DE102018127219A1 - Catalyst for use in selective NOx reduction in NOx-containing exhaust gases, method for producing a catalyst, device for selective NOx reduction and method for selective NOx reduction - Google Patents

Abstract

A catalyst (1) for use in a selective NO reduction in NO-containing exhaust gases while supplying hydrogen to the exhaust gases has a base body (3), a support layer (4) made of zirconium oxide applied to the base body (3), one on the Carrier layer (4) applied active component (5b) and a promoter (5a) applied to the carrier layer (4). The zirconium oxide of the carrier layer (4) has a crystal structure, the amorphous proportion of which is at least 20%.

Description

The invention relates to a catalyst for use in a selective NO _x reduction in NO _x -containing exhaust gases with supply of hydrogen to the exhaust gases according to the type defined in the preamble of claim 1. The invention further relates to a method for producing a catalyst for selective reduction of NO _x in the NO _x -containing exhaust gases, a device for the selective reduction of NO _x in the NO _x -containing exhaust gases from internal combustion engines and to a method for the selective reduction of NO _x in the NO _x -containing exhaust gases.

Due to increasingly restrictive emission regulations, it is already largely necessary to post-treat the exhaust gas in motor vehicles driven by internal combustion engines to remove nitrogen oxides. Various nitrogen oxidation levels, such as nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ), are summarized under the collective term of nitrogen oxides. The gases are very toxic to humans. In addition to sulfur dioxide, the nitrogen oxides contribute to acid rain, since the reaction of nitrogen dioxide with water produces nitric acid and nitrous acid. This acid rain is partly responsible for the forest dieback caused by the washing out of the nutrients in the soil and for damage to buildings with acid-sensitive building materials. Furthermore, the nitrogen oxides play a central role in the formation of ozone in layers near the ground. Ozone can irritate and inflame the respiratory tract in humans and acts as a cell poison in plants. In the stratosphere, on the other hand, ozone is destroyed by nitrogen monoxide, which contributes to the formation of the ozone hole. Nitrogen oxide emissions can be of natural origin, e.g. from microbial processes and vegetation fires, as well as anthropogenic origin, e.g. from power plants, industry, small combustion plants in the home and in traffic. Catalysts have therefore been used for after-treatment of exhaust gases for some time.

A method for removing nitrogen oxides from an exhaust gas stream is in the EP 0 666 099 B1 described. The catalyst used adsorbs the nitrogen oxides in the exhaust gas, whereupon a gas with a certain content of a reducing substance is supplied to the catalyst at predetermined time intervals and for certain periods of time. Storage catalysts of this type, in which basic components, such as lithium oxide, potassium oxide, sodium oxide, barium oxide or similar oxides, are used, however, require a relatively complicated control and usually have a high need for regeneration.

In these NO _x storage catalysts, the mainly emitted NO is oxidized to NO ₂ on a platinum-containing catalyst, which is subsequently adsorbed on special storage media, for example BaCO ₃ . When the storage capacity of this catalyst is exhausted, engine-induced regeneration of the catalyst is initiated, in which the nitrogen oxides introduced are converted into nitrogen. Another disadvantage of the known NO _x storage catalysts, which operate according to the so-called NSK process, is the risk of poisoning the NO _x sorbents by the sulfur oxides SO ₂ and SO ₃ contained in the exhaust gas. To avoid this problem, complex engine management strategies are usually required.

From the EP 0 960 649 B1 An exhaust gas purification catalyst is known in which the materials used have cerium oxide and / or zirconium dioxide mixed oxides which serve to remove saturated hydrocarbons from the exhaust gas. Ammonia is used as a reducing agent for the nitrogen oxides contained in the exhaust gas.

However, the active component V ₂ O ₅ frequently used in such SCR catalysts is toxicologically unsafe and can also melt or evaporate at very high exhaust gas temperatures. Another limiting factor with regard to the activity of the SCR process at low temperatures lies in the on-board production of the reducing agent NH ₃ from urea, which is currently only technically mastered above approx. 220 ° C.

The EP 0 763 380 A1 describes shell catalysts which consist of a core and at least one outer shell or of a support, at least one inner and at least one outer shell, the outer shells containing oxides of certain elements.

A disadvantage of the known solutions for NO _x removal from oxygen-rich exhaust gases is in most cases also that the nitrogen oxides are only converted above 200 ° C. and thus at temperatures such as occur in particular in diesel or hydrogen engines.

Because the temperature of the exhaust gases is constantly reduced due to the continuous optimization of the efficiency of the internal combustion engines, the known solutions pose a major problem with regard to their effectiveness. For example, in modern internal combustion engines for cars, which operate on the diesel principle, the exhaust gas temperature in the relevant EU certification cycle is below 150 ° C for around 60% of the time and below 200 ° C for around 75% of the time. This value is very similar for hydrogen combustion engines.

In the case of NO _x catalyst technology, the activity at low temperatures is limited by the required generation of NO ₂ in the exhaust line, since the oxidation catalysts based on platinum or palladium show sufficient activity only from approximately 220 ° C.

The SCR and NSK processes therefore do not meet the central point of the selective conversion of NO _x to nitrogen and water at low temperatures.

From the DE 11 2006 003 078 T5 an emission system for the reduction of nitrogen oxides in diesel engine exhaust gases under lean combustion conditions is known, in which, for example, palladium is used as the active component and a γ-aluminum oxide as the carrier layer. This system and the resulting catalyst also show insufficient activity at low temperatures. Here, hydrogen and carbon monoxide are used as reducing agents.

From the WO 2007/020035 A1 Such a catalyst, a production method for the same and a device and a method for selective NO _x reduction in NO _x -containing exhaust gases are also known.

However, the catalysts described there cannot be used to achieve a selective conversion of the nitrogen oxides which is sufficient in practice. In particular, in the WO 2007/020035 A1 described process generates a relatively large proportion of laughing gas, which is very disadvantageous, since laughing gas contributes more than 300 times to the greenhouse effect than, for example, CO ₂ . A further disadvantage of the catalyst described there is that only the tetragonal crystal modification can be used for the support material consisting of zirconium oxide, which requires a very large outlay in terms of production technology.

From the EP 1 475 149 A1 Another catalyst for the reduction of NO _x to N ₂ with hydrogen under conditions rich in O _{2 is} known. This known catalyst is based on platinum, which is distributed in an amount between 0.1 and 2% by weight on a support material consisting of magnesium or cerium oxide or a precursor thereof.

Although this catalyst already achieves very good results in NO _x reduction, this catalyst will also reach its limits with future pollutant limit values.

The DE 102 16 748 A1 describes modified catalysts for the selective hydrogenation of aromatic hydrocarbons with bulky or branched substituents. However, NO _x reduction in NO _x -containing exhaust gases cannot be carried out with these catalysts.

In the DE 44 36 890 A1 describes a method for simultaneously reducing the hydrocarbons, carbon monoxide and nitrogen oxides contained in the exhaust gas of an internal combustion engine. The catalyst used has an aluminum silicate as a high-surface support material.

A generic catalyst and a device and a method for selective NO _x reduction in NO _x -containing exhaust gases are from the DE 10 2005 038 547 A1 known. The describes a similar prior art DE 10 2010 040 808 A1 . Hydrogen is used as a reducing agent, which results in an improved low-temperature activity of the catalyst. Despite promising approaches, these catalysts did not show the desired success.

In the DE 10 2016 107 466 A1 describes a further catalyst for use in a selective NO _x reduction in NO _x -containing exhaust gases, in which the carrier layer consists of aluminum oxide present in an ETA modification. However, it has been found that this catalyst is less effective than initially thought.

It is therefore an object of the present invention to provide a catalyst for use in selective NO _x reduction in NO _x -containing exhaust gases and a device and a method for selective NO _x reduction in NO _x -containing exhaust gases with which nitrogen oxides already exist can be reduced at very low temperatures with high turnover rates.

According to the invention, this object is achieved for the catalyst by the features mentioned in claim 1.

The inventors have surprisingly found that the use of a zirconium oxide, which has a crystal structure with an amorphous content of at least 20%, significantly improves the activity of the catalyst with respect to the NO _x reduction for the support layer of the catalyst according to the invention. This is all the more surprising since earlier approaches to the use of zirconium oxide for carrier layers, such as for example in US Pat DE 10 2005 038 547 A1 or the DE 10 2010 040 808 A1 described led to a significantly lower activity. Due to the lack of success, the inventors then switched to using aluminum oxide substrates, as in the DE 10 2016 107 466 A1 described.

In a very advantageous development of the invention it can be provided that the promoter consists of tungsten oxide. By using a promoter made of tungsten oxide, the activity of the catalyst according to the invention with respect to NO _x reduction is significantly improved.

An even higher activity of the catalyst results if the tungsten oxide is 100% amorphous.

Another very advantageous embodiment of the invention can consist in that tungsten has a ratio of 0.0016 g _tungsten / m ^{2 to} 0.00001 g _tungsten / m ² , preferably 0.0013, to the surface of the carrier layer determined by the BET method g _tungsten 1m ² - 0.0001 g _tungsten / m ² , more preferably 0.0010 - 0.0002 g _tungsten / m ² , more preferably 0.0008 - 0.0003 g _tungsten / m ² , most preferably 0.0006- 0.0003 g _tungsten / m ² is present. It has been found in practical tests that such a proportion of tungsten in or on the carrier layer produces a still significantly improved activity of the catalyst according to the invention.

This effect can be further increased if the zirconium oxide of the carrier layer has a crystal structure, the amorphous proportion of which is at least 60%.

A particularly preferred embodiment of the invention can consist in the fact that the carrier layer has a surface area of 90-500 m ² / g determined by the BET method. By using such an increased surface, the size of the catalyst can be significantly reduced with the same activity.

In order to further increase the activity of the catalyst according to the invention with respect to the NO _x reduction, it can further be provided that the active component consists of platinum or palladium.

In claim 8, a method for producing a catalyst according to the invention is described.

With this method, the catalyst according to the invention can be produced very easily and a high activity thereof with regard to the NO _x reduction can be achieved.

A device for selective NO _x reduction in NO _x -containing exhaust gases from internal combustion engines with a catalyst according to the invention is specified in claim 9.

This device, which, among other things, also has a hydrogen supply device for introducing hydrogen into the exhaust pipe and / or into the internal combustion engine, enables an optimal use of the catalyst according to the invention. The hydrogen supplied can be fed to the catalyst by means of a separate device, but it is also possible to use the so-called slip, that is to say the proportion of hydrogen which is not burned in the combustion chambers.

A method for selective NO _x reduction in NO _x -containing exhaust gases results from claim 10 by means of such a device.

This method ensures that the high activity of the catalyst according to the invention is used at every time of operation, since sufficient hydrogen is available at every time of operation.

Exemplary embodiments of the invention are shown in principle below with reference to the drawing.

• 1 eine schematische Darstellung einer ersten Ausführungsform des Aufbaus des erfindungsgemäßen Katalysators;
• 2 eine schematische Darstellung einer zweiten Ausführungsform des Aufbaus des erfindungsgemäßen Katalysators;
• 3 eine schematische Darstellung einer dritten Ausführungsform des Aufbaus des erfindungsgemäßen Katalysators;
• 4 eine schematische Darstellung einer erfindungsgemäßen Vorrichtung zur selektiven NO_x-Reduktion bei einem Verbrennungsmotor;
• 5 ein Diagramm, in dem der Einfluss der Oberfläche der Trägerschicht auf den NO_x-Umsatz bei verschiedenen Katalysatoren dargestellt ist;
• 6 ein Diagramm, in dem der Einfluss der Oberfläche der Trägerschicht auf die N₂O-Bildung bei verschiedenen Katalysatoren dargestellt ist;
• 7 ein Diagramm, in dem der Einfluss der Verteilung der aktiven Komponente auf den NO_x-Umsatz bei verschiedenen Katalysatoren dargestellt ist;
• 8 ein Diagramm, in dem der Einfluss der Verteilung der aktiven Komponente auf die N₂O-Bildung bei verschiedenen Katalysatoren dargestellt ist;
• 9 ein Diagramm, in dem der Einfluss des CO-Signals auf den NO_x-Umsatz bei verschiedenen Katalysatoren dargestellt ist;
• 10 ein Diagramm, in dem der Einfluss des CO-Signals auf die N₂O-Bildung bei verschiedenen Katalysatoren dargestellt ist;
• 11 ein erstes Diagramm, in dem der Einfluss der Kristallinität der Trägerschicht auf den NO_x-Umsatz bei verschiedenen Katalysatoren dargestellt ist;
• 12 ein zweites Diagramm, in dem der Einfluss der Kristallinität der Trägerschicht auf den NO_x-Umsatz bei verschiedenen Katalysatoren dargestellt ist;
• 13 ein drittes Diagramm, in dem der Einfluss des monoklinen Anteils der Trägerschicht auf den NO_x-Umsatz bei verschiedenen Katalysatoren dargestellt ist;
• 14 ein viertes Diagramm, in dem der Einfluss des tetragonalen Anteils der Trägerschicht auf den NO_x-Umsatz bei verschiedenen Katalysatoren dargestellt ist;
• 15 ein Diagramm, in dem der Einfluss des Anteils von Wolfram an der Trägerschicht auf den NO_x-Umsatz bei verschiedenen Katalysatoren dargestellt ist; und
• 16 ein Diagramm, in dem Raman-Verschiebungen der einzelnen Katalysatoren dargestellt sind;

It shows:

• 1 a schematic representation of a first embodiment of the structure of the catalyst according to the invention;
• 2nd a schematic representation of a second embodiment of the structure of the catalyst according to the invention;
• 3rd is a schematic representation of a third embodiment of the structure of the catalyst according to the invention;
• 4th a schematic representation of a device according to the invention for selective NO _x reduction in an internal combustion engine;
• 5 a diagram in which the influence of the surface of the support layer on the NO _x conversion is shown for various catalysts;
• 6 a diagram in which the influence of the surface of the support layer on the N ₂ O formation is shown for various catalysts;
• 7 a diagram showing the influence of the distribution of the active component on the NO _x conversion for different catalysts;
• 8th a diagram showing the influence of the distribution of the active component on the N ₂ O formation in various catalysts;
• 9 a diagram showing the influence of the CO signal on the NO _x conversion for various catalysts;
• 10th a diagram showing the influence of the CO signal on the N ₂ O formation in various catalysts;
• 11 a first diagram in which the influence of the crystallinity of the support layer on the NO _x conversion is shown for various catalysts;
• 12th a second diagram in which the influence of the crystallinity of the support layer on the NO _x conversion is shown for various catalysts;
• 13 a third diagram, in which the influence of the monoclinic portion of the support layer on the NO _x conversion is shown for various catalysts;
• 14 a fourth diagram, in which the influence of the tetragonal portion of the carrier layer on the NO _x conversion is shown for different catalysts;
• 15 a diagram in which the influence of the proportion of tungsten in the support layer on the NO _x conversion is shown for various catalysts; and
• 16 a diagram in which Raman shifts of the individual catalysts are shown;

1 shows in a very schematic, not to scale and greatly enlarged representation of a first embodiment of a catalyst 1 for selective NO _x reduction in the exhaust gases of an in 4th illustrated internal combustion engine 2nd . With those from the internal combustion engine 2nd escaping exhaust gases are in particular oxygen-rich exhaust gases, that is to say exhaust gases with an oxygen content of more than 1%. In the present case, it is the internal combustion engine 2nd a hydrogen combustion engine, basically the catalyst 1 however also with other internal combustion engines 2nd can be used, for example in diesel engines.

The catalyst 1 has a basic body 3rd on the support structure of the catalyst 1 forms. The basic body 3rd For example, it can be designed as a honeycomb body and it can consist, for example, of a ceramic material. Alternatively, the base body 3rd for example, can also be formed from a metal substrate. The basic body 3rd can also be designed as a soot filter to filter out any soot particles contained in the exhaust gases.

On the base body 3rd is a carrier layer made of zirconium oxide 4th upset. The zirconium oxide of the carrier layer 4th has a crystal structure, the amorphous portion of which is at least 20%. The zirconium oxide of the carrier layer 4th can also have other or more specified amorphous components, some of which will be described later.

The backing layer 4th is porous and preferably has a surface area of 90-500 m ² / g determined by the BET method. This large surface area of the support layer increases the effectiveness of the catalyst 1 supported.

On the the main body 3rd opposite side of the carrier layer 4th is the same with a coating 5 provided a promoter in the present case 5a and an active component 5b having. The promoter 5a , which can act as a thermal stabilizer, is preferably made of tungsten oxide. Preferably the tungsten oxide is 100% amorphous.

Furthermore, it is preferred if tungsten is in a ratio to the surface of the carrier layer determined using the BET method 4th from 0.0016 g _tungsten / m ² - 0.00001 g _tungsten / m ² , preferably 0.0013 g _tungsten / m ² - 0.0001 g _tungsten / m ² , more preferably 0.0010 - 0.0002 g _tungsten / m ² , more preferably 0.0008-0.0003 g _tungsten / m ² , most preferably 0.0006-0.0003 g _tungsten / m ² .

The active component 5b consists in the present case of a noble metal, in particular of platinum or palladium, but it would in principle also be conceivable to use gold, silver, rhodium or iridium as the active component 5b to use. The coating 5 the backing layer 4th is in the in 1 illustrated embodiment constructed so that on the base body 3rd opposite side, i.e. on an outer surface 1a of the catalyst 1 , both the promoter 5a as well as the active component 5b available.

In a process for producing the catalyst 1 is on the main body 3rd the backing layer 4th made of zirconium oxide, which has a crystal structure with an amorphous content of at least 20%. On the backing 4th become the promoter 5a and the active component 5b upset. At the in 1 illustrated embodiment of the catalyst 1 become the promoter 5a and the active component 5b together on the carrier layer 4th upset. This causes the active component to mix 5b and the promoter 5a . The active component 5b can be in the form of individual particles in the promoter 5a are present as this in 1 is indicated. As the further steps required in the preparation of the catalyst 1 can be done in a manner known per se, it is not discussed in more detail here.

In the embodiment of the catalyst 1 according to 2nd first becomes the promoter 5a and then the active component 5b on the carrier layer 4th upset. Accordingly, there are two separate layers that together form the coating 5 form.

Another embodiment of the catalyst 1 is in 3rd shown. In principle, this represents a combination of the embodiments of FIG 1 and 2nd because the active component 5b both as according to 1 in by the promoter 5a formed layer is present as well as according to 2nd is applied as an additional layer to this layer. Again form the promoter 5a and the active component 5b the coating 5 .

4th shows a device 6 for selective NO _x reduction in the exhaust gases of the internal combustion engine designed as a hydrogen internal combustion engine in the present case 2nd , with which it is possible to implement a method for selective NO _x reduction in the exhaust gases of the internal combustion engine 2nd carry out, the exhaust gases being supplied with hydrogen as a reducing agent. The supply of hydrogen to the exhaust gases results in the catalyst 1 an immediate conversion of NO _x with H ₂ to N ₂ and H ₂ O.

In order to be able to reduce the exhaust gases directly, the catalyst is 1 in one of the internal combustion engine 2nd outgoing exhaust pipe 7 arranged. The device 6 in this case also has a hydrogen supply device 8th on, which basically serves in the event of an insufficient amount of hydrogen in the exhaust gases of the internal combustion engine 2nd an additional amount of hydrogen in the exhaust pipe 7 initiate. The hydrogen supply device 8th has a container, for example in the form of a pressure cylinder 9 on that with a feed opening 10th is provided. To the feed opening 10th is a feed line 11 connected which to the exhaust pipe 7 leads. The feed opening 10th is with a clasp 12th provided, its open state by means of a control device 13 can be changed. The control device 13 is in turn with one in the exhaust pipe 7 arranged NO _x sensor 14 and with another sensor 15 connected to the internal combustion engine in a 2nd leading suction pipe 16 is arranged. The further sensor 15 is in the present case as a known air mass sensor trained and serves to the internal combustion engine 2nd to measure the flowing air mass flow. Alternatively, the sensor could 15 also in the exhaust pipe 7 be arranged. In a manner not shown, it is possible to have a temperature sensor in the exhaust pipe 7 to provide. If necessary, it could also be on one of the two sensors 14 or 15 to be dispensed with.

By the two sensors 14 and 15 it is possible to have a certain condition in the exhaust pipe 7 and / or in the intake line 16 determine and to the control device 13 forward. The control device 13 is thereby able to find itself in the container 9 located hydrogen depending on the NO _x concentration within the exhaust pipe 7 or depending on one by the internal combustion engine 2nd flowing air mass flow into the exhaust pipe 7 to lead. In this way, for example, during an acceleration process in which a higher NO _x emission is expected, a larger amount of hydrogen can enter the exhaust pipe 7 be initiated. It is also possible to record the required data in a map in the control device 13 to be deposited in order to supply an increased amount of hydrogen at certain times. Of course, the hydrogen can also flow continuously into the exhaust pipe 7 be directed. Another option is to add a certain amount of hydrogen to the exhaust pipe 7 to lead and at one by one of the sensors 14 or 15 determined need to increase the amount of hydrogen introduced.

In order to make an additional refueling of hydrogen unnecessary, the hydrogen supply device can 8th with a device, not shown, for reforming hydrocarbon or derivatives thereof into hydrogen from that for the internal combustion engine 2nd provided fuel, that is, a reformer or the like. The hydrogen required could also be produced by electrolysis of a suitable substance, for example water. Both of these possibilities are summarized here under the term “H ₂ generator”. The container 9 In such a case, it can either be omitted or replaced by a smaller buffer. In the preferred embodiment of the internal combustion engine 2nd Such a device is not required as a hydrogen internal combustion engine because the required hydrogen can be taken directly from the fuel tank and no additional fuel is required for the exhaust gas aftertreatment.

Instead of supplying the hydrogen from the hydrogen supply device 8th into the exhaust pipe 7 If the amount of hydrogen in the exhaust gases is too low, it is also possible to transfer the hydrogen directly into the internal combustion engine 2nd feed. A separate hydrogen supply device can be used for this purpose 8th are used, however, it is simpler to add the additionally required amount of hydrogen to the amount already required for the combustion and directly into the internal combustion engine 2nd initiate. Stoichiometrically operated engines, in which the additionally injected amount of hydrogen is not also burned, are particularly suitable for such an extension of the blowing time.

It is particularly preferred that the internal combustion engine 2nd initiated additional amount of hydrogen immediately before opening at least one exhaust valve, not shown, of the internal combustion engine 2nd is initiated. Such additional injection should take place during extension, i.e. with the outlet valve open. The in the internal combustion engine 2nd The additional amount of hydrogen introduced per working cycle of the internal combustion engine 2nd less than 10%, preferably less than 2%, more preferably less than 1%, to operate the hydrogen internal combustion engine 2nd injected amount of hydrogen per work cycle of the internal combustion engine 2nd be. It is therefore a very small amount of additionally required hydrogen.

Furthermore, arises during the operation of the internal combustion engine 2nd Usually a so-called slip, i.e. hydrogen, which is not burned in the combustion chambers. This slip is also used for the above-described reaction of NO _x with H ₂ to N ₂ and H ₂ O on the catalyst 1 used, which may also dispense with the hydrogen supply device 8th enables.

If the main body 3rd of the catalyst 1 is not designed at the same time as a soot filter, as is briefly described above, it can in the flow direction of the exhaust gas in the exhaust pipe 7 the catalyst 1 a particle filter, not shown, can be connected upstream or downstream. The basic body 3rd thus only serves to hold the carrier layer 4th .

In a manner not shown, the in 4th described device 6 can also be used for industrial applications, for example for a power plant.

In the 5 to 25th different diagrams are shown, the different properties of different embodiments of the catalyst 1 point out. The different versions of the catalyst 1 are labeled in the figures I. , II , III , IV , V , VI , VII and VIII specified. Furthermore, various properties of the catalysts are in the table below I - VIII specified. No. of the catalyst I. II III IV V VI VII VIII Adsorption hysteresis n / A medium n / A low medium low Very little low Average Pore diameter [nm] n / A 8.4 n / A 5 5.8 2.5 3.4 10.9 BET surface area [m ² / g] 138 46 187 154 122 277 92 107 Calcination temperature [° C] 500 750 400 450 550 Not calc. Not calc. Not calc. Calculation time [h] 1 6 1 1 1 Not calc. Not calc. Not calc. Pt distribution [%] 11 45 30th 78 38 39 CO-DRIFTS signal [cm-1] 2079 2089 2074 2077 2081 2071 2087 2080 Main phase ZrO ₂ before calcination (XRD) tetraragogonal tetraragogonal tetraragogonal tetraragogonal tetraragogonal Amo rph Amo rph monokli n Monoclinic ZrO ₂ before calcination [% by weight] 5 2nd 23 19th 11 Amo rph cupid ph 5 Main phase ZrO ₂ after calcination (XRD) tetraragogonal tetraragogonal tetraragogonal tetraragogonal tetraragogonal Amo rph tetraragogonal monokli n Main phase ZrO ₂ (Raman) tet / mkl tet / mkl tet / mkl tet / mkl tet / mkl tet / mkl cupid ph monokli n Theoretical monolayer WO ₃ [%] 42 126 31 38 47 21 63 54 Crystalline WO _{3 found} No Yes No No No No No No Amorphous WO ₃ signal [cm-1] 834, 958 996 834, 965 834, 968 834, 962 950 880, 986 852, 975 X (NOx) max [%] 70 50 76 72 60 78 80 60 y (N2O) max [ppm] 6.1 6.0 4.2 4.0 3.5 5.6 1.0 3.0 In the diagram of 5 is on the abscissa of the maximum NO _x conversion in% and on the ordinate the determined by the BET method surface of the carrier layer 4th of the respective catalysts I - VIII shown in m ² / g. The respective value that the individual catalysts I - VIII is shown in the diagram by means of a point. It follows from this that a surface or BET surface area of greater than 90 m ² / g determined by means of the BET method is advantageous for a high NOx conversion.

In all diagrams, the horizontal lines starting from the point indicate the possible measurement deviations for the respective measurement variable.

6 shows the lowest maximum N ₂ O formation in ppm on the abscissa and on the ordinate the surface of the carrier layer determined using the BET method 4th of the respective catalysts I - VIII in m ² / g. It becomes clear that there is no direct connection between a high BET surface area and the maximum N ₂ O formation, since materials with a high and with a lower BET surface area produce N ₂ O to a small extent. This can be exemplified by the samples II and VI be shown as sample II a very low NOx conversion and sample VI has a very high NOx conversion. However, both samples have comparable N ₂ O production. In the 5 The optimization of the material shown to a high BET surface area and thus high NOx conversions is recommended.

In both 7 and 8th is the distribution of the active component on the ordinate 5b , in this case platinum, shown in%. The abscissa of the diagram of 7 represents, as in 5 , represents the maximum NO _x conversion in%. Analogous to 6 is in the diagram of 8th the lowest maximum N ₂ O formation in ppm is shown on the abscissa. It follows that there is a distribution of the active component 5b is to be striven for by more than 20%, even if the in 8th maximum N ₂ O formation shown is not clearly correlated with the distribution.

In 9 the maximum _NOx conversion in% for the catalysts I - VIII shown on the abscissa and the CO signal in 1 / cm on the ordinate. In contrast shows 10th the lowest maximum N ₂ O formation in ppm on the abscissa and again the CO signal in 1 / cm (wavenumber) on the ordinate. The CO signal is an indicator of the electronic activation of the active center, in this case platinum, by the tungsten oxide / zirconium oxide carrier layer. A CO signal at low wavenumber shows a strong activation of the active center. As in 9 strong electronic activation is strongly correlated with high NOx conversion. It is therefore advantageous if the carrier layer 4th is selected from ZrO ₂ so that a low CO signal is obtained. In the 10th maximum N ₂ O formation shown again does not clearly correlate with the CO signal. It is therefore advisable to optimize the material with regard to a low CO signal or a strong electronic activation of the active center.

The 11 to 14 each show the maximum NO _x conversion in% on the abscissa. Different crystal structures of the carrier layer are in each case on the ordinate 4th shown.

Here is in 11 the crystalline phase of the zirconium oxide in% by weight and in 12th the amorphous phase of the zirconium oxide in% by weight, in each case on the ordinate. From these diagrams it follows that it is preferable that the amorphous part of the crystal structure of the carrier layer 4th is at least 20. It is particularly preferable if the amorphous fraction is at least 60. The most effective catalyst VII is the amorphous part of the crystal structure of the carrier layer 4th 72%.

13 shows on the ordinate the proportion of monoclinic zirconium oxide in% by weight and 14 the proportion of tetragonal zirconium oxide in% by weight. It can be seen from these diagrams that the proportion of the tetragonal or monoclinic crystal structure has no decisive influence on the NOx conversion, as long as the amorphous proportion is at least 20%, preferably at least 60%.

15 shows a diagram in which the abscissa represents the maximum _NOx conversion in% and the ordinate the proportion of tungsten to the carrier layer 4th or the ratio of tungsten on the surface of the carrier layer determined using the BET method 4th shows. From this it can be seen that it is preferable if the above-described ratio of tungsten on the carrier layer 4th lies in the areas specified there.

In 16 are Raman shifts of the catalysts I - VIII shown. This shows that the tungsten oxide should be in a non-crystalline, i.e. amorphous form. It is particularly preferable if the tungsten oxide is 100% amorphous.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 0666099 B1 [0003]
• EP 0960649 B1 [0005]
• EP 0763380 A1 [0007]
• DE 112006003078 T5 [0012]
• WO 2007/020035 A1 [0013, 0014]
• EP 1475149 A1 [0015]
• DE 10216748 A1 [0017]
• DE 4436890 A1 [0018]
• DE 102005038547 A1 [0019, 0023]
• DE 102010040808 A1 [0019, 0023]
• DE 102016107466 A1 [0020, 0023]

Claims (10)

Catalyst (1) for use in selective NO _x reduction in NO _x -containing exhaust gases while supplying hydrogen to the exhaust gases, with a base body (3), a support layer (4) made of zirconium oxide applied to the base body (3), one on the carrier layer (4) applied active component (5b) and a promoter (5a) applied on the carrier layer (4), characterized in that the zirconium oxide of the carrier layer (4) has a crystal structure, the amorphous proportion of which is at least 20%. Catalyst (1) after Claim 1 , characterized in that the promoter (5a) consists of tungsten oxide. Catalyst (1) after Claim 2 , characterized in that the tungsten oxide is 100% amorphous. Catalyst (1) after Claim 1 , 2nd or 3rd , characterized in that tungsten in a ratio to the surface of the carrier layer (4) determined by means of the BET method of 0.0016 g _tungsten / m ² -0.00001 g _tungsten / m ² , preferably 0.0013 g _tungsten / m ^{2 to} 0.0001 g _tungsten / m ^2, more preferably from 0.0010 to 0.0002 g _tungsten / m ^2, more preferably from 0.0008 to 0.0003 g _tungsten / m ^2, at 0.0006 to 0.0003 bevorzugtesten g of _tungsten / m ² . Catalyst (1) according to one of the Claims 1 to 4th , characterized in that the zirconium oxide of the carrier layer (4) has a crystal structure, the amorphous proportion of which is at least 60%. Catalyst (1) according to one of the Claims 1 to 5 , characterized in that the carrier layer (4) has a surface area of 90-500 m ² / g determined by the BET method. Catalyst (1) according to one of the Claims 1 to 6 , characterized in that the active component (5b) consists of platinum or palladium. Method for producing a catalyst (1) for selective NO _x reduction in exhaust gases containing NO _x , characterized in that a support layer (4) made of zirconium oxide with a crystal structure with an amorphous content of at least 20% is applied to a base body (3) and that an active component (5b) and a promoter (5a) are applied to the carrier layer (4). Device (6) for selective NO _x reduction in NO _x -containing exhaust gases from internal combustion engines (1), with a catalyst (1) arranged in an exhaust pipe (7) according to one of the Claims 1 to 7 , and with a hydrogen supply device (8) for introducing hydrogen into the exhaust pipe (7) and / or into the internal combustion engine (2). Method for selective NO _x reduction in NO _x -containing exhaust gases by means of a device (6) Claim 9 If, in the case of an insufficient amount of hydrogen in the exhaust gases, hydrogen is introduced into the exhaust line (7) through which the exhaust gases flow and / or into the internal combustion engine (2).

Images