Title of Invention	DIESEL OXIDATION CATALYST WITH GOOD LOW-TEMPERATURE ACTIVITY
Abstract	The invention relates to a method for producing a catalyst, wherein the catalyst has a high activity and selectivity with regard to the oxidation of CO and NO. The invention also relates to the catalyst produced using the method according to the invention, the use of the catalyst as oxidation catalyst as well as a catalyst component which contains the catalyst according to the invention. Finally, the invention is directed towards an exhaust-gas cleaning system which comprises the catalyst component containing the catalyst according to the invention.

Title of Invention

DIESEL OXIDATION CATALYST WITH GOOD LOW-TEMPERATURE ACTIVITY

Abstract

Full Text	The invention relates to a method for producing a catalyst, wherein the catalyst has a high activity and selectivity with regard to the oxidation of CO and NO. The invention also relates to the catalyst produced using the method according to the invention, the use of the catalyst as oxidation catalyst as well as a catalyst component which contains the catalyst according to the invention. Finally, the invention is directed towards an exhaust-gas cleaning system which comprises the catalyst component containing the catalyst according to the invention. In the early stages of exhaust-gas cleaning of combustion engines, only the exhaust gases from petrol engines were cleaned with three-way catalysts (TWC). The nitrogen oxides are reduced with the reductive hydrocarbons (HC) and carbon monoxide (CO). For this, the petrol engine is always driven under approximately stoichiometric conditions {X=l). This cannot always be guaranteed precisely in this way, with the result that the conditions in the exhaust gas always fluctuate around A,= l. In other words, the catalyst is exposed alternately to an oxidative or a reductive gas atmosphere. For about 15 years, attempts have also been made to aftertreat the exhaust gases from diesel engines with catalysts. The exhaust gas from diesel engines contains carbon monoxide, unburnt hydrocarbons, nitrogen oxides and soot particles as air pollutants. The unburnt hydrocarbons comprise paraffins, olefins, aldehydes and aromatics. Unlike the petrol engine, the diesel engine always runs with an excess of oxygen. The result of this is that the catalyst is never exposed to reductive conditions. This has the following consequences: 1. The oxygen storage capacity of the catalyst material does not play the same role as with the TWC. 2. The noble metal particles are not always reduced again to metal of oxidation state 0. 3. The nitrogen oxides cannot be fully reduced when there is an excess of oxygen with the hydrocarbons (HC) present in the exhaust gas and CO. 4. The hydrocarbons and CO can be oxidized both with oxygen and with NOx. Diesel exhaust gases are much colder than exhaust gases from petrol engines and contain oxygen in a concentration between 3 and 10 vol.-%, which is why the catalytic activity of the catalyst on average is not always sufficient to oxidize HC and CO. In partial-load operation, the exhaust-gas temperature of a diesel engine lies in the range between 100 and 250°C and only in full-load operation does it reach a maximum temperature between 550 and 650°C. In contrast, the exhaust-gas temperature of a petrol engine lies between 400 and 450°C in partial-load operation and, in full load, can rise to up to 1000°C. It is therefore an aim to achieve as low as possible a CO light-off temperature. In past years, diesel particle filters (DPF) have increasingly been introduced onto the market. These are normally fitted downstream of the DOCs. Soot is collected and oxidized in the DPF. The oxidation of soot is much more possible with NO2 than with oxygen. Thus, the more N02 is contained in the gas stream after the DOC, the more soot continuously reacts. Thus, there has been a tendency in past years to oxidize as much NO to N02 as possible in the DOC. But N02 is an even more toxic gas than NO, with the result that this shift towards increased nitrogen oxide emissions manifests itself in a very negative way. An increasing NO2 concentration due to DOC is also already detectable in cities. Thus, the trend is returning to a limiting of the oxidation of NO to NO2. Markedly reduced emissions of nitrogen oxides have thus also been prescribed for the Euro VI standard. It will be possible to achieve these either only by means of NOx-trap catalysts or by means of a selective catalytic reduction by means of ammonia. The closer the NO/NO2 ratio is to 1:1, the more efficiently such an SCR reaction runs, thus a substantial oxidation of NO to NO2 is desirable for this. This should, however, be achieved with continuingly very good oxidation of CO and hydrocarbons HC. SCR (selective catalytic reduction) denotes the selective catalytic reduction of nitrogen oxides from exhaust gases of combustion engines and also power stations. Only the nitrogen oxides NO and NO2 (called N0X in general) are selectively reduced with an SCR catalyst, wherein NH3 (ammonia) is usually admixed for the reaction. Only the harmless substances water and nitrogen thus form as reaction product. The transportation of ammonia in compressed-gas bottles is a safety risk for use in motor vehicles. Therefore precursor compounds of ammonia which are broken down in the exhaust-gas system of the vehicles accompanied by the formation of ammonia are customarily used. For example the use of AdBlue®, which is an approximately 32.5% eutectic solution of urea in water, is known in this connection. Other ammonia sources are for example ammonium carbamate, ammonium formate or urea pellets. Ammonia must first be formed from urea before the actual SCR reaction. This occurs in two reaction steps which together are called hydrolysis reaction. Firstly, NH3 and isocyanic acid are formed in a thermolysis reaction. In the actual hydrolysis reaction isocyanic acid is then reacted with water to ammonia and carbon dioxide. To avoid solid depositions it is necessary for the second reaction to take place sufficiently quickly by choosing suitable catalysts and sufficiently high temperatures (from 250°C). Simultaneously, modern SCR reactors act as the hydrolysis catalyst. The ammonia formed through thermohydrolysis reacts at the SCR catalyst according to the following equations: 4N0 + 4NH3 + 02 -* 4N2 + 6H20 (1) NO + N02 + 2NH3 -»¦ 2N2 + 3H20 (2) 6N02 + 8NH3 -» 7N2 + 12H20 (3) At low temperatures ( via reaction (2). For a good low-temperature conversion it is therefore necessary to set an N02:NO ratio of approximately 1:1. Under these conditions the reaction (2) can already take place at temperatures from 170-200°C. The oxidation of NO to N0X takes place according to the invention in an upstream oxidation catalyst which is necessary for an optimum degree of efficiency. The basis of the catalytic exhaust-gas cleaning in a diesel engine is thus clearly the upstream oxidation catalyst which is to have an efficient oxidation action for CO, HC and NO. This is achieved for example by reducing the CO light-off temperature. In the publication SAE 2005/01-0476 (Rhodia), it is clear that above all support materials with smaller interactions with Pt (II) , e.g. aluminium oxide and zirconium oxide, make possible very low light-off temperatures for the oxidation of CO. Because of the larger BET surface area of aluminium, aluminium oxide is preferably used for DOC applications. One way of reducing the light-off temperature for CO as much as possible can be found in the patent application EP 706817 from Umicore. EP 706817 describes a DOC catalyst with .Pt on an Al/Si mixed oxide (in the best case 5% Si) . The further development using an H+ and Na+ zeolite is disclosed in EP 800856 Bl, where light-off temperatures of approximately 150°C for CO are already achieved. A further improvement is described in EP 1129764 Bl, where very finely distributed Pt particles with an average oxidation state of the Pt It is to be borne in mind that combustion exhaust gases can contain a wide variety of components, such as CO, nitrogen oxides and residual hydrocarbons. In addition, combustion exhaust gases can also contain different quantities'of oxygen depending on the guidance of the combustion. The gas mixture can thus be reductive or oxidative. In this case, it is not absolutely clear. Although the injection of a platinum precursor into a flame results in a catalyst that has a good activity with regard to a CO oxidation, the oxidation activity with regard to the oxidation of NO to NO2 cannot be controlled with this method. Thus, there is still a need for catalysts with as low as possible a light-off temperature for CO and, at the same time, a high activity and selectivity for the oxidation of NO to N02. The object of the present invention was therefore to provide such catalysts. The object is achieved by a method for producing a catalyst, comprising the steps: (a) impregnating a support material with a platinum compound, (b) drying the impregnated support material below the decomposition point of the platinum compound, (c) calcining the impregnated support material in a gas stream which contains NO and inert gas. N2, He, Ne or Ar is preferably used as inert gas, particularly preferably N2. The gas stream preferably contains 0.5 to 3 vol.-% NO, particularly preferably 1 vol.-% NO, relative to the total volume of the gas stream. Accordingly, the gas stream preferably contains 97 to 99.5 vol.-% inert gas, in particular N2, particularly preferably 99 vol.-% inert gas, relative to the total volume of the gas stream. It was surprisingly found that heating a support material impregnated with a platinum compound in a gas stream that predominantly contains inert gas, in particular N2, and too small proportions of NO results in a catalyst that displays a high activity for the oxidation of CO to C02, but at the, same time also has a very high activity and selectivity with regard to the oxidation of NO to N02. This behaviour is very desirable in particular for a use as diesel oxidation catalyst (DOC) followed by SCR (selective catalytic reduction) or followed by DPF (diesel particle filter) and SCR. Particularly preferably, the calcining (first calcining) of the impregnated support material takes place heating within 10 minutes, particularly preferably within 6 minutes and quite particularly preferably within 5 minutes. The calcining temperature is preferably 400°C to 650°C, particularly preferably 450°C to 600°C. A further (second) calcining then takes place, optionally after a short pause, over a period of 10 - 40 min, preferably 20 min, under the same conditions. According to the invention, it is advantageous if the dried, impregnated support material is present as a thin'layer or finely distributed, as this guarantees that the thermal energy can be optimally utilized during the calcining and thus a complete calcining can take place during the short time period of less than 10 minutes. In a preferred embodiment of the invention, the dried, impregnated support material is therefore applied to a catalyst support body prior to the calcining. Particularly preferably, the dried, impregnated support material is applied to the catalyst support body in the form of a washcoat coating and then dried again below the decomposition temperature of the platinum compound. The drying of the impregnated support material takes place according to the present invention preferably at temperatures of from 60°C to 100°C, more preferably from 70 to 90°C, most preferably at 80°C. However, the temperature depends on the platinum compound used, as these can have different decomposition points and thus the temperature must be adapted accordingly. The drying preferably takes place under reduced pressure, particularly preferably under fine vacuum. For the impregnating, the noble metal (Pt) is usually present as salt solution, for example as chloride, nitrate or sulphate. Normally, all customary salts and complex salts of platinum are suitable, e.g. hexachloroplatinic acid, tetrachloroplatinic acid, dinitro diamine platinate (II), tetraamine platinum (II) chloride, ammonium tetrachloroplatinate (II), ammonium hexachloroplatinate (IV), dichloro(ethylenediamine) platinum, tetraamine platinum (II) nitrate, tetraamine platinum (II) hydroxide, methylethanolamine platinum (II) hydroxide, platinum nitrate, ethanolammonium hexahydroxoplatinate (platinum ethanolamine, PtEA) and similar. A metal oxide is preferably used as support material. The metal oxide is preferably selected from the group consisting of aluminium oxide, silicon oxide, aluminosilicate, zirconium oxide, titanium oxide, Al/Si mixed oxide or combinations thereof. The necessary coating techniques for coating a catalyst support body are known to a person skilled in the art. Thus, e.g. the impregnated and dried metal oxide or mixed oxide is processed to an aqueous coating dispersion. This dispersion can be added as binder, e.g. silica sol. The viscosity of the dispersion can be set by the appropriate additives, with the result that it becomes possible to apply the necessary quantity of coating to the walls of the flow channels in a single work step. If this is not possible, the coating can be repeated several times, wherein each freshly applied coating is fixed by an intermediate drying. The finished coating is then calcined at the temperatures given above within the temperature range in less than 10 min, preferably less than 6 min, particularly preferably less than 5 min (first calcining). A second calcining step then takes place, optionally after a short pause, over a period of 10 - 40 min, preferably 20 min, under the same conditions. For the exhaust-gas cleaning of diesel engines, coating quantities of from 50 to 500 g/1 volume of the catalyst support body are advantageous. The catalyst component is preferably matched such that the catalytically active components are present in the metal oxide in a concentration of from approximately 0.01 to 7 g/1, preferably 2-4 g/1 of the honeycomb body. A metallic or ceramic monolith, a non-woven or metal foam can be used as catalyst support body. Other catalyst shaped bodies or catalyst support bodies known in the state of the art are also suitable according to the invention. A metallic or ceramic monolith that has a plurality of parallel passage openings which are provided with the washcoat coating is particularly preferred. With this, a uniform and in particular thin application of the washcoat suspension can be guaranteed, which thus supports the calcining. Metallic honeycomb bodies are often formed from sheet metals or metal foils. The honeycomb bodies are produced for example by alternating arrangement of layers of structured sheets or foils. Preferably, these arrangements consist of one layer of "a smooth sheet alternating with a corrugated sheet, wherein the corrugation can be formed for example sinusoidal, trapezoidal, omega-shaped or zigzag-shaped. Suitable metallic honeycomb bodies and methods for their production are described for example in EP 0 049 489 Al or DE 28 56 030 Al. In the field of catalyst support bodies, metallic honeycomb bodies have the advantage that they heat up more quickly and thus catalyst support bodies based on metallic substrates normally display a better response behaviour in cold-start conditions. The honeycomb body preferably has a cell density of from 200 to 600 cpsi, in particular 400 cpsi. The catalyst support body to which the catalyst according to the invention can be applied can be formed from any metal or a metal alloy and be produced e.g. by extrusion or by coiling or stacking or folding of metal foils. In the field of exhaust-gas cleaning, temperature-resistant alloys with the main constituents iron, chromium and aluminium are known. Monolithic catalyst support bodies that can be freely flowed through with or without internal leading edges for the agitation of the exhaust gas or metal foams which have a large internal surface area and to which the catalyst according to the invention adheres very well are preferred for the catalyst according to the invention. However, catalyst support bodies with slits, holes, perforations and impressions in the metal foil can also be used. In the same way, catalyst support bodies made of ceramic material can be used. Preferably, the ceramic material is an-inert material with a small surface area, such as cordierite, mullite or a-aluminium oxide. However, the catalyst support used can also consist of support material with a large surface area, such as Y-aluminium oxide. A metal foam, for example a metallic open-pored foam material, can also be used as catalyst support body. Within the framework of the present invention, by the term "metallic open-pored foam material" is meant a foam material made of any metal or of any alloy which can optionally also contain additives and which has a plurality of pores which are connected to each other by conduit, with the result that for example a gas can be conducted through the foam material. Metallic open-pored foam materials have a very low density because of the pores and cavities, but have a substantial stiffness and strength. The production of metal foams takes place for example by means of a metal powder and a metal hydride. Both powders are normally admixed together and then compacted to a shaped material by hot pressing or extrusion. The shaped material is then heated to a temperature above the melting point of the metals. The metal hydride releases hydrogen gas and the mixture foams. However, there are also still other possibilities for producing metal foams, for example by blowing gas into a metal melt which has previously been made foamable by adding solid constituents. For aluminium alloys for example, 10 to 20 vol.-% silicon carbide or aluminium oxide is added for the stabilization. In addition, open-pored metallic foam structures with a pore diameter of from 10 ppi to approximately 50 ppi can be produced by special precision casting techniques. A further subject of the invention is a catalyst which can be obtained using the method according to the invention. The catalyst is characterized by a very good activity and a selective oxidation potential for an oxidation of CO and NO. The catalyst also displays very good conversion rates for HC. The catalyst can accordingly be used as oxidation catalyst. In particular, the oxidation catalyst is to be used for the selective oxidation of CO and NO. HC is also oxidized very well. Preferably, the catalyst is present as coating on a catalyst support body, preferably a metallic or ceramic monolithic shaped body, a non-woven or a metal foam. The scope of the invention also includes a catalyst component which contains the catalyst according to the invention. The catalyst component is accordingly equipped with a housing in which the catalyst is located. The housing has an inlet and outlet opening for the exhaust gas to be treated. The catalyst component can be used as component in an exhaust-gas system. In a preferred embodiment of the invention, the catalyst component is fitted upstream of a diesel particle filter and/or an SCR catalyst. Through the high activity of the catalyst for the oxidation of NO to NO2, for example a particle filter is supplied with enough NO2 to oxidize soot particles, wherein N02 itself is reduced. NO2 that is not required is preferably converted to harmless nitrogen in a downstream SCR catalyst using ammonia or an ammonia precursor. A subject of the invention is thus also an exhaust-gas system comprising a catalyst according to the invention and in addition a diesel particle filter and/or an SCR catalyst. The invention will now be described in more detail with the help of some embodiment examples which are however to be considered as not limiting the scope of the invention. Reference is made in addition to Figures 1 to 3. Embodiment examples: Example 1 1. Impregnation The water absorption of an aluminium oxide (Puralox SCF a-140 L3 from Sasol) stabilized with lanthanum was first determined by weighing the powder, slurrying in water, filtering and then weighing again while wet. It was 50.18 wt.-%. In a planetary mixer, 110.4 g of a 13.59% solution of platinum ethanolamine (ethanolammonium hexahydroxoplatinate) was added slowly dropwise to 300 g of the dry Puralox powder accompanied by stirring. The powder was dried for 2 days at 80°C in the vacuum drying cupboard, with the result that 5 wt.-% platinum would be. contained on a completely dry powder. 2. Washcoat production, coating: 500 g of this vacuum-dried powder (from 2 impregnation batches) was topped up with 2500 g water, de-agglomerated with an Ultra-Turrax stirrer and then milled with a bead mill (4000 rpm, 1.2-mm Zr02 beads). 400-cpsi cordierite honeycombs were coated with this washcoat by immersion and blowing. The honeycombs were then in each case dried again at 80 °C in the vacuum drying cupboard. As a drying at 80°C under vacuum in this way does not necessarily take place completely, a loading of 60 g washcoat/1 honeycomb was first produced by repeated coating. When the aluminium oxide is dry, this should correspond to a platinum loading of 3.0 g/1. A honeycomb from a series of identically coated and only vacuum-dried honeycombs was then calcined at 500°C for 3 h and the platinum content analytically (pulping and ICP analysis) determined. This honeycomb (diameter 3 cm, length 8.8 cm) was coated with 3.68 g washcoat and weighed 33.4 g. With a Pt content of 5 wt.-%, the honeycomb should thus contain 0.55 wt.-% Pt when completely dry. 0.44 wt.-% platinum was determined from the analysis, because the 3.68 g weight of the washcoat was not completely dry and still contained water. The weight of the honeycomb after vacuum drying and the weight of the honeycomb after calcining and the platinum concentration were used to calculate how much platinum must still be coated on the honeycomb for there to be 3.5 g/1 platinum on a honeycomb. The platinum quantity which was already on the honeycomb and the washcoat loading after vacuum drying were able to be used to calculate what weight the not completely dry honeycomb vacuum-dried at 8 0°C must have at the end in order to have 3.5 g Pt/1 honeycomb volume. The honeycombs were then coated up to this weight, with the result that, at the end, each honeycomb had a platinum content of 3.5 g/1 honeycomb volume. 3. Calcining of the vacuum-dried honeycombs under a gas mixture which contained 1 vol.-% NO in nitrogen. The coated honeycombs were introduced into a quartz glass tube using a ceramic fibre blanket for the sealing. A gas mixture of 1 vol.-% NO in nitrogen was conducted over the catalyst in the calcining unit. In front of the quartz glass tube there was a heater which very quickly heated the gas mixture to up to 490 °C immediately before the honeycomb. Around the quartz glass tube there was an IR oven which was also able to heat up the honeycombs quickly by means of IR radiation. In this structure, the gas stream of 1 vol.-% CO in nitrogen was heated before the honeycomb from room temperature to 450°C within 50 s and then further via a PID controller to 4 90°C within a further minute. At the same time, a heating-up of the IR oven to 600 °C at 100°C/min was started. A measurement with a thermocouple in the honeycomb produced at the end a temperature of 500°C in the honeycomb. This temperature was reached after 6 min. Under these conditions, after these 6 min, calcining was continued for another 20 min at a gas inlet temperature of 490°C and an IR oven temperature of 600°C. Comparison example 1: 1. Impregnation: The water absorption of an aluminium oxide (Puralox SCF a-140 L3 from Sasol) stabilized with lanthanum was first determined by weighing the powder, slurrying in water, filtering and then weighing again while wet. It was 50.18 wt.-%. In a planetary mixer, 144.2 g of a 13.87% solution of platinum ethanolamine (ethanolammonium hexahydroxoplatinate) was added slowly dropwise to 400 g of the dry Puralox powder accompanied by stirring. The powder was then dried in the drying oven at 8 0°C for 3 hours. The powder was then calcined in a calcining oven in air for 3 h at 500°C (heat-up rate 2°C/min). 2. Washcoat production, coating: 140 g of this already calcined powder was topped up to 700 g with water, de-agglomerated with an Ultra-Turrax stirrer and then milled with a bead mill (4000 rpm, 1.2-mm Zr©2 'beads) . 400-cpsi cordierite honeycombs were coated with this washcoat by immersion and blowing. The honeycombs were then in each case dried again and calcined for 3 h at 500CC. This coating was repeated until a loading of 7 0 g washcoat/1 honeycomb was reached. As the powder had a platinum content of 5 wt.-%, this meant that the honeycomb also had a platinum content of 3.5 g/1. Comparison example 2: 1. A honeycomb impregnated with platinum ethanolamine and vacuum-dried was produced as described in Example 1. 2. Calcining of the vacuum-dried honeycombs under air. The coated honeycombs were introduced into a quartz glass tube using a ceramic fibre blanket for the sealing. In the calcining unit, air was conducted over the catalyst. In front of the quartz glass tube there was a heater which very quickly heated the air to up to 490°C immediately before the honeycomb. Around the quartz glass tube there was an IR oven which also heated up the honeycombs quickly by means of IR radiation. In this structure, the air stream was heated before the honeycomb from room temperature to 450°C within 50 s and then further via a PID controller to an inlet temperature of 490°C within a further minute. At the same time, a heating-up of the IR oven to 600°C at 100°C/min was started. The measurement with a thermocouple in the honeycomb thus produced at the end a temperature of 500°C in the honeycomb. This temperature was reached after 6 min. Under these conditions, after these 6 min, calcining was continued for another 20 min at a gas inlet temperature of 490°C and an IR oven temperature of 600°C. Comparison example 3: 1. A honeycomb impregnated with platinum ethanolamine and vacuum-dried is produced as described in Example 1. 2. Calcining with 2000 ppm propylene in air: The coated honeycombs were introduced into a quartz glass tube using a ceramic fibre blanket for the sealing. The calcining of the vacuum-dried honeycombs took place in a calcining unit with a gas mixture of 2000 ppm propylene in air by conducting the gas stream over the catalyst. In front of the quartz glass tube there was a heater which very quickly heated the gas mixture to up to 490°C immediately before the honeycomb. Around the quartz glass tube there was an IR oven which also heated up the honeycombs quickly by means of IR radiation. In this structure, the gas stream was heated up before the honeycomb from room temperature to 450°C within 50 s and then further via a PID controller to an inlet temperature of 490°C within a further minute. At the same time, a heating-up of the IR oven to 600°C at 100°C/min was started. The measurement with a thermocouple in the honeycomb produced at the end a temperature of 500°C in the honeycomb. This temperature was reached after 6 min. Under these conditions, after these 6 min, calcining was continued for another 20 min at a gas inlet temperature of 490°C and an IR oven temperature of 600°C. Comparison example 4 1. A honeycomb impregnated with platinum ethanolamine and vacuum-dried is produced as described in Example 1. 2. Calcining of the vacuum-dried honeycombs under a gas mixture of 1 vol.-% CO in nitrogen. The coated honeycombs were introduced into a quartz glass tube using a ceramic fibre blanket for the sealing. A gas mixture of 1 vol.-% CO in nitrogen was conducted over the catalyst in the calcining unit. In front of the quartz glass tube there was a heater which very quickly heated the gas mixture to up to 490°C immediately before the honeycomb. Around the quartz glass tube there was an IR oven which also heated up the honeycombs quickly by means of IR radiation. In this structure, the gas stream was heated up before the honeycomb from room temperature to 450 °C within 50 s and then further via a PID controller to an inlet temperature of 490°C within a further minute. At the same time, a heating-up of the IR oven to 600°C at 100°C/min was started. The measurement with a thermocouple in the honeycomb thus produced at the end a temperature of 550°C in the honeycomb. This temperature was reached after 6 min. Under these conditions, after these 6 min, calcining was continued for another 20 min at a gas inlet temperature of 4 90°C and an IR oven temperature of 600°C. Example 5: Comparison test of the catalysts: The catalyst honeycombs produced in Example 1 and the comparison examples were tested for the oxidation of CO, propylene and NO in a reactor under the following conditions. The gas stream was heated up before the catalyst. For the test, the catalyst was first operated for 30 min under these gas conditions at 390°C and then cooled down in steps of 10°C. Each temperature was maintained for 8 min and the product gas composition determined between 7 and 8 min. Below 250°C, the cooling down took place in 5°C steps in order to be able to more precisely determine in particular the CO light-off temperature (50% CO conversion). Figure 1: shows the CO conversion of the catalysts used: It is clear that the catalyst calcined with NO in N2 has the best CO light-off temperature with at the same time a 4very high NO oxidation (see Figure 3). The catalyst which was calcined with 1 vol.-% CO in nitrogen displays a very good light-off temperature for CO, but also a lower oxidation activity for the oxidation of NO to NO2, as can be seen from Figure 3. Figure 2 shows the propylene conversion (a hydrocarbon, HC) of the catalysts used. Here too, the catalyst calcined with NO in nitrogen is very good. The yield for the oxidation of NO to NO2 is represented in Figure 3. It is clear that not only is the catalyst which was calcined with CO in nitrogen better for an oxidation reaction, but the catalyst surprisingly oxidizes much less NO to N02 under the same conditions in the same test. However, this is not the case with a calcining with 1 vol.-% NO in nitrogen. Although the catalyst which was calcined with propylene in air delivers the best NO oxidation, it displays a clearly poorer CO light-off temperature. The catalyst according to the invention which was calcined with NO in nitrogen displays the best combination of very good CO light-off temperature and a very high activity for the oxidation of NO to N02. In all ranges, the catalyst calcined with propylene in air is at least better than the catalysts calcined only in'air. We claim: 1. Method for producing a catalyst, comprising the steps: a) impregnating a metal oxide support material with a platinum compound, b) drying the impregnated metal oxide support material below the decomposition point of the platinum compound, c) calcining the impregnated metal oxide support material in a gas stream which consists of NO and inert gas. 2. Method according to claim 1, wherein in step c) a first calcining takes place heating up within 10 min and a second calcining within from 10 to 40 min under the same conditions. 3. Method according to claim 1 or 2, wherein the gas stream contains 0.5 to 3 vol.-% NO and 97 to 99.5 vol.-% inert gas. 4. Method according to one of the previous claims, wherein N2, He, Ne or Ar, preferably N2, is used as inert gas. 5. Method according to one of the previous claims, wherein the calcining takes place at a temperature of from 400 to 650°C. 6. Method according to one of the previous claims, wherein the dried, impregnated metal oxide support material is applied to a catalyst support body before the calcining. 7. Method according to claim 6, wherein the dried, impregnated support material is applied to the catalyst support body in the form of a washcoat coating and then dried below the decomposition temperature of the platinum compound. 8. Method according to claim 6 or 7, wherein a metallic or ceramic monolith, a non-woven or a metal foam is used as catalyst support body. 9. Method according to one of claims 1 to 8, wherein the metal oxide is selected from the group consisting of aluminium oxide, silicon oxide, aluminosilicate, zirconium oxide, titanium oxide, Al/Si mixed oxide or combinations thereof. 10. Catalyst that can be obtained using a method according to one of claims 1 to 9. 11. Catalyst according to claim 10, wherein the catalyst is present as coating on a catalyst support body. 12. Use of the catalyst according to one of claims 10 to 11 as oxidation catalyst. 13. Use according to claim 12 for the selective oxidation of CO and NO, wherein the catalyst is a constituent of a catalyst component. 14. Catalyst component containing a catalyst according to one of claims 10 to 11 or a catalyst produced using a method according to one of claims 1 to 9. 15. Exhaust-gas cleaning system containing a catalyst component according to claim 14. 16. Exhaust-gas cleaning system according to claim 15, wherein the exhaust-gas cleaning system comprises a diesel particle filter and/or an SCR catalyst. 17. Exhaust-gas cleaning system according to claim 16, wherein the particle filter and/or the SCR catalyst is fitted downstream of the catalyst component according to claim 18. The invention relates to a method for producing a catalyst, wherein the catalyst has a high activity and selectivity with regard to the oxidation of CO and NO. The invention also relates to the catalyst produced using the method according to the invention, the use of the catalyst as oxidation catalyst as well as a catalyst component which contains the catalyst according to the invention. Finally, the invention is directed towards an exhaust-gas cleaning system which comprises the catalyst component containing the catalyst according to the invention.

Full Text

The invention relates to a method for producing a catalyst, wherein
the catalyst has a high activity and selectivity with regard to
the oxidation of CO and NO. The invention also relates to the
catalyst produced using the method according to the invention, the
use of the catalyst as oxidation catalyst as well as a catalyst
component which contains the catalyst according to the invention.
Finally, the invention is directed towards an exhaust-gas cleaning
system which comprises the catalyst component containing the
catalyst according to the invention.
In the early stages of exhaust-gas cleaning of combustion engines,
only the exhaust gases from petrol engines were cleaned with
three-way catalysts (TWC). The nitrogen oxides are reduced with
the reductive hydrocarbons (HC) and carbon monoxide (CO). For this,
the petrol engine is always driven under approximately
stoichiometric conditions {X=l). This cannot always be guaranteed
precisely in this way, with the result that the conditions in the
exhaust gas always fluctuate around A,= l. In other words, the
catalyst is exposed alternately to an oxidative or a reductive gas
atmosphere.
For about 15 years, attempts have also been made to aftertreat the
exhaust gases from diesel engines with catalysts. The exhaust gas
from diesel engines contains carbon monoxide, unburnt hydrocarbons,
nitrogen oxides and soot particles as air pollutants. The unburnt
hydrocarbons comprise paraffins, olefins, aldehydes and aromatics.
Unlike the petrol engine, the diesel engine always runs with an
excess of oxygen. The result of this is that the catalyst is never
exposed to reductive conditions. This has the following
consequences:
1. The oxygen storage capacity of the catalyst material does not
play the same role as with the TWC.
2. The noble metal particles are not always reduced again to
metal of oxidation state 0.
3. The nitrogen oxides cannot be fully reduced when there is an
excess of oxygen with the hydrocarbons (HC) present in the
exhaust gas and CO.
4. The hydrocarbons and CO can be oxidized both with oxygen and
with NOx.
Diesel exhaust gases are much colder than exhaust gases from petrol
engines and contain oxygen in a concentration between 3 and 10
vol.-%, which is why the catalytic activity of the catalyst on
average is not always sufficient to oxidize HC and CO. In
partial-load operation, the exhaust-gas temperature of a diesel
engine lies in the range between 100 and 250°C and only in full-load
operation does it reach a maximum temperature between 550 and 650°C.
In contrast, the exhaust-gas temperature of a petrol engine lies
between 400 and 450°C in partial-load operation and, in full load,
can rise to up to 1000°C. It is therefore an aim to achieve as low
as possible a CO light-off temperature.
In past years, diesel particle filters (DPF) have increasingly been
introduced onto the market. These are normally fitted downstream
of the DOCs. Soot is collected and oxidized in the DPF. The
oxidation of soot is much more possible with NO2 than with oxygen.
Thus, the more N02 is contained in the gas stream after the DOC,
the more soot continuously reacts. Thus, there has been a tendency
in past years to oxidize as much NO to N02 as possible in the DOC.
But N02 is an even more toxic gas than NO, with the result that
this shift towards increased nitrogen oxide emissions manifests
itself in a very negative way. An increasing NO2 concentration due
to DOC is also already detectable in cities. Thus, the trend is
returning to a limiting of the oxidation of NO to NO2.
Markedly reduced emissions of nitrogen oxides have thus also been
prescribed for the Euro VI standard. It will be possible to achieve
these either only by means of NOx-trap catalysts or by means of
a selective catalytic reduction by means of ammonia. The closer
the NO/NO2 ratio is to 1:1, the more efficiently such an SCR
reaction runs, thus a substantial oxidation of NO to NO2 is
desirable for this. This should, however, be achieved with
continuingly very good oxidation of CO and hydrocarbons HC.
SCR (selective catalytic reduction) denotes the selective
catalytic reduction of nitrogen oxides from exhaust gases of
combustion engines and also power stations. Only the nitrogen
oxides NO and NO2 (called N0X in general) are selectively reduced
with an SCR catalyst, wherein NH3 (ammonia) is usually admixed for
the reaction. Only the harmless substances water and nitrogen thus
form as reaction product. The transportation of ammonia in
compressed-gas bottles is a safety risk for use in motor vehicles.
Therefore precursor compounds of ammonia which are broken down in
the exhaust-gas system of the vehicles accompanied by the formation
of ammonia are customarily used. For example the use of AdBlue®,
which is an approximately 32.5% eutectic solution of urea in water,
is known in this connection. Other ammonia sources are for example
ammonium carbamate, ammonium formate or urea pellets.
Ammonia must first be formed from urea before the actual SCR
reaction. This occurs in two reaction steps which together are
called hydrolysis reaction. Firstly, NH3 and isocyanic acid are
formed in a thermolysis reaction. In the actual hydrolysis reaction
isocyanic acid is then reacted with water to ammonia and carbon
dioxide.
To avoid solid depositions it is necessary for the second reaction
to take place sufficiently quickly by choosing suitable catalysts
and sufficiently high temperatures (from 250°C). Simultaneously,
modern SCR reactors act as the hydrolysis catalyst.
The ammonia formed through thermohydrolysis reacts at the SCR
catalyst according to the following equations:
4N0 + 4NH3 + 02 -* 4N2 + 6H20 (1)
NO + N02 + 2NH3 -»¦ 2N2 + 3H20 (2)
6N02 + 8NH3 -» 7N2 + 12H20 (3)
At low temperatures ( via reaction (2). For a good low-temperature conversion it is
therefore necessary to set an N02:NO ratio of approximately 1:1.
Under these conditions the reaction (2) can already take place at
temperatures from 170-200°C.
The oxidation of NO to N0X takes place according to the invention
in an upstream oxidation catalyst which is necessary for an optimum
degree of efficiency.
The basis of the catalytic exhaust-gas cleaning in a diesel engine
is thus clearly the upstream oxidation catalyst which is to have
an efficient oxidation action for CO, HC and NO. This is achieved
for example by reducing the CO light-off temperature.
In the publication SAE 2005/01-0476 (Rhodia), it is clear that
above all support materials with smaller interactions with Pt (II) ,
e.g. aluminium oxide and zirconium oxide, make possible very low
light-off temperatures for the oxidation of CO. Because of the
larger BET surface area of aluminium, aluminium oxide is preferably
used for DOC applications.
One way of reducing the light-off temperature for CO as much as
possible can be found in the patent application EP 706817 from
Umicore. EP 706817 describes a DOC catalyst with .Pt on an Al/Si
mixed oxide (in the best case 5% Si) .
The further development using an H+ and Na+ zeolite is disclosed
in EP 800856 Bl, where light-off temperatures of approximately
150°C for CO are already achieved.
A further improvement is described in EP 1129764 Bl, where very
finely distributed Pt particles with an average oxidation state
of the Pt It is to be borne in mind that combustion exhaust gases can contain
a wide variety of components, such as CO, nitrogen oxides and
residual hydrocarbons. In addition, combustion exhaust gases can
also contain different quantities'of oxygen depending on the
guidance of the combustion. The gas mixture can thus be reductive
or oxidative. In this case, it is not absolutely clear.
Although the injection of a platinum precursor into a flame results
in a catalyst that has a good activity with regard to a CO oxidation,
the oxidation activity with regard to the oxidation of NO to NO2
cannot be controlled with this method. Thus, there is still a need
for catalysts with as low as possible a light-off temperature for
CO and, at the same time, a high activity and selectivity for the
oxidation of NO to N02.
The object of the present invention was therefore to provide such
catalysts.
The object is achieved by a method for producing a catalyst,
comprising the steps:
(a) impregnating a support material with a platinum compound,
(b) drying the impregnated support material below the
decomposition point of the platinum compound,
(c) calcining the impregnated support material in a gas stream
which contains NO and inert gas.
N2, He, Ne or Ar is preferably used as inert gas, particularly
preferably N2.
The gas stream preferably contains 0.5 to 3 vol.-% NO, particularly
preferably 1 vol.-% NO, relative to the total volume of the gas
stream. Accordingly, the gas stream preferably contains 97 to 99.5
vol.-% inert gas, in particular N2, particularly preferably 99
vol.-% inert gas, relative to the total volume of the gas stream.
It was surprisingly found that heating a support material
impregnated with a platinum compound in a gas stream that
predominantly contains inert gas, in particular N2, and too small
proportions of NO results in a catalyst that displays a high
activity for the oxidation of CO to C02, but at the, same time also
has a very high activity and selectivity with regard to the
oxidation of NO to N02. This behaviour is very desirable in
particular for a use as diesel oxidation catalyst (DOC) followed
by SCR (selective catalytic reduction) or followed by DPF (diesel
particle filter) and SCR.
Particularly preferably, the calcining (first calcining) of the
impregnated support material takes place heating within 10 minutes,
particularly preferably within 6 minutes and quite particularly
preferably within 5 minutes. The calcining temperature is
preferably 400°C to 650°C, particularly preferably 450°C to 600°C.
A further (second) calcining then takes place, optionally after
a short pause, over a period of 10 - 40 min, preferably 20 min,
under the same conditions.
According to the invention, it is advantageous if the dried,
impregnated support material is present as a thin'layer or finely
distributed, as this guarantees that the thermal energy can be
optimally utilized during the calcining and thus a complete
calcining can take place during the short time period of less than
10 minutes.
In a preferred embodiment of the invention, the dried, impregnated
support material is therefore applied to a catalyst support body
prior to the calcining. Particularly preferably, the dried,
impregnated support material is applied to the catalyst support
body in the form of a washcoat coating and then dried again below
the decomposition temperature of the platinum compound.
The drying of the impregnated support material takes place
according to the present invention preferably at temperatures of
from 60°C to 100°C, more preferably from 70 to 90°C, most preferably
at 80°C. However, the temperature depends on the platinum compound
used, as these can have different decomposition points and thus
the temperature must be adapted accordingly. The drying preferably
takes place under reduced pressure, particularly preferably under
fine vacuum.
For the impregnating, the noble metal (Pt) is usually present as
salt solution, for example as chloride, nitrate or sulphate.
Normally, all customary salts and complex salts of platinum are
suitable, e.g. hexachloroplatinic acid, tetrachloroplatinic acid,
dinitro diamine platinate (II), tetraamine platinum (II) chloride,
ammonium tetrachloroplatinate (II), ammonium hexachloroplatinate
(IV), dichloro(ethylenediamine) platinum, tetraamine platinum
(II) nitrate, tetraamine platinum (II) hydroxide,
methylethanolamine platinum (II) hydroxide, platinum nitrate,
ethanolammonium hexahydroxoplatinate (platinum ethanolamine,
PtEA) and similar.
A metal oxide is preferably used as support material. The metal
oxide is preferably selected from the group consisting of aluminium
oxide, silicon oxide, aluminosilicate, zirconium oxide, titanium
oxide, Al/Si mixed oxide or combinations thereof.
The necessary coating techniques for coating a catalyst support
body are known to a person skilled in the art. Thus, e.g. the
impregnated and dried metal oxide or mixed oxide is processed to
an aqueous coating dispersion. This dispersion can be added as
binder, e.g. silica sol. The viscosity of the dispersion can be
set by the appropriate additives, with the result that it becomes
possible to apply the necessary quantity of coating to the walls
of the flow channels in a single work step. If this is not possible,
the coating can be repeated several times, wherein each freshly
applied coating is fixed by an intermediate drying. The finished
coating is then calcined at the temperatures given above within
the temperature range in less than 10 min, preferably less than
6 min, particularly preferably less than 5 min (first calcining).
A second calcining step then takes place, optionally after a short
pause, over a period of 10 - 40 min, preferably 20 min, under the
same conditions.
For the exhaust-gas cleaning of diesel engines, coating quantities
of from 50 to 500 g/1 volume of the catalyst support body are
advantageous. The catalyst component is preferably matched such
that the catalytically active components are present in the metal
oxide in a concentration of from approximately 0.01 to 7 g/1,
preferably 2-4 g/1 of the honeycomb body.
A metallic or ceramic monolith, a non-woven or metal foam can be
used as catalyst support body. Other catalyst shaped bodies or
catalyst support bodies known in the state of the art are also
suitable according to the invention. A metallic or ceramic monolith
that has a plurality of parallel passage openings which are
provided with the washcoat coating is particularly preferred. With
this, a uniform and in particular thin application of the washcoat
suspension can be guaranteed, which thus supports the calcining.
Metallic honeycomb bodies are often formed from sheet metals or
metal foils. The honeycomb bodies are produced for example by
alternating arrangement of layers of structured sheets or foils.
Preferably, these arrangements consist of one layer of "a smooth
sheet alternating with a corrugated sheet, wherein the corrugation
can be formed for example sinusoidal, trapezoidal, omega-shaped
or zigzag-shaped. Suitable metallic honeycomb bodies and methods
for their production are described for example in EP 0 049 489 Al
or DE 28 56 030 Al.
In the field of catalyst support bodies, metallic honeycomb bodies
have the advantage that they heat up more quickly and thus catalyst
support bodies based on metallic substrates normally display a
better response behaviour in cold-start conditions.
The honeycomb body preferably has a cell density of from 200 to
600 cpsi, in particular 400 cpsi.
The catalyst support body to which the catalyst according to the
invention can be applied can be formed from any metal or a metal
alloy and be produced e.g. by extrusion or by coiling or stacking
or folding of metal foils. In the field of exhaust-gas cleaning,
temperature-resistant alloys with the main constituents iron,
chromium and aluminium are known. Monolithic catalyst support
bodies that can be freely flowed through with or without internal
leading edges for the agitation of the exhaust gas or metal foams
which have a large internal surface area and to which the catalyst
according to the invention adheres very well are preferred for the
catalyst according to the invention. However, catalyst support
bodies with slits, holes, perforations and impressions in the metal
foil can also be used.
In the same way, catalyst support bodies made of ceramic material
can be used. Preferably, the ceramic material is an-inert material
with a small surface area, such as cordierite, mullite or
a-aluminium oxide. However, the catalyst support used can also
consist of support material with a large surface area, such as
Y-aluminium oxide.
A metal foam, for example a metallic open-pored foam material, can
also be used as catalyst support body. Within the framework of the
present invention, by the term "metallic open-pored foam material"
is meant a foam material made of any metal or of any alloy which
can optionally also contain additives and which has a plurality
of pores which are connected to each other by conduit, with the
result that for example a gas can be conducted through the foam
material.
Metallic open-pored foam materials have a very low density because
of the pores and cavities, but have a substantial stiffness and
strength. The production of metal foams takes place for example
by means of a metal powder and a metal hydride. Both powders are
normally admixed together and then compacted to a shaped material
by hot pressing or extrusion. The shaped material is then heated
to a temperature above the melting point of the metals. The metal
hydride releases hydrogen gas and the mixture foams.
However, there are also still other possibilities for producing
metal foams, for example by blowing gas into a metal melt which
has previously been made foamable by adding solid constituents.
For aluminium alloys for example, 10 to 20 vol.-% silicon carbide
or aluminium oxide is added for the stabilization. In addition,
open-pored metallic foam structures with a pore diameter of from
10 ppi to approximately 50 ppi can be produced by special precision
casting techniques.
A further subject of the invention is a catalyst which can be
obtained using the method according to the invention. The catalyst
is characterized by a very good activity and a selective oxidation
potential for an oxidation of CO and NO. The catalyst also displays
very good conversion rates for HC.
The catalyst can accordingly be used as oxidation catalyst. In
particular, the oxidation catalyst is to be used for the selective
oxidation of CO and NO. HC is also oxidized very well.
Preferably, the catalyst is present as coating on a catalyst
support body, preferably a metallic or ceramic monolithic shaped
body, a non-woven or a metal foam.
The scope of the invention also includes a catalyst component which
contains the catalyst according to the invention. The catalyst
component is accordingly equipped with a housing in which the
catalyst is located. The housing has an inlet and outlet opening
for the exhaust gas to be treated.
The catalyst component can be used as component in an exhaust-gas
system. In a preferred embodiment of the invention, the catalyst
component is fitted upstream of a diesel particle filter and/or
an SCR catalyst. Through the high activity of the catalyst for the
oxidation of NO to NO2, for example a particle filter is supplied
with enough NO2 to oxidize soot particles, wherein N02 itself is
reduced. NO2 that is not required is preferably converted to
harmless nitrogen in a downstream SCR catalyst using ammonia or
an ammonia precursor.
A subject of the invention is thus also an exhaust-gas system
comprising a catalyst according to the invention and in addition
a diesel particle filter and/or an SCR catalyst.
The invention will now be described in more detail with the help
of some embodiment examples which are however to be considered as
not limiting the scope of the invention. Reference is made in
addition to Figures 1 to 3.
Embodiment examples:
Example 1
1. Impregnation
The water absorption of an aluminium oxide (Puralox SCF a-140 L3
from Sasol) stabilized with lanthanum was first determined by
weighing the powder, slurrying in water, filtering and then
weighing again while wet. It was 50.18 wt.-%.
In a planetary mixer, 110.4 g of a 13.59% solution of platinum
ethanolamine (ethanolammonium hexahydroxoplatinate) was added
slowly dropwise to 300 g of the dry Puralox powder accompanied by
stirring. The powder was dried for 2 days at 80°C in the vacuum
drying cupboard, with the result that 5 wt.-% platinum would be.
contained on a completely dry powder.
2. Washcoat production, coating:
500 g of this vacuum-dried powder (from 2 impregnation batches)
was topped up with 2500 g water, de-agglomerated with an
Ultra-Turrax stirrer and then milled with a bead mill (4000 rpm,
1.2-mm Zr02 beads).
400-cpsi cordierite honeycombs were coated with this washcoat by
immersion and blowing. The honeycombs were then in each case dried
again at 80 °C in the vacuum drying cupboard.
As a drying at 80°C under vacuum in this way does not necessarily
take place completely, a loading of 60 g washcoat/1 honeycomb was
first produced by repeated coating. When the aluminium oxide is
dry, this should correspond to a platinum loading of 3.0 g/1. A
honeycomb from a series of identically coated and only vacuum-dried
honeycombs was then calcined at 500°C for 3 h and the platinum
content analytically (pulping and ICP analysis) determined. This
honeycomb (diameter 3 cm, length 8.8 cm) was coated with 3.68 g
washcoat and weighed 33.4 g. With a Pt content of 5 wt.-%, the
honeycomb should thus contain 0.55 wt.-% Pt when completely dry.
0.44 wt.-% platinum was determined from the analysis, because the
3.68 g weight of the washcoat was not completely dry and still
contained water.
The weight of the honeycomb after vacuum drying and the weight of
the honeycomb after calcining and the platinum concentration were
used to calculate how much platinum must still be coated on the
honeycomb for there to be 3.5 g/1 platinum on a honeycomb. The
platinum quantity which was already on the honeycomb and the
washcoat loading after vacuum drying were able to be used to
calculate what weight the not completely dry honeycomb
vacuum-dried at 8 0°C must have at the end in order to have 3.5 g
Pt/1 honeycomb volume. The honeycombs were then coated up to this
weight, with the result that, at the end, each honeycomb had a
platinum content of 3.5 g/1 honeycomb volume.
3. Calcining of the vacuum-dried honeycombs under a gas mixture
which contained 1 vol.-% NO in nitrogen.
The coated honeycombs were introduced into a quartz glass tube
using a ceramic fibre blanket for the sealing. A gas mixture of
1 vol.-% NO in nitrogen was conducted over the catalyst in the
calcining unit. In front of the quartz glass tube there was a heater
which very quickly heated the gas mixture to up to 490 °C immediately
before the honeycomb. Around the quartz glass tube there was an
IR oven which was also able to heat up the honeycombs quickly by
means of IR radiation.
In this structure, the gas stream of 1 vol.-% CO in nitrogen was
heated before the honeycomb from room temperature to 450°C within
50 s and then further via a PID controller to 4 90°C within a further
minute. At the same time, a heating-up of the IR oven to 600 °C at
100°C/min was started. A measurement with a thermocouple in the
honeycomb produced at the end a temperature of 500°C in the
honeycomb. This temperature was reached after 6 min. Under these
conditions, after these 6 min, calcining was continued for another
20 min at a gas inlet temperature of 490°C and an IR oven temperature
of 600°C.
Comparison example 1:
1. Impregnation:
The water absorption of an aluminium oxide (Puralox SCF a-140 L3
from Sasol) stabilized with lanthanum was first determined by
weighing the powder, slurrying in water, filtering and then
weighing again while wet. It was 50.18 wt.-%.
In a planetary mixer, 144.2 g of a 13.87% solution of platinum
ethanolamine (ethanolammonium hexahydroxoplatinate) was added
slowly dropwise to 400 g of the dry Puralox powder accompanied by
stirring. The powder was then dried in the drying oven at 8 0°C for
3 hours. The powder was then calcined in a calcining oven in air
for 3 h at 500°C (heat-up rate 2°C/min).
2. Washcoat production, coating:
140 g of this already calcined powder was topped up to 700 g with
water, de-agglomerated with an Ultra-Turrax stirrer and then
milled with a bead mill (4000 rpm, 1.2-mm Zr©2 'beads) .
400-cpsi cordierite honeycombs were coated with this washcoat by
immersion and blowing. The honeycombs were then in each case dried
again and calcined for 3 h at 500CC.
This coating was repeated until a loading of 7 0 g washcoat/1
honeycomb was reached. As the powder had a platinum content of 5
wt.-%, this meant that the honeycomb also had a platinum content
of 3.5 g/1.
Comparison example 2:
1. A honeycomb impregnated with platinum ethanolamine and
vacuum-dried was produced as described in Example 1.
2. Calcining of the vacuum-dried honeycombs under air.
The coated honeycombs were introduced into a quartz glass tube
using a ceramic fibre blanket for the sealing.
In the calcining unit, air was conducted over the catalyst.
In front of the quartz glass tube there was a heater which very
quickly heated the air to up to 490°C immediately before the
honeycomb. Around the quartz glass tube there was an IR oven which
also heated up the honeycombs quickly by means of IR radiation.
In this structure, the air stream was heated before the honeycomb
from room temperature to 450°C within 50 s and then further via
a PID controller to an inlet temperature of 490°C within a further
minute. At the same time, a heating-up of the IR oven to 600°C at
100°C/min was started. The measurement with a thermocouple in the
honeycomb thus produced at the end a temperature of 500°C in the
honeycomb. This temperature was reached after 6 min. Under these
conditions, after these 6 min, calcining was continued for another
20 min at a gas inlet temperature of 490°C and an IR oven temperature
of 600°C.
Comparison example 3:
1. A honeycomb impregnated with platinum ethanolamine and
vacuum-dried is produced as described in Example 1.
2. Calcining with 2000 ppm propylene in air:
The coated honeycombs were introduced into a quartz glass tube
using a ceramic fibre blanket for the sealing. The calcining of
the vacuum-dried honeycombs took place in a calcining unit with
a gas mixture of 2000 ppm propylene in air by conducting the gas
stream over the catalyst.
In front of the quartz glass tube there was a heater which very
quickly heated the gas mixture to up to 490°C immediately before
the honeycomb. Around the quartz glass tube there was an IR oven
which also heated up the honeycombs quickly by means of IR
radiation.
In this structure, the gas stream was heated up before the honeycomb
from room temperature to 450°C within 50 s and then further via
a PID controller to an inlet temperature of 490°C within a further
minute. At the same time, a heating-up of the IR oven to 600°C at
100°C/min was started. The measurement with a thermocouple in the
honeycomb produced at the end a temperature of 500°C in the
honeycomb. This temperature was reached after 6 min. Under these
conditions, after these 6 min, calcining was continued for another
20 min at a gas inlet temperature of 490°C and an IR oven temperature
of 600°C.
Comparison example 4
1. A honeycomb impregnated with platinum ethanolamine and
vacuum-dried is produced as described in Example 1.
2. Calcining of the vacuum-dried honeycombs under a gas mixture
of 1 vol.-% CO in nitrogen.
The coated honeycombs were introduced into a quartz glass tube
using a ceramic fibre blanket for the sealing. A gas mixture of
1 vol.-% CO in nitrogen was conducted over the catalyst in the
calcining unit. In front of the quartz glass tube there was a heater
which very quickly heated the gas mixture to up to 490°C immediately
before the honeycomb. Around the quartz glass tube there was an
IR oven which also heated up the honeycombs quickly by means of
IR radiation. In this structure, the gas stream was heated up before
the honeycomb from room temperature to 450 °C within 50 s and then
further via a PID controller to an inlet temperature of 490°C within
a further minute. At the same time, a heating-up of the IR oven
to 600°C at 100°C/min was started. The measurement with a
thermocouple in the honeycomb thus produced at the end a
temperature of 550°C in the honeycomb. This temperature was reached
after 6 min. Under these conditions, after these 6 min, calcining
was continued for another 20 min at a gas inlet temperature of 4 90°C
and an IR oven temperature of 600°C.
Example 5:
Comparison test of the catalysts:
The catalyst honeycombs produced in Example 1 and the comparison
examples were tested for the oxidation of CO, propylene and NO in
a reactor under the following conditions.
The gas stream was heated up before the catalyst. For the test,
the catalyst was first operated for 30 min under these gas
conditions at 390°C and then cooled down in steps of 10°C. Each
temperature was maintained for 8 min and the product gas
composition determined between 7 and 8 min. Below 250°C, the
cooling down took place in 5°C steps in order to be able to more
precisely determine in particular the CO light-off temperature
(50% CO conversion).
Figure 1: shows the CO conversion of the catalysts used:
It is clear that the catalyst calcined with NO in N2 has the best
CO light-off temperature with at the same time a 4very high NO
oxidation (see Figure 3). The catalyst which was calcined with 1
vol.-% CO in nitrogen displays a very good light-off temperature
for CO, but also a lower oxidation activity for the oxidation of
NO to NO2, as can be seen from Figure 3.
Figure 2 shows the propylene conversion (a hydrocarbon, HC) of the
catalysts used. Here too, the catalyst calcined with NO in nitrogen
is very good.
The yield for the oxidation of NO to NO2 is represented in Figure
3. It is clear that not only is the catalyst which was calcined
with CO in nitrogen better for an oxidation reaction, but the
catalyst surprisingly oxidizes much less NO to N02 under the same
conditions in the same test. However, this is not the case with
a calcining with 1 vol.-% NO in nitrogen. Although the catalyst
which was calcined with propylene in air delivers the best NO
oxidation, it displays a clearly poorer CO light-off temperature.
The catalyst according to the invention which was calcined with
NO in nitrogen displays the best combination of very good CO
light-off temperature and a very high activity for the oxidation
of NO to N02.
In all ranges, the catalyst calcined with propylene in air is at
least better than the catalysts calcined only in'air.
We claim:
1. Method for producing a catalyst, comprising the steps:
a) impregnating a metal oxide support material with a
platinum compound,
b) drying the impregnated metal oxide support material
below the decomposition point of the platinum
compound,
c) calcining the impregnated metal oxide support
material in a gas stream which consists of NO and inert
gas.
2. Method according to claim 1, wherein in step c) a first
calcining takes place heating up within 10 min and a second
calcining within from 10 to 40 min under the same
conditions.
3. Method according to claim 1 or 2, wherein the gas stream
contains 0.5 to 3 vol.-% NO and 97 to 99.5 vol.-% inert gas.
4. Method according to one of the previous claims, wherein N2,
He, Ne or Ar, preferably N2, is used as inert gas.
5. Method according to one of the previous claims, wherein the
calcining takes place at a temperature of from 400 to 650°C.
6. Method according to one of the previous claims, wherein the
dried, impregnated metal oxide support material is applied
to a catalyst support body before the calcining.
7. Method according to claim 6, wherein the dried, impregnated
support material is applied to the catalyst support body in
the form of a washcoat coating and then dried below the
decomposition temperature of the platinum compound.
8. Method according to claim 6 or 7, wherein a metallic or
ceramic monolith, a non-woven or a metal foam is used as
catalyst support body.
9. Method according to one of claims 1 to 8, wherein the metal
oxide is selected from the group consisting of aluminium
oxide, silicon oxide, aluminosilicate, zirconium oxide,
titanium oxide, Al/Si mixed oxide or combinations thereof.
10. Catalyst that can be obtained using a method according to
one of claims 1 to 9.
11. Catalyst according to claim 10, wherein the catalyst is
present as coating on a catalyst support body.
12. Use of the catalyst according to one of claims 10 to 11 as
oxidation catalyst.
13. Use according to claim 12 for the selective oxidation of CO
and NO, wherein the catalyst is a constituent of a catalyst
component.
14. Catalyst component containing a catalyst according to one
of claims 10 to 11 or a catalyst produced using a method
according to one of claims 1 to 9.
15. Exhaust-gas cleaning system containing a catalyst component
according to claim 14.
16. Exhaust-gas cleaning system according to claim 15, wherein
the exhaust-gas cleaning system comprises a diesel particle
filter and/or an SCR catalyst.
17. Exhaust-gas cleaning system according to claim 16,
wherein the particle filter and/or the SCR catalyst is fitted
downstream of the catalyst component according to claim 18.

The invention relates to a method for producing a catalyst, wherein
the catalyst has a high activity and selectivity with regard to
the oxidation of CO and NO. The invention also relates to the
catalyst produced using the method according to the invention, the
use of the catalyst as oxidation catalyst as well as a catalyst
component which contains the catalyst according to the invention.
Finally, the invention is directed towards an exhaust-gas cleaning
system which comprises the catalyst component containing the
catalyst according to the invention.

Documents:

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Patent Number

272276

Indian Patent Application Number

2980/KOLNP/2011

PG Journal Number

14/2016

Publication Date

01-Apr-2016

Grant Date

28-Mar-2016

Date of Filing

15-Jul-2011

Name of Patentee

SÜD-CHEMIE AG

Applicant Address

LENBACHPLATZ 6, 80333 MÜNCHEN, GERMANY

Inventors:

#	Inventor's Name	Inventor's Address
1	BENTELE, ANDREAS	SCHUSTERSTR. 12A, 83043 BAD AIBLING, GERMANY
2	WANNINGER, KLAUS	AM EGLSEE 2, 83059 KOLBERMOOR, GERMANY
3	SCHNEIDER, MARTIN	PANORAMASTR. 34/1, 76327 PFINZTAL, GERMANY
4	MALETZ, GERD	HOCHFELLNSTR. 6, 83043 BAD AIBLING, GERMANY

PCT International Classification Number

B01J 23/42

PCT International Application Number

PCT/EP2010/000487

PCT International Filing date

2010-01-27

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10 2009 006 404.4	2009-01-28	Germany