DE102010040808A1 - Catalyst for use in selective NOx reduction - Google Patents

Abstract

A catalyst for use in a selective NOx reduction in NOx-containing exhaust gases with the supply of hydrogen to the exhaust gases has a base body, a carrier layer made of zirconium oxide applied to the base body, a promoter made of tungsten oxide and an active component applied to the carrier layer on. The active component consists of palladium.

Description

The invention relates to a catalyst for use in a selective reduction of NO _x in NO _x -containing exhaust gases while supplying hydrogen to the exhaust gases according to the closer defined in the preamble of claim 1. The invention further relates to a method for producing a catalyst for selective NO _x reduction in NO _x -containing exhaust gases according to the preamble of claim 5 and a device for selective NO _x reduction in NO _x -containing exhaust gases and a method for selective NO _x reduction in NO _x -containing exhaust gases.

Due to the increasingly stringent emission regulations, it will be necessary in the future, in particular in the case of motor vehicles powered by diesel engines, but also in industrial plants, in which NO _x -containing exhaust gases, to treat the exhaust gas to remove nitrogen oxides. Under the generic term of nitrogen oxides, various oxidation states of nitrogen, such as nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ), are summarized. The gases are very toxic to humans. In addition to sulfur dioxide, the nitrogen oxides contribute to the 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 dying caused by the washing out of nutrients in the soil and for damage to buildings with acid-sensitive building materials. Furthermore, nitrogen oxides play a central role in the formation of ozone in layers close to the ground. Ozone can cause irritation and inflammation of the respiratory tract in humans and acts as a cytotoxin in plants. In the stratosphere, on the other hand, ozone is destroyed by nitrogen monoxide, which contributes to the formation of the ozone hole. The emission of nitrogen oxides may be of natural origin, for example from microbial and vegetative fires, as well as of anthropogenic origin, such as power plants, industry, domestic and commercial small combustion plants.

To achieve a reduction of these nitrogen oxides are from the WO 2007/020035 A1 a generic catalyst, a corresponding manufacturing method for the same and an apparatus and a method for selective NO _x reduction in NO _x -containing exhaust gases known.

However, with the catalyst described there, it is still not possible to achieve any selective conversion of the nitrogen oxides which is sufficient for practice. In particular, in the process carried out there, a relatively large proportion of nitrous oxide is produced, which is very disadvantageous, since nitrous oxide contributes about 310 times more to the greenhouse effect than, for example, CO ₂ . Another disadvantage of the catalyst described therein is that only the tetragonal crystal modification can be used for the zirconia existing carrier material, which requires a very large manufacturing effort. Also, the platinum used for the active component is a relatively large cost factor and increases the cost of the entire catalyst considerably.

From the EP 1 475 149 A1 For example, a catalyst for the reduction of NO _x to N ₂ with hydrogen under O ₂ -rich conditions is known. This known catalyst is based on platinum, which is distributed in an amount between 0.1 and 2 percent by weight on a carrier material consisting of magnesium or cerium oxide or a precursor thereof. Although quite good results in the NO _x reduction are already achieved with this catalyst, with future pollutant limit values, however, this catalyst could also reach its limits.

A method of removing nitrogen oxides from an exhaust gas stream is disclosed in US Pat EP 0 666 099 B1 described. The catalyst used in this case adsorbs the nitrogen oxides present in the exhaust gas, whereupon the catalyst is supplied with a gas having a specific content of a reducing substance at predetermined time intervals and for certain periods of time. Such storage catalysts, 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 regeneration requirement.

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

From the EP 0 960 649 B1 For example, an exhaust gas purification catalyst is known in which the materials used comprise ceria and / or zirconia mixed oxides which serve to remove saturated hydrocarbons from the exhaust gas. As a reducing agent for the nitrogen oxides contained in the exhaust gas, ammonia is used. However, the active component V ₂ O ₅ frequently used in such SCR catalysts is of toxicological concern and may also melt or vaporize at very high exhaust gas temperatures.

The EP 0 763 380 A1 describes shell catalysts, which consist of a core and at least one outer shell or of a carrier, at least one inner and at least one outer shell, wherein the outer shells contain oxides of certain elements. Furthermore, a method for the catalytic removal of nitrogen oxides, carbon monoxide and hydrocarbons from the exhaust gases of internal combustion engines is described. Here, the exhaust gas has a temperature of 50 to 800 ° C and a pressure of 0.01 to 200 bar and it is again ammonia used as a reducing agent.

A disadvantage of the known solutions for NO _x removal from O ₂ -rich exhaust gases is in most cases also the fact that the nitrogen oxides are effectively implemented only above 200 ° C. The fact that due to the continuous optimization of the efficiency of internal combustion engines, the temperature of the exhaust gases is constantly reduced, results in the known solutions, a major problem in terms of their effectiveness. For example, in modern, diesel-powered internal combustion engines for passenger cars, the exhaust gas temperature in the relevant EU certification cycle is around 60 ° C below 150 ° C and approximately 75% of the time below 200 ° C.

The DE 102 16 748 A1 describes modified catalysts for the selective hydrogenation of aromatic hydrocarbons having bulky or branched substituents. A NO _x reduction in NO _x -containing exhaust gases is not feasible with these catalysts.

In the DE 44 36 890 A1 is a method for the simultaneous reduction of the hydrocarbons contained in the exhaust gas of an internal combustion engine, carbon monoxide and nitrogen oxides described. The catalyst used in this case has an aluminum silicate as a high surface area support material.

It is an object of the present invention to provide a catalyst for use in a selective NO _x reduction in NO _x -containing exhaust gases while supplying hydrogen to the exhaust gases and a method of manufacturing the same, as well as an apparatus and method for selective NO _x reduction NO _x -containing exhaust gases with which nitrogen oxides can be reduced even at very low temperatures with high conversion rates.

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

The inventors have found that, surprisingly, with the palladium used for the active component, a very good conversion of nitrogen oxides to nitrogen can be achieved, although a combination of the carrier layer of zirconium oxide with the promoter of tungsten oxide applied on the carrier layer per se for platinum as the active component was tailored. This achievable with palladium as an active component high selective reaction in conjunction with a very high activity is all the more surprising, since the activity of the active component is very much dependent on the material of the carrier layer and the promoter used and the literature for this no reference can be found.

A major advantage of the use of palladium as the active component of the catalyst according to the invention is that in contrast to a catalyst having platinum as active component, the carrier layer of zirconium oxide does not have to be present in a specific crystal modification or crystal structure, but any desired crystal modification can be used , which significantly reduces the manufacturing and cost compared to known solutions. The cost of the catalyst according to the invention is significantly reduced by the fact that the raw material price of palladium is much lower than that of platinum.

Furthermore, it is advantageous that the catalyst according to the invention shows a high activity even at very low temperatures, so that it can be used without problems even in future internal combustion engines, where much lower exhaust gas temperatures are to be expected. In particular, this property is also advantageous when using the catalyst according to the invention in industrial applications, since there the air stream to be cleaned frequently has to be heated in order to be able to achieve a NO _x reduction.

In particular, the use of hydrogen as a reducing agent contributes to the high activity at low temperatures, as a result of which NO _{x is} effectively reacted on the catalyst according to the invention already at temperatures above 120 ° C. The direct conversion of NO _x with H ₂ to N ₂ and H ₂ O avoids the disadvantages associated with NO _x storage catalysts. The use of hydrogen as a reducing agent is toxicologically completely harmless, since the reaction product is water.

In a very advantageous development of the invention it can be provided that the zirconium oxide of the carrier layer has a monoclinic crystal modification.

Alternatively, it may be provided that the zirconium oxide of the carrier layer has a cubic crystal modification.

Both of the mentioned crystal modification, monoclinic or cubic, are relatively easy to prepare and therefore bring about a tetragonal crystal modification, as for example in the WO 2007/020035 A1 is required, significant cost advantages.

A particularly good selective conversion and a high activity of the catalyst could be observed when the mass ratio of the active component of palladium to the promoter of tungsten oxide is 1: 150 to 1:10, in particular 1: 100 to 1:25.

A process for the preparation of the catalyst according to the invention results from the features of claim 5.

With the aid of this process, the catalyst according to the invention can be produced particularly easily.

From claim 8, an apparatus for selective NO _x reduction results in NO _x -containing exhaust gases with a arranged in an exhaust pipe, catalyst according to the invention.

The device according to the invention enables optimal use of the catalyst for selective NO _x reduction of exhaust gases, wherein the hydrogen can be introduced into the exhaust pipe in a simple manner by means of a hydrogen supply. The combination of the use of zirconium oxide for the carrier layer, tungsten oxide for the promoter and palladium for the active component, a very high DeNO _x activity and a very high N ₂ selectivity can be achieved compared to known solutions, including in particular the supply of hydrogen contributes to the exhaust gases. The use of tungsten oxide as a promoter, which increases both the activity of the active component of palladium and the selectivity in the reduction of NO _x to N ₂ , is particularly advantageous, since this is a toxicologically harmless substance that is neither in the Production even with a possible later disposal problems.

A method for selective NO _x reduction in NO _x -containing exhaust gases with such a device is given in claim 9. With the aid of this method, the above-explained advantages of the device according to the invention are used particularly well, resulting in a very high conversion of NO _x . The method is also feasible by simple means and leads to a very high N ₂ selectivity.

This method can be used particularly well when the temperature of the exhaust gases is 120-200 ° C.

Further advantageous embodiments and modifications of the invention will become apparent from the remaining dependent claims. Embodiments of the invention are shown in principle with reference to the drawings.

It shows:

1 a schematic representation of a first embodiment of the structure of the catalyst of the device according to the invention;

2 a schematic representation of a second embodiment of the structure of the catalyst of the device according to the invention;

3 a schematic representation of an embodiment of the catalyst as a pellet;

4 a schematic representation of an embodiment of the catalyst as a honeycomb body;

5 a schematic representation of an embodiment of the catalyst as an extrudate;

6 a schematic representation of the inventive device for selective NO _x reduction in an internal combustion engine;

7 a schematic representation of the inventive device for selective NO _x reduction in an industrial application;

8th a graph showing the conversion and the selectivity of a first composition of the catalyst according to the invention; and

9 a graph showing the conversion and the selectivity of a second composition of the catalyst according to the invention.

1 shows in a very schematic, in particular not to scale, and greatly enlarged representation of a first embodiment of a catalyst 1 , which for selective NO _x reduction in the exhaust gases of an in 6 illustrated, preferably operating on the diesel principle internal combustion engine 2 serves. The catalyst 1 has a rigidity generating same basic body 3 on, which may be formed for example as a honeycomb body and may consist of a ceramic material. The main body 3 can also be designed as a soot filter to filter out any soot particles contained in the exhaust gases. Alternatively, the main body 3 for example, be formed from a metal substrate.

On the main body 3 is a carrier layer 4 applied, which consists of zirconium oxide (ZrO ₂ ). The carrier layer 4 is preferably highly porous, may consist of a hydrophilic material and has a surface area of at least 50 m ² / g, preferably of at least 100 m ² / g, of the carrier layer 4 on. The zirconium oxide may have a monoclinic or a cubic, but optionally also a tetragonal crystal modification.

On the body 3 opposite side of the carrier layer 4 is the same with a coating 5 provided a promoter 5a and an active component 5b having. The active component 5b consists of palladium and the promoter 5a consists of tungsten oxide. The coating 5 the carrier layer 4 is constructed so that at the base body 3 facing away, so on the outer surface 1a of the catalyst 1 both palladium and tungsten oxide are present.

At the in 1 illustrated embodiment of the catalyst 1 are used to make the same the active component 5b and the promoter 5a together on the carrier layer 4 applied, causing some mixing of the active component 5b and the promoter 5a comes, ie the palladium is in the form of individual particles in the tungsten oxide. The tungsten oxide and the palladium are present as tungsten salt or palladium salt in an aqueous solution, which is on the support layer 4 applied and then dried. For the preparation of the catalyst 1 In addition, a chemical or electrochemical deposition are also suitable.

In the embodiment of the catalyst 1 according to 2 first becomes the promoter 5a and then the active component 5b on the carrier layer 4 applied. The tungsten oxide is present as a tungsten salt in an aqueous solution, which is on the support layer 4 is applied. Specifically, per gram of the backing layer 4 a solution consisting of 0.776 g of ammonium metatungstate (Fluka, W content: 67%) and 0.32 g of distilled water are prepared and applied to forming zirconia. After impregnation of the carrier with the ammonium metatungstate solution, it is dried at 100.degree. C. for 5 hours. After drying the carrier layer 4 optionally followed by calcination and reduction in a reducing agent-containing gas stream, the palladium salt also present in an aqueous solution is applied to the tungsten oxide-coated carrier layer 4 applied and then dried again. To activate the palladium component, the substance is heated, for example, at a heating rate of 100 K / h in a volume flow (500 ml / min consisting of 10 vol .-% hydrogen and 90 vol .-% nitrogen to 300 ° C and 30 min at this Only tungsten oxide and zirconium oxide are not reduced, then the material is calcined for 5 hours at 500 ° C. in a static atmosphere, the heating rate once again being 100 K / min In order to expose the catalytic converter to typical exhaust gas temperatures, the following activity studies may show temperature - dependent changes in the catalytic converter Catalyst and related artifacts are excluded. The nitrates used are completely converted into the corresponding oxides during the conditioning with release of NO _x . In the 2 The procedure described therefore requires two drying steps, whereas in the preparation of the catalyst 1 according to 1 only one drying step is required.

In the 3 . 4 and 5 are different forms of the catalyst 1 shown, in addition to which, however, other embodiments are conceivable.

So shows 3 an embodiment of the catalyst 1 in the form of a pellet. Such pellets, which may be spherical as shown, but also rod-shaped or formed in a similar form, can be advantageously used in a suitable number, especially in stationary applications, since there the inflow surface of the catalyst 1 can be chosen almost freely. The size of the pellets may vary depending on the application. In this embodiment, the carrier layer 4 the function of the basic body 3 take over, ie it can affect the actual body 3 be waived, as this by the carrier layer 4 is formed. This may allow a larger proportion of the active component 5b in a catalyst of equal size in volume 1 contribute, whereby higher nitrogen oxide conversions can be achieved.

In 4 is the catalyst 1 in an already mentioned form of a honeycomb body 17 represented that can be advantageously used in particular in exhaust gases with high flow rates, since they produce a very low exhaust back pressure. On the honeycomb body 17 is a so-called washcoat 18 applied, the application of which can be used in principle on known techniques. The washcoat 18 In a first embodiment, only the zirconium oxide can be used, and in this case tungsten oxide and palladium are applied to the washcoat 18 applied. Furthermore, it is possible that the washcoat 18 consists of zirconium oxide and tungsten oxide and palladium on the washcoat 18 is applied. Another possibility is that the washcoat 18 consists of zirconium oxide, tungsten oxide and palladium, which is then preferably applied as a powder. The washcoat 18 can therefore according to 1 or according to 2 be constructed, or as a powder. For applying the washcoat 18 In addition known binders can be used.

Finally, in 5 the catalyst 1 as an extrudate 19 , ie as a product made by extrusion. The carrier layer takes over 4 again the function of the basic body 3 , ie it can be as in the embodiment of 3 on the actual body 3 be waived. In principle, the waiver of the body 3 also conceivable in all other embodiments, if it is possible that the carrier layer 4 the function of the basic body 3 takes over. The extrudate consists entirely of the "finished" catalyst material, the main body 3 or the material of the carrier layer 4 So is the catalyst powder itself. From the catalyst powder is therefore the ceramic body, for. As a honeycomb body made. For making the extrudate 19 In addition known binders can be used.

6 shows a device 6 for selective NO _x reduction in the exhaust gases of the internal combustion engine 2 , with which it is possible, a method for selective NO _x reduction in the exhaust gases of the internal combustion engine 2 to carry out, wherein the exhaust gases hydrogen is supplied as a reducing agent. By the supply of hydrogen to the exhaust gases results in the in the 1 to 5 in various embodiments described catalyst 1 an immediate reaction of NO _x with H ₂ to N ₂ and H ₂ O. In order to reduce the exhaust gases directly, is the catalyst 1 in one of the internal combustion engine 2 outgoing exhaust pipe 7 arranged. The device 6 further comprises a hydrogen supply device 8th on which a trained example in the form of a printing cylinder container 9 having, with a feed opening 10 is provided. To the feed opening 10 is a supply line 11 connected, which to the exhaust pipe 7 leads. The feed opening 10 is with a lock 12 provided, the opening 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 as well as with a sensor 15 connected in one to the internal combustion engine 2 leading suction line 16 is arranged. The sensor 15 is designed in the present case as per se known air mass sensor and serves to the to the internal combustion engine 2 to measure flowing air mass flow. Alternatively, the sensor could 15 also in the exhaust pipe 7 be arranged. Furthermore, it would be possible to have a temperature sensor in the exhaust pipe 7 provided. Optionally, it could also be on one of the two sensors 14 or 15 be waived.

Through the two sensors 14 and 15 is it possible to have a specific condition in the exhaust pipe 7 or in the suction line 16 and to the controller 13 forward. The control device 13 is thus able to be in the container 9 located hydrogen as a function of the NO _x concentration within the exhaust pipe 7 or in dependence of an air mass flow through the internal combustion engine 2 in the exhaust pipe 7 to lead. In this way, for example, in an acceleration process in which a higher NO _x emissions is to be expected, a larger amount of hydrogen in the exhaust pipe 7 be initiated. It is also possible to store the required data in a map in the controller 13 deposit in order to supply at certain times an increased amount of hydrogen. Of course, the hydrogen can also continuously into the exhaust pipe 7 be directed. Another possibility is to introduce a certain basic amount of hydrogen into the exhaust pipe 7 to conduct and at one by one of the sensors 14 or 15 identified need to increase the amount of hydrogen introduced.

To make additional fueling of hydrogen superfluous, the hydrogen supply can 8th with a device, not shown, for the reforming of hydrocarbon or derivatives to hydrogen from that for the internal combustion engine 2 be provided fuel, so a reformer or the like, connected. The required hydrogen could also by means of an electrolysis of a suitable substance, for. As water, are produced. These two possibilities are summarized herein by the term "HZ generator". The container 9 can be omitted in such a case either or replaced by a smaller cache.

If the main body 3 is not formed at the same time as a soot filter, as described briefly above, so may in the flow direction of the exhaust gas in the exhaust pipe 7 an unillustrated particulate filter the catalyst 1 be advanced or downstream. The main body 3 thus serves only to hold the carrier layer 4 ,

In 7 is the device 6 in an industrial application, so for selective NO _x reduction in the exhaust gases of an industrial plant indicated only schematically 17 , For example, a power plant shown. The device 6 that except for the waiver of the sensor 15 and the suction line 16 similar to that according to 6 is formed, it works in contrast to the application in the internal combustion engine 2 in a stationary operation. The most important difference to the transient operation of the catalyst 1 at the internal combustion engine 2 It consists in the fact that in stationary operation a much faster equilibrium is established, whereby very good working conditions for the catalyst 1 result.

In the table below are some exemplary compositions of the catalyst 1 stated: support material Tungsten [mass%] Palladium [% by mass] Catalyst abbreviation zirconia 8.7 0,136 0.14 Pd / 8.7 W / ZrO ₂ zirconia 8.7 0,273 0.27 Pd / 8.7 W / ZrO ₂ zirconia 8.7 0.409 0.41 Pd / 8.7 W / ZrO ₂ zirconia 8.7 0.546 0.55 Pd / 8.7 W / ZrO ₂ zirconia 8.7 .682 0.68 Pd / 8.7 W / ZrO ₂ zirconia 8.7 0.818 0.82 Pd / 8.7 W / ZrO ₂

In principle, the palladium content may be between 0.1-1% by mass, in particular between 0.35-0.55% by mass, a lower palladium content tending to require a higher exhaust-gas temperature, the cost of the particular catalyst 1 However, depending on the size of the same sometimes significantly reduced. Furthermore, a mass ratio of the active component has 5b from palladium to the promoter 5a from tungsten oxide of 1: 150 to 1:10, especially 1: 100 to 1:25 proved particularly advantageous. In the present case, the mass% of tungsten and palladium is 100% of the support material 4 Calculated, that is, it results with the carrier material 4 in total more than 100%. It should also be noted that the said 8.7 mass% tungsten correspond to about 11 mass% tungsten oxide.

For the determination of the activity or selectivity behavior of the different catalyst materials, the method of the temperature-programmed reaction (TPR) was used. To carry out the measurements, first the catalyst mass was pressed at 5 bar and then pressed on a Grain size of 125-250 microns brought. With the aid of two suitable sieves, particles larger than 250 μm and smaller than 125 μm were sorted out. Subsequently, 500 mg of the material was baked for 15 minutes at 500 ° C in an argon stream (500 ml / min) to adsorb adsorbed species such. As water, hydrocarbons or carbon dioxide to remove. This ensured reproducible experimental conditions. Subsequently, synthetic diesel model exhaust gas, the composition of which was based on typical values of a real exhaust gas, and hydrogen were added. In order to ensure a linear temperature profile, the measurement was carried out with a cooling ramp of 2 K / min in the range between 50 ° C and 500 ° C. The measurement conditions, which may vary in certain ranges indicated in parentheses, are listed in the following table: parameter Value (range) c (NO _x ) 500 ppm (5-5000) c (O ₂ ) 6 vol.% (0.5-21) c (H ₂ ) 2000 ppm (0.05-5%) balance Ar (N ₂ ) River 500 ml / min (STP) SV 80000 h ^-1 (5,000-200,000) _cat 500 mg _cat 125-250 μm heating rate 2 K / min, cooling temperature range 50-500 ° C

The experiments with the catalyst compositions given above led to the following result:
As the Pd loading increases from 0.14 to 0.27 mass% on the Pd / 8.7 W / ZrO2 catalyst system, integral N ₂ selectivity increases dramatically. However, as the Pd loading is further increased to 0.82 mass%, there is no longer any significant change in nitrogen selectivity in the H ₂ -deNO _x reaction. While at a Pd loading of 0.55% by mass of palladium, the maximum possible NO (62%) is achieved _x conversion, the integral NO _x takes -Sales with increasing Pd loading. At 0.41 mass% palladium, the maximum of the integral NO _x conversion is achieved. Considering the reproducibility of the measurements, the catalysts with Pd loadings of 0.27; 0.41; 0.55; and 0.68 very similar X (NO _x ) _int and S (N ₂ ) _int . The following table summarizes the most important criteria for assessing the individual catalysts with regard to their activity or selectivity behavior. Optimal conditions exist when the integral NO _x conversion and the integral N ₂ selectivity are as high as possible. Catalyst abbreviation Loading [Pd-eq] T _Xmax [_C] X (NO _x ) _max [%] X (NO _x ) _int [%] S (N ₂ ) _int [%] 0.14 Pd / 8.7 W / ZrO ₂ 1 180 59 40 86 0.27 Pd / 8.7 W / ZrO ₂ 2 155 53 36 95 0.41 Pd / 8.7 W / ZrO ₂ 3 160 55 38 95 0.55 Pd / 8.7 W / ZrO ₂ 4 150 62 34 97 0.68 Pd / 8.7 W / ZrO ₂ 5 150 56 34 95 0.82 Pd / 8.7 W / ZrO ₂ 6 150 43 30 94

For the catalyst composition with the catalyst short name 0.41 Pd / 8.7 W / ZrO ₂ are in the 8th and 9 given respective graphs in which the conversion and the selectivity is plotted against the exhaust gas temperature. Here are in 8th the NO _x conversion X and the N ₂ and N ₂ O selectivity S in the temperature-programmed H ₂ -deNO _x reaction under standard reaction conditions as indicated in the table above and in US Pat 9 the NO _x conversion X and the N ₂ - and N ₂ O selectivity S in the stationary H ₂ -deNO _x reaction under standard reaction conditions as shown in the table above.

When comparing the TPR test according to 8th with the stationary measurement according to 9 It can be seen that the NO _x conversion and the integral NO _x conversion are much higher for stationary reaction control. However, in terms of measurement accuracy, the deviations in terms of integral N ₂ selectivity and N ₂ selectivity in the NO _x conversion maximum are only marginal. This result shows that the temperature programmed reaction proceeds too fast with a ramp of 2 K / min, so that the steady state conditions are not completely given.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely 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.

Cited patent literature

• WO 2007/020035 A1 [0003, 0021]
• EP 1475149 A1 [0005]
• EP 0666099 B1 [0006]
• EP 0960649 B1 [0008]
• EP 0763380 A1 [0009]
• DE 10216748 A1 [0011]
• DE 4436890 A1 [0012]

Claims (10)

Catalyst for use in a selective NO _x reduction in NO _x -containing exhaust gases while supplying hydrogen to the exhaust gases, comprising a base body, a support layer of zirconium oxide applied to the base body, a tungsten oxide promoter applied to the support layer and one on the support layer applied active component, characterized in that the active component ( 5b ) consists of palladium. Catalyst according to claim 1, characterized in that the zirconium oxide of the carrier layer ( 4 ) has a monoclinic crystal modification. Catalyst according to claim 1, characterized in that the zirconium oxide of the carrier layer ( 4 ) has a cubic crystal modification. Catalyst according to claim 1, 2 or 3, characterized in that the mass ratio of the active component ( 5b ) from palladium to the promoter ( 5a ) of tungsten oxide is 1: 150 to 1:10, in particular 1: 100 to 1:25. A method for producing a catalyst for the selective reduction of NO _x in NO _x -containing exhaust gases, wherein a support layer of zirconium oxide is applied to a base body, wherein on the support layer a promoter of tungsten oxide and an active component is applied, characterized in that as the active component ( 5b ) Palladium is used. Method according to claim 5, characterized in that for the carrier layer ( 4 ) Zirconia having a monoclinic crystal modification is used. Method according to claim 5, characterized in that for the carrier layer ( 4 ) Zirconia having a cubic crystal modification is used. Contraption ( 6 ) for selective NO _x reduction in NO _x -containing exhaust gases, with one in an exhaust pipe ( 7 ) arranged catalyst ( 1 ) according to one of claims 1 to 4, and with a hydrogen supply device ( 8th ) for the introduction of hydrogen into the exhaust pipe ( 7 ). Process for the selective reduction of NO _x in NO _x -containing exhaust gases by means of a device according to claim 8, wherein into the exhaust gas line ( 7 ), which is traversed by the exhaust gases, hydrogen is introduced. A method according to claim 9, characterized in that the temperature of the exhaust gases is 120-200 ° C.

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