DE102006013234A1 - oxidation catalyst - Google Patents

Abstract

A catalyst characterized in that it contains a composition comprising palladium, platinum, tin oxide, a carrier oxide and zeolite. The catalyst can optionally be doped with oxides of gallium, indium or iron. Furthermore, a method for producing the catalyst, its use for removing pollutants from lean internal combustion engines and venting and methods for removing pollutants from exhaust gases from lean internal combustion engines using the catalyst by oxidizing carbon monoxide and hydrocarbons with simultaneous removal of soot particles by oxidation are disclosed.

Description

The The present invention relates to a simultaneous catalyst Removal of carbon monoxide and hydrocarbons from oxygen-rich Exhaust gases, for example from the exhaust gases of diesel engines lean Otto engines and stationary Sources. The catalyst contains a composition comprising platinum, palladium, tin oxide, zeolite and carrier oxide. Optionally contains the catalyst doping elements in the form of gallium, indium or iron oxide. The invention also relates to a process for the preparation of Catalyst and a method for exhaust gas purification using of the catalyst. The catalyst has a high conversion performance for carbon monoxide and hydrocarbons and high thermal stability.

The main pollutants from the exhaust gas of diesel engines are carbon monoxide (CO), unburned hydrocarbons (HC), such as paraffins, olefins, aldehydes, aromatics, as well as nitrogen oxides (NO _x ), sulfur dioxide (SO ₂ ) and soot particles containing the carbon both as a solid and in the form of the so-called "volatile organic fraction" (VOF) Furthermore, the diesel exhaust gas also contains oxygen in a concentration which, depending on the operating point, is between approximately 1.5 and 15%.

The pollutants that are emitted from lean gasoline engines, for example from directly injecting gasoline engines, consist essentially of CO, HC, NO _x and SO ₂ . The oxygen is in stoichiometric excess over CO and HC.

industrial Waste air as well as exhaust gases from domestic fire can also contain unburned hydrocarbons and carbon monoxide.

Under the term "oxygen-rich Exhaust "is a Understood exhaust gas, wherein the oxygen in stoichiometric excess over the oxidizable pollutants such as CO and HC is present.

to Removal of pollutants from these exhaust gases become oxidation catalysts used. They have the task of carbon monoxide and hydrocarbons by oxidation, ideally water and carbon dioxide arise. additionally can also get soot through Oxidation be removed, where also water and carbon dioxide be formed.

The Technically used catalysts usually contain platinum as an active component.

To compensate for thermal damage, platinum-containing oxidation catalysts for exhaust gases from diesel passenger cars are therefore usually equipped with very high platinum contents. They are typically in the range of 2.1-4.6 g / L (60-130 g / ft ³ ). For example, up to 9 grams of platinum are used in a 2 liter catalyst. The use of high platinum amounts is a significant cost factor in the exhaust aftertreatment of diesel vehicles. A reduction of the platinum content in the catalyst is of great economic interest. For this reason, platinum catalysts are also loaded with palladium, with platinum-palladium ratios of 2: 1 or 3: 1 being set especially in applications for purifying exhaust gas from direct-injection ("DI") diesel engines the addition of palladium to platinum lead to a decrease in the activity in the fresh state of the catalyst.

A Description of Pt / Pd catalysts is described, for example, in Applied Catalysis B: Environmental 60 (2005), 191-199 ".

The use of tin in platinum and palladium-containing oxidation catalysts for the purification of diesel exhaust gases is in the literature DE 10 2004 020 259.1 (Filing date 26.04.04), PCT / EP2005 / 004421 (filing date 25.04.2005), DE 10 2004 048 247 (Filing date 04.10.2004) and EP 05010515.4 (Filing date 13.05.2005).

A the tasks of the invention was to develop catalysts that have very good performance characteristics in the removal of pollutants from oxygen-rich exhaust gases, particularly of lean internal combustion engines and stationary sources, exhibit. At the same time should be a cost-effective manufacturing process for the Catalysts are developed.

The object according to the invention and other objects have been achieved with a catalyst which is characterized in that it has a composition comprising platinum, palladium, tin oxide, contains an aluminum-containing carrier oxide and zeolite.

Of the The term "carrier oxide" preferably means an oxide that is thermally stable and has a high surface area. The term concludes also a mixture of at least two different carrier oxides.

Of the Term "tin oxide" includes all potential Oxides and suboxides as well as all possible ones Hydroxides and carbonates.

The The term "palladium" includes both Element as well as compounds thereof, for example oxides and suboxides.

It can one or more zeolites are used in each case.

As carrier oxides are preferably oxides having a BET surface area greater than 50 m ² / g. Particular preference is given to oxides having a BET surface area in the range from 60 to 200 m ² / g.

Preferably, carrier oxides are used which, even after high temperature loading, have a high BET surface area. Also preferred is a carrier oxide having a low tendency to bind sulfur oxides (SO _x ).

When carrier oxide Aluminum-containing materials are used.

Under an aluminum-containing carrier oxide is a carrier oxide especially aluminum oxide, silicon / aluminum mixed oxide, Titanium / aluminum oxide, Zirconium / alumina, aluminosilicate, kaolin, modified kaolin or mixtures thereof.

Prefers can also pyrogenic alumina, α-alumina, δ-alumina, theta alumina and gamma alumina be used.

Besides, too Aluminum oxides can be used with silica, zirconia or titanium oxide are doped.

zeolites are known compounds and in part commercially available.

in the Within the scope of the present invention, it is possible to use only a single zeolite or a single zeolite modification or mixtures of different ones Zeolites or zeolite modifications. The term modification includes the zeolite type and the specific chemical composition, eg. As the Si / Al ratio.

Of the Zeolite is preferably present in the so-called H-form. Especially Also suitable are hydrothermal-stable zeolites with a Si / Al ratio> 8, with higher Si / Al ratios are preferred.

Especially suitable zeolite types are Y zeolite, DAY zeolite (dealuminated Y), USY (Ultra Stabilized Y), ZSM-5, ZSM-11, ZSM-20, Silicalite, Ferrierite, mordenite and β-zeolite.

The Zeolites can also be treated hydrothermally.

It can also several zeolites are used. These differ then preferably in that they have different pore radii or different Si / Al ratios or different Pore radii and different Si / Al ratios exhibit.

ever according to the requirement profile of the catalyst, i. the under real conditions occurring exhaust gas temperatures and concentrations of carbon monoxide and hydrocarbons, it may be useful to use the catalyst to dope with the oxides of gallium, indium or iron.

Under The oxides of gallium, indium and iron are all oxides, suboxides, Sulfates and cationic forms of gallium, indium and iron be understood. In summary, the oxides of gallium, Indium and iron hereinafter also referred to as doping elements.

The especially high activity and stability The catalyst is characterized by the special properties of the composition from platinum, palladium, tin oxide, carrier oxide, zeolite and possibly the Doping elicited.

Farther are the specific proportions all in the catalyst oxides and elements significant.

In a particular embodiment, the mixture of at least two different zeolite types is preferred. For example, it may be useful to use a small to medium pore zeolite along with a medium to large pore zeolite to optimally adsorb both small and large hydrocarbon molecules and oxidize them to CO ₂ and H ₂ O.

One An essential feature of the catalyst is that on the carrier oxide deposited tin oxide a X-ray amorphous or a nanoparticulate Form has. Typically, the tin oxide particles have particle sizes of about 0.5 to 10 nm.

Of the Term "X-ray amorphous "should mean that no evaluable for a substance characteristic reflexes by means of x-ray wide-angle diffraction to be obtained. This statement applies at least to those in the experimental part revealed experimental conditions.

In general, particle sizes can be determined using the Scherrer equation from X-ray diffractograms:
Scherrer's equation: D = (0.9 × λ) / (Bcosθ B )

Herein, "D" is the thickness of a crystallite, "λ" is the wavelength of the X-ray used, "B" is the half-width of the respective reflection and θ _{B is} its position The fresh catalysts, ie calcined at 500 ° C, are of the Scherrer method In some cases, even no reflections of the tin oxide are more visible, so that the tin oxide present on these catalysts are referred to as "X-ray amorphous" can. After aging at 700 ° C, no or only a very small growth of the tin oxide particles can be determined, depending on the carrier oxide used. However, the sizes of corresponding tin oxide particles remain in the nanoparticulate dimension, that is, at sizes of a few nm to a maximum of 100 nm, depending on the temperatures to which the catalyst is exposed. This emphasizes the very good durability of the catalysts of the invention.

These Distribution also includes that the catalyst, for example Blends of at least two, platinum, palladium and tin oxide containing carrier oxides contains the respective different concentrations of tin oxide and / or of palladium or platinum. Furthermore, this includes Ver division also that the applied to a honeycomb-shaped carrier body catalyst according to the method of gradient coating or zone coating will be produced. A gradient coating becomes a gradient of platinum and palladium the length of the honeycomb body set. In this way, at the place of entry of the exhaust gas of the internal combustion engine in the catalyst a higher concentration of noble metal provided, which, depending on the application, for better use of the precious metal.

Of the Catalyst is used for the application preferably as a powder, granules, extrudate, shaped article or as coated honeycomb body used.

In a preferred embodiment If the catalyst is coated as a shaped body, preferably as a coated honeycombs before, wherein it is structured in the form of a double layer.

Preferably the catalyst is present as a coated molded body, wherein a layer on the molded body from the composition consisting of platinum, palladium, tin oxide, carrier oxide and zeolite is applied. Optionally, this layer can be oxides of gallium, indium and iron as doping elements.

Of the Catalyst preferably has a structure in which formed into channels Macropores coexist with meso- and / or micropores.

• (i) Inkontaktbringen einer Zinnverbindung, einer Palladiumverbindung, einer Platinverbindung, eines Trägeroxids und eines Zeolithen und ggf. einer Verbindung des Galliums, Indiums oder Eisens,
• (ii) Kalzinierung der in (i) gebildeten Zusammensetzung.

The catalyst is prepared by a process characterized in that it comprises steps (i) and (ii):

• (i) contacting a tin compound, a palladium compound, a platinum compound, a carrier oxide and a zeolite and optionally a compound of gallium, indium or iron,
• (ii) calcination of the composition formed in (i).

at The calcination is, as described below, the catalyst precursor by transferred a thermal treatment in the catalytically active form.

Under "Palladium, Platinum, and tin compound "are to understand all compounds which are suspended in a liquid medium can and / or in this medium completely or at least partially soluble are.

Under "Connection of gallium, indium and iron " to understand all compounds which are suspended in a liquid medium can and / or in this medium completely or at least partially soluble are.

Preferably be platinum, palladium, tin compounds and possibly compounds of gallium, indium and iron used in the liquid medium Completely or at least partially soluble are.

Preferably is the liquid Medium water.

Preferably are salts of palladium, platinum, tin and possibly gallium, Indium and iron used. Salts are, for example, the salts inorganic and organic acids, such as chlorides, bromides, cyanides, nitrates, oxalates, acetates or tartrates. The use of complex compounds is also possible.

When Tin compound is preferably used in water dissolved or suspended tin oxalate, the solubility by addition of acids, for example, nitric acid, further increased can be.

Should the compounds of platinum and palladium together with those in acidic solutions present compounds of the tin are applied to the carrier oxide, so the use of platinum and palladium nitrates is particularly advantageous.

Should the compounds of gallium, indium and iron together with present in acidic solutions Compounds of the tin are applied to the carrier oxide, so their use in the form of nitrates is particularly advantageous.

at the preparation of the catalyst is preferably a process used in which the compounds of platinum, palladium, tin and possibly of gallium, indium and iron by means of aqueous medium with the carrier oxide be associated.

to Preparation of the catalysts, a method is preferred, at the possible Chloride-free tin, platinum and palladium compounds used be there later Release of chloride-containing compounds from the catalyst to damages lead the exhaust systems can. The same applies to the compounds of gallium, indium and iron.

"Contacting" of step (i) means that compounds of tin, platinum, palladium, zeolite and optionally the compounds of gallium, indium and iron in suspended or preferably dissolved Form either simultaneously, in mixes or sequentially applied the common carrier oxide become. For example, you can first the compounds of the tin are applied to the carrier oxide, while the compounds of palladium and platinum in a subsequent step with the carrier oxide be brought into contact. It is particularly economical, all To submit links in a common solution and then this in the form of a co-impregnation with the carrier oxide to bring into contact.

In As a rule, a drying takes place after each contacting.

To Stage (i) and after drying are applied to the carrier oxide applied compounds by a thermal treatment in their transferred catalytically active form.

• (ii) Kalzinierung.

Accordingly, the method also includes the step (ii):

• (ii) calcination.

The Calcination step is carried out at a temperature of preferably 200 up to 1000 ° C, more preferably 300 ° C up to 900 ° C, in particular 400 to 800 ° C carried out.

By The calcination will also increase the mechanical strength of the catalyst elevated.

The Calcination can be carried out, for example, in dry or moist air, be carried out in nitrogen forming gas or steam.

For the loading of the carrier oxide by contacting with the dissolved platinum compounds, palladium compounds, Compounds of tin and possibly the compounds of gallium, indium and ice, as well as for drying and calcination, all known methods are used. These depend on the chosen production variants in particular, whether the "Washcoat" consisting of carrier oxide and zeolite initially on a shaped body and then the compounds of tin, platinum and the Palladium impregnated be chosen or whether a powder process in which the compounds of platinum, palladium, tin and possibly of gallium, indium and Iron first on the mixture of carrier oxide and Zeolite is applied and this then processed into a washcoat becomes.

For example allows the powder process a higher flexibility in the preparation of the catalysts, as the aforementioned compounds for example exclusively on the carrier oxide be impregnated can, while the zeolite until later Time the carrier oxide is added and thus not with the aforementioned compounds comes into contact. Possible it is also carrier oxide and zeolite separately with the aforementioned compounds to impregnate, thus different concentrations of platinum, palladium, Tin oxide and the doping elements on the carrier oxide and the zeolite represent.

The Stage (i) thus comprises contacting a tin compound, a palladium compound, a platinum compound, a zeolite and optionally a compound of gallium, indium or iron with a carrier oxide, or contacting a tin compound, a palladium compound, a platinum compound and possibly a compound of gallium, indium or iron with a carrier oxide, Drying and calcination followed by contacting the calcined composition with a zeolite.

Becomes the catalyst shown as honeycomb technology, so offers It is, the appropriate Honeycomb substrate first through Dipping in a suspension of ground zeolite and carrier oxide with Zeolite / support oxide to load and after drying of the so loaded substrate this according to step (i) with the compounds of platinum, palladium, tin and optionally of gallium, indium and iron. This is the easiest and least expensive Method to produce the catalyst as honeycomb technology.

apart Of the Honeycomb technologies can be the assembly of the catalyst also take place by other known methods, for example by Extrude or Extrude.

In summary can be said that the catalyst according to the invention after the preparation preferably as a powder, granules, extrudate or as a shaped body, for example, as a coated honeycomb body, is present.

in the The following is the chemical composition of the catalysts of the invention explained. The weights in% refer to the respective Elemental masses of platinum, palladium, tin and doping elements. For the support oxides as well as the zeolites refer to the weight data on the respective oxidic compounds.

Typical palladium levels of the catalyst of this invention are 0.35 g / L-0.59 g / L (15-60 g / ft ³ ) while that of the platinum is 1.06 to 1.59 g / L (30 g / ft ³ -45 g / ft ³ ). Depending on the application, however, the amounts of palladium and platinum may differ from these quantities. The units "g / L" or "g / ft ³ " relate, as is familiar to those skilled in the supported catalysts on the elemental mass noble metal in relation to the carrier volume, for example to the volume of a honeycomb carrier body.

The total amount of tin is 0.1-7 wt .-% (calculated as element) based on the Trägero dioxide. In this case, a total amount of 0.5 to less than 3 wt .-% is particularly preferred.

The Total amount of doping elements is 0.01-5 wt .-% (calculated as element) based on the carrier oxide, wherein a total amount of 0.1-3 wt .-% is preferred.

The Total amount of palladium (calculated as element) relative to the carrier oxide is preferably 0.2-5% by weight. Stronger preferred is a total amount of 0.4-2 wt .-%.

The Total amount of platinum (calculated as element) based on the carrier oxide is preferably 0.2-5% by weight. Stronger preferred is a total amount of 0.4-2 wt .-%.

The weight ratio of tin to the total weight of palladium and platinum (calculated as Elements) is preferably in a range of 0.5: 1 to 3: 1.

The optimal ratio the total mass of platinum and palladium to tin (relative to the elements) depends strongly from the mass ratio of platinum to palladium. For example, at a platinum / palladium mass ratio of 2.7: 1 already by the addition of a small amount of tin one significant improvement in the performance of the corresponding Catalysts observed. In this case, a mass ratio of Tin to the total amount of palladium and platinum in a range of 0.2: 1 to 2.5: 1 as particularly favorable. An increase the amount of tin over The relationship 2.5: 1 leads out to no further improvement in the performance of the catalysts.

at a reduction of the platinum / palladium mass ratio, for example, to 0.33: 1, however, can increase the mass ratio of tin to the total mass of platinum and palladium be useful. In this case, a range of 0.6: 1 to 3: 1 proves to be special Cheap. In a further reduction of the platinum / palladium mass ratio can mass relations of tin to the total mass of platinum and palladium to 7: 1 as advantageous prove.

In summary can be said that at platinum rather than palladium Amounts of tin are preferred while enrichment of palladium versus platinum rather larger quantities are advantageous to tin

The Total amount of zeolite based on the carrier oxide (calculated as oxides) is preferably 3-60% by weight. Stronger preferred is a total amount of zeolite in a range of 8-50 Wt .-%. Particularly preferred is a range of 10-35 wt .-%.

Preferably, aluminum oxides are used with BET surface areas of 60 to 200 m ² / g.

Preferably is used as zeolite, a silicon-rich zeolite Beta type (β-zeolite). In a further preferred embodiment, the catalyst contains another zeolite in the form of a silicon-rich ZSM-5.

Preferably For example, zeolite beta and ZSM-5 are each in the H form. This includes however, that does not matter while the stages (i) "contacting" and (ii) "calcination" to a certain extent Degree a so-called ion exchange takes place, in which the proton of the zeolite by the platinum, palladium, tin oxide or possibly by the oxides of gallium, indium and iron are exchanged.

The catalysts of the invention also show a very good sulfur tolerance, that of the Superior to tin-free Pt / Pd catalysts is.

The The invention also relates in particular to the use of the catalyst for the removal of pollutants from exhaust gases of lean internal combustion engines and venting.

One Another subject of the invention is thus also the use of the Catalyst for removing pollutants from lean internal combustion engines and venting by oxidation, the pollutants carbon monoxide and hydrocarbons include, which are oxidized to water on the catalyst.

Contain the exhaust gases soot, so they are also oxidized, preferably simultaneously with Carbon monoxide and hydrocarbons.

Farther The present invention also relates to a method for exhaust gas purification of lean internal combustion engines and venting using the above disclosed catalyst.

Preferably For example, the exhaust gas purification method is performed such that exhaust gas purification the simultaneous oxidation of hydrocarbons and carbon monoxide and the removal of soot by oxidation.

• (i) Inkontaktbringen eines Abgasstroms von mageren Verbrennungsmotoren mit dem Katalysator.

The method for removing pollutants from exhaust gases of lean internal combustion engines is characterized in that it comprises the step (i):

• (i) contacting an exhaust gas stream of lean internal combustion engines with the catalyst.

This Method is further characterized in that carbon monoxide and hydrocarbons are oxidized, with carbon dioxide and water arises.

The Method is also characterized in that at the same time soot particles be removed by oxidation.

in the The following is intended in exemplary embodiments illustrating the preparation of exemplary catalysts as well their properties compared to the prior art shown become. The fact that this is based on concrete examples under the Specification of specific numerical values is done, should in no case as restriction the statements made in the description and claims understood become.

The pictures show:

• a) Verlauf der CO-Konvertierung als Funktion der Temperatur
• b) Verlauf der HC-Konvertierung als Funktion der Temperatur

In the pictures 1 - 5 mean:

• a) Course of CO conversion as a function of temperature
• b) Course of HC conversion as a function of temperature

On the x axis is the temperature in degrees Celsius (° C) and on the y axis the conversion divided by 100.

 Activity measurement of the catalysts

Activity measurements were performed in an automated synthesis gas plant. The catalysts were tested under diesel exhaust-like conditions in a continuous operation with oxygen excess under the following conditions: Temperature range: 120-400 ° C Heating rate: 14 ° C / minute Exhaust gas composition: 1500 vppm CO, 200 vppm C ₁ (decane), 100 vppm C ₁ (toluene), 140 vppm (propene), 100 vppm NO, 13% O ₂ , 5% CO ₂ , 5% H ₂ O, Rest - N ₂ . total gas: 450 L / hour

The Honeycomb-shaped Catalysts had a diameter of 2.54 cm and a length of 2.54 cm.

• VB01: Zinn-freier Platin-Palladium Katalysator mit 1,59 g/L Platin und 0,59 g/L Palladium.
• VB02: Zinn-freier Platin-Palladium Katalysator mit 1,06 g/L Platin und 0,35 g/L Palladium.
• VB03: Kommerziell erhältlicher Dieseloxidationskatalysator mit 4,6 g/L Platin (130 g/ft³)* für Pkw Dieselfahrzeuge des Baujahrs 2005.
• * ermittelt durch micro-Röntgenfluoreszensanalyse mit dem Gerät „Eagle-II"

As reference catalysts, the following commercial diesel oxidation catalysts for exhaust gases from diesel engines were used:

• VB01: Tin-free platinum-palladium catalyst with 1.59 g / L platinum and 0.59 g / L palladium.
• VB02: Tin-free platinum-palladium catalyst with 1.06 g / L platinum and 0.35 g / L palladium.
• VB03: Commercially available diesel oxidation catalyst with 4.6 g / L platinum (130 g / ft ³ ) * for passenger cars, diesel vehicles built in 2005.
• * determined by micro X-ray fluorescence analysis with the device "Eagle-II"

The Comparative measurements between the catalysts of the invention and the reference catalyst were based on the same catalyst volumes.

The Determination of CO was carried out with ND-IR analyzers from ABB (type "Advance Optima "). The determination of the hydrocarbon took place with a FID from ABB (type "Advance Optima ").

For the evaluation of the catalysts, the T ₅₀ values (temperature at which 50% conversion is reached) of the CO oxidation and the integral HC reduction between 123 and 250 ° C, hereinafter referred to as HC _int is used. With regard to the HC reduction, it should be noted that the hydrocarbons are first adsorbed only at the catalyst at lower temperatures and only oxidized to CO ₂ and H ₂ O at higher temperatures. The term HC conversion thus includes the adsorption and oxidation of hydrocarbons.

The T ₅₀ values for the catalysts after hydrothermal aging are summarized in Table 2. Table 3 contains the integral HC conversion HC _int determined over the temperature range of 130 to 250 ° C.

Hydrothermal aging

The Hydrothermal aging took place in a muffle furnace at a temperature from 800 ° C in an air stream containing 10% water. The catalysts were held at this temperature for 5 hours and then on Room temperature cooled.

Cyclic preconditioning

at the cyclic preconditioning, the catalysts become a simulated diesel exhaust exposed to the exhaust gas composition the activity measurements equivalent. The catalyst is at a heating rate of 2 ° C / minute of 140 ° C at 400 ° C heated, with a cooling rate from about 2 ° C Minute at 140 ° C cooled, then reheats, etc. The total duration of this conditioning cycle is 20 hours. The cyclic preconditioning serves to catalyze the catalyst at low and medium exhaust gas temperatures.

Unlike hydrothermal aging, the catalyst is exposed to high CO, NO _x and HC emissions.

Examples

The Catalysts of the following examples make use of a washcoat / honeycomb technology, at the a honeycomb-shaped carrier was loaded with washcoat. Subsequently, the compounds were of tin, platinum, palladium and possibly gallium and iron impregnated together. The carriers consisted of cordierite with 400 cpsi (channels per square inch) and were manufactured by the company NGK.

Example B01

To the Preparation of Catalyst B01 became a mechanical mixture from 80% by weight of alumina (Puralox SCFa 140) from Sasol, 10% by weight Beta zeolite (CP 7104) from the company Zeolyst and 10 wt .-% ZSM-5 zeolite (Zeocat PZ-2 / 100H) from Zeochem in deionized water suspended and in a mill (Dyno-Mill Type Multi Lab) of the company Willy A. Bachofen ground. The The resulting coating suspension had 20 wt .-% solids. This coating suspension showed very good adhesion properties and was without the addition of other binders for making the washcoat used.

When catalyst support became a honeycomb Cordierite core with 400 cpsi (channels per square inch) of the Fa. NGK used previously to a dimension of 1 inch in diameter and cut 2 inches in length has been.

Of the Drill core was made by repeated immersion in the coating suspension coated with the alumina / zeolite washcoat, stepping after each dip the channels of the core were blown out to remove excess suspension. After each coating step, the core was air-flow dried and finally Calcined in a stream of air at 500 ° C for 15 minutes. The washcoat load was 120 g / L. This loading places the applied on the molding Solid content of the washcoat after calcination.

The tin and precious metals were applied to the washcoated core by impregnation with an aqueous solution containing tin oxalate, platinum nitrate, palladium nitrate and nitric acid. To this was added 216.8 μl of an aqueous, nitric acid-containing, 1.0 molar tin oxalate solution containing 209.7 μl of a 1.0 molar platinum nitrate solution and 142.7 μl of a 1.0 molar palladium nitrate Mixed solution and diluted with 9 ml of water. The resulting solution was applied to the washcoat coated core in two steps. The thus impregnated core was then in the air stream dried and calcined for 15 minutes at 300 ° C in a stream of air.

Subsequently was the catalyst calcined for 2 hours at 700 ° C in a muffle furnace under air (referred to as "fresh").

Of the finished catalyst contained 96 g / L Puralox SCFa 140, 12 g / L zeocate PZ-2 / 100H, 12g / L CP 7104, 1.0 g / L tin, 1.59 g / L platinum and 0.59 g / L palladium.

Of the Drill core was split. One part (1 inch in length) was added for 5 hours 800 ° C in Calcined air containing 10% by volume of water (as "hydrothermal aged ").

Examples B02 to B04

The Catalysts were prepared analogously to Example B01, the Loading with platinum, palladium and tin were varied. Farther In the example B04 iron was used as doping element, which in Form of nitrate of nitric acid solution of tin oxalate, platinum nitrate, and palladium nitrate impregnation solution has been.

In Table 1 shows the compositions of the catalysts according to Example B02 to B04 reproduced on a weight basis in the unit g / L, this information being based on the oxidic form of the carrier oxide and the zeolite and the elemental form of the platinum, palladium, Tin and iron.

Examples B05 to B07

The Catalysts were prepared analogously to Example B01, wherein for the washcoat a mechanical mixture of silica-doped alumina (Siralox 5/170) of the company. Sasol and the zeolites was used. Thereby and the loading amounts of platinum, palladium and tin were varied. Furthermore, the catalysts contained Examples B06 and B07 in addition Gallium as doping elements, in the form of the nitrate of nitric acid solution consisting of tin oxalate, platinum nitrate, and palladium nitrate added has been.

In Table 1 shows the compositions of the catalysts according to Example B05 to B07 on weight basis in unit g / L, this information being based on the oxidic form of the carrier oxide and the zeolite and the elemental form of the platinum, palladium, Tin and gallium relate.

Comparative Examples VB01 and VB02

To the For comparison, two catalysts were prepared without tin. The washcoat composition and the loadings with platinum and palladium correspond to the catalysts according to the invention Examples B01 or B02 and B03.

Comparative Example VB03

For further comparison, a commercial Pt oxidation catalyst with a platinum content of 4.59 g / L (130 g / ft ³ ) was used.

Results of the activity measurements

The "light-off" values for CO ("Tso (CO)") of Table 2 determined from the activity measurements and the values of the integral HC reduction ("HC _int ") of Table 3 showed that the catalysts according to the invention have undergone hydrothermal aging had a better activity for the oxidation of CO than the commercial Pt-only reference catalyst (VB03), although this had a more than double platinum loading.

If, on the other hand, the catalysts according to the invention are compared with the platinum-palladium, platinum-palladium reference catalysts VB01 and VB02, it can clearly be seen that the activities for CO and HC were practically the same in the first activity test, but the catalysts according to the invention were significantly more active after the cyclic preconditioning. It can be seen that the tin-free platinum-palladium reference catalyst deteriorated with 1.59 g / L Pt and 0.59 g / L Pd with respect to T50 from 150 ° C to 173 ° C, while the inventive catalysts B01 and B02 deteriorated only from 150 ° C to 161 ° C and 156 to 161 ° C.

The inventive catalyst B03, in which a reduction in the amount of noble metal to 1.09 g of Pt and 0.35 Pd was carried out with respect to the CO activity T ₅₀ values of 152 ° C (before the cyclic preconditioning) and 158 ° C (according to cyclic preconditioning). In contrast, the corresponding tin-free catalyst showed a T ₅₀ value of 183 ° C after cyclic preconditioning.

One Comparison of catalysts B01 to B04 and VB01 to VB03 showed that the catalysts of the invention a total saving of precious metal up to about 50% made possible.

Claims (21)

Catalyst, characterized in that it contains a composition comprising platinum, palladium, tin oxide, carrier oxide and zeolite. Catalyst according to claim 1, characterized in that that the carrier oxide Containing aluminum. Catalyst according to claim 1 or 2, characterized in that that the carrier oxide selected is from the group alumina, silica-doped alumina, Titania-doped alumina or zirconia-doped alumina. Catalyst according to one of the preceding claims, characterized characterized in that it comprises at least one zeolite selected from the group Y zeolite, DAY zeolite, USY zeolite, ZSM-5, ZSM-11, ZSM-20, Silicalite, ferrierite, mordenite and β-zeolite contains. Catalyst according to claim 4, characterized in that the at least one zeolite has an Si / Al ratio> 10. Catalyst according to claim 4 or 5, characterized in that that a zeolite mixture consisting of ZSM-5 and β-zeolite is used. Catalyst according to one of the preceding claims, characterized characterized in that it comprises a doping element selected from contains the oxides of gallium, indium or iron. Catalyst according to one of the preceding claims, characterized in that the tin oxide deposited on the carrier oxide Particle sizes of 0.5-10 nm. Catalyst according to one of the preceding claims, characterized characterized in that the total amount of tin (calculated as an element) based on the carrier oxide (calculated as oxide) 0.1-7 wt .-%, wherein a total amount from 0.5 to less than 3 wt .-% is particularly preferred. Catalyst according to one of the preceding claims, characterized characterized in that the total amount of doping elements (calculated as element) to carrier oxide 0.01-5 wt .-% is. Catalyst according to one of the preceding claims, characterized characterized in that the total amount of palladium (calculated as Element) based on the carrier oxide preferably 0.2-5% by weight, wherein a total amount of palladium in the range of 0.4-2 wt .-% more preferred. Catalyst according to one of the preceding claims, characterized characterized in that the total amount of platinum (calculated as an element) based on the carrier oxide preferably 0.2-5% by weight, wherein a total amount of platinum in the range of 0.4-2 wt .-% further is preferred. Catalyst according to one of the preceding claims, characterized characterized in that the total amount of zeolite based on the carrier oxide (calculated as oxides) is preferably 3-60% by weight, more preferably 8-50 wt .-% and in particular 10-35 wt.% Is. Process for the preparation of a catalyst according to one of the claims 1 to 13, characterized in that the method comprises the stages (i) and (ii) comprises: (i) contacting a tin compound, a palladium compound, a platinum compound, a zeolite and possibly a compound of gallium, indium or iron with a carrier oxide, or contacting a tin compound, a palladium compound, a platinum compound and possibly a compound of gallium, indium or iron with a carrier oxide, Drying and calcination followed by contacting the calcined composition with a zeolite, (ii) calcination the composition formed in (i). Process for the preparation of a catalyst according to one of the claims 1 to 13, characterized in that it is the production of a Composites consisting of carrier oxide and tin oxide, and this production step comprises the step of "spray drying", "spray calcination", "rotary tube drying" or "rotary tube calcination". Use of a catalyst according to any one of claims 1 to 13 or a catalyst prepared according to any one of claims 14 or 15 for the removal of pollutants from lean internal combustion engines and flash off by oxidation. Use according to claim 16, characterized that the pollutants include carbon monoxide and hydrocarbons. Use according to claim 17, characterized that the pollutants include soot. Process for the removal of pollutants from exhaust gases of lean internal combustion engines, characterized in that it the step (i) comprises: (i) contacting an exhaust gas stream of lean internal combustion engines with a catalyst according to one of claims 1 to 13 or a catalyst prepared according to any one of claims 14 or 15th Method according to claim 19, characterized that carbon monoxide and hydrocarbons are oxidized. Method according to claim 20, characterized in that that at the same time soot particles be removed by oxidation.