DE102004058210A1 - Integrated catalyst system to remove e.g. nitric oxides from exhaust gases comprises nitric oxide storing component, ammonia-generating component, ammonia-storing component and selective catalytic reduction component on common substrate - Google Patents

Abstract

Integrated catalyst system for removal of harmful substances containing nitric oxides comprises at least one nitric oxide storing component, at least one in situ ammonia-generating component, which converts nitric oxide to ammonia, at least one ammonia-storing component, and at least one selective catalytic reduction component to decompose nitric oxide by ammonia. At least two of the components are present on a common substrate or on a joined substrate system. An independent claim is included for preparation of the catalyst using washcoat process.

Description

The present invention relates to a catalyst for removing pollutants containing nitrogen oxides from exhaust gases of internal combustion engines, in particular exhaust gases from lean-burn engines in cyclic lean-rich operation. The invention also relates to processes for the preparation of the catalyst. Further subject matters of the invention are catalyst systems which contain the catalyst and processes for removal of pollutants from exhaust gases of internal combustion engines containing nitrogen oxides, in particular from exhaust gases of lean-burn engines in cyclic lean-rich operation using the catalyst. In the catalyst, a process takes place which involves the storage of nitrogen oxides in a NO _x storage component, the reduction of nitrogen oxides to ammonia, the storage of ammonia in an NH ₃ storage component and the oxidation of NH ₃ with NO _x to nitrogen.

A particular embodiment of three-way catalysts for removing pollutants from lean internal combustion engines, preferably from passenger car engines, are NO _x storage catalysts. These catalysts are greased alternately with the help of the engine control and exposed to lean exhaust conditions. During the lean-burn operation, they store the nitrogen oxides NO _x formed during combustion. The stored nitrogen oxides are then catalytically decomposed to nitrogen in short "enrichment phases" (ie in the case of oxygen deficiency) under reducing conditions under a complicated and program-intensive motor control. Accordingly, such Ka catalysts are also referred to as "NO _x adsorber" or as "NO _x storage / reduction catalysts".

The catalysts generally used in the methods of the prior art typically include both an active metal component as well as a containing NO _x storage component is usually an oxide of the alkali metal elements, alkaline earth metal or the rare earth elements.

As active metal mostly platinum is used. An essential task of the active metal is to oxidize NO in the lean phase to NO ₂ . The thus-formed NO ₂ is stored with the oxidic NO _x storage component usually in the form of nitrate or nitrite. Falls due to the increasing saturation of the NO _x storage component by nitrate (nitrite), the NO _x -Konvertierungsleistung to an unacceptable level, takes place by means of internal engine measures enrichment of the exhaust gas. The enrichment causes the sudden decomposition of the nitrates (nitrites) with the release of NO _x . Since there is sufficient reducing agent during enrichment and also only little oxygen, the NO _x can be reduced directly to carbon monoxide (CO) and hydrocarbons (HC) to N ₂ . To accelerate this reduction, NO _x storage catalysts usually contain small amounts of rhodium in addition to platinum. Both the platinum and the rhodium are on temperature-stable, usually highly porous carrier oxides such as the oxides of Al, Si, Zr or Ti or mixtures thereof. In particular, the alumina is widely used as a carrier for platinum. Prior art NO _x storage catalysts are disclosed in, for example EP 1317 953 A1 . EP 0 716 876 B1 . EP 0 730 901 B1 , US 2002/0048542 A1, EP 0 982 066 A1 . DE 100 36 886 A1 . EP 1 010 454 A2 . US 6,004,521 . EP 1 036 591 A1 ,

In particular, the active metal components and additives contained in the NO _x storage catalyst, such as mostly on cerium zirconia-based oxygen storage materials ensure that carbon monoxide (CO) and hydrocarbons (HC) under both rich, stoichiometric and lean exhaust conditions effectively to carbon dioxide and water can be implemented. Likewise, the conversion of NO _x to N ₂ under rich and stoichiometric exhaust conditions succeeds.

From the DE 101 13 947 B4 Also already known is a method for reducing the nitrogen oxide content in the exhaust gas of an engine operable in lean-fat alternation, in which a starting catalyst, a NO _x storage catalytic converter and an SCR catalytic converter are arranged sequentially. This nitrogen oxides are reduced to ammonia under rich exhaust conditions on a NO _x storage catalyst and a starting catalyst. In a further step, the nitrogen oxides on the SCR catalyst react with the ammonia thus formed to form nitrogen. By means of a suitable adjustment of the engine control, the reduction conditions required for the individual stages (rich operation) or oxidation conditions (lean operation) are set.

It is also already known, zeolites in catalysts for cleaning use of car exhaust.

US Pat. No. 6,689,709 B1 discloses a hydrothermally stable zeolite beta containing iron and cerium containing the Reduction of NO _x with ammonia (ammonia SCR reaction (Selective Catalytic Reduction by Ammonia) catalyzed. The method for the reduction of NO _x envisages that ammonia is permanently added to the exhaust gas stream.

US 6,004,521 discloses the use of a zeolite in NO _x storage catalysts for exhaust gases from engines operating in the conventional rich-lean cycle. The zeolite serves as a carrier for the active metal. The method for the reduction of NO _x provides that the stored NO _x reacts at the moment of enrichment with the hydrocarbons and CO to N ₂ . Thus, there is no formation of NH ₃ and caching in the zeolite.

EP 0 970 737 A2 discloses a catalyst comprising a support comprising a zeolite and a metal oxide, and a storage and release component and a noble metal located outside the pores of the zeolite. The zeolite should only serve as a carrier for the active metal.

The EP 1 129 764 A1 discloses catalysts for the purification of the exhaust gases of diesel engines containing at least one zeolite and additionally at least one of the support oxides alumina, silica, titania, zirconia and aluminosilicate and their mixed oxides and at least one of the noble metals platinum, palladium, rhodium, iridium, gold or silver.

The EP 0970 737 A2 and the technical publication SAE 900496 disclose zeolites for the direct conversion of NO _x with hydrocarbons in the sense of the so-called HC-SCR (Selective Catalytic Reduction by Hydrocarbons). It is, in accordance with the NH ₃ -SCR process, a continuous process in which NO _{x is} reduced directly to N ₂ with a hydrocarbon. In this context, transition-metal-exchanged and noble metal-exchanged or -loaded zeolites such as ZSM-5 and zeolite-β are used.

The inventive task was to contain a catalyst for removing pollutants Nitrogen oxides from exhaust gases of internal combustion engines, in particular from Exhaust gases from lean-burn engines in cyclic lean-rich operation, for disposal to provide, by using the catalyst with respect to the The prior art simplified and more effective method for Reduction of the pollutant content in the exhaust gases of these engines should be achieved.

• (i) Stickoxide (NO_x) in einer NO_x-Speicherkomponente speichert,
• (ii) NO_x zu Ammoniak (NH₃) umsetzt,
• (iii) Ammoniak in einer NH₃-Speicherkomponente speichert,
• (iv) NH₃ mit NO_x umsetzt.

The problem could be solved with a catalyst for the removal of pollutants containing nitrogen oxides (NO _x ) from the exhaust gases of lean-burn engines in the cyclic lean / rich operation, which is characterized in that

• (i) storing nitrogen oxides (NO _x ) in a NO _x storage component,
• (ii) NO _x converts to ammonia (NH ₃ ),
• (iii) storing ammonia in an NH ₃ storage component,
• (iv) reacting NH ₃ with NO _x .

in the Difference to the state of the art running the nitrogen oxide storage, the reduction to ammonia, the storage of ammonia and the Ammonia oxidation in one catalyst and not in several catalysts from. In the new catalyst are the components of the catalyst, which cause these processes in physical contact while they are separated from each other in the catalysts of the prior art are.

Exhaust aftertreatment using the new catalyst allows NO _x removal with increased efficiency. Surprisingly, such a catalyst can also cause a significant reduction in the undesirable secondary NH ₃ emission compared to the prior art processes and catalysts.

The NO _x removal process from exhaust gases using the catalyst containing NO _x and NH ₃ storage components may also be referred to as NSR-C-SCR (NO _x -Storage-Reduction Coupled with Selective-Catalytic Reduction) ).

The term "NO _x storage" can be understood to mean both NO _x adsorption and NO _x absorption NO _x adsorption is present when NO _x is physisorbed in the form of a surface species on the surface of one of the components present in the catalyst or is chemisorbed NO _x absorption refers to the formation of a nitrogen-containing "bulk phase" of the NO _x storage medium, and analogously applies to NH ₃ storage and the NH ₃ storage component.

• (1) Pt, Pd, Rh, Ir und Ru, jeweils alleine oder im Gemisch, vorliegend auf einem Trägermaterial ausgewählt aus: Oxiden, Mischoxiden, Phosphaten und Sulfaten des Al, Si, Zr, Ti, Ce, der Erdalkalimetall- und Seltenerdelemente; Heteropolysäuren; Zeolithen; sowie Mischungen daraus;
• (2) Zeolithe; Heteropolysäuren; sulphatierte Zirkonoxide oder Zirkonphosphate; sowie Mischungen daraus;
• (3) Oxide und Mischoxide der Alkalimetall-, Erdalkalimetall-, Seltenerdelemente, des Zirkons, des Titans;
• (4) anorganische Verbindungen von V, Cr, Mn, Fe, Co, Ni, Cu, In, Ga, Ag und Sn sowie Mischungen daraus; wobei der Katalysator (i) Stickoxide (NO_x) in einer NO_x-Speicherkomponente speichert, (ii) NO_x zu Ammoniak (NH₃) umsetzt, (iii) Ammoniak in einer NH₃-Speicherkomponente speichert, (iv) NH₃ mit NO_x umsetzt.

In a particular embodiment, the catalyst for removing pollutants containing nitrogen oxides (NO _x ) from the exhaust gases of lean-burn engines in cyclic lean / rich operation is characterized in that the catalyst is at least one of the materials from group (1) and at least one acid Solid from group (2) and optionally at least one of the materials from groups (3) and (4) contains:

• (1) Pt, Pd, Rh, Ir and Ru, each alone or in admixture, present on a support material selected from: oxides, mixed oxides, phosphates and sulfates of Al, Si, Zr, Ti, Ce, the alkaline earth metal and rare earth elements; heteropolyacids; zeolites; and mixtures thereof;
• (2) zeolites; heteropolyacids; sulphated zirconium oxides or zirconium phosphates; and mixtures thereof;
• (3) oxides and mixed oxides of the alkali metal, alkaline earth metal, rare earth elements, zirconium, titanium;
• (4) inorganic compounds of V, Cr, Mn, Fe, Co, Ni, Cu, In, Ga, Ag and Sn, and mixtures thereof; wherein the catalyst stores (i) nitrogen oxides (NO _x ) in a NO _x storage component, (ii) converts NO _x to ammonia (NH ₃ ), (iii) stores ammonia in an NH ₃ storage component, (iv) NH ₃ NO _x converts.

The materials of group (1) and optionally (3) and optionally (4) act as NO _x storage component and the acidic solids of group (2) as NH ₃ storage component. The materials of group (1) and optionally (3) and (4) thus act as NO _x adsorption or absorption component, and the acidic solids of group (2) as NH ₃ adsorption or absorption component.

In a further embodiment of the catalyst is one of the support materials from the group (1) even an acidic solid of the group (2).

• (1) Pt, Pd, Rh, Ir und Ru, jeweils alleine oder im Gemisch, vorliegend auf einem Trägermaterial ausgewählt aus: Oxiden, Mischoxiden, Phosphaten und Sulfaten des Al, Si, Zr, Ti, Ce, der Erdalkalimetall- und Seltenerdelemente; Heteropolysäuren; Zeolithen; sowie Mischungen daraus;
• (3) Oxide und Mischoxide der Alkalimetall-, Erdalkalimetall-, Seltenerdelemente, des Zirkons, des Titans;
• (4) anorganische Verbindungen von V, Cr, Mn, Fe, Co, Ni, Cu, In, Ga, Ag und Sn sowie Mischungen daraus; wobei mindestens eines der Trägermaterialien aus der Gruppe (1) ein saurer Feststoff mit der Bedeutung ist, wie sie oben für die Gruppe (2) angegeben ist, und der Katalysator (i) Stickoxide (NO_x) in einer NO_x-Speicherkomponente speichert, (ii) NO_x zu Ammoniak (NH₃) umsetzt, (iii) Ammoniak in einer NH₃-Speicherkomponente speichert, (iv) NH₃ mit NO_x umsetzt.

This further embodiment of the catalyst for removing pollutants containing nitrogen oxides (NO _x ) from the exhaust gases of lean-burn engines in cyclic lean / rich operation is characterized in that the catalyst is at least one of the materials from group (1) and optionally at least one of Materials from groups (3) and (4) contain:

• (1) Pt, Pd, Rh, Ir and Ru, each alone or in admixture, present on a support material selected from: oxides, mixed oxides, phosphates and sulfates of Al, Si, Zr, Ti, Ce, the alkaline earth metal and rare earth elements; heteropolyacids; zeolites; and mixtures thereof;
• (3) oxides and mixed oxides of the alkali metal, alkaline earth metal, rare earth elements, zirconium, titanium;
• (4) inorganic compounds of V, Cr, Mn, Fe, Co, Ni, Cu, In, Ga, Ag and Sn, and mixtures thereof; wherein at least one of the carrier materials from group (1) is an acidic solid having the meaning given above for group (2) and the catalyst (i) stores nitrogen oxides (NO _x ) in a NO _x storage component, (ii) converting NO _x to ammonia (NH ₃ ), (iii) storing ammonia in an NH ₃ storage component, (iv) reacting NH ₃ with NO _x .

• (1) Pt, Pd, Rh, Ir und Ru, jeweils alleine oder im Gemisch, vorliegend auf einem Trägermaterial ausgewählt aus: Oxiden, Mischoxiden, Phosphaten, Sulfaten und Carbonaten des Al, Si, Zr, Ti, Ce, der Erdalkalimetall- und Seltenerdelemente; Heteropolysäuren; Zeolithen; sowie Mischungen daraus;
• (2) Zeolithe, Heteropolysäuren, sulphatierte Zirkonoxide oder Zirkonphosphate sowie Mischungen daraus;
• (3) Oxide und Mischoxide der Alkalimetall-, Erdalkalimetall-, Seltenerdelemente, des Zirkons, des Titans;
• (4) anorganische Verbindungen von V, Cr, Mn, Fe, Co, Ni, Cu, In, Ga, Ag und Sn sowie Mischungen daraus.

In a further embodiment, it is also possible to use a catalyst which is characterized in that it comprises at least one of the materials from group (1) and at least one acidic solid from group (2) and optionally at least one of the materials from the groups (3 ) and (4) contains:

• (1) Pt, Pd, Rh, Ir and Ru, each alone or in admixture, present on a support material selected from: oxides, mixed oxides, phosphates, sulfates and carbonates of Al, Si, Zr, Ti, Ce, the alkaline earth metal and rare earth elements; heteropolyacids; zeolites; and mixtures thereof;
• (2) zeolites, heteropolyacids, sulphated zirconium oxides or zirconium phosphates and mixtures thereof;
• (3) oxides and mixed oxides of the alkali metal, alkaline earth metal, rare earth elements, zirconium, titanium;
• (4) Inorganic compounds of V, Cr, Mn, Fe, Co, Ni, Cu, In, Ga, Ag and Sn, and mixtures thereof.

The Effectiveness of the catalysts depends also in particular of the macroscopic embodiment and the Morphology of the catalyst. Especially good results will be achieved with catalysts that are produced by the known "washcoat" method.

• (1) Pt, Pd, Rh, Ir und Ru, jeweils alleine oder im Gemisch, vorliegend auf einem Trägermaterial ausgewählt aus: Oxiden, Mischoxiden, Phosphaten und Sulfaten des Al, Si, Zr, Ti, Ce, der Erdalkalimetall- und Seltenerdelemente; Heteropolysäuren; Zeolithen; sowie Mischungen daraus;
• (2) Zeolithe, Heteropolysäuren, sulphatierte Zirkonoxide oder Zirkonphosphate sowie Mischungen daraus;
• (3) Oxide und Mischoxide der Alkalimetall-, Erdalkalimetall-, Seltenerdelemente, des Zirkons, des Titans;
• (4) anorganische Verbindungen von V, Cr, Mn, Fe, Co, Ni, Cu, In, Ga, Ag und Sn sowie Mischungen daraus. wobei der Katalysator nach einem Washcoat-Verfahren herstellbar ist.

In a further embodiment, a catalyst is used, which is characterized in that it comprises at least one of the materials from group (1) and at least one acidic solid from group (2) and optionally at least one of the materials from groups (3) and (4) contains:

• (1) Pt, Pd, Rh, Ir and Ru, each alone or in admixture, present on a support material selected from: oxides, mixed oxides, phosphates and sulfates of Al, Si, Zr, Ti, Ce, the alkaline earth metal and rare earth elements; heteropolyacids; zeolites; and mixtures thereof;
• (2) zeolites, heteropolyacids, sulphated zirconium oxides or zirconium phosphates and mixtures thereof;
• (3) oxides and mixed oxides of the alkali metal, alkaline earth metal, rare earth elements, zirconium, titanium;
• (4) Inorganic compounds of V, Cr, Mn, Fe, Co, Ni, Cu, In, Ga, Ag and Sn, and mixtures thereof. wherein the catalyst can be prepared by a washcoat process.

The Precious metals of group (1) act as active metals, so are authoritative for the catalytic activity responsible. The term active metal is not only the corresponding element but also possible oxides and suboxides of Understood precious metals.

Among heteropolyacids of the group (1) btw. (2) are inorganic polyacids which have two kinds of central atoms. They may be present in the acidification of polybasic metal oxygen acids, such as those of chromium, molybdenum, tungsten and vanadium, and element cations, such as those of Ti ⁴⁺ , Zr ⁴⁺ , Al ³⁺ , Co ²⁺ or Co ³⁺ , Cu ¹⁺ or Cu ²⁺ among others or form non-metal oxygen acids.

When Ammonia storage component of group (2) are acidic solids, those from the group of zeolites, heteropolyacids, sulphated zirconium oxides and the zirconium phosphates are formed.

at Zeolites are solids that have different acid strengths, For example, the ion-exchanged zeolites often lower Have solid state acidity. At a high aluminum content, the acidity of zeolites can be very low be. About that It is also possible the acidity of zeolites by thermal or chemical treatments to minimize so these do not have typical properties of strongly acidic solids have more.

At the Use of zeolites as carrier oxides for the Active components (i.e., the noble metal component) is therefore the Suitability of the particular zeolite used, also simultaneously Ammonia storage component to be able to act on the acidic properties depending on the zeolite itself.

In one of the embodiments the zeolite or zeolites and the heteropolyacids are Group (1) identical to the zeolite or zeolites and the heteropolyacids the group (2).

In this embodiment, the NO _x storage component simultaneously also assumes the function of the NH ₃ storage component.

Prefers become as acidic solid of the group (2) a zeolite or zeolites used in which the Si / Al ratio is greater than 3. The Si / Al ratio of Acid zeolites should therefore be at least 3, because with such Zeolites have sufficient hydrothermal stability of the zeolite guaranteed is.

preferred Zeolites of group (2) are selected from the group pentasils, Y zeolite, USY, DAY, mordenite and zeolite-β.

Said zeolites can be used either in the pure form or as mixtures, this also including using the forms of doped zeolites obtained by ion exchange or by other treatment. The zeolite may be present in the sodium form, ammonium form or in the H form. In addition, it is possible to convert the sodium, ammonium or H form by impregnation with metal salts and oxides or by ion exchange in another ionic form. As an example, the conversion of Na-Y zeolite in SE zeolite (SE = rare earth element) by ion exchange in aqueous rare earth element chloride solution may be mentioned. In particular, ion exchange with the alkaline earth metal elements, rare earth elements, gallium, indium and iron is preferred. The corresponding elements may then be present on or in the zeolite as ions, oxides, suboxides or carbonates.

The acidic zeolites can function both as NH ₃ storage components and as SCR catalysts.

Optionally, the catalyst may contain a third component in addition to the NO _x storage component and the NH ₃ storage component. This component consists of at least one ion-exchanged zeolite. It acts as an additional NH ₃ -SCR component. Iron-exchanged and / or rare earth-exchanged zeolites are preferably used here.

The Materials of group (4) serve as doping. They are generally as an inorganic compound or in elemental form. Preferably they are in oxidic form.

Of the Term oxides concludes also all Suboxides, hydroxides and carbonates with a.

in the Catalyst is the proportion of the sum of the precious metals in the total mass the catalyst in the range of 0.05 to 10 wt .-%, wherein the proportion of the noble metals in the total mass of the catalyst in the range of 0.1 to 5 wt .-% is.

Of the Catalyst is also characterized in that the proportion of acidic solid from the group (2) in the total mass of catalyst is in the range of 5 to 95 wt%, with a range of 10 to 75 % By weight is preferred.

In a further embodiment contains the catalyst from group (1) palladium on zirconium oxide or cerium oxide or alumina or silicon-aluminum mixed oxide as a carrier oxide.

In a special embodiment the above embodiment contains the catalyst in addition to Pd Ru or Rh or Pt.

In a further embodiment contains the catalyst in addition from group (2) ceria or from group (2) ceria and from group (3) iron or group (2) ceria and praseodymium oxide and Group (3) iron.

In a further embodiment the catalyst is present on a monolithic honeycomb body.

• (i) Inkontaktbringen der NO_x-Speicherkomponente mit der NH₃-Speicherkomponente des Katalysators oder Inkontaktbringen mindestens eines der Materialien der Gruppe (1) mit mindestens einem sauren Feststoff der Gruppe (2) und gegebenenfalls mindestens einem der Materialien der Gruppen (3) und (4).

The novel catalyst can be prepared by a process comprising step (i):

• (i) contacting the NO _x storage component with the NH ₃ storage component of the catalyst or contacting at least one of the materials of group (1) with at least one acidic solid of group (2) and optionally at least one of the materials of groups (3) and (4).

ever according to embodiment the catalyst can be contacted purely mechanically by Mixing the solid materials of groups (1) and optionally (3) and / or (4) with the materials of group (2) or through a Washcoat procedure done.

For the macroscopic Design and morphology of the catalyst, which has a great impact to be effective, Therefore, all embodiments preferred, in the catalyst production in general already proven to have. These are in particular the known "washcoat" and / or "honeycomb" technologies.

The The latter technologies are based on the fact that the predominant Proportion of carrier material in aqueous Suspension on particle sizes of milled a few microns and then on a ceramic or metallic shaped body is applied. in principle can other components in water-soluble or water-insoluble Form introduced before or after the coating in the washcoat become. After applying all the components of the catalyst the shaped body this is usually dried and optionally at elevated temperatures calcined.

Particular preference is given to arrangements of the catalyst material with a high BET surface area and high retention of the BET surface after thermal aging. With regard to the pore structure, in particular macropores which have been formed into channels and coexist with meso- and / or micropores are preferred. The meso and / or micropores contain the active metal. Furthermore, it is particularly preferred that the acidic solid of group (2), which is to perform the NH ₃ storage and SCR function, as well as possible with the or the NO _x storage components is mixed.

Of the for the Catalyst used is preferably as a powder, Granules, extrudate, shaped bodies or as a coated honeycomb body in front.

The Integration of the catalytic components on a common substrate, preferably in the form of a monolithic honeycomb body preferably done so that the aforementioned components of the catalyst on a common Substrate by contacting the components by means of known Washcoat method can be applied.

However, it is also possible to mechanically mix the components, namely the NO _x and the NH ₃ storage component, and then to use the mixture, for example in the form of mixed powders, granules, extrudates or shaped bodies.

In spite of of high complexity of the catalyst it is therefore possible all, for the Representation of the catalyst necessary components on a common To unite substrate. Thus, an efficient and cost effective Exhaust aftertreatment system can be created.

One Another object of the invention is also a catalyst system, in which the catalyst described above in combination is present with at least one further catalyst.

In one embodiment, at least one further catalyst is a NO _x storage catalyst. The NO _x storage catalysts described in the prior art can be used.

In the catalyst system, the new catalyst and the NO _x storage catalysts are preferably arranged sequentially.

In a further embodiment, the catalyst with the NO _x storage catalyst is present as a mixture in the catalyst system.

In further embodiments, downstream of the catalyst of the catalyst system, an oxidation catalyst or downstream of the at least one further catalyst, a NO _x sensor.

Another object of the invention is the use of the novel catalyst or a catalyst system containing the catalyst for removing pollutants containing nitrogen oxides (NO _x ) from exhaust gases of lean-burn engines, ie an internal combustion engine, in cyclic lean-rich operation.

Another object of the invention relates to a method for removing pollutants containing nitrogen oxides (NO _x ) from the exhaust gases of lean-burn engines in the cyclic lean-rich operation, characterized in that a catalyst or a catalyst system is used as described above.

• (i) Speicherung von NO_x in einer NO_x-Speicherkomponente,
• (ii) Umsetzung des gespeicherten NO_x zu Ammoniak NH₃,
• (iii) Speicherung von Ammoniak in einer NH₃-Speicherkomponente,
• (iv) Umsetzung von NH₃ mit NO_x.

In a particular embodiment, this process is characterized in that a catalyst or a catalyst system are used as described above, the process comprising steps (i) to (iv):

• (i) storing NO _x in a NO _x storage component,
• (ii) conversion of the stored NO _x to ammonia NH ₃ ,
• (iii) storage of ammonia in an NH ₃ storage component,
• (iv) reaction of NH ₃ with NO _x .

The Method of exhaust gas purification is also characterized in that Stage (i) under lean exhaust conditions and stage (ii) run under rich exhaust conditions, and stages (iii) and (iv) under both rich and lean exhaust conditions expire.

Further can the steps (i) and (iv) at least temporarily simultaneously and / or in parallel expire.

The term internal combustion engines is understood to mean thermal energy converters which convert chemical energy stored in fuels into heat and mechanical energy by combustion. For internal combustion engines, the air trapped in a gas-tight and variable working space (eg a piston) is the working medium defined in the sense of a heat engine at the same time carrier of the necessary oxygen for combustion. Combustion occurs cyclically, with both the fuel and the (air) oxygen being reloaded before each cycle. Depending on the leadership of the cycle ', z. As described by a Carnot's pV working diagram, thermodynamically can be distinguished exactly between gasoline engine and diesel engine. A practical working definition of these engine types is given below.

When an essential criterion for the classification of both engine types as well as catalysts, the ratio of gasoline to air, expressed by the "air ratio" λ. This corresponds to a value of λ = 1.0 exactly the stoichiometric relationship from gasoline to dry air, i. there is just enough air in the combustion chamber, so that all gasoline stoichiometric to carbon dioxide and can burn water. In the technical literature will be Mixtures with λ> 1 referred to as "lean" (excess oxygen) and those with λ <1 as "fat" (oxygen deficiency). For the purposes of the present invention, mixtures with λ> 1.2 are said to be "lean" and those where λ <1.0 is referred to as "bold", a clear demarcation from the stoichiometric To get area. Accordingly, the so defined fats and / or lean mixtures also as non-stoichiometric mixtures in the sense of the invention.

conventional Otto engines are by the formation of a homogeneous gasoline-air mixture outside of the working space, i. of the piston chamber, in which the combustion takes place, and characterized by controlled spark ignition. Petrol engines need slightly boiling and ignore Fuels (the ignition limits an Otto engine are typically between λ = 0.6 and λ = 1.4). In the context of the present invention, it is of particular concern for exhaust gas catalysis Meaning that conventional petrol engines, over a by λ probe controlled three-way Katalysatorverfügen, predominantly at a λ value of approximately One operated (= stoichiometric Business).

Under "lean engines" are such gasoline engines understood, the predominant under oxygen excess operate. For For purposes of the present invention, lean-burn engines are defined quite concretely over their λ value, i.e. Lean motors in the sense of the present invention are motors, the outside too thrust shutdowns, at least partially in the lean condition, i. at a λ value operated by 1.2 or greater become. In addition, you can for lean-burn engines, of course also fat operating conditions and stöchimetrische operating conditions occur: A brief enrichment of the engine and thus also the Exhaust gases can be initiated by the engine electronics with the help of modern injection systems be or in the natural Driving operation occur (eg at load increases, at full load or at the start). An alternate mode of operation of rich and lean cycles is referred to as "fat-lean operation" in the sense of the present Invention referred to.

• • alle Otto-Motoren mit Direkteinspritzung (BDE-Motoren) und mit Betriebszuständen von λ > 1, sowie alle Otto-Motoren mit externer Gemisch-Aufbereitung. In diese Klasse fallen unter anderem Schichtlade-Motoren, d.h. Motoren, die in der Nähe der Zündkerze ein zündwilliges Gemisch, ansonsten aber ein insgesamt mageres Gemisch aufweisen sowie Otto-Motoren mit höherer Verdichtung in Verbindung mit direkter Einspritzung. Hierunter fallen beispielsweise Motoren nach dem Mitsubishi-Verfahren (GDI = gasoline direct injection; common rail Einspritzung), der von VW entwickelte FSI (= fuel stratified injection)-Motor oder der von Renault konzipierte IDE (= injection directe essence)-Motor;
• • alle Diesel-Motoren (siehe unten);
• • Vielstoff-Motoren, d.h. Motoren, die zündwillige und/oder zündunwillige Kraftstoffe, Kraftstoff-Gemische wie Alkohole, Bio-Alkohole, Pflanzenöle, Kerosin, Benzin sowie beliebige Mischungen aus zwei oder mehr der vorstehende genannten Substanzen verbrennen.

In particular, under lean-burn engines within the meaning of the invention, the following embodiments are understood quite generally:

• • all petrol engines with direct injection (BDE engines) and operating states of λ> 1, as well as all petrol engines with external mixture preparation. This category includes, inter alia, stratified charge engines, ie engines that have an ignitable mixture in the vicinity of the spark plug, but otherwise an overall lean mixture and gasoline engines with higher compression in conjunction with direct injection. These include, for example, Mitsubishi engines (GDI = gasoline direct injection, common rail injection), the FSI (= fuel stratified injection) engine developed by VW or the IDE (= injection directe essence) engine designed by Renault;
• • all diesel engines (see below);
• • Multi-fuel engines, ie engines that burn ignitable and / or ignitable fuels, fuel blends such as alcohols, bio-alcohols, vegetable oils, kerosene, gasoline and any mixtures of two or more of the aforementioned substances.

Diesel engines are characterized by internal mixture formation, a heterogeneous fuel-air mixture and by auto-ignition. Accordingly, diesel engines demand ignitable fuels. In the context of the present invention is of particular importance that diesel exhaust gases have similar characteristics as the exhaust gases of lean-burn engines, ie continuously lean, so are oxygen-rich. Consequently, similar demands have to be made on the catalysts for NO _x reduction in connection with diesel engines with regard to nitrogen oxide removal as on catalysts used for Otto engines in lean operation. A major difference of diesel car engines in comparison Otto-car engines, however, lies in the generally lower exhaust gas temperatures of diesel car engines (100 ° C to 350 ° C) compared to gasoline engine cars (250 ° C to 650 ° C), which occur within the legally prescribed driving cycles. A lower exhaust gas temperature makes the use of catalysts which are not or only slightly contaminated with sulfates particularly attractive, since the desulfurization, as mentioned above, occurs only at the exhaust gas temperature temperatures above about 600 ° C is effectively possible. Everything said in the present invention with regard to catalysts for lean-burn engines also applies accordingly to catalysts used for diesel engines.

Depending on the mixture formation and the load-rpm characteristic curve, it is found that catalysts adapted to different exhaust gas treatment are necessary for different engines. So z. As a catalyst for a conventional gasoline engine, the gasoline-air mixture with the aid of injection and throttle continuously set to λ ≈ 1 and its air ratio is optionally controlled by means of a λ-probe, completely different functionality for the reduction of NO _x as, for example, a catalyst for a lean-burn engine, which is operated at λ> 1.2, that has an oxygen excess in normal driving operation. It is obvious that in the case of excess oxygen, a catalytic reduction of NO _x on an active metal is difficult.

Of the The term "diesel oxidation catalyst" refers entirely generally on catalysts used in the exhaust gas of internal combustion engines remove two major pollutants, namely carbon monoxide by oxidation Carbon dioxide as well as hydrocarbons through oxidation too, ideally Water and carbon dioxide. When using a catalyst in diesel engines For the two mentioned tasks, a third can occur, namely the Remove soot by Oxidation.

The term "three-way catalyst" broadly refers to catalysts that remove three major pollutants in the exhaust gas of internal combustion engines, namely, nitrogen oxides (NO _x ) by reduction to nitrogen, carbon monoxide by oxidation to carbon dioxide, and hydrocarbons by oxidation, ideally , Water and carbon dioxide. When using a catalytic converter in diesel engines, a fourth can be done to the three mentioned tasks, namely the removal of soot by oxidation.

conventional Three-way catalysts for Otto engines according to the prior art are in the stoichiometric Operation used, i. at λ values, which move in a narrow range around 1.0. The λ value becomes doing so by regulating the gasoline-air mixture in the combustion chamber adjusted with the help of injector and throttle. In non-stoichiometric Operation, ie in non-conventional operation, λ values are possible, the significantly different from 1.0, for example, λ> 1.2 or λ> 2.0 but also λ <0.9. The discontinuous operation of an engine, i. the alternation between lean and fat Operation of the engine is referred to as fat-lean operation.

in the Following are the technical advantages of the process illustrated and compared to the known methods and Catalysts discussed.

It is already known from the prior art that the active metals Pt, Pd, Rh, Ir and Ru in the exhaust gas purification of lean engines have multiple functions. On the one hand, they can themselves serve as NO _x adsorbents and store NO _x in the lean phase. On the other hand, they support the storage of NO _x in the NO _x storage components. For example, Pt catalyzes the oxidation of NO to NO ₂ , which is adsorbed or absorbed in a subsequent step as nitrate or nitrite on or in a NO _x storage material.

Furthermore, the active metals catalyze the reduction of the stored NO _x to NH ₃ within the enrichment phase. In this case, the ammonia is not formed exclusively from the nitrogen oxides stored in the NO _x storage catalytic converter, but also, to a lesser extent, from those nitrogen oxides which are emitted from the engine during the enrichment phases or during the substoichiometric mode of operation (ie the rich mode of operation).

In addition, the support Precious metals also the oxidation of CO and HC during the lean phases as well all 3-way functionality while the stoichiometric Motor operation.

The ammonia formed is stored in the NH ₃ storage component of the catalyst. This is able to sorb the released NH ₃ under lean as well as under rich exhaust conditions in a wide temperature range. The NH ₃ storage component thus serves to absorb the NH ₃ produced in the fat phase as quantitatively as possible. As already explained above, the retting times and depths should be as low as possible in order to minimize the additional fuel consumption. On the other hand, in the context of the present invention, richening times and depths should be large enough to completely empty the NO _x storage catalyst and to ensure efficient reduction of the nitrogen oxides liberated at the moment of enrichment to ammonia.

Switching from rich operation to lean operation, one can imagine that the emission of engine-emitted NO _{x is} reduced in two different ways simultaneously: A part of the NO _x is stored in the NO _x storage catalyst, while the other part directly with the bound in the NH ₃ storage medium NH ₃ to N ₂ . Since the NO _x reduction takes place simultaneously and on two different reaction paths, overall a significantly higher NO _x conversion performance can be achieved than in the known processes using known NO _x storage catalysts.

The emitted NH ₃ is bound by the present method in an NH ₃ storage component. During the subsequent lean phase, the NH _{3 can} then according to the so-called SCR reaction (Selective Catalytic Reduction) with the emitted from the engine NO _x under lean exhaust conditions to N _{2 are} degraded.

The combined for the process NH ₃ storage / SCR catalyst is chemically constructed so that the stored NH _{3 is} not oxidized in lean operation or only to a very limited extent with the oxygen contained in the exhaust gas to NO _x and emitted. Since in this way at least part of the stored first in the NO _x storage catalytic NO _x in ammonia converted, and is then reacted in accordance with the SCR reaction to N _2, the method allows for increased NO _x -Konvertierungsleistungen, since the SCR reaction the NO _x storage supported.

In order to enable the simultaneous execution of SCR reaction and NO _x storage, it is not only economically desirable to integrate the NO _x storage catalyst, the NH ₃ storage medium and the SCR catalyst, for example in the form of a physical Mixture. In contrast, a sequential arrangement of these components would not be expedient, since in the case of a sequential arrangement, the SCR reaction and NO _x storage could be done only to a very small extent simultaneously, but instead largely in succession. If, for example, the NO _x storage catalytic converter upstream of the NH ₃ storage and the SCR catalytic converter, the lean NO _x storage catalyst would initially be filled with NO _x in lean operation mode. Only in the case of decreasing NO _x storage with increasing lean operation, the SCR reaction could make a significant contribution to the overall NO _x conversion.

In one embodiment of the method, the latter is operated in such a way that the catalytic converter or the catalyst system is followed by an NO _x sensor, the measured values of which are transmitted to an engine control of the internal combustion engine which performs the rich / lean adjustments of the exhaust gas. In a preferred embodiment, an enrichment is induced when an adjustable NO _x threshold value is exceeded.

The method using the catalysts defined above has a higher NO _x -Konvertierungsleistung especially in the low temperature range than conventional methods with known NO _x storage catalysts.

The advantages of the invention become particularly clear when, for example, the exhaust-gas temperatures either fall below or exceed the temperatures necessary for the storage of NO _x , for example caused by sudden load changes. In these cases, provided that sufficient NH _{3 is present} in the NH ₃ store, the SCR reaction alone can allow high NO _x conversions to N ₂ . Another advantage is to run the engine longer in lean operation and thus minimize secondary emissions.

The method of pollutant removal can also be operated so that the catalyst is also used in combination with a conventional catalyst, for example, a NO _x storage catalyst from the prior art. It has been found that in addition to the high conversion performance in the low temperature range, such a combination also has a high conversion performance in the high temperature range. Apparently, this combination has a synergistic effect that was unexpected.

Around CO and HC breakthroughs while Minimizing the richening phases can add another catalyst Catalyst, preferably in the form of an oxidation catalyst, downstream be downstream.

For the procedure the pollutant removal, the catalyst is preferably in close to the engine Position or in underfloor position of a motor vehicle mounted.

Of the Catalyst of the process may also be used in combination with at least another catalyst or filter selected from the following group operated: conventional start-up or light-off catalysts, HC-SCR catalysts, Soot or Soot particle filter.

there Can the soot particulate filter with the for The method used to be coated catalyst.

Description of the figures:

1 shows the concentration of NO _x as a function of time in the cyclic rich / lean operation using the inventive catalyst according to Example 2 (B2) at 150 and 200 ° C (test conditions I).

2 shows the concentration of NO _x as a function of time in the cyclic rich / lean operation using a conventional storage catalyst (reference) according to Comparative Example 1 (VB1) at 150 and 200 ° C (test conditions I).

3 shows the concentration of NH ₃ as a function of time in the fat / lean cyclic operation using the inventive catalyst according to Example 2 (B2) at 200 and 250 ° C (Test Conditions II).

4 shows the concentration of NH ₃ as a function of time in the fat / lean cyclic operation using the inventive catalyst according to Example 3 (B3) at 200 and 250 ° C (test conditions II).

5 shows the concentration of NH ₃ as a function of time in the cyclic rich / lean operation using a conventional storage catalyst (reference) according to Comparative Example 01 (VB01) at 200 and 250 ° C (Test Conditions II).

6 shows the concentration of NH ₃ as a function of time in the cyclic rich / lean operation using the storage component (KI) of the inventive catalyst according to Comparative Example 02 (VB02) at 150, 200 and 250 ° C (Test Conditions II).

7 shows the average NO _x conversion in the rich / lean cycles as a function of the reaction temperature under test conditions I on the fresh catalysts according to Example 2 (B02) and Comparative Example 2 (VB02).

8th shows the mean NO _x conversion in the rich / lean cycles as a function of the reaction temperature under test conditions I on the fresh catalysts according to Example 6 (B06) and Comparative Example 3 (VB03).

9 shows the average NO _x conversion in the rich / lean cycles as a function of the reaction temperature under test conditions I on the fresh catalysts according to Examples 79 (B79), Example 81 (B81) and Comparative Example 1 (VB01).

The figures relate to the embodiments described below:
In the following, the preparation of exemplary catalysts according to the invention will be illustrated in exemplary embodiments and their properties improved compared with the prior art. The fact that this is done on concrete examples with the specification of specific numerical values should under no circumstances be construed as limiting the general statements made in the description and the claims.

Example 1 (B01)

Of the Catalyst consists of two components I and II.

To the Preparation of component I (KI) was a zirconium oxide (XZ16075, From Norton) suspended in water and ground in a ball mill. After drying, 1.25 g of the milled material was used as carrier oxide submitted.

147 μl aqueous 1.6 molar palladium nitrate solution was 178 μl 2.5 molar cerium nitrate solution mixed and with 675 μl Water diluted. The carrier oxide was with 1000 ul the resulting solution, which corresponded to the water absorption of zirconium oxide, impregnated. The so impregnated carrier oxide was then dried at 80 ° C for 16 hours.

The resulting loading based on the amount of carrier oxide was 2 wt .-% palladium and 5% by weight of cerium.

When Component II was a beta-zeolite (H-BEA-25, Fa. Süd-Chemie) used.

To the Preparation of a catalyst was 1.25 g of component I, 0.53 g of component II and 3 ml of water in a mortar. That resulted Material was then dried at 80 ° C for 16 hours.

Subsequently was the material for 2 hours at 500 ° C calcined in air (referred to as "fresh").

One Part of the fresh material was additionally 16 hours at 650 ° C in a Air stream containing 10% water, calcined (referred to as "aged").

Examples 2 to 45 (B02-B45)

The Catalysts were prepared analogously to Example 1, wherein the Preparing the component I (KI) the zirconium oxide with aqueous solution one or more salts, such as palladium nitrate, trinitratonitrosylruthenium (II), Rhodium nitrate, platinum nitrate, iron nitrate, praseodymium nitrate, cerium nitrate, Potassium nitrate, impregnated was and component II was varied.

In the example table (Table 1) are the compositions of corresponding catalysts based on weight percentages.

Example 46 (B46)

Of the Catalyst consists of two components.

To the Preparation of component I (KI) was cerium (III) nitrate (Aldrich) at 500 ° C calcined for two hours. After calcination, 1 g of the Materials as carrier oxide submitted.

118 μl of aqueous 1.6 molar palladium nitrate solution was 982 μl Water diluted. The carrier oxide was 1100 μl the resulting solution, the water absorption of the carrier material corresponded, impregnated. The so impregnated carrier oxide was then dried at 80 ° C for 16 hours.

The resulting loading based on the amount of carrier oxide was 2 wt .-% palladium.

When Component II was a beta-zeolite (H-BEA-25, Fa. Süd-Chemie) used.

To the Preparation of a catalyst was 1 g of component I, 1 g of Component II and 3 ml of water mixed in a mortar. That resulted Material was then dried at 80 ° C for 16 hours.

Subsequently was the material for 2 hours at 500 ° C calcined in air (referred to as "fresh").

One Part of the fresh material was additionally 16 hours at 650 ° C in a Air stream containing 10% water vapor calcined (referred to as "aged").

Examples 47 to 75 (B47-B75)

The Catalysts were prepared analogously to Example 46, wherein the Preparation of component I (KI) the carrier oxide with aqueous solution one or more salts, such as palladium nitrate, trinitratonitrosylruthenium (II), Rhodium nitrate, Platinum nitrate, iron nitrate, praseodymium nitrate, cerium nitrate, impregnated and the component II was varied.

In the example table (Table 1) are the compositions of corresponding catalysts based on weight percentages.

Example 76

Of the Catalyst consists of two components I and Π.

To the Preparation of component I (KI) was silica-alumina (Siralox 5/170, Fa. Sasol) suspended in water and ground in a ball mill. After drying, 5 g of the milled material was used as carrier oxide submitted.

513 μl of an aqueous, 1.0 molar platinum nitrate solution were with 15600 μl an aqueous, 0.35 molar barium nitrate solution mixed and with 387 .mu.l Diluted with water. The carrier oxide was 16500 μl this solution mixed, and the water evaporated with stirring. The so impregnated carrier oxide was then dried for 16 hours at 80 ° C in a drying oven. Subsequently Component I was calcined for two hours at 500 ° C under air in a muffle furnace.

The resulting loading based on the amount of carrier oxide was 2 wt .-% platinum and 15% by weight of barium.

When Component II was a beta-zeolite (Zeocat PB / H, Zeochem). used.

To the Preparation of a catalyst was 0.25 g of component I with 0.25 g of component II mixed.

Example 77

Of the Catalyst consists of two components I and II.

To the Preparation of component I (KI) was silica-alumina (Siralox 5/170, Fa. Sasol) suspended in water and ground in a ball mill. After drying, 5 g of the milled material was used as carrier oxide submitted.

384 μl of an aqueous, 1.0 molar platinum nitrate solution were mixed with 243 μl an aqueous, 1.0 molar rhodium nitrate solution and 54610 μl an aqueous, 0.1 molar barium nitrate solution mixed. The carrier oxide was 55237 μl this solution mixed, and the water evaporated with stirring. The so impregnated carrier oxide was then dried for 16 hours at 80 ° C in a drying oven. Subsequently was the component I calcined for two hours at 500 ° C under air in a muffle furnace.

The resulting loading based on the amount of carrier oxide was 1.5 wt .-% platinum, 0.5 wt .-% rhodium and 15% by weight of barium.

When Component II was a beta-zeolite (Zeocat PB / H, Zeochem). used.

To the Preparation of a catalyst was 0.25 g of component I with 0.25 g of component II mechanically mixed.

Example 78

Of the Catalyst consists of three components.

To the Preparation of component I (KI) was a zirconium oxide (XZ16075, From Norton) suspended in water and ground in a ball mill. After drying, 5 g of the milled material was used as carrier oxide submitted.

752 μl of an aqueous 1.0 molar palladium nitrate solution were mixed with 198 μl an aqueous 1.0 molar Trinitratonitrosylruthenium (II) solution, mixed 714 .mu.l of an aqueous 2.5 molar cerium nitrate solution and with 2336 μl Water diluted. The carrier oxide was charged with 4000 μl the resulting solution, which corresponded to the water absorption of zirconium oxide, impregnated. The so impregnated carrier oxide was then dried at 80 ° C for 16 hours.

The resulting loading based on the amount of carrier oxide was 1.6 wt .-% palladium, 0.4 wt .-% Ru and 5 wt .-% Ce.

When Component II was a beta-zeolite (H-BEA25, Fa. Süd-Chemie).

To prepare component III (KIII), 0.5 g of NH ₄ -beta zeolite (NH ₄ -BEA 25, from Süd-Chemie) was added to a 1 molar cerium nitrate solution and stirred at 80 ° C. for two hours. Thereafter, the zeolite material was filtered off, washed with deionized water and dried at 120 ° C for 16 hours. The resulting material was calcined in a muffle furnace for two hours at 500 ° C in air.

To the Preparation of a catalyst was 1.25 g of component I, 0.75 g of component II, 0.5 g of component II and 5 ml of water in mortar mixed. The resulting material then became for 16 hours 80 ° C dried.

Subsequently was the material for 2 hours at 500 ° C calcined in air (referred to as "fresh").

One Part of the fresh material was additionally 16 hours at 650 ° C in a Air stream containing 10% water, calcined (referred to as "aged").

Example 79 (B79)

Of the Catalyst consists of mechanical mixture of two catalysts.

To the Preparation of the catalyst (referred to as "fresh") was 0.18 g of the catalyst according to example 1 (B01) with 0.15 g of the reference catalyst (VB01).

Example 80 (B80)

Of the Catalyst consists of a mechanical mixture of two catalysts. To prepare the catalyst (referred to as "fresh"), 0.18 g of the aged was used Catalyst from Example 34 (B34) with 0.15 g of the reference catalyst (VB01) mixed.

Example 81 (B81)

Of the Catalyst consists of a mechanical mixture of two catalysts.

To the Preparation of the catalyst (referred to as "fresh") was 0.18 g of the aged one Catalyst from Example 35 (B35) with 0.15 g of the reference catalyst (VB01) mixed.

Comparative Example 01 (VB01)

Comparative Example 01 includes a Pt / Pd / Rh / Ba / Ce-based (reference catalyst) NO _x storage catalyst as known in the art.

Comparative Example 02 (VB02)

Comparative example 02 includes the component I (KI) of the catalyst according to Example 2 (B02), which at 500 ° C calcination for two hours.

The Loading based on the amount of zirconium oxide was 2 wt .-% palladium, 0.4% by weight of ruthenium and 5% by weight of cerium.

Comparative Example 03 (VB03)

Comparative example 03 contains the component I (KI) of the catalyst according to Example 6 (B06), which at 500 ° C calcination for two hours.

The Loading based on the amount of zirconium oxide was 2 wt .-% palladium, 0.4% by weight of ruthenium, 2% by weight of iron and 5% by weight of cerium.

catalyst testing

The Measurements on the for The catalysts used in the process were in fixed bed laboratory reactors made of stainless steel with simulated engine exhaust. The Catalysts were in cyclic rich / lean operation in the temperature range between 150 and 400 ° C tested.

The test parameters were as follows: Test conditions I Fat-lean settings: 2 s fat / 60 s lean Gas mixture composition: Skinny: 300 vppm NO, 1000 vppm CO, 100 vppm propene, 10% O ₂ , 5% H ₂ O, balance - N ₂ . Fat: 0.03% O ₂ , ~ 6% CO, ~ 2% H ₂ Gas flow rate: 45 l / h Catalyst mass: 0.15-0.5 g Test conditions II Fat-lean settings: 2 s fat / 60 s lean Gas mixture composition: Skinny: 300 vppm NO, 1000 vppm CO, 100 vppm propene, 10% O ₂ , balance - N ₂ Fat: 0.03% O2, ~ 6% CO, ~ 2% H ₂ Gas flow rate: 45 l / h Catalyst mass: 0.15-0.5 g

The for the Method used catalysts were measured as bulk material. On the application of the washcoat on a molding was omitted. to activity measurement For the most part, a sieve fraction with particle sizes of 315-700 μm was used.

As a reference catalyst (VB01), a commercial honeycomb-shaped NO _x storage catalyst was used. The reference catalyst was crushed and also used as bulk material for the activity measurements. With regard to the comparison between the reference system and the catalysts according to the invention, the masses of noble metal used were identical in each case in the activity measurements.

The measurement of O _{2 was} carried out with a lambda meter from. Etas. NO _x was measured using a chemiluminescer from Ecophysics. The measurement of NH _{3 was} carried out under test conditions II with a mass spectrometer from. Balzers.

Hydrothermal aging

The Hydrothermal aging of the catalysts took place in a muffle furnace at a temperature of 650 ° C in an air stream with 10 vol .-% water vapor. The catalysts were held at this temperature for 16 hours and then cooled to room temperature.

For the evaluation of the catalysts, the mean NO _x conversions in the rich / lean cycles were calculated at different reaction temperatures. The corresponding values for the catalysts in the fresh state and after hy drothermal aging are summarized in Tables 2 to 5 and in the 7 to 9 shown.

Table 2. Results of the catalytic tests for NO _x conversion in the lean-fat operation on the fresh catalysts (test conditions I, noble metal amount in the catalyst: 0.05 g)

Table 2. Results of the catalytic tests for NO _x conversion in the lean-fat mode on the fresh catalysts (test conditions I, amount of noble metal in the catalyst: 0.0025 g)

Table 3. Results of the catalytic tests for NO _x conversion in fat-lean operation on the catalysts hydrothermally aged at 650 ° C. (test conditions I, noble metal amount in the catalyst: 0.05 g)

Table 4. Results of the catalytic tests for NO _x conversion in the lean-fat mode on the hydrothermally aged catalysts (test conditions I, noble metal amount in the catalyst: 0.025 g)

The results of the catalytic measurements show that the catalysts comprising components I and II have significantly higher NO _x conversions at low exhaust gas temperatures (<300 ° C.) than the reference NO _x storage catalyst. This applies both in the fresh state and after the hydrothermal aging.

The in the 1 to 2 Measurements of the NO _x concentrations in the rich / lean cycles shown allow a comparison of the NO _x conversion between the catalyst (B2) and the conventional storage catalyst (VB1) at the exhaust gas temperatures of 150 and 200 ° C.

The 3 to 4 show the formation of NH ₃ on the catalysts.

5 shows the formation of NH ₃ on the conventional storage catalyst (VB01).

• (i) die die NO_x- und NH₃-Speicherkomponenten enthaltenden Katalysatoren im Gegensatz zum NO_x-Speicherkatalysator keine NH₃-Emissionen aufweisen und zudem
• (ii) insbesondere bei tiefen Abgastemperaturen eine effizientere Entfernung von NO_x gewährleisten.

From the measurements it is clear that

• (i) in contrast to the NO _x storage catalyst, the catalysts containing the NO _x and NH ₃ storage components have no NH ₃ emissions, and moreover
• (ii) ensure more efficient removal of NO _x , especially at low exhaust gas temperatures.

The catalysts of the invention contain a zeolite-based component which functions both as NH ₃ storage and as SCR catalyst. The 7 and 8th show the comparison of NO _x conversion between the catalysts (B02 and B06) and memory components (AI) without using a zeolite component (VB02 and VB03).

In the 9 shown results show that the use of a mechanical mixture of the NO _x - and NH ₃ storage components containing catalysts with a conventional NO _x storage catalyst (B79 and B81) an improvement of NO _x conversion in the temperature range between 150 and 400 ° C. was achieved compared to the reference NO _x storage catalytic converter.

Claims (21)

Catalyst for removing pollutants containing nitrogen oxides (NO _x ) from the exhaust gases of lean-burn engines in cyclic lean / rich operation, characterized in that the catalyst (i) stores nitrogen oxides (NO _x ) in a NO _x storage component, (ii) NO _x converts to ammonia (NH ₃ ), (iii) stores ammonia in an NH ₃ storage component, (iv) reacts NH ₃ with NO _x . Catalyst for removing pollutants containing nitrogen oxides (NO _x ) from the exhaust gases of lean-burn engines in cyclic lean / rich operation, characterized in that the catalyst comprises at least one of the materials from group (1) and at least one acidic solid from the group (1). 2) and optionally at least one of the materials from groups (3) and (4) contains: (1) Pt, Pd, Rh, Ir and Ru, each alone or in admixture, present on a support material selected from: oxides, mixed oxides, Phosphates and sulfates of Al, Si, Zr, Ti, Ce, the alkaline earth metal and rare earth elements; heteropolyacids; zeolites; and mixtures thereof; (2) zeolites; heteropolyacids; sulphated zirconium oxides or zirconium phosphates; and mixtures thereof; (3) oxides and mixed oxides of the alkali metal, alkaline earth metal, rare earth elements, zirconium, titanium; (4) inorganic compounds of V, Cr, Mn, Fe, Co, Ni, Cu, In, Ga, Ag and Sn, and mixtures thereof; wherein the catalyst stores (i) nitrogen oxides (NO _x ) in a NO _x storage component, (ii) converts NO _x to ammonia (NH ₃ ), (iii) stores ammonia in an NH ₃ storage component, (iv) NH ₃ NO _x converts. Catalyst for the removal of pollutants containing nitrogen oxides (NO _x ) from the exhaust gases of lean-burn engines in cyclic lean / rich operation, characterized in that the catalyst is at least one of the materials from group (1) and optionally at least one of the materials from the groups (3) and (4) contains: (1) Pt, Pd, Rh, Ir and Ru, each alone or in admixture, present on a support material selected from: oxides, mixed oxides, phosphates and sulfates of Al, Si, Zr, Ti , Ce, the alkaline earth metal and rare earth elements; heteropolyacids; zeolites; and mixtures thereof; (3) oxides and mixed oxides of the alkali metal, alkaline earth metal, rare earth elements, zirconium, titanium; (4) inorganic compounds of V, Cr, Mn, Fe, Co, Ni, Cu, In, Ga, Ag and Sn, and mixtures thereof; wherein at least one of the support materials from group (1) is an acidic solid as defined in claim 2 and the catalyst (i) stores nitrogen oxides (NO _x ) in a NO _x storage component, (ii) NO _x to ammonia ( NH ₃ ), (iii) stores ammonia in an NH ₃ storage component, (iv) reacts NH ₃ with NO _x . Catalyst, characterized in that it contains at least one of the materials from group (1) and at least one acidic solid from group (2) and optionally at least one of the materials from groups (3) and (4) contains: (1) Pt, Pd, Rh, Ir and Ru, in each case alone or in a mixture, present on a support material selected from: oxides, mixed oxides, phosphates and sulfates of Al, Si, Zr, Ti, Ce, the alkaline earth metal and rare earth elements; heteropolyacids; zeolites; and mixtures thereof; (2) zeolites, heteropolyacids, sulphated zirconium oxides or zirconium phosphates and mixtures thereof; (3) oxides and mixed oxides of the alkali metal, alkaline earth metal, rare earth elements, zirconium, titanium; (4) Inorganic compounds of V, Cr, Mn, Fe, Co, Ni, Cu, In, Ga, Ag and Sn, and mixtures thereof. Catalyst, characterized in that it is at least one of the materials from group (1) and at least one acidic one Solid from group (2) and optionally at least one the materials from groups (3) and (4) contains: (1) Pt, Pd, Rh, Ir and Ru, each alone or in admixture, present on a support material selected from: Oxides, mixed oxides, phosphates, and sulfates of Al, Si, Zr, Ti, Ce, the alkaline earth metal and rare earth elements; heteropolyacids; zeolites; and mixtures thereof; (2) zeolites, heteropolyacids, sulphated Zirconium oxides or zirconium phosphates and mixtures thereof; (3) Oxides and mixed oxides of the alkali metal, alkaline earth metal, rare earth elements, of the zircon, of the titan; (4) inorganic compounds of V, Cr, Mn, Fe, Co, Ni, Cu, In, Ga, Ag and Sn and mixtures thereof; in which it can be produced by a washcoat process. Catalyst according to one of Claims 2 to 5, characterized the zeolite from group (2) has a Si / Al ratio greater than 3 has. Catalyst according to one of Claims 2 to 6, characterized the zeolite of group (2) is selected from the group consisting from pentasile, Y zeolite, USY, DAY, mordenite and zeolite-β. Catalyst according to one of Claims 2 to 7, characterized that the catalyst is another component consisting of ion-exchanged Zeolite, preferably an iron-exchanged and / or rare earth-exchanged zeolite contains. Catalyst according to one of claims 2 to 8, characterized that the proportion of the sum of precious metals in the total mass of Catalyst in the range of 0.05 to 10 wt .-%, wherein the Proportion of precious metals in the total mass of the catalyst in the range from 0.1 to 5 wt .-% is. Catalyst according to one of Claims 2 to 9, characterized that the proportion of acidic solid from the group (2) in the total mass catalyst is in the range of 5 to 95 wt%, with one range from 10 to 75% by weight is preferred. Catalyst according to one of claims 1 to 10, characterized that it is present on a monolithic honeycomb body. A process for preparing a catalyst as defined in any of the preceding claims, characterized in that the method comprises the step (i) comprises: _x (i) contacting the NO storage component with the NH ₃ storage component of the catalyst according to claim 1 or contacting at least one of the materials of group (1) with at least one acidic solid from group (2) and optionally with at least one of the materials from groups (3) and (4) in the catalysts according to any one of claims 2 to 5, wherein the Contacting at least the catalyst according to claim 5 comprises a washcoat process. Catalyst system for the removal of pollutants containing nitrogen oxides (NO _x ) from the exhaust gases of lean-burn engines in cyclic lean-rich operation, characterized in that in addition to a catalyst according to one of claims 1 to 11 or a catalyst prepared according to claim 12 at least one further Catalyst contains. Catalyst system according to claim 13, characterized in that at least one further catalyst is a NO _x storage catalyst. Use of a catalyst according to any one of claims 1 to 11 or a catalyst prepared according to claim 12 or a catalyst system according to claim 13 or 14 for the removal of pollutants containing nitrogen oxides (NO _x ) from the exhaust gases of lean-burn engines in lean rich operation. A process for the removal of pollutants containing nitrogen oxides (NO _x ) from the exhaust gases of lean-burn engines in the lean-fat cyclic operation, characterized in that a catalyst according to any one of claims 1 to 11 or a catalyst prepared according to claim 12 or a catalyst system according to claim 13 or 14 is used. A process for the removal of pollutants containing nitrogen oxides (NO _x ) from the exhaust gases of lean-burn engines in the lean-fat cyclic operation, characterized in that a catalyst according to any one of claims 1 to 11 or a catalyst prepared according to claim 12 or a catalyst system according to claim 13 or 14, the method comprising steps (i) to (iv): (i) storing nitrogen oxides (NO _x ) in a NO _x storage component, (ii) converting the NO _x to ammonia (NH ₃ ), (iii) storage of ammonia in an NH ₃ storage component, (iv) reaction of NH ₃ with NO _x . Method according to claim 17, characterized in that that stage (i) under lean exhaust conditions and the stage (ii) occur under rich exhaust conditions and that the stages (iii) and (iv) under both rich and lean exhaust conditions expire. Method according to claim 18, characterized that the steps (i) and (iv) at least temporarily simultaneously and / or run in parallel. A method according to any one of claims 17 to 19, characterized in that the catalyst or the catalyst system is a NO _x sensor downstream, whose measured values are transmitted to an engine control of the internal combustion engine, the rich-lean settings makes the exhaust gas. soot filter, containing a catalyst as claimed in any one of claims 1 to 11 or a catalyst prepared according to claim 12th