Exhaust gas purifying catalyst for combustion engines with two catalytically active layers on one support structure

The present invention relates to an exhaust gas purification catalyst for internal combustion engines with two catalytically active layers on a support body.

Internal combustion engines emit as essential pollutants with the exhaust gas carbon monoxide CO, unburned hydrocarbons HC and nitrogen oxides NO_x, which are converted by modern exhaust gas purifying catalysts to a high percentage into the innocuous components water, carbon dioxide and nitrogen. The reaction takes place essentially at stoichiometric conditions, that is, the oxygen contained in the exhaust gas is adjusted by means of a so-called lambda probe so that the oxidation of carbon monoxide and hydrocarbons and the reduction of nitrogen oxides to nitrogen can be almost quantitative. The catalysts developed for this purpose are referred to as three-way catalysts.

Stoichiometric conditions are present at air ratios λ of 1. The air ratio λ is the normalized to stoichiometric conditions air / fuel ratio. The air / fuel ratio indicates how many kilograms of air are needed for the complete combustion of one kilogram of fuel. For standard gasoline engine fuels, the stoichiometric air / fuel ratio is 14.6. Depending on the load and engine speed, the engine exhaust gas has more or less strong, periodic variations in the air ratio. For better implementation of the oxidizable pollutant components under these conditions, oxygen storage components such as pure ceria or ceria-containing components are used which bind oxygen when it is present in excess and release it again for the oxidative reaction when the oxygen in the exhaust gas is in deficit.

The present invention relates to catalyst coatings on inert, monolithic support bodies, in particular honeycomb bodies with parallel flow channels for the exhaust gas. The number of flow channels per cross-sectional area is referred to as cell density. Depending on the application requirement, inert support bodies with cell densities between 10 and 250 cm can be used^-2 for use. These may be extruded, ceramic support bodies made of cordierite, mullite or similar, temperature-resistant materials. Alternatively, honeycomb bodies made of steel foils are used.

For the purposes of the present invention, a layer is referred to as catalytically active, if it is able to at least partially catalyze the aforementioned reaction of the pollutants contained in the exhaust gas from internal combustion engines to harmless components. The pollutants include, in particular, carbon monoxide, nitrogen oxides and hydrocarbons, the hydrocarbons also comprising the hydrocarbons which are present on soot particles of the exhaust gas in condensed form.

The catalytic coating contains as catalytically active components usually several precious metals of the platinum group of the periodic table of elements as well as high surface area materials and other components such as oxygen storage materials, promoters and stabilizers. The coating is applied to the inner walls of the flow channels using an aqueous coating dispersion containing the various components of the catalyst by known coating techniques.

The components of the catalyst can be added in various forms to the coating dispersion:<ul id="ul0001" list-style="none" compact="compact"><li>a) <img file="EP0885650A2_D0001.tif" />finely divided solids " This is understood to mean powdery materials with particle sizes between 1 and about 50 μm. In the English-language literature for this are the terms<img file="EP0885650A2_D0002.tif" />bulk material "or <img file="EP0885650A2_D0003.tif" />particulate material ".</li><li>b) when <img file="EP0885650A2_D0004.tif" />Colloidal solids " They have particle sizes of less than 1 micron. The particulate structure of the finely divided and colloidal solids also remains in the final catalyst coating.</li><li>c) in the form of soluble <img file="EP0885650A2_D0005.tif" />Precursors " The precursor compounds are deposited on usually high-surface solids and transferred by thermal treatment in an oxidative or reductive atmosphere in the actual catalytic components and are then present in highly dispersed form with crystallite sizes of usually less than 10 nm. At extremely high concentration or very low solubility precursor substances may also be present between the finely divided solids and have similar particle sizes as the latter.</li></ul>

The finely divided solids of the coating dispersion serve in part as support materials for the highly dispersed materials resulting from the precursor compounds. The finely divided solids must have a high specific surface area for this purpose. Within the scope of this invention, materials having a specific surface area, also referred to as BET surface area, of more than 10 m are considered high surface areas²/G. The specific surface area can be measured according to DIN 66132 using nitrogen adsorption isotherms.

Examples of high-surface solids are the so-called active aluminas. These are finely divided aluminum oxides which have the crystal structures of the transition phases of the aluminum oxide. These include chi-, delta, gamma, kappa, theta and eta alumina.

The active aluminas have specific surface areas of up to 400 m²/ g on. As the temperature increases, the abovementioned crystal structures interconvert with simultaneous reduction in the specific surface area (see Ullmann's Encyclopedia of Industrial Chemistry;^th Edition 1985; Vol A1; Pages 557-563). Above 1150 ° C, only the low surface alpha alumina is stable. This process can be slowed down by stabilization with alkaline earth metal oxides, in particular barium oxide, rare earth oxides, preferably lanthanum oxide, or silicon dioxide. For this purpose, the stabilized, active aluminas usually contain from 1 to 10% by weight of barium oxide, lanthanum oxide or silicon dioxide, based on the total weight of the stabilized material.

In order to distinguish the high-surface-area carrier materials from the inert, monolithic carrier for the coating, it is referred to as a carrier body in the context of this invention, whereas the high-surface area carrier materials are referred to as carriers or carrier materials.

As oxygen-storing materials, pure cerium oxide or mixed oxides of cerium with zirconium are often used. The mixed oxides are obtainable, for example, by coprecipitation of precursor compounds of both elements. Cerium-rich mixed oxides containing more than 50% by weight of cerium and also zirconium-rich mixed oxides containing more than 50% by weight of zirconium are known. Cerium-rich mixed oxides are referred to below as cerium / zirconium mixed oxides and zircon-rich mixed oxides as zirconium / cerium mixed oxides.

EP 0 314 057 B1 describes a rhodium-free three-way catalyst which has two catalytically active layers on a carrier body, the first layer resting on the carrier body containing platinum and the second, upper layer containing palladium. As support material for these components, active alumina is used in both cases. The layers also contain ceria, which is introduced by means of a cerium salt and / or a solid cerium compound. The layers may additionally contain zirconium oxide, lanthanum oxide, neodymium oxide, praseodymium oxide and nickel oxide as a single substance or in a mixture. The precious metals are incorporated by impregnation in the layers. In an analogous manner, EP 0 314 058 B1 describes a platinum-free three-way catalyst which consists of two catalytically active layers on a support body. The first layer contains palladium and the second layer contains rhodium. The support material used in this case again active alumina. Both layers additionally contain cerium oxide and optionally the same promoters and stabilizers as according to EP 0 314 057 B1.

US 5,057,483 also describes a catalyst composition of two discrete layers on a monolithic support body. The first layer contains a stabilized alumina as a support material for platinum and finely divided ceria. The first layer may also contain finely divided iron oxide and nickel oxide to suppress the emission of hydrogen sulfide, and dispersed throughout the layer, highly dispersed barium oxide and zirconium oxide as thermal stabilizers. The second layer contains a co-precipitated cerium / zirconium mixed oxide, on which rhodium is deposited, and an activated alumina as support material for platinum. The co-precipitated zirconium / cerium mixed oxide preferably contains from 2 to 30% by weight of cerium oxide.

Another two-layered three-way catalyst is disclosed in WO 95/35152. It contains in the first layer a first support material and a first palladium component and optionally a first platinum group component, optionally at least one first stabilizer, optionally at least one first rare earth metal component and optionally a zirconium component. The second layer contains a second support material, a second platinum component, a rhodium component, a second oxygen-storing component in dilute form and optionally a zirconium component.

EP 0 734 757 A1 discloses a catalytic converter with the three platinum group metals platinum, palladium and rhodium. The catalyst consists of two layers on a support body. According to the EP document, it has been found that the levels of conversion of the pollutants are improved when palladium is in the inner layer and platinum and rhodium are in the outer layer. In addition, the degrees of conversion are improved when the masses of the two layers (inner layer to outer layer) behave as 3: 1 to 1.25: 1.

The future statutory exhaust emission limits are subject to an increasing tightening. The currently valid and proposed for the future limits z. As the EU for the individual pollutants are listed in Table 1. The limit values ​​must be complied with when carrying out the MVEG-A driving cycle with cold start, acceleration and part-load driving.<tables id="tabl0001" num="0001"><table frame="all"><title>Table 1</title><tgroup cols="4" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row><entry namest="col1" nameend="col4" align="center">Current and future proposed limit values ​​for pollutant emissions</entry></row><row><entry namest="col1" nameend="col1" rowsep="0" align="center">pollutant</entry><entry namest="col2" nameend="col4" align="center">limits^*) [G / km]</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="center">1996/97</entry><entry namest="col3" nameend="col3" align="center">2000/01</entry><entry namest="col4" nameend="col4" align="center">2005/06</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">CO</entry><entry namest="col2" nameend="col2" align="char" char=",">2.7</entry><entry namest="col3" nameend="col3" align="char" char=",">2.3</entry><entry namest="col4" nameend="col4" align="char" char=",">1.0</entry></row><row><entry namest="col1" nameend="col1" align="left">HC + NO_x</entry><entry namest="col2" nameend="col2" align="char" char=",">0.5</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /></row><row><entry namest="col1" nameend="col1" align="left">HC</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" align="char" char=",">0.2</entry><entry namest="col4" nameend="col4" align="char" char=",">0.1</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">NO_x</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" align="char" char=",">0.15</entry><entry namest="col4" nameend="col4" align="char" char=",">0.08</entry></row></tbody></tgroup><tgroup cols="4" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><tbody valign="top"><row><entry namest="col1" nameend="col4" align="justify">*) These values ​​must be observed when carrying out the MVEG-A driving cycle</entry></row></tbody></tgroup></table></tables>

According to Table 1, it is planned to reduce the limit values ​​for carbon monoxide, hydrocarbons and nitrogen oxides to around one third of the limits in 1996 by the year 2005. Such improvements are only possible if it is possible to further increase the catalytic activity of the currently known catalysts. This is only possible with a careful selection of the catalyst components and their coordination with each other in the already achieved high activity level of the catalysts.

Of particular importance is the increase in the temperature stability of the catalytic activity, since a significant portion of the emissions during the MVEG-A driving cycle are emitted in the cold start phase during the first 120 seconds after the engine is started. In order to reduce the cold-start emissions, starting and main catalytic converters installed close to the engine are used, which are heated very quickly by the hot exhaust gases to their light-off temperatures, but are also exposed to peak temperatures at the catalyst inlet of up to 1050 ° C. during normal driving. The object of the present invention is therefore to provide a catalyst which has a higher activity and temperature stability compared with known catalysts. In addition, these goals should be achieved with the lowest possible use of precious metals, that is, as cost-effectively as possible.

This object is achieved by an exhaust gas purification catalyst with two catalytically active layers on a support body, whose first layer located on the support body several finely divided solids, contains one or more highly dispersed alkaline earth metal oxides and at least one platinum group metal, wherein the finely divided solids at least one finely divided, Having oxygen-storing material and at least one further finely divided component and the platinum group metals are in close contact with all components of the first layer.

In the catalyst according to the invention, the platinum group metals form the actual catalytically active components. The platinum group metals include platinum, palladium, rhodium, osmium and iridium. They are present in the catalyst in highly dispersed form with particle sizes of generally less than 10 nm. The term platinum group metals and the reference to the individual platinum group metals themselves encompasses in the context of the present invention all catalytically active forms of these metals. In addition to the metallic state, these are also higher oxidation states of these metals. Palladium and optionally platinum are preferably used in the first layer of the catalyst.

The second catalytically active layer of the catalyst, which is in direct contact with the exhaust gas, can be constructed differently according to the desired catalytic function. To achieve a good three-way catalyst, a layer structure of the second layer has proven which, like the first layer, also contains several finely divided solids and at least one platinum group metal, wherein the finely divided solids of this second layer at least one finely divided, Oxygen-storing material and at least one further finely divided component and only a portion of these finely divided solids of the second layer serve as a carrier for the platinum group metals of the second layer.

In the context of this invention, a distinction is made between "finely divided components" and "finely divided, oxygen-storing materials". In both cases, it is finely divided solids. In contrast to the oxygen-storing materials, the finely divided components have no significant oxygen storage capacity. Both the finely divided components and the finely divided, oxygen-storing materials serve in the catalyst partly as support materials. The finely divided components may be oxides of alkaline earth metals, oxides of scandium, yttrium, gallium, indium, silicon, titanium, zirconium, hafnium, germanium, tin, lead, vanadium, niobium, tantalum, chromium, molybdenum and tungsten. In addition, carbides, borides, silicides and nitrides of the transition metals can be used. However, preference is given to using oxides, in particular active aluminas. Furthermore, mixed oxides such as aluminum silicates and titanates (barium or aluminum titanate) and zeolites can be used as finely divided components.

According to the current understanding of the invention, the temperature resistance of the overall coating is substantially increased by the stated arrangement of the constituents of the first layer relative to one another. The arrangement is characterized by the fact that the platinum group metals of the first layer are in close contact with all constituents of this layer, that is to say both with all finely divided solids of the layer and with all fractions of the highly dispersed materials. In order to achieve this, special measures must be taken in the production of the first layer, which will be described in detail below. The temperature and aging resistance of the overall coating is further improved by the fact that the platinum group metals are deposited in the second layer only on a part of the finely divided components. The uncoated part can thus serve as an adsorber for catalyst poisons. For this purpose, in the second layer, the mass ratio of the solids components serving as carriers for the platinum group metals to the remaining solids content of the second layer should be between 1:10 and 5: 1, preferably between 1: 4 and 1: 1. The most appropriate mass ratio depends on the structure and composition of both layers of the catalyst and on the average composition of the exhaust gas. With increasing dilution (decreasing mass ratios) of the platinum group metal-coated carrier particles in the second layer, the contact of the exhaust gas diffusing through the second layer with those catalytically active centers deteriorates. Mass ratios below 1:10 are therefore generally not recommended. With increasing mass ratios, on the other hand, the amount of platinum-metal-free solid constituents available for the adsorption of catalyst poisons decreases. The mass ratio should therefore be kept smaller than 5: 1.

Advantageous embodiments of the catalyst according to the invention are described in the claims 4 to 22.

In a specific embodiment of the invention, a high-surface-area ceria is used in the first layer as finely divided, oxygen-storing material, and a cerium-rich cerium / zirconium mixed oxide is used in the second layer. In both layers, aluminum oxide is used as finely divided component. The platinum group metals used in the first layer are palladium and optionally platinum, while in the second layer rhodium and optionally platinum are used. As a support for rhodium and optionally platinum serves a part of the active alumina of the second layer.

In the first layer of the catalyst, one or more highly dispersed alkaline earth metal oxides such as magnesium oxide, barium oxide and calcium oxide are used for stabilization. However, in all embodiments of the invention it is preferred to use barium oxide as some alkaline earth metal oxide.

To ensure a high temperature stability of the catalytic activity of the rhodium and the optionally present platinum, it is advantageous to use a stabilized alumina at least for that part of the alumina which serves as a carrier for rhodium and optionally platinum. The remaining alumina may also be stabilized. To stabilize the alumina, all known stabilizing components can be used. Preferably, an alumina stabilized with lanthanum oxide is used.

A further advantageous embodiment of the catalyst provides over the previous embodiment that in the first layer instead of the high surface area cerium oxide a finely divided cerium / zirconium mixed oxide and in addition to the highly dispersed alkaline earth metal oxides or ceria and zirconium oxide in highly dispersed form in the first layer. As in the previous embodiment, platinum group metals used in the first layer are palladium and optionally platinum and in the second layer rhodium and optionally platinum. Rhodium and optionally platinum are deposited as on the previous embodiments only on a part of the alumina of the second layer. Again, it is advisable to increase the temperature stability of the catalyst to stabilize at least the portion of the active alumina of the second layer, which serves as a support for rhodium and optionally platinum. The active alumina of the first layer may also be stabilized. The only alkaline earth metal oxide is barium oxide.

As an alternative to the embodiment just discussed, the cerium / zirconium mixed oxide may also be used in the second layer as a support for rhodium and, if appropriate, platinum instead of a portion of the active aluminum oxide.

A further increase in the temperature stability of the catalyst is achieved when the cerium / zirconium mixed oxide is stabilized in one or both catalyst layers according to the non-prepublished patent application DE 197 14 707.0 with 0.1 to 10 wt .-% praseodymium to thermal loads. Alternatively, in the second layer, instead of the active alumina, the cerium / zirconium mixed oxide may be used as a substrate for rhodium and optionally platinum. In this case, the stabilization of the cerium / zirconium mixed oxide with praseodymium oxide is particularly advantageous.

The finely divided, oxygen-storing materials used in the previously discussed embodiments of the catalyst according to the invention were either pure cerium oxide or cerium-rich cerium / zirconium mixed oxides containing 60 to 90% by weight of cerium oxide, preferably 70% by weight on the total weight of the mixed oxide. These materials are commercially available. They have a specific surface area between 60 and 200 m²/ g, which is relatively stable to thermal stress. Alternatively or in addition thereto, finely divided, zirconium-rich zirconium / cerium mixed oxides with a cerium oxide content of from 10 to 30, preferably 20,% by weight, based on the total weight of the mixed oxide, can be used. The preparation and use of such a material is described, for example, in the already cited US 5,057,483.

These latter, zirconium-rich mixed oxides are more stable to thermal stress than the cerreichen mixed oxides, but have a lower storage capacity for oxygen. This deficiency can be compensated for by being used in larger quantities.

A disadvantage of the cerreichen as well as the zirconium rich mixed oxides is the fact that the ceria is available in the interior of the mixed oxides only to a limited extent for the oxygen storage. A better availability of cerium oxide for oxygen storage offers a material according to the non-prepublished patent application DE 197 14 707.0. It is a powdered zirconia. Cerium oxide is applied on the surface of the powder particles. As a result, the full amount of cerium oxide of the material for oxygen storage is available.

Further advantageous embodiments of the catalyst provide that finely divided nickel oxide is introduced into the first and optionally into the second layer for suppression of hydrogen sulfide emissions.

The first layer of the catalyst is applied to the carrier body at a concentration of 100 to 300 g / l carrier body volume, while for the second layer concentrations of 40 to 150 g / l carrier body volume are provided. The following concentration ranges have proven to be advantageous for the individual components of the layers: The finely divided components of the first layer represent the main components of the layer and are used in concentrations of 60 to 150 g / l. The finely divided, oxygen-storing materials are introduced in each case with 20 to 100 g / l of carrier volume in the coating. For the alkaline earth metal oxide, amounts of from 10 to 40 g / l are sufficient to stabilize the coating. Concentrations of 10 to 70 g / l have proven successful for the optionally additionally present highly dispersed materials cerium oxide and zirconium oxide.

The second layer is much thinner than the first layer. It is applied to the support body with only about 25 to 75, preferably 30 to 50%, of the coating amount of the first layer. The finely divided, oxygen-storing components of the second layer are each used in concentrations of 5 to 70 g / l.

The platinum group metals of the first layer are introduced into the layer in a concentration of 0.1 to 5 wt .-%, based on the total weight of the first layer. Based on the volume of the carrier, this corresponds to a concentration of up to 15 g / l. The platinum group metals of the second layer are, based on the respective support material, in concentrations of 0.1 to 10, preferably from 0.1 to 5 wt .-%, used. It has been found that the catalyst according to the invention with equal or lower noble metal concentrations as in commercially available catalysts has a better or at least equivalent catalytic activity.

The mass ratio of the platinum group metals to one another can vary within relatively wide ranges. When using platinum, palladium and rhodium mass ratios of platinum to rhodium of 3: 1 to 1: 3 have proven. Preferably, however, a mass ratio close to 1: 1 is applied. Palladium is used in much larger quantities. Preferably, its mass ratio to platinum is in the range between 10: 1 and 20: 1. In the presence of platinum in the catalyst, it is preferably used only as an alternative in the two layers: either together with palladium in the first layer or together with rhodium in the second layer. If platinum is omitted in the catalyst, then mass ratios between palladium and rhodium between 10: 1 and 1: 2 are applicable. Preference is given to using mass ratios of less than 5: 1, which enable a good catalytic activity for the reaction of all three types of pollutants.

Essential for the catalyst of the invention is the fact that the platinum group metals (palladium and optionally platinum), the alkaline earth metal oxides and optionally ceria and zirconia are deposited in highly dispersed form on the finely divided components and on the finely divided, oxygen-storing materials of the first layer. As a result, the catalytic activity and stability of the catalyst is significantly increased.

The deposition of the highly dispersed solids on the finely divided solids can be realized in various ways: Thus, it is possible first to make an aqueous coating dispersion from the finely divided solids and thus to coat a catalyst support body. After drying and calcination of the coating, it is impregnated with an aqueous solution of precursor compounds of the platinum group metals and alkaline earth metal oxides, re-dried and calcined. Alternatively, the precursor compounds of the platinum group metals and the alkaline earth metal oxides may already be added to the aqueous coating dispersion of the finely divided solids. Another possibility is to add only the precursor compounds of the alkaline earth metal oxides of the coating dispersion, to coat the support body and to impregnate the coating only then with the precursor compounds of the noble metals.

With additional use of highly disperse ceria and zirconia in the first layer, these oxides are applied to the finely divided solids of the first layer in an upstream operation. For this purpose, the precursor compounds of cerium oxide, zirconium oxide and the alkaline earth metal oxides are dissolved in water. In this solution, the finely divided solids (finely divided components and oxygen-storing compounds) are dispersed. The dispersion is then dewatered, dried and precalcined. The precalcined powder is, as described above, used for the preparation of the first catalytically active layer.

The above description includes only a few possible process steps for the preparation of the first layer of the catalyst. There are other, different combinations of impregnation steps, adsorption and Vorkalzinierungen for the preparation of the layer possible. It is important that the chosen method ensures that in the finished layer the platinum group metals are in close contact with all constituents of the layer. For this purpose, it is necessary to introduce the precursor compounds of the platinum group metals alone or together with remaining precursor compounds of the other highly disperse components into the coating dispersion or into the layer already deposited on the support body in a last working step.

Essential for the second layer is that rhodium and optionally platinum are deposited only on a part of the finely divided constituents of the second layer. This may be part of the total amount of alumina provided for the second layer or one of the oxygen-storing solids. This ensures that there is always a sufficient amount of noble metal-free alumina as a poison scavenger in the second layer. In order to achieve this, the proportion of finely divided solids provided as support material for rhodium and possibly platinum is impregnated separately with the noble metals, intermediately dried and precalcined, before the coating dispersion for the second layer is prepared with the powder thus obtained and the remaining finely divided solids. Intermediate drying and precalcination can be dispensed with if an aqueous dispersion, to which a solution of the precursor compounds of the noble metals is added, is first prepared with the part of the finely divided solids provided as support material. Only after a waiting time of at least 30 minutes, in which the precursor compounds are adsorbed on the carrier material, the remaining finely divided solids are added to complete the coating dispersion. A prerequisite for this cost-effective variant of the preparation of the coating dispersion is that the selected precursor compounds of the noble metals can be easily adsorbed by the carrier material. Well suited for this are the nitrates of precious metals.

Apart from this limitation, all conventional precursor compounds of the platinum group metals can be used for the preparation of the catalyst according to the invention. As precursors for the alkaline earth metal oxide and ceria and zirconia, acetates and nitrates are preferably used.

The above-mentioned drying and calcination steps are carried out in air at temperatures of 120 to 180 ° C (drying) and at temperatures between 250 and 500 ° C (calcination). The calcination temperatures must ensure the decomposition of the precursor compounds and their conversion into the actual catalytic components. In the case of barium, cerium and zirconium, these are barium oxide, cerium oxide and zirconium oxide in highly dispersed form. The platinum group metals are present after the calcination partly in metallic form and partly also in higher oxidation states.

During operation, the catalysts are heated to temperatures up to 1050 ° C. The transfer of the precursor compounds into the actual catalytic components can therefore be left to a formation phase during the commissioning of a motor vehicle. The necessary during the catalyst preparation drying and calcination then have only the task of fixing the respective coating before the next step on the support body and to convert water-soluble compounds into insoluble compounds. Optionally, therefore, can be dispensed with all or some of the calcination steps.

Some advantageous process variants for the preparation of the catalyst are described by the claims 23 to 28.

Some embodiments of the catalyst according to the invention are compared below with a catalyst according to WO 95/35152. To prepare the catalysts, the following raw materials were used:<dl id="dl0001"><dt><b>La / Al</b>_<b>2</b><b>O</b>_<b>3</b><b>:</b></dt><dd>γ-alumina stabilized with 2 to 4% by weight of lanthanum, calculated as lanthanum oxide; BET surface area: 140 m²/G;</dd><dt><b>γ-Al</b>_<b>2</b><b>O</b>_<b>3</b><b>:</b></dt><dd>pure gamma alumina; BET surface area: 140 m²/G; initial grain size: d₅₀ ≈ 15 μm;</dd><dt><b>CeO</b>_<b>2</b><b>:</b></dt><dd>pure, high surface area ceria; BET surface area: 100 m²/G; initial grain size: d₅₀ ≈ 10 μm;</dd><dt><b>CeO</b>_<b>2</b><b>/ ZrO</b>_<b>2</b><b>:</b></dt><dd>co-precipitated cerium / zirconium mixed oxide; Content of cerium oxide: 70% by weight; BET surface area: 60 m²/G; initial grain size: d₅₀ ≈ 30 μm;</dd><dt><b>ZrO</b>_<b>2</b><b>/ CeO</b>_<b>2</b><b>:</b></dt><dd>co-precipitated zirconium / cerium mixed oxide; Content of zirconia: 80% by weight; BET surface area: 50 m²/G; initial grain size: d₅₀ ≈ 3 μm; <b>CeO</b>_<b>2</b><b>/ ZrO</b>_<b>2</b><b>/ Pr</b>_<b>6</b><b>O</b>_<b>11</b><b>:</b> highly dispersed Pr₆O₁₁ on cerium / zirconium mixed oxide with 67% by weight of cerium oxide, 28% by weight of zirconium oxide and 5% by weight of praseodymium oxide; BET surface area: 60 m²/G; initial grain size: d₅₀ ≈ 17 μm;</dd><dt><b>Ce (C</b>_<b>2</b><b>H</b>_<b>3</b><b>O</b>_<b>2</b><b>)</b>_<b>3</b><b>:</b></dt><dd>cerium acetate</dd><dt><b>ZrO (C</b>_<b>2</b><b>H</b>_<b>3</b><b>O</b>_<b>2</b><b>)</b>_<b>2</b><b>:</b></dt><dd>zirconyl</dd><dt><b>Ba (C</b>_<b>2</b><b>H</b>_<b>3</b><b>O</b>_<b>2</b><b>)</b>_<b>2</b><b>:</b></dt><dd>barium</dd><dt><b>NiO:</b></dt><dd>nickel oxide; BET surface area: 20 m²/G; initial grain size: d₅₀ ≈ 14 μm;</dd><dt><b>Catalyst-supporting body:</b></dt><dd>cordierite; 62 cells / cm² Volume: 1.67 L Dimensions: 118.4 mm ⌀; 152.4 mm in length</dd></dl>

The temperature stability of the catalytic activity of the catalyst is substantially influenced by the relative arrangement of the components of the first layer to each other. This found fact was checked in preliminary tests. For this purpose, catalyst support bodies were coated in each case only with the first layer of the catalyst. As platinum group metal only palladium was used, which was introduced in different relative arrangement to the remaining components of the layer. The remaining ingredients included stabilized alumina, cerium / zirconium mixed oxide, nickel oxide, and fumed ceria, zirconia, and barium oxide.

In preliminary experiment 1, the arrangement according to the invention was chosen, that is, palladium was brought into close contact with all remaining constituents of the layer. In preliminary experiment 2, palladium was deposited only on aluminum oxide and in preliminary experiment 3, half of the palladium was deposited on alumina and on cerium / zirconium mixed oxide.

<b>Preliminary test 1</b>

An aqueous coating dispersion was sprayed which, based on aluminum oxide, also contained 30% by weight of cerium / zirconium mixed oxide, 30% by weight of cerium oxide as cerium acetate, 30% by weight of zirconium oxide as zirconyl acetate, 20% by weight of barium oxide as barium acetate and Contains 4.3 wt .-% nickel oxide. The coating dispersion was carefully homogenized by milling. The finished coating dispersion had a solids content of 34 wt .-% and an average particle size of the finely divided solids of about 2 to 4 microns.

The support was coated by dipping it once in this coating dispersion, dried at 120 ° C for 0.5 hours in air and calcined for 4 hours at 500 ° C in air. Thereafter, the coating was impregnated by immersing the support body in an aqueous solution of palladium nitrate, re-dried and calcined. After drying and calcining, the support body had a coating concentration of about 218 g / l, composed as follows:<tables id="tabl0002" num="0002"><table frame="all"><tgroup cols="3" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="52.50mm" /><colspec colnum="2" colname="col2" colwidth="52.50mm" /><colspec colnum="3" colname="col3" colwidth="52.50mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">La / Al₂O₃</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" align="char" char=",">100 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">CeO₂/ ZrO₂</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" align="char" char=",">30 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">CeO</entry><entry namest="col2" nameend="col2" align="left">ex acetate</entry><entry namest="col3" nameend="col3" align="char" char=",">30 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">ZrO₂</entry><entry namest="col2" nameend="col2" align="left">ex acetate</entry><entry namest="col3" nameend="col3" align="char" char=",">30 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">BaO</entry><entry namest="col2" nameend="col2" align="left">ex acetate</entry><entry namest="col3" nameend="col3" align="char" char=",">20 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">NiO</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" align="char" char=",">4.3 g / l</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Pd</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" align="char" char=",">3.8 g / l</entry></row></tbody></tgroup></table></tables>

The relative arrangement of the constituents can be represented as follows:<chemistry id="chem0001" num="0001"><img file="EP0885650A2_D0006.tif" /></chemistry>

<b>Preliminary test 2</b>

In contrast to preliminary experiment 1, palladium was prefixed on the stabilized aluminum oxide before the coating dispersion was prepared. For this purpose, the required amount of aluminum oxide was impregnated by the method of pore volume impregnation with an aqueous solution of palladium nitrate. The finished coating had the same coating quantities as in preliminary experiment 1. The relative arrangement of the constituents can be represented as follows:<chemistry id="chem0002" num="0002"><img file="EP0885650A2_D0007.tif" /></chemistry>

<b>Preliminary test 3</b>

In contrast to preliminary experiment 1 and preliminary experiment 2, half of each palladium was prefixed to cerium / zirconium mixed oxide and aluminum oxide. The finished coating had the same coating amounts as in Preliminary Test 1. The relative arrangement of the components can be represented as follows:<chemistry id="chem0003" num="0003"><img file="EP0885650A2_D0008.tif" /></chemistry>

<b>Preliminary test 4</b>

The conversion rates of the catalysts of the three preliminary experiments 1 to 3 for the pollutants CO, HC, and NO_X were checked after aging on a 1.8 l gasoline engine. The aging was carried out at a bed temperature (temperature of the catalyst) of 1000 ° C for a period of 40 hours. The conversion rates were measured on an engine test bench at a bed temperature of 400 ° C and different air ratios λ. To simulate real conditions, the air ratio was modulated at a frequency of 1 Hz and amplitudes of ± 0.5 A / F (air / fuel ratio) and ± 1.0 A / F. The results of these measurements are listed in Tables 2 and 3 below. The measured values ​​reproduced in the tables are mean values ​​from at least two measurements. They show that the arrangement according to the invention of the constituents of the layer in the catalyst of preliminary test 1 has distinct advantages over the arrangements of preliminary experiments 2 and 3.<tables id="tabl0003" num="0003"><img file="EP0885650A2_D0009.tif" /></tables>

<b>Comparative example</b>

A catalyst was prepared on a honeycomb body having the above dimensions exactly as described in the examples of WO 95/35152. The finished catalyst contained the following coating amounts: 1. <u>layer</u><tables id="tabl0004" num="0004"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">al₂O₃</entry><entry namest="col2" nameend="col2" align="char" char=",">61.02 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">NdO₂</entry><entry namest="col2" nameend="col2" align="char" char=",">6.10 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">La₂O₃</entry><entry namest="col2" nameend="col2" align="char" char=",">4.58 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">ZrO₂</entry><entry namest="col2" nameend="col2" align="char" char=",">3.05 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">SrO</entry><entry namest="col2" nameend="col2" align="char" char=",">15.26 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">ZrO₂/ CeO₂</entry><entry namest="col2" nameend="col2" align="char" char=",">30.51 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">Pd</entry><entry namest="col2" nameend="col2" align="char" char=",">3.25 g / l</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Pt</entry><entry namest="col2" nameend="col2" align="char" char=",">0.07 g / l</entry></row></tbody></tgroup></table></tables> According to the preparation of WO 95/35152 palladium was deposited only on alumina and platinum only on the zirconium / cerium mixed oxide with a cerium content of 20 wt .-%. The relative arrangement of the constituents of the layer can be represented as follows:<chemistry id="chem0004" num="0004"><img file="EP0885650A2_D0010.tif" /></chemistry>Second <u>layer</u><tables id="tabl0005" num="0005"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">ZrO₂/ CeO₂</entry><entry namest="col2" nameend="col2" align="char" char=",">73.23 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">al₂O₃</entry><entry namest="col2" nameend="col2" align="char" char=",">30.51 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">ZrO₂</entry><entry namest="col2" nameend="col2" align="char" char=",">4.58 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">rh</entry><entry namest="col2" nameend="col2" align="char" char=",">0.26 g / l</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Pt</entry><entry namest="col2" nameend="col2" align="char" char=",">0.18 g / l</entry></row></tbody></tgroup></table></tables> In the second layer, rhodium and platinum were deposited together only on the zirconium / cerium mixed oxide, which was also used in the first layer. The relative arrangement of the constituents of this layer can be represented as follows:<chemistry id="chem0005" num="0005"><img file="EP0885650A2_D0011.tif" /></chemistry> The total precious metal content of the coating was:    Pt + Pd + Rh = 3.76 g / l with    Pt: 0.25 g / l; Pd: 3.25 g / l; Rh: 0.26 g / l Thus, the weight ratio of the platinum group metals among each other was Pt: Pd: Rh = 1: 13: 1.04.

<b>example 1</b>

A catalyst was prepared on a same honeycomb body as in the comparative example according to claim 6. To apply the first layer, an aqueous coating dispersion of aluminum oxide and cerium oxide (ratio by volume Al₂O₃ : CeO₂ = 3: 2) having a solids content of 55% by weight and a density of 1.65 kg / l. The dispersion was homogenized in a mill until the mean particle size of the solids was about 2-3 μm.

The honeycomb body was coated by dipping in this dispersion. The coating was dried at 120 ° C for 1 hour and then calcined at 250 ° C for 2 hours. Subsequently, the coating was impregnated with a common solution of palladium nitrate and barium acetate, re-dried and calcined. The finished first layer contained the following coating amounts:<tables id="tabl0006" num="0006"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">al₂O₃</entry><entry namest="col2" nameend="col2" align="char" char=",">120 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">CeO₂</entry><entry namest="col2" nameend="col2" align="char" char=",">80 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">BaO</entry><entry namest="col2" nameend="col2" align="char" char=",">15 g / l</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Pd</entry><entry namest="col2" nameend="col2" align="char" char=",">1.18 g / l</entry></row></tbody></tgroup></table></tables> The relative arrangement of the constituents of this layer can be represented as follows:<chemistry id="chem0006" num="0006"><img file="EP0885650A2_D0012.tif" /></chemistry>

To prepare the coating dispersion for the second layer, an alumina stabilized with lanthanum oxide was initially coated with 2.4% by weight of rhodium, based on the aluminum oxide used. For this purpose, the stabilized aluminum oxide was dispersed in water. To this dispersion was added a solution of rhodium nitrate. After a sorption time of 30 minutes, a cerium / zirconium mixed oxide and pure alumina were added to the dispersion. The amounts of stabilized alumina, the mixed oxide and the pure alumina were in the following relationship:    La / Al₂O₃ : CeO₂/ ZrO₂ : Al₂O₃ = 1: 2: 2 With this coating dispersion, the honeycomb body was coated a second time, dried and calcined. The second layer contained the following coating amounts:<tables id="tabl0007" num="0007"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">La / Al₂O₃</entry><entry namest="col2" nameend="col2" align="char" char=",">10 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">CeO₂/ ZrO₂</entry><entry namest="col2" nameend="col2" align="char" char=",">20 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">al₂O₃</entry><entry namest="col2" nameend="col2" align="char" char=",">20 g / l</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">rh</entry><entry namest="col2" nameend="col2" align="char" char=",">0.24 g / l</entry></row></tbody></tgroup></table></tables>

The relative arrangement of the constituents of this layer can be represented as follows:<ul id="ul0002" list-style="none" compact="compact"><li>La / Al₂O₃   + Rh</li><li>CeO₂/ ZrO₂</li><li>al₂O₃</li></ul>

The total precious metal content of the coating scam    Pd + Rh = 1.42 g / l with    Pd: 1.18 g / l and Rh: 0.24 g / l and a weight ratio of    Pd: Rh = 5: 1

<b>Examples 2 - 4</b>

Analogous to Example 1, further catalysts with different noble metal loadings were prepared.<dl id="dl0002" compact="compact"><dt>Example 2:</dt><dd>Pd + Rh = 1.98 g / l Pd: Rh = 3: 2</dd><dt>Example 3:</dt><dd>Pd + Rh = 2.37 g / l Pd: Rh = 1: 1</dd><dt>Example 4:</dt><dd>Pd + Rh = 2.93 g / l Pd: Rh = 2: 3</dd></dl>

<b>Example 5</b>

A catalyst according to claim 11 was prepared.

To prepare the first layer, an aqueous solution of cerium acetate and zirconium acetate was first prepared. In this solution, stabilized alumina was dispersed. Subsequently, a solution of barium acetate was added. Finally, the cerium / zirconium mixed oxide was dispersed in this dispersion. The dispersion was dehydrated, dried and calcined at 500 ° C for 2 hours.

Thereafter, the powder obtained was redispersed and homogenized with a mill until a uniform particle size of the finely divided materials of 2-3 microns was reached. To this dispersion was added a solution of palladium nitrate. Subsequently, a honeycomb body was coated by dipping in this dispersion, dried and calcined at 300 ° C for 2 hours. The finished layer contained the following coating amounts:<tables id="tabl0008" num="0008"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">La / Al₂O₃</entry><entry namest="col2" nameend="col2" align="char" char=",">100 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">CeO₂/ ZrO₂</entry><entry namest="col2" nameend="col2" align="char" char=",">30 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">CeO₂</entry><entry namest="col2" nameend="col2" align="char" char=",">30 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">ZrO₂</entry><entry namest="col2" nameend="col2" align="char" char=",">30 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">BaO</entry><entry namest="col2" nameend="col2" align="char" char=",">20 g / l</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Pd</entry><entry namest="col2" nameend="col2" align="char" char=",">2.51 g / l</entry></row></tbody></tgroup></table></tables>

The relative arrangement of the components can be represented as follows:<chemistry id="chem0007" num="0007"><img file="EP0885650A2_D0013.tif" /></chemistry> The second layer was prepared as in Example 1. Instead of the pure rhodium nitrate, a mixture of rhodium nitrate and platinum nitrate with a weight ratio of rhodium to platinum of 1: 1 was used. The second layer, when completed, contained the following coating amounts:<tables id="tabl0009" num="0009"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">La / Al₂O₃</entry><entry namest="col2" nameend="col2" align="char" char=",">10 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">CeO₂/ ZrO₂</entry><entry namest="col2" nameend="col2" align="char" char=",">20 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">al₂O₃</entry><entry namest="col2" nameend="col2" align="char" char=",">20 g / l</entry></row><row><entry namest="col1" nameend="col1" align="left">rh</entry><entry namest="col2" nameend="col2" align="char" char=",">0.16 g / l</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Pt</entry><entry namest="col2" nameend="col2" align="char" char=",">0.16 g / l</entry></row></tbody></tgroup></table></tables>

The relative arrangement of the components can be represented as follows:<ul id="ul0003" list-style="none" compact="compact"><li>La / Al₂O₃   + Rh + Pt</li><li>CeO₂/ ZrO₂</li><li>al₂O₃</li></ul>

The total precious metal content of the coating scam:    Pt + Pd + Rh = 2.83 g / l With    Pt: Pd: Rh = 1: 16: 1.

<b>Application example 1</b>

The catalysts of the comparative example and Examples 1 to 4 were first aged at 850 ° C exhaust gas temperature at the catalyst inlet and for a period of 160 hours on a 1.8 l gasoline engine. Subsequently, their pollutant conversion was determined via the MVEG-A driving cycle. The results are listed in Table 4. The raw emissions of the engine without exhaust gas detoxification amounted to over the mentioned driving cycle:    CO: 7.29 g / Km; HC: 1.17g / Km: NO_x: 2.88 g / Km <tables id="tabl0010" num="0010"><table frame="all"><title>Table 4</title><tgroup cols="7" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="22.50mm" /><colspec colnum="2" colname="col2" colwidth="22.50mm" /><colspec colnum="3" colname="col3" colwidth="22.50mm" /><colspec colnum="4" colname="col4" colwidth="22.50mm" /><colspec colnum="5" colname="col5" colwidth="22.50mm" /><colspec colnum="6" colname="col6" colwidth="22.50mm" /><colspec colnum="7" colname="col7" colwidth="22.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col7" align="center">Measured pollutant conversions</entry></row><row><entry namest="col1" nameend="col1" rowsep="0" align="center"><b>catalyst</b></entry><entry namest="col2" nameend="col2" rowsep="0" align="center"><b>Ratio Pt / Pd / Rh</b></entry><entry namest="col3" nameend="col3" rowsep="0" align="center"><b>Load [g / l]</b></entry><entry namest="col4" nameend="col4" rowsep="0" align="center"><b>Cost [%]</b></entry><entry namest="col5" nameend="col7" align="center"><b>Emissions [g / Km]</b></entry></row><row rowsep="1"><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /><entry namest="col5" nameend="col5" align="center"><b>CO</b></entry><entry namest="col6" nameend="col6" align="center"><b>HC</b></entry><entry namest="col7" nameend="col7" align="center"><b>NO</b>_<b>x</b></entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">VB</entry><entry namest="col2" nameend="col2" align="center">1/14/1</entry><entry namest="col3" nameend="col3" align="char" char=",">3.76</entry><entry namest="col4" nameend="col4" align="right">100</entry><entry namest="col5" nameend="col5" align="char" char=",">1.10</entry><entry namest="col6" nameend="col6" align="char" char=",">0.19</entry><entry namest="col7" nameend="col7" align="char" char=",">0.31</entry></row><row><entry namest="col1" nameend="col1" align="left">B1</entry><entry namest="col2" nameend="col2" align="center">0/5/1</entry><entry namest="col3" nameend="col3" align="char" char=",">1.42</entry><entry namest="col4" nameend="col4" align="right">40</entry><entry namest="col5" nameend="col5" align="char" char=",">1.42</entry><entry namest="col6" nameend="col6" align="char" char=",">0.23</entry><entry namest="col7" nameend="col7" align="char" char=",">0.45</entry></row><row><entry namest="col1" nameend="col1" align="left">B2</entry><entry namest="col2" nameend="col2" align="center">0/3/2</entry><entry namest="col3" nameend="col3" align="char" char=",">1.98</entry><entry namest="col4" nameend="col4" align="right">65</entry><entry namest="col5" nameend="col5" align="char" char=",">1.16</entry><entry namest="col6" nameend="col6" align="char" char=",">0.20</entry><entry namest="col7" nameend="col7" align="char" char=",">0.31</entry></row><row><entry namest="col1" nameend="col1" align="left">B3</entry><entry namest="col2" nameend="col2" align="center">0/1/1</entry><entry namest="col3" nameend="col3" align="char" char=",">2.37</entry><entry namest="col4" nameend="col4" align="right">85</entry><entry namest="col5" nameend="col5" align="char" char=",">1.05</entry><entry namest="col6" nameend="col6" align="char" char=",">0.17</entry><entry namest="col7" nameend="col7" align="char" char=",">0.25</entry></row><row><entry namest="col1" nameend="col1" align="left">B4</entry><entry namest="col2" nameend="col2" align="center">0/2/3</entry><entry namest="col3" nameend="col3" align="char" char=",">2.93</entry><entry namest="col4" nameend="col4" align="right">110</entry><entry namest="col5" nameend="col5" align="char" char=",">0.92</entry><entry namest="col6" nameend="col6" align="char" char=",">0.15</entry><entry namest="col7" nameend="col7" align="char" char=",">0.22</entry></row><row rowsep="1"><entry namest="col1" nameend="col7" align="justify">VB: Comparative Example; B1 Example 1</entry></row></tbody></tgroup></table></tables>

In addition to noble metal ratios of the catalysts, their noble metal loading and the costs for the precious metals resulting at the time of the patent application are given in Table 4, based on the catalyst of the comparative example as 100.

Table 4 shows that even at only 65% ​​of the precious metal costs of the comparative catalyst, the catalyst according to the invention has the same pollutant conversions as this one. At still only 85% of the precious metal costs of the comparative catalyst, the catalyst of the invention provides significantly better performance.

<b>Application Example 2</b>

The pollutant conversions of the catalysts of the comparative example and of Example 5 were measured after aging at different rates on a synthesis gas plant under the following test conditions:<dl id="dl0003" compact="compact"><dt>bed temperature:</dt><dd>400 ° C</dd><dt>Speed:</dt><dd>50,000 h^-1</dd><dt>Air ratios:</dt><dd>λ₁ = 0.998 λ₂ = 1.000 λ₃ = 1.002</dd></dl>

The measurements were at three different air ratios λ₁, λ₂ and λ₃ performed. During the measurements, the air numbers were modulated at a frequency of 1 Hz and an amplitude of ± 0.8 A / F.

Two sets of catalysts were available for the measurements, one of which was aged for 7 hours at a temperature of 950 ° C in air and the second at 1050 ° C in air.

The results of the measurements are listed in Tables 5 and 6. <tables id="tabl0011" num="0011"><table frame="all"><title>Table 5</title><tgroup cols="10" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="15.75mm" /><colspec colnum="2" colname="col2" colwidth="15.75mm" /><colspec colnum="3" colname="col3" colwidth="15.75mm" /><colspec colnum="4" colname="col4" colwidth="15.75mm" /><colspec colnum="5" colname="col5" colwidth="15.75mm" /><colspec colnum="6" colname="col6" colwidth="15.75mm" /><colspec colnum="7" colname="col7" colwidth="15.75mm" /><colspec colnum="8" colname="col8" colwidth="15.75mm" /><colspec colnum="9" colname="col9" colwidth="15.75mm" /><colspec colnum="10" colname="col10" colwidth="15.75mm" /><thead valign="top"><row><entry namest="col1" nameend="col10" align="center">Pollution conversion after aging for 7 hours at 950 ° C</entry></row><row><entry namest="col1" nameend="col1" rowsep="0" align="center"><b>Cat.</b></entry><entry namest="col2" nameend="col4" align="center"><b>λ = 0.998</b></entry><entry namest="col5" nameend="col7" align="center"><b>λ = 1.000</b></entry><entry namest="col8" nameend="col10" align="center"><b>λ = 1.002</b></entry></row><row rowsep="1"><entry namest="col1" nameend="col1" rowsep="0" /><entry namest="col2" nameend="col2" align="center"><b>CO</b></entry><entry namest="col3" nameend="col3" align="center"><b>HC</b></entry><entry namest="col4" nameend="col4" align="center"><b>NO</b>_<b>x</b></entry><entry namest="col5" nameend="col5" align="center"><b>CO</b></entry><entry namest="col6" nameend="col6" align="center"><b>HC</b></entry><entry namest="col7" nameend="col7" align="center"><b>NO</b>_<b>x</b></entry><entry namest="col8" nameend="col8" align="center"><b>CO</b></entry><entry namest="col9" nameend="col9" align="center"><b>HC</b></entry><entry namest="col10" nameend="col10" align="center"><b>NO</b>_<b>x</b></entry></row><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="center"><b>[%]</b></entry><entry namest="col3" nameend="col3" align="center"><b>[%]</b></entry><entry namest="col4" nameend="col4" align="center"><b>[%]</b></entry><entry namest="col5" nameend="col5" align="center"><b>[%]</b></entry><entry namest="col6" nameend="col6" align="center"><b>[%]</b></entry><entry namest="col7" nameend="col7" align="center"><b>[%]</b></entry><entry namest="col8" nameend="col8" align="center"><b>[%]</b></entry><entry namest="col9" nameend="col9" align="center"><b>[%]</b></entry><entry namest="col10" nameend="col10" align="center"><b>[%]</b></entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">VB</entry><entry namest="col2" nameend="col2" align="right">97</entry><entry namest="col3" nameend="col3" align="center">100</entry><entry namest="col4" nameend="col4" align="right">98</entry><entry namest="col5" nameend="col5" align="right">99</entry><entry namest="col6" nameend="col6" align="right">99</entry><entry namest="col7" nameend="col7" align="right">96</entry><entry namest="col8" nameend="col8" align="center">100</entry><entry namest="col9" nameend="col9" align="right">97</entry><entry namest="col10" nameend="col10" align="right">91</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">B1</entry><entry namest="col2" nameend="col2" align="right">95</entry><entry namest="col3" nameend="col3" align="center">99</entry><entry namest="col4" nameend="col4" align="right">98</entry><entry namest="col5" nameend="col5" align="right">97</entry><entry namest="col6" nameend="col6" align="right">99</entry><entry namest="col7" nameend="col7" align="right">97</entry><entry namest="col8" nameend="col8" align="center">99</entry><entry namest="col9" nameend="col9" align="right">99</entry><entry namest="col10" nameend="col10" align="right">94</entry></row></tbody></tgroup></table></tables><tables id="tabl0012" num="0012"><table frame="all"><title>Table 6</title><tgroup cols="10" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="15.75mm" /><colspec colnum="2" colname="col2" colwidth="15.75mm" /><colspec colnum="3" colname="col3" colwidth="15.75mm" /><colspec colnum="4" colname="col4" colwidth="15.75mm" /><colspec colnum="5" colname="col5" colwidth="15.75mm" /><colspec colnum="6" colname="col6" colwidth="15.75mm" /><colspec colnum="7" colname="col7" colwidth="15.75mm" /><colspec colnum="8" colname="col8" colwidth="15.75mm" /><colspec colnum="9" colname="col9" colwidth="15.75mm" /><colspec colnum="10" colname="col10" colwidth="15.75mm" /><thead valign="top"><row><entry namest="col1" nameend="col10" align="center">Pollution conversion after aging for 7 hours at 1050 ° C</entry></row><row><entry namest="col1" nameend="col1" rowsep="0" align="center"><b>Cat.</b></entry><entry namest="col2" nameend="col4" align="center"><b>λ = 0.998</b></entry><entry namest="col5" nameend="col7" align="center"><b>λ = 1.000</b></entry><entry namest="col8" nameend="col10" align="center"><b>λ = 1.002</b></entry></row><row rowsep="1"><entry namest="col1" nameend="col1" rowsep="0" /><entry namest="col2" nameend="col2" align="center"><b>CO</b></entry><entry namest="col3" nameend="col3" align="center"><b>HC</b></entry><entry namest="col4" nameend="col4" align="center"><b>NO</b>_<b>x</b></entry><entry namest="col5" nameend="col5" align="center"><b>CO</b></entry><entry namest="col6" nameend="col6" align="center"><b>HC</b></entry><entry namest="col7" nameend="col7" align="center"><b>NO</b>_<b>x</b></entry><entry namest="col8" nameend="col8" align="center"><b>CO</b></entry><entry namest="col9" nameend="col9" align="center"><b>HC</b></entry><entry namest="col10" nameend="col10" align="center"><b>NO</b>_<b>x</b></entry></row><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="center"><b>[%]</b></entry><entry namest="col3" nameend="col3" align="center"><b>[%]</b></entry><entry namest="col4" nameend="col4" align="center"><b>[%]</b></entry><entry namest="col5" nameend="col5" align="center"><b>[%]</b></entry><entry namest="col6" nameend="col6" align="center"><b>[%]</b></entry><entry namest="col7" nameend="col7" align="center"><b>[%]</b></entry><entry namest="col8" nameend="col8" align="center"><b>[%]</b></entry><entry namest="col9" nameend="col9" align="center"><b>[%]</b></entry><entry namest="col10" nameend="col10" align="center"><b>[%]</b></entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">VB</entry><entry namest="col2" nameend="col2" align="right">78</entry><entry namest="col3" nameend="col3" align="right">92</entry><entry namest="col4" nameend="col4" align="right">86</entry><entry namest="col5" nameend="col5" align="right">81</entry><entry namest="col6" nameend="col6" align="right">92</entry><entry namest="col7" nameend="col7" align="right">84</entry><entry namest="col8" nameend="col8" align="right">84</entry><entry namest="col9" nameend="col9" align="right">91</entry><entry namest="col10" nameend="col10" align="right">83</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">B1</entry><entry namest="col2" nameend="col2" align="right">89</entry><entry namest="col3" nameend="col3" align="right">95</entry><entry namest="col4" nameend="col4" align="right">96</entry><entry namest="col5" nameend="col5" align="right">94</entry><entry namest="col6" nameend="col6" align="right">95</entry><entry namest="col7" nameend="col7" align="right">93</entry><entry namest="col8" nameend="col8" align="right">95</entry><entry namest="col9" nameend="col9" align="right">94</entry><entry namest="col10" nameend="col10" align="right">87</entry></row></tbody></tgroup></table></tables>

As the two tables show, the pollutant conversions of both catalysts after aging at 950 ° C are still comparable. After a more severe aging at 1050 ° C, however, the pollutant conversion of the comparative catalyst is substantially below the level of the catalyst according to the invention. The better aging stability is achieved with a much lower use of precious metals.