WO2009103549A1 - Scr catalyst with ammonia accumulator function - Google Patents

Abstract

The invention relates to an SCR catalyst comprising a supporting material, through which exhaust gases can flow and a coating of a catalytically active composition that is applied to regions of the supporting material, the SCR active component and the NH3 accumulator component being different from one another. The invention further relates to the use of the SCR catalyst according to the invention for reducing nitrogen oxides of mobile or stationary combustion units.

Description

 SCR catalytic converter with ammonia storage function

The present invention relates to an SCR catalyst which comprises an SCR-active component and an NH ₃ storage component, wherein the NH ₃ storage component is preferably a zeolite. The invention further relates to the use of the SCR catalyst for reducing nitrogen oxides of mobile or stationary incinerators.

SCR (Selective Catalytic Reduction) refers to the selective catalytic reduction of nitrogen oxides from exhaust gases of combustion engines and also power plants. With an SCR catalyst, only the nitrogen oxides NO and NO ₂ (commonly referred to as NO _x ) are selectively reduced, with NH ₃ (ammonia) usually added to the reaction. Therefore, only the harmless substances water and nitrogen are formed as reaction products. For the use of motor vehicles carrying ammonia in compressed gas cylinders is a security risk. Therefore, precursor compounds of ammonia are usually used, which are decomposed in the exhaust line of the vehicles with ammonia formation. Known in this context is, for example, the use of ^AdBlue® , which is an approximately 32.5% eutectic solution of urea in water. Other ammonia sources are, for example, ammonium carbamate, ammonium formate or urea pellets.

Before the actual SCR reaction, ammonia must first be formed from urea. This is done in two reaction steps, collectively referred to as a hydrolysis reaction. net. First, NH ₃ and isocyanic acid are formed in a thermolysis reaction. Isocyanic acid is then reacted with water to form ammonia and carbon dioxide in the actual hydrolysis reaction.

To avoid solid precipitates, it is necessary that the second reaction by the choice of suitable catalysts and sufficiently high temperatures (from 250 ⁰ C) is sufficiently fast. Modern SCR reactors simultaneously take over the function of the hydrolysis catalyst.

The ammonia produced by the thermohydrolysis reacts on the SCR catalyst according to the following equations:

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O (1)

NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O (2) 6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O (3)

At low temperatures (<300 ⁰ C), sales uberwie- quietly through reaction (2) runs off. For a good low-temperature conversion, it is therefore necessary to set a NO ₂ : NO ratio of about 1: 1. Under these circumstances, the reaction (2) already at temperatures from 170-200 ⁰ C take place.

The oxidation of NO to NO _x takes place in an upstream oxidation catalyst which is required for optimum efficiency.

If more reducing agent is metered than is reacted during the reduction with NO _x , undesirable NH ₃ slip may occur. The removal of the NH ₃ can be achieved by an additional oxidation catalyst downstream of the SCR catalyst. This barrier catalyst oxidizes the possibly ammonia to N ₂ and H ₂ O. In addition, careful application of urea dosing is essential.

An important parameter for SCR catalysis is the so-called feed ratio α, defined as the molar ratio of metered NH ₃ to the NO _x present in the exhaust gas. Under ideal operating conditions (no NH ₃ slip, no side reactions, no NH ₃ oxidation), α is directly proportional to the NO _x reduction rate:

At ot = 1 theoretically a one percent NO _x reduction is achieved. In practical use, with NH ₃ slip of <20 ppm, a NO _x reduction of 90% in stationary and transient operation can be achieved.

Through the upstream hydrolysis a _NOx conversion is achieved> 50% only at temperatures above about 250 ⁰ C with today's SCR catalysts, optimum conversion rates are within the temperature window of 250 - achieved 450 ° C.

The dosing strategy is of great importance in high NH ₃ storage capacity catalysts because the NH ₃ storage capability of prior art SCR catalysts typically decreases with increasing temperature.

At present, catalysts based on titanium dioxide, vanadium pentoxide and tungsten oxide are predominantly used both in the power plant sector and in the automotive sector. Also, the use of SCR catalysts based on zeolites is known in the art.

A disadvantage of the SCR catalysts used in the prior art, even in the zeolite-based SCR catalysts. Catalysts, is the relatively poor conversion of the exhaust gases in cold start operation. That is, the exhaust gases occurring at the start of the engine flow over a still cold catalyst and are therefore not implemented. Also, the urea dosage is due to a possible condensation usually only above 250 ⁰ C. This means that in the cold start phase almost no nitrogen oxide emissions are reduced.

Further problems arise with fast load changes. With a load change, a sudden change in the exhaust gas concentration is connected and the urea dosing can be adjusted only offset in time due to the inertia of the dosing system. In particular, the prior art catalysts have problems in the occurrence of NH ₃ slip. This leads to unnecessary emission of NO _x .

The object of the present invention was thus to provide an improved SCR catalyst with respect to the SCR catalysts known from the prior art, which is also suitable for use in exhaust systems of internal combustion engines.

It has now surprisingly been found that SCR catalysts comprising a certain NH ₃ storage component do not show the problems of the catalysts known from the prior art.

Surprisingly, it has been found within the scope of the present invention that the presence of the NH ₃ storage component does not require impregnation with a noble metal such as palladium, platinum, etc. on the SCR catalyst. It has also been shown that the existence of the Ammo niak storage component in the SCR catalyst, a further oxidation catalyst behind the SCR catalyst in an exhaust system is unnecessary. This barrier catalyst hitherto used in the prior art for removing the NH ₃ oxidizes the possibly occurring ammonia to N ₂ and H ₂ O. Due to the storage of the excess NH ₃ , the barrier catalyst can thus surprisingly be dispensed with.

Furthermore, it has surprisingly been found that SCR catalysts comprising a NH ₃ storage component with a zeolite containing SiO ₂ and Al ₂ O ₃ in a specific specific ratio and which in a certain percentage based on the amount of the catalytically active composition in the SCR catalyst is present, have particularly advantageous properties. It has been found, in particular, that a zeolite comprising a very specific SiO ₂ / Al ₂ O ₃ molar ratio and used in a certain percentage of the catalytically active composition in an SCR catalyst has an optimized absorption and desorption character - shows characteristic. As a result, a SCR catalyst designed in this way already releases enough NH ₃ during a cold start, so that the SCR-active constituent also has optimum NO _x conversion rates in cold start behavior. An additional effect here is that at fast Lastwech-, as they are common, for example in the automotive industry, an existing inert urea dosing is relieved, as can be compensated by optimized absorption and desorption the associated concentration peaks.

The present invention therefore relates, in a first aspect, to an SCR catalyst comprising a catalytically active composition comprising an SCR-active component and an a NH ₃ storage component, wherein the SCR active component and the NH ₃ storage component are different from each other, and wherein the NH ₃ storage component comprises a zeolite having a Si0 ₂ / Al ₂ θ ₃ molar ratio of 5: 1 to 150: 1 and the zeolite is contained in an amount of 2 to 30 wt .-% in the catalytically active composition.

Furthermore, the subject matter of the present invention also includes an exhaust gas purification system for the purification of diesel engine exhaust gases comprising a group of catalyst devices arranged one behind the other, consisting of an oxidation catalyst and an SCR catalyst according to the invention.

Finally, the present invention also relates to the use of the SCR catalyst according to the invention for reducing the nitrogen oxide emission of mobile or stationary combustion devices.

The term "SCR active component" refers to a material that catalyzes the aforementioned SCR reaction.

The term "NH ₃ storage component" is understood as meaning a material which is capable of reversibly adsorbing NH _3. It is preferably a porous or particularly preferably a microsoporous material.

In the context of the present invention, the storage component is a zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of 5: 1 to 150: 1.

The term "zeolite" generally used in the definition of the International Mineralogical Association (DS Coombs et al., Can. Mineralogist, 35, 1997, 1571) is a crystalline substance. dance from the group of aluminum silicates with spatial network structure of the general formula

M ^{n +} [(AlO ₂ ) X (SiO ₂ ) Y] XH ₂ O

understood that consist of Siθ ₄ / Alθ ₄ tetrahedra, which are linked by common oxygen atoms to a regular three-dimensional network. The ratio of Si / Al = y / x is always> 1 according to the so-called "Löwenstein rule", which prohibits the adjacent occurrence of two adjacent negatively charged AlO ₄ tetrahedra. Although there are more exchange sites for metals available at a low Si / Al ratio, the zeolite is becoming increasingly thermally unstable.

The zeolite structure contains voids and channels characteristic of each zeolite. The zeolites are classified according to their topology into different structures (see above). The zeolite framework contains open cavities in the form of channels and cages that are normally occupied by water molecules and extra framework cations that can be exchanged. An aluminum atom has an excess negative charge which is compensated by these cations. The interior of the pore system represents the catalytically active surface. The more aluminum and the less silicon a zeolite contains, the denser the negative charge in its lattice and the more polar its internal surface. The pore size and structure are determined by the Si / Al ratio, which determines most of the catalytic character of a zeolite, in addition to the parameters in the preparation (use or type of template, pH, pressure, temperature, presence of seed crystals) , Due to the presence of z. B. 3-valent atoms (eg., Al or Ga), the zeolite receives a negative lattice charge in the form of so-called Anionstellen, in the vicinity of which are the corresponding cation positions. The negative charge is compensated by the incorporation of cations into the pores of the zeolite material. The zeolites are distinguished mainly by the geometry of the cavities formed by the rigid network of SiO4 / AlO4 tetrahedra. The entrances to the cavities are formed by 8, 10 or 12 "rings" (narrow, medium and large pore zeolites). Certain zeolites show a uniform structure structure (eg ZSM-5 with MFI topology) with linear or zigzag running channels, in others close behind the pore openings larger cavities, eg. As in the Y and A zeolites, with the topologies FAU and LTA.

In principle, any zeolite, in particular any 10 and 12 "ring" zeolite, which has a SiO ₂ / Al ₂ O ₃ molar ratio of from 5: 1 to 150: 1, can be used in the context of the present invention the topologies AEL, BEA, CHA, EUO, FAO, FAU, FER, KFI, LTA, LTL, MAZ, MOR, MEL, MTW, LEV, OFF, TON and MFI Very particular preference is given to zeolites of the topological structures FAU, MOR, BEA , MFI and MEL.

There are usually three different centers in zeolites, referred to as α, β and γ positions, which define the position of the exchange sites (also referred to as "interchangeable locations"). All of these three positions are accessible to reactants during the NH ₃ -SCR reaction, especially when using MFI, BEA, FAU, MOR, MTW, and MEL zeolites. Surprisingly, it has been found that the improvement in cold start emissions is dependent on the NH ₃ storage capability of the SCR catalyst. However, the NH ₃ storage capacity depends on the (BrOnstedt) acidic surface centers of the zeolite preferably used according to the invention. Different zeolite types have different acid sites and thus different adsorption and desorption behaviors. Strongly acidic centers form stronger bonds to the adsorbed NH ₃ molecules than weakly acidic centers.

It has been found that the desorption temperature is significantly higher for a zeolite with predominantly strongly acidic centers than for weakly acidic centers. Thus, according to the invention, the NH ₃ storage function, ie the amount of adsorbing NH ₃ or of the NH ₃ to be desorbed, can be adjusted in a targeted manner by suitably selecting the type of zeolite. Since the number of acidic centers can be influenced by the molar ratio of SiO ₂ to Al ₂ O ₃ (the so-called "module"), the NH ₃ storage capacity of an SCR catalyst can thus be precisely adjusted by varying this ratio.

The preferred SiO ₂ / Al ₂ O ₃ modulus (molar ratio) is in the range from 5: 1 to 150: 1, more preferably in the range from 5: 1 to 50: 1 and most preferably in the range from 10: 1 to 30: 1st

The NH ₃ storage zeolite is preferably present in an amount of from 2 to 30% by weight, more preferably in an amount of from 5 to 15% by weight, in the catalytically active composition.

In addition to the amount of zeolite, as already explained above, the type of zeolite used is important since not all zeolites have an optimum NH ₃ storage capacity. sen. The zeolite is therefore preferably selected from the group comprising FAU (faujasite), MOR (mordenite), BEA (beta zeolite), MFI (Mobil Five, ZSM-5, Zeolite Secondary Mobile No. 5) and MEL, combinations of which above-mentioned zeolite can be used. Preferably, all said zeolites are used in the H form. The cited catalysts and processes for their preparation are known in the art.

In preferred developments of the invention, the NH ₃ storage zeolite is a metal-exchanged zeolite, for example an iron, copper or cobalt-exchanged zeolite. Preferably, the metal-exchanged zeolite is also selected from the group comprising FAU (faujasite), MOR (mordenite), BEA (beta zeolite), MFI (Mobil Five, ZSM-5, Zeolite Secondary Mobile No. 5) and MEL, including combinations said zeolites can be used.

However, it is particularly preferred if the metal-exchanged zeolite is not an iron-exchanged zeolite in combination with a transition-metal-exchanged zeolite and / or in combination with a metal oxide-exchanged zeolite, wherein the transition metal oxide is selected from the group consisting of vanadium pentoxide, tungsten trioxide or titanium dioxide.

In the case of metal-exchanged or doped zeolites, the metal content or the degree of exchange of a zeolite is decisively determined by the metal species present in the zeolite. As a result, the zeolite can be doped with only a single metal or with different metals. The preferred metals for exchange and doping are catalytically active metals such as Fe, Ce, Co, Ni, Ag, V, Rh, Pd, Pt, Ir. He- According to the invention, very particular preference is given to zeolites which contain iron, copper or cobalt species. The production processes for metal-exchanged zeolites, for example via solid or liquid phase exchange, are known to the person skilled in the art.

In addition to the NH ₃ storage component, the SCR catalyst also requires an SCR active component. This may be, for example, a conventional vanadium / titanium / tungsten based component. Typically, the vanadium / titanium / tungsten based component is an oxide coating that essentially contains TiO ₂ in the anatase modification. As a rule, TiO ₂ is stabilized by WO _{3 in} order to achieve an improvement in its thermal stability. The proportion of WO ₃ is typically about 10 wt .-%. The actually active component forms the V ₂ O ₅ , which is typically present as a monolayer on the TiO ₂ particles. It is also possible to add another NH ₃ storage component, as will be suggested below.

An advantage of, for example, a vanadium based component as the SCR active component is the excellent low temperature activity of such a system. The inventive combination of vanadium-based catalysts with zeolites can thus make use of the low-temperature activity of these catalysts and, at the same time, the NH ₃ storage capacity of the zeolites, thus providing an SCR catalyst with excellent cold-start properties.

As an alternative to the vanadium-based SCR-active component, it is also possible according to the invention to use an SCR-active zeolite (for example a metal-doped or exchanged zeolite, such as a Cu zeolite or Fe zeolite. In further advantageous embodiments of the invention, this provides many possible combinations for an SCR catalyst, which can be specifically adapted to the respective area of use. For example, according to the invention, an SCR-active zeolite which is active at low temperatures can be combined with an SCR-active zeolite which is active at higher temperatures and an NH ₃ storage zeolite.

In the present context, "low temperatures" are temperatures in the range below 280 ^° C., preferably below 250 ^° C. "high temperatures" are understood to mean temperatures in the range of more than 350 ^° C., preferably more than 400 ^° C. A corresponding example of such a combination is, for example, a mixture of a copper-exchanged zeolite such as Cu-ZSM-5 with a modulus of 150, which has a low-temperature, an iron-exchanged zeolite, such. B. Fe-BEA with a modulus of 35 exhibiting high temperature activity and a non-metal exchanged zeolite such as H-BEA with a modulus of 20 serving as the NH ₃ storage zeolite.

Thus, a good catalytic reaction of low to high temperatures is given to a catalyst which receives the combination according to the invention as a catalytic composition.

According to the invention, it has also turned out to be an advantage if the catalytically active composition of the SCR

Catalyst in the form of an at least partially coating on a preferably monolithic carrier is present. When For example, monolithic carriers are metallic or ceramic carriers, for example in honeycomb or foam form.

It has proven to be particularly advantageous if the NH ₃ storage component is applied only on the inlet side and the SCR-active component only on the outlet side of such a coated monolithic carrier. It would also be possible for all of the components, such as the NH ₃ storage component and the SCR active component (s), to be applied as a homogeneous coating to the entire surface of the monolith, thus greatly simplifying the preparation of such catalysts.

The application of the SCR catalyst is carried out according to methods known in the art, for example by applying a washcoat, by coating in an immersion bath or by spray coating.

Accordingly, the SCR catalyst according to the invention is outstandingly suitable for reducing nitrogen oxide emission from mobile or stationary combustion devices.

Mobile combustion devices in the context of this invention are, for example, internal combustion engines of motor vehicles, in particular diesel engines, power generators based on internal combustion engines, or other units based on internal combustion engines.

The stationary combustion facilities are usually power plants, combustion plants, waste incineration plants and also heating systems of private households. Thus, the subject matter of the invention is also a method for reducing nitrogen oxide emissions in mobile or stationary incinerators, the method being characterized in that an exhaust gas stream is passed over an SCR catalyst according to the invention.

The invention will now be explained in more detail with reference to the following examples and figures, which, however, are not intended to be limiting.

Show it

Fig. l the NH ₃ storage capacity of zeolites as a function of the Si0 ₂ / Al ₂ O 3 modulus,

2 shows a TPD diagram of the NH ₃ desorption in a Fe-doped zeolite of type MFI with a modulus of 25.

FIG. 1 shows the NH ₃ storage capacity of zeolites as a function of the SiO ₂ / Al ₂ O ₃ module.

As can be seen from Figure 1, the optimum modulus is in the range of 5 to 50, most preferably in the range of 10 to 30.

This applies in particular to the types of zeolites which may be preferred in the automotive sector with the topology FAU, MOR, BEA, MFI, MEL. These are used individually or as mixtures.

However, the selection of the module is also determined by the analysis of the later field of application and the conditions. The range of application of the catalyst is determined by several factors Right. For example, the temperature range in operation varies considerably from car to truck. Typical work areas of internal combustion engines in trucks are between 180 and 430 ⁰ C, and in the case of passenger cars temperatures of up to 600 ⁰ C are often reached. Basically, the smaller the engines are (in terms of their cubic capacity), the more intensively a full-load operation occurs and thus the temperatures rise. Plays a role, whether installed in the exhaust system of the SCR catalyst before or after the diesel particulate filter (DPF), there can form high temperature peaks during the regeneration of the diesel particulate filter by burning off the collected PM in the filter above about 600 ⁰ C. It follows that high-temperature-stable zeolites with the highest possible modulus are used, in particular for longer thermal loads on the SCR catalyst, for which Fe-BEA with a modulus of 50 or Fe-ZSM-5 with a modulus of 150 is mentioned as non-limiting examples become.

As the modulus increases, so does the hydrothermal stability and thus the high temperature stability. The NH ₃ absorption capacity runs as shown in FIG. 1 and is exactly opposite. This results in the above-mentioned preferred range according to the invention.

However, not all areas of the module are accessible with any type of zeolite which can be used according to the invention. For example, with a BEA zeolite, only SiO ₂ : Al ₂ O ₃ ratios of above 19 can be achieved. In order to achieve a certain storage capacity of NH3, therefore, in the case of using such zeolites, the amount must be increased. In the case of the zeolites preferred according to the invention, the lower and upper limits for the SiO ₂ : Al ₂ O ₃ ratios (modules) are as follows: FAU: 3 - 10, MOR: 10 - 400, BEA: 19 - 1000, MFI: 19-1000, MEL: 19-1000.

FIG. 2 shows the result of temperature-programmed desorption (TPD) of NH ₃ in an iron-exchanged zeolite with the topology MFI and a SiO ₂ / Al ₂ O ₃ modulus of 25.

From Figure 2 it can be seen that the highest desorption in the range of 200 - 290 ° C followed by another maximum between 310 - 400 ⁰ C takes place.

The procedure was as follows:

The zeolite with the module according to the invention was saturated with NH ₃ . That is, the maximum possible NH ₃ concentration was adsorbed on the surface and then desorbed by increasing the temperature. The amount of NH ₃ was detected by a mass spectrometer and simultaneously correlated with the discharge temperature. Thus, both the quantity and the temperature at which the desorption occurred could be determined what evidence was obtained to the strength of the bond between NH ₃ and the zeolite.

The test conditions were as follows:

NH ₃ loading: gas: 0.473% NH ₃ in He

Loading temperature [ ⁰ C]: 110

NH ₃ desorption: gas: helium

Heating rate [° C / min]: 5

Final temperature [ ⁰ C]: 750

Holding time [h]: 1 NH3 detection with mass spectrometer, mass number 16: Peak area calibration (FE / μmol NH ₃ ): l, 16E-08 peak area desorption [FE]: l, 13E-06

embodiments

Example 1:

Preparation of the catalyst 1

The carrier structure used was a ceramic carrier from NGK with a honeycomb density of 400 cpsi. To prepare the washcoat with the catalytically active composition for the SCR catalyst, 90 g of TiO ₂ powder, 10 g of WO ₃ , 20 g

ZSM-5, 20 g SiO ₂ sol, 15 g TiO ₂ sol, 20 ml 10% aqueous

Vanadyl oxalate solution and 80 g of distilled water mixed together. The ZSM-5 zeolite had a modulus of 25.

The washcoat thus prepared was vibrated on the ceramic monolith with the volume of the washcoat equal to 50-120% of the carrier volume. By means of known methods, the monolith was emptied. The washcoat residues on the outlet side of the monolith were sucked off. The SCR catalyst thus obtained was then dried at 80 ^° C. and calcined at about 500 ^° C. for 5 hours.

The same applies to the use of, for example, metallic monoliths which can be used in place of the ceramic monoliths used in Example 1 as well.

Example 2:

Preparation of the catalyst 2 As the support structure, the same structure as in Example 1 was used. To prepare the washcoat, 90 g of TiO ₂ powder, 10 g of WO ₃ , 10 g of ZSM-5, 10 g of BEA, 20 g of SiO ₂ sol, 15 g of TiO ₂ sol, 20 ml of 10% aqueous vanadyl oxalate solution and 80 g of distilled water mixed together. The ZSM-5 zeolite had a modulus of 25, the BEA zeolite a modulus of 150.

The washcoat thus prepared was applied to the monolith as in Example 1 and then calcined.

Example 3:

Preparation of the Comparative Catalyst, Catalyst 3

As the support structure, the same structure as in Example 1 was used.

To prepare the washcoat, 110 g of TiO ₂ powder, 10 g of WO ₃ , 20 g of SiO ₂ sol, 15 g of TiO ₂ sol, 20 ml of 10% aqueous vanadyl oxalate solution and 80 g of distilled water were mixed together. The washcoat so prepared was applied to the monolith as in Example 1 and calcined.

With the catalysts of Examples 1 to 3 thus obtained, laboratory test investigations with simulated cold start and simulated load changes were carried out on a dynamic test stand for rapid changes of temperature, exhaust gas and throughput. The evaluation was carried out as a correlation of the inventive catalysts 1 and 2 with respect to the comparative catalyst from Example 3. The criteria were in particular the cold start behavior and the behavior during load changes.

The cold start was simulated by a temperature increase from room temperature to 400 ⁰ C with a heating rate of 50 K / min. Rapid change of throughput and temperature simulates a load change from full load to idle and vice versa. The space velocity of 100,000 h ^"1 and the temperature of 400 ⁰ C (full load) were changed to a space velocity of 30,000 h ^{" 1} and a temperature of 180 ⁰ C (idle).

It was found that by the adsorption of NH ₃ by an inventive NH ₃ - storage component in the catalytic composition in the cold start phase significant increases in sales were achieved (see Table 1). The (preconditioned) catalyst had already adsorbed NH ₃ and therefore exhibited this effect. The same was obtained with a sudden increase in the NO _x concentration (change idle to full load), which also here on the NH ₃ reservoir could be accessed. In the event of a sudden reduction in NO _x (change from full load to idling), overdosed NH ₃ is stored in the storage component and thus the NH ₃ slip is reduced (see Table 1).

The exhaust gas composition corresponded to a typical diesel car and a load change between full load and idle was simulated.

The results are shown in Table 1. Table 1: Results of the catalysts according to the invention in relation to the comparative catalyst 3

Both catalysts according to the invention showed a significant improvement with respect to the NO _x conversion and a reduced NH ₃ slip at the catalyst outlet.

Claims

claims An SCR catalyst comprising a catalytically active composition containing an SCR active component and an NH ₃ storage component, wherein the SCR active component and the NH ₃ storage component are different from each other, and wherein the NH ₃ storage component comprises a zeolite with a SiC> ₂ / Al ₂ θ ₃ molar ratio of 5: 1 to 150: 1, and the zeolite is contained in an amount of from 2 to 30% by weight in the catalytically active composition. 2. SCR catalyst according to claim 1, wherein the zeolite is selected from the group comprising zeolites of topology FAU, MOR, BEA, MFI and MEL, or combinations thereof. 3. SCR catalyst according to claim 2, wherein the zeolite is a metal-exchanged zeolite. 4. SCR catalyst according to one of the preceding claims, characterized in that the SCR-active component is a vanadium-based component and / or an SCR-active zeolite. 5. SCR catalyst according to claim 4, wherein the SCR active component a cryogenic SCR-active and / or a High-temperature SCR-active zeolites. 6. SCR catalyst according to one of the preceding claims, characterized in that the SCR catalyst is present as a coating on a monolithic carrier, wherein the carrier is a honeycomb body, a monolith or a metal or ceramic foam. 7. SCR catalyst according to claim 6, wherein the NH ₃ - storage component on the inlet side and the SCR active component on the outlet side of the carrier are located. 8. An exhaust gas purification system for the purification of diesel engine exhaust gases comprising a group of successively arranged catalyst devices, consisting of a Oxidati- onskatalysator and an SCR catalyst according to one of claims 1 to 7. 9. Use of the SCR catalyst according to one of claims 1 to 7 for reducing nitrogen oxide emissions of mobile or stationary combustion facilities. 10. Use according to claim 9, wherein an emerging during combustion exhaust gas flow over an SCR catalyst according to one of claims 1 to 7 is passed.