be chosen, provided that a sufficient amount of nitrogen oxide may be stored, and that the function of the remaining components comprised in the NOx storage catalyst is not impaired.
• the loading of the nitrogen oxide storage material in the first washcoat layer may range from 0.05 to 1.0 g/in 3 , with respect to the weight of the metal contained in the respective compound, wherein the loading preferably ranges from 0.10 to 0.8 g/in 3 , more preferably from 0.15 to 0.6 g/in 3 , more preferably from 0.20 to 0.55 g/in 3 , and even more preferably from 0.25 to 0.50 g/in 3 .
• any conceivable element or compound may be used, either alone or in combination with further elements or compounds, provided that said element or compound is capable of converting nitrogen oxide, preferably of converting nitrogen oxide to diatomic nitrogen.
• the conversion of nitrogen oxide in the nitrogen oxide conversion material is primarily achieved by chemical conversion thereof to another compound, preferably to diatomic nitrogen.
• conversion of nitrogen oxide in the nitrogen oxide conversion material is substantially achieved by chemi- cal conversion thereof to another compound.
• said material comprises an oxygen storage component.
• any oxygen storage component may be used, provided that it may reversibly store oxygen.
• the oxygen storage component of the nitrogen oxide conversion material comprises at least one compound selected from the group consisting of zirconia, ceria, baria, ianthana, pra- seodymia, neodymia, and mixtures thereof. More preferably, the oxygen storage component comprises ceria and/or zirconia, wherein even more preferably the oxygen sto- rage component comprises ceria.
• any possible loading of the oxygen storage component may be chosen, provided that a sufficient amount of oxygen may be stored for the oxidation processes taking place in the NOx storage catalyst and that the function of the remaining compo- nents comprised in the NOx storage catalyst is not impaired.
• the loading of an oxygen storage component in the second washcoat layer may range from 0.1 to 1.5 g/in 3 , wherein the loading of the oxygen storage component preferably ranges from 0.2 to 1.2 g/in 3 , more preferably from 0.3 to 1.0 g/in 3 , more preferably from 0.4 to 0.9 g/in 3 , more preferably from 0.45 to 0.8 g/in 3 , and even more preferably from 0.50 to 0.75 g/in 3 .
• the nitrogen oxide conversion material comprises at least one platinum group metal.
• the nitrogen oxide conversion materia! comprises at ieast one platinum group metal selected from the group consisting of Pt, Pd, Rh, and mixtures thereof, wherein more preferably the at Ieast one platinum group metal is Pt and/or Rh, and even more preferably the nitrogen oxide conversion material comprises Pt and Rh, preferably, Pt, Pd, and Rh.
• the one or more platinum group metal may be present in an amount of up to 200 g/ft 3 , preferably from 10 to 150 g/ft 3 , more preferably from 20 to 120 g/ft 3 , more preferably from 30 to 100 g/ft 3 , more preferably from 40 to 90 g/ft 3 , more preferably from 45 to 85 g/ft 3 , and even more preferably from 50 to 80 g/ft 3 .
• the loading thereof in said layers may respectively range from 10 to 150 g/in 3 , wherein the loading of Pt is preferably from 20 to 100 g/in 3 , more preferably from 30 to 90 g/in 3 , more preferably from 35 to 80 g/in 3 , and even more preferably from 40 to 75 g/in 3 .
• the respective loading of said platinum group metals in said layers is generally in the range of from 1 to 15 g/in 3 , and preferably in the range of from 1.5 to 12 g/in 3 , more preferably in the range of from 2.0 to 10 g/in 3 , more preferably in the range of from 2.5 to 9 g/in 3 , more preferably in the range of from 3.0 to 8 g/in 3 , more preferably in the range of from 3.5 to 7 g/in 3 , and even more preferably in the range of from 4.0 to 6.5 g/in 3 .
• the amount of Pd is generally in the range of from 1 to 8 g/in 3 , and preferably in the range of from 2 to 7 g/in 3 , more preferably of from 2.5 to 6 g/in 3 , more preferably of from 3.0 to 5 g/in 3 , and even more preferably of from 3.5 to 4.5 g/in 3
• the amount of Rh is generally in the range, of from 1 to 15 g/in 3 , and preferably in the range of from 2 to 12 g/in 3 , more preferably of from 3 to 10 g/in 3 , more preferably of from 4 to 9 g/in 3 , more preferably of from 5 to 8 g/in 3 , and even more preferably of from 6 to 7 g/in 3 .
• the nitrogen oxide conversion material comprises one or more platinum group metals
• the nitrogen oxide conversion materia! comprises metal oxide support particles, wherein preferably at least part of the metal oxide support particles support at least part of the at least one platinum group metal.
• any metal oxide particles may be used, provided that they may adequately support the at least one platinum group metal and that they can withstand the conditions encountered during the treatment of automotive exhaust gas, in particular with respect to the temperatures incurred by the NOx storage catalyst.
• high sur- face area refractory metal oxide supports such as alumina support materials, also referred to as "gamma alumina” or “activated alumina,” are used. Said materials typically exhibit a BET surface area ranging from 60 to 200 m 2 /g or higher.
• Such activated alumina is usually a mixture of the gamma and delta phases of alumina, but may also contain substantial amounts of eta, kappa and theta alumina phases.
• Refractory metal oxides other than activated alumina can be used as a support for at least some of the catalytic components.
• bulk ceria, zirconia, alpha alumina and other materials are known for such use. Although many of these materials suffer from the disadvantage of having a considerably lower BET surface area than activated alumina, that disadvantage tends to be offset by a greater durability of the resulting catalyst.
• BET surface area has its usual meaning of referring to the Brunauer, Emmett, Teller me- thod for determining surface area by N 2 adsorption. Pore diameter and pore volume can also be determined using BET-type N 2 adsorption.
• the active alumina has a specific surface area comprised in the range of from 60 to 350 m z /g, and typically 90 to 250 m 2 /g.
• At least part of the metal oxide support particles comprise at least one compound selected from the group consisting of a!umina, silica, titania, silica-alumina, titania-alumina, zirconia, zirconia-alumina, ba- ria-alumina, ceria, ceria-aiumina, baria-ceria-a!umina, lanthana-aiumina, lanthana- zirconia-alumina, baria-lanthana-alumina, baria-lanthana-neodymia-alumina, zirconia- silica, titania-silica, titania-zirconia, and mixtures thereof, in particularly preferred embodiments, at least part of the metal oxide support particles comprise at least one compound selected from the group consisting of alumina, ceria, ceria-alumina, and mixtures thereof, wherein even more preferably at least part of the metal oxide support particles comprise
• the second washcoat layer and/or a washcoat layer provided between the first and second washcoat layers may contain any possible amount of metal oxide support particles, provided that the function of the remaining components comprised in the NOx storage catalyst is not impaired.
• the loading of the metal oxide component in the second washcoat layer may range from 0.1 to 5 g/in 3 , with respect to the weight of the metal contained in the respective compound, wherein the loading preferably ranges from 0.5 to 3.5 g/in 3 , more preferably from 0.8 to 3.0 g/in 3 , more preferably from 0.9 to 2.5 g/in 3 , more preferably from 1 to 2.3 g/in 3 , and even more preferably from 1 to 1.5 g/in 3 .
• the ratio of ceria to alumina be comprised in the range of from 1 : 4 to 5 : 1 , more preferably from 1 : 3 to 4 : 1 , more preferably from 2 : 5 to 7 : 2, and even more preferably from 1 : 2 to 3 : 1.
• the platinum group metals supported on at least part of the metal oxide particles comprise Rh as well as at least one further platinum group metal being preferably Pt and/or Pd, more preferably Pt and Pd.
• Rh is supported on other meta! oxide support particles than Pt and/or Pd, preferably Pt and Pd, wherein Rh is preferably supported on metal oxide particles comprising ceria and/or ceria-alumina, even more preferably on metal oxide particles comprising ceria.
• said platinum group metals are preferably supported on the same metal oxide support particles, wherein said metal oxide particles prefera- bly comprise alumina.
• the second washcoat layer and/or a washcoat layer provided between the first and second washcoat layers contains substantially no Mg and no Ba.
• the second washcoat layer and/or a washcoat layer provided between the first and second washcoat layers contains substantially no element selected from the group consisting of Mg, Ca, Sr, Ba, and combinations thereof, wherein even more preferably, the second washcoat layer and/or a washcoat layer provided between the first and second washcoat layers contains substantially no alkaline earth element.
• any material may be used, provided that it has the ability of reversibiy trapping hydrocarbons, and in particular hydrocarbon emissions produced during the cold start period in automotive exhaust gas treatment.
• the hydrocarbon trap materials which may be used in the present invention are capable of binding hydrocarbons at lower temperatures and subsequently releasing them at higher temperatures, in particular at temperatures at which effective catalytic conversion thereof may be achieved.
• lower temperatures as used in the context of the present invention refer to those encountered in automotive exhaust gas purification during cold start conditions, prior to which the engine is at most at ambient temperature.
• Higher temperatures refer to those temperatures encountered when the exhaust gas system has attained a temperature at which it is fully operative with respect to exhaust gas treatment, in particular with respect to the catalytic conver- sion of hydrocarbon emissions.
• the hydrocarbon trap material comprises beta zeolite, preferably H-beta zeolite.
• the zeolites used have a high silica to alumina ratio.
• such zeolites will have a silica/alumina molar ratio of at least about 25/1 , preferably of at least about 50/1 , more preferably wherein the silica/alumina molar ratio ranges from 25/1 to 000/1 , more preferably from 50/1 to 500/1.
• zeolites of which the silica/alumina molar ratio ranges from 25/1 to 300/1 , more preferably from about 100/1 to 250/1.
• the silica/alumina molar ratio of the zeolites range from 35/1 to 180/ .
• the second washcoat layer may contain any possible amount of hydrocarbon trap materia!, provided that the function of the remaining components comprised in the NOx storage catalyst is not impaired.
• the loading of the hydrocarbon trap material in the washcoat layer may range from 0.10 to 1.5 g/in 3 , preferably from 0.15 to 1.0 g/in 3 , more preferably from 0.20 to 0.7 g/in 3 , more preferably from 0.25 to 0.6 g/in 3 , and even more preferably from 0.3 to 0.5 g/in 3 .
• the hydrocarbon trap material further comprises Pt and/or Pd, more preferably Pt, wherein the platinum group metals in the hydrocarbon trap material will typically be present in an amount of up to 50 g/ft 3 , preferably from 0.05 to 20 g/ft 3 , more preferably from 0.1 to 15 g/ft 3 , more preferably from 0.5 to 12 g/ft 3 , more preferably from 1.0 to 10 g/ft 3 , and even more preferably of from 2 to 8 g/ft 3 .
• the NOx storage catalyst comprises a washcoat layer provided between the first and second washcoat layers, and preferably wherein furthermore the second washcoat layer does not comprise a nitrogen oxide conversion material
• the second washcoat layer comprises metal oxide support particles.
• the metal oxide support particles support at least part of the at least one platinum group metal.
• any metal oxide particles may be used, provided that they may adequately support the at least one platinum group metal and that they can withstand the conditions encountered during the treatment of automotive exhaust gas, in particular with respect to the temperatures incurred by the NOx storage catalyst during exhaust gas treatment.
• the metal oxide support particles comprise alumina.
• the second washcoat layer may contain any possible amount of metal oxide support particles, provided that the function of the re- maining components comprised in the NOx storage catalyst is not impaired.
• the loading of the metal oxide component in the second washcoat layer of said preferred embodiments may range from 0.01 to 3.0 g/in 3 , wherein the loading preferably ranges from 0.05 to 2.0 g/in 3 , more preferably from 0.10 to 1.0 g/in 3 , more preferably from 0.15 to 0.5 g/in 3 , and even more preferably from 0.2 to 0.3 g/in 3 .
• the hydrocarbon trap material comprises substantially no element or compound in a in a state in which it would be capable of catalyzing selective catalytic reduction.
• selective catalytic reduction refers to the catalytic treatment of gasoline en- gine exhaust gas, wherein nitrogen oxide is reduced to diatomic nitrogen by reaction with reductive emissions present in the exhaust gas.
• the term refers to the catalytic treatment of automotive exhaust gas in general.
• the term "selective catalytic reduction” refers to a catalyzed reaction wherein gaseous nitrogen oxide is reduced to diatomic nitrogen.
• the hydrocarbon trap material substantially does not catalyze the selective catalytic reduction of nitrogen oxide.
• this refers to hydrocarbon trap materials of which the catalytic activity towards the selective catalytic reduction of nitrogen oxide within the meaning of the present invention does not exceed the catalytic activity of a hydrocarbon trap material comprising substantially no Cu and/or Co, more preferably of a hydrocarbon trap material comprising substantially no Cu, Co, Mn, Ag, In, Ir, and/or Rh, and even more preferably comprising substantially no Cu, Co, Fe, Mn, Ag, In, Ir, and/or Rh.
• the hydrocarbon trap material does not display a catalytic activity towards selective catalytic reduction within the meaning of the present invention which would exceed the activity of a hydrocarbon trap material which contains substantially no transition metal element apart from Pt and/or Pd, preferably of a hydrocarbon trap material which contains substantially no transition metal element apart from Pt, and more preferably of a hydrocarbon trap material which contains substantially no transition metal element, wherein the hydrocarbon trap material preferably refers to the respectively preferred hydrocarbon trap materials of the present invention.
• a material is defined as not comprising a substantial amount of a specific element when it contains 1 w -% or less of said e!e- ment, preferably 0.5 wt.-% or less, more preferably 0.01 wt-% or less, more preferably 0.005 wt.-% or less, and even more preferably 0.001 wt.-% or less thereof.
• the nitrogen oxide storage catalyst according to the present invention can be readily prepared by processes well known in the prior art. A representative process is set forth below.
• the term "washcoat” has its usual meaning in the art of a thin, adherent coating of a catalytic or other material applied to a substrate carrier material, such as a honeycomb-type carrier member, which is preferably sufficiently porous to permit the passage there through of the gas stream being treated.
• the several components of the nitrogen oxide storage catalyst material may be applied to the substrate as mixtures of one or more components in sequential steps in a manner which will be readily apparent to those skilled in the art of catalyst manufacture.
• a typical method of manufacturing the nitrogen oxide storage catalyst of the present invention is to respectively provide the nitrogen oxide storage material, the nitrogen oxide conversion material, and the hydrocarbon trap material as a coating or washcoat layer on the walls of the gas-flow passages of a suitable carrier member.
• the nitrogen oxide conversion material and the hydrocarbon trap material are provided in a single washcoat on the substrate.
• the components of the individual washcoat layers may respectively be processed to a slurry, preferably to an aqueous slurry.
• the substrate may then be sequentially immersed into the respective slurries for the individual washcoats, after which excess slurry is removed to provide a thin coating of the two or more slurries on the walls of the gas-flow passages of the substrate.
• the coated sub- strate is then dried and calcined to provide an adherent coating of the respective component to the walls of the passages.
• the coated substrate may then be immersed into a further slurry of the nitrogen oxide conversion material or a mixture of the nitrogen oxide conversion material and the hydrocarbon trap material to form a second washcoat layer deposited over the first washcoat layer.
• the present invention is also directed to treatment systems for an automobile exhaust gas stream.
• the treatment system of the present invention comprises a combustion engine, preferably a diesel engine, an exhaust gas conduit in fluid communication with the engine, and a nitrogen oxide storage catalyst as described herein which is provided within the exhaust gas conduit.
• any conceivable combustion engine may be used in the treatment system of the present invention, wherein preferably a lean burn engine is used such as a diesel engine or a lean burn gasoline engine, more preferably a diesel engine.
• a lean burn engine such as a diesel engine or a lean burn gasoline engine, more preferably a diesel engine.
• the present invention also relates to a treatment system for an automobile exhaust gas stream comprising
• a combustion engine preferably a diesel engine or a lean burn gasoline engine, more preferably a diesel engine,
• a nitrogen oxide storage catalyst according to the present invention provided within the exhaust gas conduit.
• the treatment system further comprises a soot filter component and/or a selective catalytic reduction (SCR) component.
• the nitrogen oxide storage catalyst can be located upstream or downstream from the soot filter and/or selective catalytic reduction component.
• the soot filter is a catalyzed soot filter (CSF). Any suitable CSF can be used according to the present invention.
• the CSF of the present invention comprises a substrate coated with a washcoat layer containing one or more catalysts for burning off trapped soot and/or oxidizing exhaust gas stream emissions.
• the soot burning catalyst can be any known catalyst for combustion of soot.
• the CSF can be coated with a one or more high surface area refractory oxides (such as e.g. alumina, silica, silica alumina, zirconia, and zirconia alumina) and/or with an oxidation catalyst (such as e.g. a ceria-zirconia) for the combustion of unburned hydrocarbons and to some degree particulate matter.
• a soot burning catalyst is an oxidation catalyst comprising one or more precious metal catalysts (platinum, palladium, and/or rhodium).
• the treatment system of the present invention further comprises a selective catalytic reduction (SCR) component.
• SCR selective catalytic reduction
• the SCR component is preferably located downstream of the nitrogen oxide storage catalyst and upstream or downstream of the soot filter.
• a suitable SCR catalyst component for use in the emission treatment system is able to effectively catalyze the reduction of the NO* component at temperatures below 600°C, so that adequate NO x levels can be treated even under conditions of !ow load which typically are associated with lower exhaust temperatures.
• the catalyst article is capable of converting at least 50% of the NO x component to N 2 , depending on the amount of a reductant such as NH 3 which is preferably added to the system.
• compositions used in the emission treatment system should also have thermal resistance to temperatures greater than 650°C. Such high temperatures may be encountered during regeneration of the upstream catalyzed soot filter. Suitable SCR catalyst compositions are described, for instance, in US 4,961 ,917 and US 5,516,497.
• Suitable compositions include one or both of an iron and a copper promoter present in a zeolite in an amount of from about 0.1 to 30 percent by weight, preferably from about 1 to 5 percent by weight, of the total weight of promoter plus zeolite.
• the disclosed compositions can also promote the oxidation of excess NH 3 with 0 2 , especially for those compositions having higher promoter concentrations.
• the present invention a!so relates to a method for the treatment of automobile engine exhaust gas using the nitrogen oxide storage catalyst of the present invention. More specifically, the method of the present invention includes conducting an automobile engine exhaust gas over and/or through the nitrogen oxide storage catalyst, wherein the automobile engine exhaust gas is preferably only conducted through the nitrogen oxide storage catalyst.
• the present invention also concerns a method for the treatment of automobile engine exhaust gas comprising:
• the automobile engine exhaust gas is from a lean burn combustion engine, preferably from a diesel engine or a lean burn gasoline engine, more preferably a diesel engine.
• Fig. 1 displays results from testing of the NOx storage catalysts of Example 1
• Comparative Examples 1 and 2 with respect to the conversion of hydrocarbons, carbon monoxide, and NOx emissions contained in automotive exhaust gas under cold start conditions.
• the values of "Conversion / %" indicate the percentage of the respective substances originally contained in the automotive exhaust gas which have been converted after the exhaust has passed the NOx storage catalyst according to said examples.
• Fig. 2 displays results from testing of the NOx storage catalysts of Example 3.
• Comparative Example 3 with respect to the conversion of hydrocarbons, carbon monoxide, and NOx emissions contained in automotive exhaust gas under cold start conditions.
• the values of "Conversion / %" have the same meaning as described above for Figure 1.
• Example 1 Onto a honeycomb flow-through monolith substrate (5.66 in x 5.66 in x 3 in; 1.2 L; 400 cpsi / 6 mil) was provided a first washcoat layer washcoat containing 2.4 g/in 3 activated alumina containing 10 wt.-% ceria and 20 wt.-% barium oxide, 0.2 g/in 3 Ce as cerium nitrate, 0.5 g/in 3 Ba as barium oxide and 0.1 g/in 3 Zr as zirconium oxide, said layer further containing 29 g/ft 3 Pt and 6 g/ft 3 Pd.
• a first washcoat layer washcoat containing 2.4 g/in 3 activated alumina containing 10 wt.-% ceria and 20 wt.-% barium oxide, 0.2 g/in 3 Ce as cerium nitrate, 0.5 g/in 3 Ba as barium oxide and 0.1 g/in 3 Zr as zirconium oxide,
• a second washcoat layer was then provided on the first layer, said second layer containing 0.25 g/in 3 Al 2 0 3 and 0.75 g/in 3 ceria, said layer further containing a loading of 75 g/ft 3 Pt and 6 g/ft 3 Rh.
• a third washcoat layer was provided on the second layer, said third layer containing 0.25 g/in 3 Al 2 0 3 and 0.5 g/in 3 H-beta-zeolite, said layer further containing 4 g/ft 3 Pt.
• the resulting layered NOx trap catalyst contained a total of 108 g/ft 3 Pt, 6 g/ft 3 Pd and 6 g/ft 3 Rh.
• Example 2 The layered NOx trap catalyst was disposed on a honeycomb flow-through monolith substrate having a volume of 73.17 in 3 (1.2 L), a cell density of 400 cells per square inch, and a wall thickness of approximately 100pm.
• the first coat provided on the substrate contained a washcoat of 3.84 g/in 3 activated alumina containing 10 wt.-% ceria and 8 wt.-% barium oxide, 1.104 g/in 3 ceria (87% of the ceria being in particulate form), 0.24 g/in 3 Mg as magnesium oxide, and 0.096 g/in 3 Zr as zirconium oxide, said layer further comprising 63 g/ft 3 Pt and 6.5 g/ft 3 Pd.
• the second coat provided on the first coat contained a washcoat of 0.7 g/in 3 activated alumina bearing 40 g/ft 3 Pt and 4 g/ft 3 Pd, 0.5 g/in 3 ceria bearing 6.5 g/ft 3 Rh, with substantially no alkaline earth component being present in the second washcoat layer.
• the third coat provided on the second coat contained a washcoat of 0.25 g/in 3 Al 2 0 3 and 0.5 g/in 3 H-beta-zeolite bearing 4g/ft 3 Pt.
• the resulting layered NOx trap catalyst contained a total of 107 g/ft 3 Pt, 10.5 g/ft 3 Pd and 6.5 g/ft 3 Rh.
• the layered NOx trap catalyst was disposed on a honeycomb flow-through monolith substrate having a volume of 73.17 in 3 (1.2 L), a cell density of 400 cells per square inch, and a wall thickness of approximately 100pm.
• the first coat provided on the substrate contained a washcoat of 3.69 g/in 3 activated alumina containing 10 wt.-% ceria and 18 wt.-% barium oxide, 1.06 g/in 3 ceria (87% of the ceria being in particulate form), 0.23 g/in 3 Mg as magnesium oxide, and 0.092 g/in 3 Zr as zirconium oxide, said layer further containing 61 g/ft 3 Pt and 6.5 g/ft 3 Pd.
• the second coat provided on the first coat contained a washcoat of 0.6 g/in 3 activated alumina bearing 40 g/ft 3 Pt and 4 g/ft 3 Pd, 0.5 g/in 3 ceria bearing 6.5 g/ft 3 Rh, and 0.3g/in 3 H-beta-zeolite bearing 2g/ft 3 Pt, with substantially no alkaline earth component being present in the second washcoat layer.
• the resulting layered NOx trap catalyst contained a total of 103 g/ft 3 Pt, 10.5 g/ft 3 Pd and 6.5 g/ft 3 Rh.
• the layered NOx trap catalyst was disposed on a honeycomb flow-through monolith substrate having a volume of 73.17 in3 (1.2 L), a cell density of 400 cells per square inch, and a wall thickness of approximately 100pm.
• the first coat provided on the substrate contained a washcoat of 0.25 g/in 3 Al 2 0 3 and 0.5 g/in 3 H-beta-zeolite bearing 4 g/ft 3 Pt.
• the second coat provided on the first coat contained a washcoat of 2.4 g/in 3 activated alumina containing 10 wt.-% ceria and 20 wt.-% barium oxide, 0.2 g/in 3 Ce as cerium nitrate, 0.5 g/in 3 Ba as barium oxide and 0.1 g/in 3 Zr as zirconium oxide, said layer further containing 29 g/ft 3 Pt and 6 g/ft 3 Pd.
• the third coat provided in the second coat contained a washcoat of 0.25 g/in 3 activated alumina bearing 75 g/ft 3 Pt and 0.75 g/in 3 , ceria bearing 6 g/ft 3 Rh, with substantially no alkaline earth component being present in said second washcoat layer.
• the resulting layered NOx trap catalyst contained a total of 108 g/ft 3 Pt, 6g/ft 3 Pd and 6 g/ft 3 Rh.
• the layered NOx trap catalyst was disposed on a honeycomb flow-through monolith substrate having a volume of 73.17 in 3 (1.2 L), a cell density of 400 cells per square inch, and a wall thickness of approximately 100pm.
• the first coat provided on the substrate contained a washcoat of 2.4 g/in 3 activated alumina containing 10 wt.-% ceria and 20 wt.-% barium oxide, 0.2 g/in 3 Ce as cerium nitrate, 0.5g/in 3 Ba as barium oxide and 0.1 g/in 3 Zr as zirconium oxide, said layer further containing 38.4 g/ft 3 Pt and 4 g/ft 3 Pd.
• the second coat provided on the first coat contained a washcoat of 1.5 g/in 3 activated alumina bearing 99.6 g/ft 3 Pt and 0.75 g/in 3 ceria bearing 8 g/ft 3 Rh, with substantially no alkaline earth component being present in the second washcoat layer.
• the resulting layered NOx trap catalyst contained a total of 134 g/ft 3 Pt, 4 g/ft 3 Pd and 8 g/ft 3 Rh.
• Comparative Example 3 The layered NOx trap catalyst was disposed on a honeycomb flow-through monolith substrate having a volume of 73.17 in 3 (1.2 L), a ce!l density of 400 cells per square inch, and a wall thickness of approximately 100 m.
• the first coat provided on the substrate contained a washcoat of 3.84 g/in 3 activated alumina containing 10 wt.-% ceria and 18 wt.-% barium oxide, 1.104 g/in 3 ceria (87% of the ceria being in particulate form), 0.24 g/in 3 Mg as magnesium oxide, and 0.096 g/in 3 Zr as zirconium oxide, said layer further comprising 63 g/ft 3 Pt and 6.5 g/ft 3 Pd.
• the second coat provided on the first coat contained a washcoat of 0.7 g/in 3 activated alumina bearing 40 g/ft 3 Pt and 4 g/ft 3 Pd, 0.5 g/in 3 ceria bearing 6.5 g/ft 3 Rh, with substantially no alkaline earth component being present in the second washcoat layer.
• the resulting NOx trap catalyst contained a total of 103 g/ft 3 Pt, 10.5 g/ft 3 Pd and 6.5 g/ft 3 Rh.
• the catalysts were ail ovenaged under hydrothermal conditions with 10% steam and 10% oxygen. Aging was done for 5h at 750°C. After aging the catalysts were tested on dynamic engine bench in MVEG driving cycle (cold start) conditions using a transient test cell with an OM 646 engine.
• Figure 1 displays results from the testing of Example 2 and Comparative Examples 1 and 2 with respect to the conversion of hydrocarbons, carbon monoxide and NOx un- der cold start conditions according to the testing procedure described in the foregoing.
• the conversion value reflects the amount of emissions which has been removed from the exhaust gas stream by means of trapping and/or of conversion to a different chemical compound.
• the test results in Figure 1 show that a hydrocarbon trapping layer as top/over coat to a NOx trap catalysts as present in Ex- ample 2 is able to lower hydrocarbon emissions while maintaining a sufficient rate of carbon monoxide and NOx conversion compared to an NOx storage catalyst which contains no hydrocarbon trap material (Comparative Example 2).
• the NOx storage catalyst's capacity of converting carbon monoxide and of storing NOx under cold start conditions is not impaired by the additional presence of the hydrocarbon trapping element in the top layer, since comparable results are achieved in this respect in for both the NOx storage catalyst according to Example 3, which contains a hydrocarbon trapping element, as well as for the catalyst according to Comparative Example 3, which contains no such hydrocarbon trapping element.

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