DE2830686A1 - CATALYST FOR THE TREATMENT OF MOTOR VEHICLE EMISSIONS AND THE METHOD FOR ITS MANUFACTURING - Google Patents

Description

The invention relates to noble metal catalysts for treating vehicle exhaust gases.

Numerous catalysts are known and are used for oxidizing, reducing, or both oxidizing and reducing of the unburned and toxic components in vehicle exhaust used.

Devices containing catalysts in particulate or monolithic form are currently used in automobiles, to bring exhaust emissions to levels required by federal or state regulations (USA regulations) and the present invention is applicable to catalysts in both forms. Because the regulations are even lower If values of unburned hydrocarbons, carbon monoxide and nitrogen oxides are required, it is necessary that to equip known catalysts with higher conversion efficiencies, these over a lifetime of at least

should work.

80,000 km (= 50,000 miles) and beyond / without deterioration due to poisoning or sintering (caking) Experienced. The present invention relates to improved catalytic converters with higher catalytic effectiveness over the required service life in the active environment of motor vehicle exhaust gases, in which precursors of lead and phosphorus are present, which are known catalyst poisons. In particular this invention relates to a platinum and palladium containing catalyst for the oxidation of unburned hydrocarbons and of carbon monoxide and a platinum and rhodium-containing catalyst which simultaneously oxidizes unburned hydrocarbons and carbon monoxide and nitrogen oxides in automobile exhaust gas reduced. The three-way catalytic converter works in a system in which the air-fuel mixture supplied to the engine is regulated at the stoic thiometric point, with only narrowly limited deviations of the mixture after the enriched one and emaciated side of the stoichiometric ratio occur.

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Extensive theoretical and practical investigations were carried out, the results of which were obtained through testing with the motor dynamometer have been checked; it became an improved catalyst with the desirable higher conversion efficiency properties and greater resistance to poisoning and caking. The improved catalyst is designed as a layer structure analyzer. With this name what is meant here is a carrier made of aluminum oxide (alumina) or a layer of this type, as follows is referred to as a carrier on which two adjacent layers or tapes are present, the first or outer layer contains platinum with good resistance to poisoning by components of vehicle exhaust gases, the greatest concentration of which is at or near the surface of the alumina support (the term "concentration" When using a platinum-palladium mixture, means the percent by weight of the respective catalyst material based on the total weight of the catalyst per unit of penetration depth or separation depth) with a Concentration which decreases with increasing depth of deposition in the carrier; the first layer contains other things at the same time catalytically active material or materials other than platinum with a greater susceptibility to poisoning than platinum with minimal concentration of the other materials or the other material in the first layer at or near it the aluminum oxide carrier surface and with increasing concentration with increasing penetration depth into the carrier up to to a depth at which the concentration of the other materials in the case of palladium approaches the concentration of platinum. This depth of equal concentration represents the boundary between the first and second layers and from since the concentration of the palladium continues to decrease up to a maximum concentration beyond that mentioned Limit lying depth of penetration. The second layer extends

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move from the border inwards. If the other catalyst material, used together with platinum is rhodium, the term "concentration" herein means that Amount of catalyst material at any penetration or deposition depth and the boundary between the first, platinum-rich Layer and the second, rhodium-rich layer is the depth at which the maximum concentration of Ehodium is present and the second layer extends inwardly into the wearer at the border and contains more than half the total amount of ehodium present in the catalyst.

According to the prior art, catalysts with special physical or physical structural features are known. In US Pat. No. 3,259,589, a catalyst for treating vo described combustible waste gases, in which an organic acid, for example citric acid, in a controlled amount with the solution of the catalytically active material is used to a limited zone of catalytic material either at the Surface of the aluminum oxide support or with a certain distance below the surface or in the entire support structure to create. The catalyst according to US Pat. No. 3,367,888 has an aluminum oxide support on which a zone of platinum is attached the outer surface is deposited "without substantial penetration". This is done through the use of a sulfurized carboxylic acid causes. In the case of the catalyst according to US Pat. No. 3,360,330, as in US Pat. No. 3,259,589, an organic acid is used, in order to deposit platinum at a certain distance below the surface of the support, whereupon an impregnation with Barium hydroxide and chromic acid to form a barium chromate or barium dichromate as a protective layer on the catalyst surface follows. The catalyst of US Pat. No. 3,288,558 is essentially complete and uniform with a palladium-copper oxide mixture impregnated or provided and also contains a zone in the outer region of the carrier which is 50% by volume

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of the pellet in which chromium oxide is additionally deposited so that a zone with three components is formed; However, chromium oxide is also present in the inner part of the support, albeit to a much lesser extent. The catalyst according to US Pat. No. 3,819,533 is completely provided with a copper oxide-chromium oxide mixture and has a palladium layer on the outer surface. The catalyst according to US Pat. No. 3 k35 is constructed similarly to the catalyst according to US Pat. No. 3,288,558 , namely the support is first substantially completely and uniformly with an oxide of one or more metals from the series of the first transition metals of the periodic System and the lanthanides soaked or interspersed and then deposited a layer of copper oxide.

In U.S. Patent No. l \ 006103 discloses a monolithic catalyst for use in a two-stage catalyst system in which nickel and rhodium successively, nickel is first deposited on the carrier, wherein both metals similar distribution have on the depth of penetration and the rhodium is used to "greatly increase the activity of nickel". US Pat. No. 3,965 Oi + 0 describes a catalyst for a two-stage atalysatorsystem in which platinum or palladium and rhodium or ruthenium are successively deposited or attached to the support, platinum or palladium being deposited first and both metals either one have similar distribution over the depth of deposition or penetration or else the ruthenium or rhodium is concentrated on the surface, especially when the impregnation solution is also a "high-melting material, eg a salt of aluminum, des'Titans, silicon oxide, des Magnesium or Zirconium "contains. US Pat. No. 3,898,181 describes a two-layer catalyst in which nickel is first deposited on an inert support, followed by a coating with a support material with a large inner surface, both

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for example aluminum oxide is applied and rhodium in this Support material with a large internal surface is attached or deposited, it being desirable that the Ehodium has its larger concentration range "on the exposed surface of the alumina".

In contrast to the state of the art, the newly developed Stratified catalyst significantly improved conversion values over the catalysts currently used in the processing of automotive exhaust gases. In the improved invention Catalyst, the aluminum oxide carrier is provided with a first layer of platinum, through the proportion of which is removed from the surface inside a second layer of catalytically active material is introduced through, from the inner one The boundary of the first layer adjacent to the carrier body penetrating inwards from the boundary with minimal concentration, the first. Overlapping layer to ensure the resistance properties of the catalyst against poisoning and caking (sintering) to obtain. The material of the second layer is at least one of the materials selected from the group consisting of ehodium and Palladium consists.

It is accordingly an object of the present invention to provide a layered catalyst for the purification of automobile exhaust gases containing platinum as the outermost layer for improved conversion efficiency and to achieve greater resistance to poisoning.

Another object of the invention is to provide an improved catalyst having a first layer of platinum, which penetrates the carrier body from its surface and catalytically with a second layer made of it creating active material adjacent to the first layer,

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which penetrates the carrier body from the inner delimitation of the first layer inward, the second layer for the Achieving the high catalyst efficiency is necessary and has a greater susceptibility to poisoning by the exhaust gas.

Another object of an embodiment of the invention is to provide an improved catalyst having a first layer of platinum to create that penetrates the support body from its surface and with a second layer of rhodium, the first Layer adjacent and penetrating the carrier body inwards from the inner boundary of the first layer, wherein the rhodium is present in the catalyst in a proportion which is only about 0.002% by weight and the greater proportion of the Rhodium is in the second layer.

Another object of the invention is to provide a method for preparing the improved catalyst of the invention to accomplish.

The invention is illustrated below with reference to the drawing, for example explained in more detail; in the drawing shows:

Figure 1 shows the radial distribution of the catalyst material

in the case of a bed catalyst constructed according to the invention with a first platinum layer and a second palladium layer,

Figure 2 shows the radial distribution of the catalyst material

in the case of a commercially available catalyst which is constructed in such a way that the maximum proportions of platinum and palladium are on the surface,

FIG. 3> W the radial distribution of the catalyst material for two different commercially available catalysts

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with a cylindrical shape, which are constructed in such a way that the maximum proportions of platinum and palladium lying on the surface

Figure 5 compares the hydrocarbon conversion as a function of operating time in an accelerated test with a poisonous fuel differently structured catalysts,

FIG. 6 shows a comparison of the temperatures for 50 % propylene conversion with unused and poisoned catalysts of different types of construction,

FIG. 7 a comparison of the temperatures for 50% carbon monoxide conversion for unused and poisoned catalytic converters of various types,

Figure 8 compares temperatures for 50% propylene conversion for fresh and baked (sintered) catalysts of various types,

FIG. 9 shows a comparison of the temperatures for 50% carbon monoxide conversion for unused and caked (sintered) catalysts of various types,

FIG. 10 shows the increase in the penetration depth of the catalyst with increasing addition of hydrogen fluoride (HF) as active ingredient cell blockers,

Figure 11 - 1 ^. the distribution of rhodium in the catalyst support for samples 1 to if,

Figure 15-21 the effectiveness curves for each of the samples 1 to 7 in the conversion of hydrocarbons

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(HC) to carbon monoxide (CO) and nitrogen oxides (NO) with different air-fuel (A / F) ratios in unused and aged condition,

Figure 22 shows the rate of decrease in NO conversion in the samples

1 to Zf and 7 after poisoning with lead and phosphorus.

When carrying out the tests it was found that the effectiveness and the stability of noble metal catalysts are very strongly influenced by the relative arrangement of the catalyst materials. In particular, to illustrate an embodiment of the invention, five platinum and / or palladium-containing catalysts were prepared, poisoned in a dynamometer and baked (sintered) in a high-temperature furnace. The results showed a significant improvement in both steady-state and initial efficiency when the catalysts had an outer layer of platinum and an inner layer of palladium. As will be discussed later _? showed effectiveness tests with 3-way-layer catalysts, which were constructed in the described manner with an outer platinum layer and inner rhodium layers for the simultaneous oxidation of the hydrocarbons and the carbon monoxide and the reduction of the NO content of the exhaust gas flow, also improved effectiveness compared to the results non-layered catalysts.

The five prepared in accordance with the present invention and tested catalysts were constructed as follows:

(1) Outer platinum (Pt) layer with inner palladium (Pd) layer, (PT / Pd),

(2) outer Pd layer with inner Pt layer, (Pd / Pt),

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(3) Mixture of Pt and Pd, each according to extended inside with maximum concentration of both substances on the support surface, (Pt-Pd),

(If) Pt layer extending inward from the support surface (Pt), and

(5) Pd layer protruding from the support surface extends inward (Pd).

These catalysts come with associated properties summarized in Table I.

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TABLE I Properties of the catalysts

Pt / Pd

Pt - outside Pd _ irrrrerr

Pd / Pt Pd - outside Pt - inside

Pt-Pd
Pt and Pd
mixture

Pt

Fd

Pt layer

■ depth. {

82 + 36

77 _ + • continuously

> 100

32 ±

Depth_

107 + _ 16 37 ± 7

100 +

! OO +

⁴⁰ pt (Gqh%)

Pd (wt%)

0.03S

0.021

O _f ö58 0.018

0.041
0.016

0.056

Metal Distribution- (%) **

Unused

catalyst

sintered catalyst

61 10

62

15th

SS 3

53

39

The values given are mean values of 10 pellets + standard deviation, determined by
the tin chloride (SnCl ₂ ) process. "

Effective distribution calculated from CO chemisorption measurements assuming a
1: 1 stoichiometry for both Pt and Pd atoms.

CD CO OO

The alumina support used to prepare the catalysts was in the form of spheres 3.2 mm in diameter. It is, however, to be understood that the carrier is also in the form of pellets or particles other than spherical shapes, e.g. cylindrical shapes, it can also be in shapes of Extrudates, be in granular or ring form, and a monolithic carrier can also be used. That means: the The carrier can be a solid body made of aluminum oxide or a ceramic monolithic body with an aluminum oxide coating be. The method of manufacture and the shape of the carrier is not relevant to the invention, which is in the described manner the arrangement of the catalyst material from the standpoint of the relative position of the layers of different catalyst materials is directed in the carrier.

As can be seen from Table I, the amounts of platinum and palladium were in percent by weight, based on the total catalyst weight, in the respective catalysts selected so that they were of the same order of magnitude to be easily comparable with one another Get results. This also applies to the metal distribution on the unused catalyst. The reference to metallic, catalytically active material and the like. happens here in such a way that the materials both in the ele- ' mental state as well as in the Oxidforra should be meant, when the prepared catalyst is mentioned in this context, as the materials are after they have been baked out or fired likely to be present in both states, at least to some extent. The physical or physical characteristics of the alumina support used are shown in Table II. It should be noted that the properties of the carrier material are not relevant for the invention described, since a layer formation in any type of as Catalyst support known active aluminum oxides or alumina is achievable. However, it becomes the optimized one

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Carrier type preferably used, which is described in US-PS Zf 051 072 is. Thus, the present invention is not limited to the use of such optimized carrier types, but rather can also be used with carriers that have, for example, a specific surface area and a specific pore volume, which is lower than it is indicated in the cited patent.

TABLE II Properties of the alumina support

Specific surface (m / g)

specific total pore volume. (cnr / g)

Density values (g / cnr) compact

Pellet

93 723 O, 59 3, 997 0,

In preparing the platinum-only catalyst and the catalyst having an outer platinum layer and an inner palladium layer, an aqueous solution of bromoplatinic acid H ₂ PtBr / -. 9HpO with a pH of about 2.7 is prepared and this solution is prepared used to impregnate an outer platinum layer on the aluminum substrate. More specifically, the ^, 96 g H ₂ PtBr .9H ^ ^ O in 5000 cnr ⁵ cm were distilled ALPO ^ beads treated by 2500 that they were brought into contact with a solution for three hours (deionized) water containing dissolved. As a result of its high reactivity with the aluminum oxide surface, the platinum salt used had a particularly sharp penetration depth, with the largest proportion of the metal occurring at a relatively shallow penetration depth, ie the existing platinum layer had a

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inner limit at a mean depth of 82 μχ & with a standard deviation of ± 36 im. It was found that lower pH values for the impregnation solution increased the depth of the platinum impregnation. Too high a pH resulted in precipitation of the Pt salt with a simultaneous loss of control of the depth of penetration. Accordingly, the pH of the solution can be up to 5 and down as low as necessary to produce the desired impregnation depth or layer thickness, a pH range of about 2 to 3 being preferred. Instead of the preferably used brominated platinum salt, as indicated above, other water-soluble platinum salts can be used, such as chloroplatinic acid and platinum chloride, it being possible to use a spray method or spray application.

Watch the impregnation with the catalytically active material the catalyst was dried in the manner described and then baked in air at 550 ° C. for four hours or burned. Temperatures down to 80 ° C for drying and down to 200 ° C for firing or baking be used. Firing or bakeout temperatures can be as high as desired provided the carrier is not baking together (does not sinter) and the dispersion of the catalyst material is not reduced. Half of the resulting The catalyst was then tested as a platinum-only catalyst segregated, in which platinum was present at about 0.036 wt%.

The other half of the platinum-containing catalysts were then treated with an aqueous solution of palladium chloride with a Impregnated at a pH of about 2.5. In particular, were 1250 cm Platinum catalyst with the use moisture method using 690 cm of an aqueous solution of 76 mg palladium impregnated as chloride salt and 5 g of hydrofluoric acid,

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using the hydrofluoric acid contained in the solution for the blocking of the active sites described later became. Even if the impregnation according to the application moisture method it is to be understood that any other known method of impregnating the carrier can be used can, for example, immersion, spraying, and shaking. Optionally, the concentrations or the amounts the materials are changed to the required amount of catalyst metal to perform the required function to get, i.e. get a functional amount.

In particular, it has been found that the inorganic hydrofluoric acid causes the palladium to form a sub-surface layer as described herein as the second or inner layer of FIG. It is believed that the acid is preferentially adsorbed by the active sites in the support so that the catalytically active material used to form the second layer is brought deeper into the pellet before it finds vacant active sites in the alumina. Accordingly, it was found that an increase in the amount of hydrogen fluoride used resulted in an increase in the depth of the active sites blocked from impregnation by the catalytically active material used to form the second layer. As shown in Table 1, gives a Impragnierungslösung as described above has an average depth of 107Von blocked and the existing palladium salt is sufficient to produce a palladium layer having an average layer width from ^31/1 ^ - too. produce.

Examination of the data shown in Figure 1 shows that the mean width of the outer or first platinum layer and the beginning of the inner platinum layer, which is indicated by the concentration of platinum and palladium at the same point.

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occurs at a depth of about 88 / cm, as indicated by a Layer removal test is determined, which is described below. According to Fig. 1, the maximum concentration of platinum is present on the surface of the carrier and the concentration decreases with increasing depth of penetration into the carrier, while the palladium is present at the surface in minimal concentration and the concentration of the palladium increases with it Depth increases. Penetration beyond the point of equal concentration shows an increase in the palladium concentration up to a maximum in the second layer with decreasing platinum concentration. It is desirable the crowd Keep palladium minimal in the first layer to reduce the catalyst's resistance to both poisoning and poisoning to prevent caking (sintering) as much as possible, since mixing of platinum with palladium and others is catalytic active materials appear to have a negative impact in this regard.

In contrast to the layered structure according to FIG. 1, as can be seen clearly from FIGS. 2, 3 and if, commercially available Oxidation catalysts for motor vehicle applications do not have such a structure. ■

Fig. 2 shows the radial distribution or the distribution along a radius of platinum and palladium in a commercially available one Alumina bed or spherical catalyst with a diameter of 3, if mm. The sample contains 0.0if8if wt% platinum and 0.0192 Weight% palladium, which by impregnating together with a both catalyst materials containing solution were applied, and the specific surface area is in this case 101 m / g. As can be clearly seen in Figure 2, the concentration of both platinum and palladium is on the support surface greatest and both concentrations decrease with the depth of penetration. Fig. 3 and if show similar distributions

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of platinum and palladium on cylindrical extrudates. The diameter for the sample according to FIG. 3 is 3.2 mm and for the sample according to. Fig. 1 + 3.3 now. Impregnation was achieved in the two samples by first impregnating with platinum and then with palladium. The samples according to FIG. 1 and If contained O, Oi + 8if and 0.0385% by weight of platinum and 0.0261 and 0.0162% by weight of palladium, respectively. It is thus clearly shown that the design or structure of commercially available oxidation catalysts is fundamentally different from that according to the invention. Distinguish structure; testing shows a considerably improved performance of the layered Pt / Pd catalyst of the present invention.

When the stratification test was carried out to obtain the data shown in FIGS. 1 to 1f, 100 g of catalyst pellets were obtained placed in a covered glass vessel with a capacity of 1.1 liters together with sufficient chloroform so that the surface of the Pellets was covered. The mixture is vibrated for a certain period of time, for example 5 minutes each time and the periods of time are increased to 10 minutes or longer and the contents of the jar are increased after each period of time Washed on a sieve, the mesh size of which is sufficient to hold back the pellets. The washed out material will analyzed for the content of catalytically active material. The percentage of the removed radius is obtained by that the pellets are carefully dried and their weight loss is determined. The percentage of radius removed is determined from the equation

₁₀₀

where Wo = initial pellet weight and

Y / n = weight of the pellets after vibrating.

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These tests were carried out using a Tyler portable sieve shaker It has been proven that repeatable Results can be achieved not only for spherical, but also for cylindrical catalysts.

The use of hydrofluoric acid as a blocking material for the active sites is preferred because it has been found to be independent of the type of alumina support used blocking has been achieved. HF reaches a level just as well as hydrochloric acid (HCl) and sulfuric acid (HpSO,) Blocking in the case of alumina supports with a content of free Alkali metal oxide at a level of about 0.35% by weight of the support, as described in U.S. Patent 4,051,072. It has however, shown that HCl and HpSO, not as blocking agents act when the aluminum oxide support has a content of free alkali metal oxide which is only about 0.05% by weight. It It has also been found that inorganic acids such as hydrobromic acid (HBr) and nitric acid (HNO,) do not blocking in the various types of aluminum oxide investigated works. Likewise, it has been found that organic materials such as 8-quinolinol and nitrito-triacetic acid no blockages with the types of aluminum oxide (alumina) used and that it does not occur with salts such as sodium fluoride (NaF) and ammonium chloride, acetate, oxalate, -Tartrate and -citrate salts is the case, although these Salts are known as good metal sequestering salts and therefore they may be good for a site blockage suitable. It has been found that organic acids, e.g. citric acid, interact with aluminum oxides with high and low free alkali metal oxides work and accordingly can the other dibasic acids and their derivatives after the description in US Pat. No. 3,259,589 may also be useful with "the required blocking effect described."

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-ζκ-

In summary, the blocking of the active sites in the Carrier from its surface through the first layer penetration depth through the selection of an acid according to the invention from the Group can be achieved, which 'from hydrogen chloride, fluorine / hydrogen, Sulfuric and citric acid and other cvveibasic acids, each selected acid having the ability to to block active sites in the carrier used and is present in sufficient quantity to prevent the blocking up to required depth. As noted earlier, HF is preferred not only because of its wide applicability, but also because it has a sharper band separation with minimal mixing of the catalytically active materials in the first layer and is not that costly.

It has also been found that different complexes of the catalytically active metals have different reactivities with the alumina support as shown in Table III and the selection of an impregnation material with high reactivity is preferred for best results.

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- 2pcs -

BOARD HI

REACTIVITY MD PENETRATION VARIOUS .

Absorbed metal-metal according to penetration depth

Height
Reactivity H PtBr 9H 0 96.7 224 + _ 16 Evenly
to the middle to the center (NH ₄ ) ₂ PdCl ₄ 83.9 205 ^ 4-6 Equal to to the center (NH ₄ ) ₂ PdCl ₆ 96.7 227 ± 35 Equal to to the center (NV ₃ RhCl ₆ 75 _? O 198 ± 39 Equal to to the Low
Reactivity (NH ₄ ) ₂ PtCl ₄ 32.4 Equal to to the center MI ^ [Pt (C ₂ H ₄ ) Cl ₃ ] 20.0 Equal to to the center (NH ₄ ) ₂ Pt (N0 ₂ ) ₄ 45.5 Equal to to the center (NH ₄ ) ₂ PtCl ₆ 29 * 6 Equal to to the center H ₂ PtCl ₆ ^ H ₂ -O 33Λ Equal to to the center K ₂ [Pt (CN) ₄ ] ^ H ₂ O 22 _f 9 Equal until IC ₂ Pt (SCN) ₄ 22 _y 5 [Pt (NH ₃ ) JCl ₂ JI ₂ O 23.2 [Pd (NH ₂ ) ₄ ] Cl ₂ .H ₂ 0 36.4 [Rh (NH), - Cl] Cl ₂ 27.0

^f The values given are the mean value + standard deviation for 10 pellets, determined by staining with SnCl ₂ or Na

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The preferred process for producing the layered catalyst according to the invention has since been described in such a way that the carrier was first impregnated or coated with platinum to form the first or outer layer, followed by impregnation with a solution containing the blocking acid for the second layer; however, other methods are also possible. For example, the preferred order can be changed in that a successive treatment takes place during the formation of the second layer, ie that first the carrier with the already applied first layer of platinum salt is treated with the blocking acid and then an impregnation with the solution for the second catalytically active layer follows. Alternatively, instead of first applying the outer layer of catalytically active material, the second layer of catalytically active material can be applied to the carrier first. As already indicated, this can either be achieved in that the blocking acid is applied in combination with the impregnating salt solution or that a treatment is carried out separately with the blocking acid before impregnation with the solution for the second layer. In both cases, the impregnated carrier must be heated in order to drive off the blocking acid and then calcining must take place before the impregnation with the solution for the first layer, ie with the platinum, takes place. Depending on the type of aluminum oxide (alumina) carrier, temperatures of up to 550 ° C for a period of up to about 1 ± hours may be necessary, with the amount and type of blocking acid used and the type of noble metal salts also playing a role . The treatment can take place in air, in neutral or in reducing atmospheres.

The amounts of catalytically active material used according to Table I correspond approximately to those currently used in

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Platinum-palladium oxidation catalysts can be used. It should be noted, however, that the amount of material used does not belong to the essential characteristics of the invention and can be varied depending on the degree or value of conversion that is to be achieved. It should be noted that changing the amounts also changes the depth of the layers of the catalytically active material. The amount of acid required is determined simply by routinely treating samples using the desired catalyst preparation method in accordance with the invention and analyzing bed depths. When preparing the catalysts according to the invention, a total depth for the first and second layers of the catalytically active material of at least 90 μm is preferred, the depth of the first, the platinum layer being the depth to which the catalyst poisons during the required service life penetrate the catalyst; this penetration depth is about 82 / na and, according to Table I, a total depth of about 118 μm is achieved for the Pt / Pd catalyst. It is to be understood that this depth must vary depending on the concentration of the poisons in the exhaust gas stream and also depending on the physical properties of the respective carrier.

The catalyst, which contains platinum and palladium as a mixture in the outer section of the support without stratification, was prepared by impregnating the aluminum oxide with an aqueous solution of chloroplatinic acid and palladium chloride, using deionized or distilled water as the solvent, as in all other cases, and the Solution was adjusted to a pH of 2.0. In particular, 1250 cm of Al ₂ O- was impregnated with 500 cm- ^{5 of} a solution containing 0.3237 g of platinum and 0.1290 g of palladium, using the wet-off method. The resulting catalyst was

8G-9 8 8S / Ö-823

dried and baked in air for four hours at a temperature of 550 C. Investigations with the electron microprobe found that under these conditions the palladium deposited closer to the outer surface of the pellets than the platinum.

When preparing the layered catalyst with palladium as the outer layer and platinum as the inner layer and the catalysts that only contain palladium in the outer section of the support, the aluminum oxide (the alumina) is first mixed with a solution of palladium chloride (PdClp) with a pH of 2, / f impregnated. At this pH value, a very sharp palladium profile is achieved on the outer surface of the catalyst pellets. In detail, 2500 cnr AlpO were impregnated with 1000 cnr of an aqueous solution containing 0.2% if g palladium. After drying and firing as above, the palladium catalyst was ready for testing. Half of the palladium catalysts produced were further impregnated with 500 cm of an aqueous solution containing 0.3233 g of H ₂ PtCl, -. 9H 4 O and 1.368 g of citric acid and which had a pH of 2.3. Citric acid works similarly to hydrofluoric acid by blocking the active sites, forcing the platinum inside the alumina pellets. This was followed by drying and firing as described to give a catalyst with an inner layer of platinum. As already described, the proportions of material were selected so that the amounts of catalytically active material shown in Table I were obtained and that the required depth of blocking resulted with minimal overlap.

When running the accelerated shown in the drawing Catalyst poisoning tests were the catalysts Poisoned in a reactor system that contained four reactor or umbrella troughs, each with a capacity of 250 cnr. Of the

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The reactor was charged with the exhaust gas from a 5.7 liter V-8 engine. The engine was operated at 1800 rpm with an engine dynamometer at an intake manifold vacuum of about 1 kPa. The air-fuel _{ratio was 15 5} 5j so that oxidizing exhaust gases resulted. The fuel contained 0.023g lead / l, 0.117g sulfur / l and 0.007g phosphorA as average values. To stabilize poison emissions, the engine and exhaust system were balanced by operating the poison-containing fuel for about 3 days before the first catalyst poisoning experiment was carried out.

The exhaust gases fed to the catalyst typically contained 0.29-0.3 % CO, 1.16-1.20 % O ₂ and 280-320 ppm hydrocarbon. The hourly volume velocity of the gas was 115,000 h ~, at standard temperature and pressure. During the tests, the catalyst bed temperature was approximately 570 ° G. This accelerated poisoning test simulated corresponding if 100 hours of actual exposure to poisoning in the case of exhaust gases in about 50,000 hours. At the end of the run, the catalyst samples were taken from the top of each of the four reactor troughs for analysis.

The precious metal penetration depths in the alumina pellets were measured by placing the pellets in an aqueous solution of SnCIp were boiled and the resulting darkened Layers were photographed under a microscope. The penetration depths of lead and phosphorus in the poisoned Catalysts were determined by the electron microprobe. The noble metal dispersions were determined by CO chemisorption. These methods and associated equipment are known in the art and do not form part of the invention.

The activity measurements were taken both during the accelerated

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th resistance tests carried out in the installed state in the test cell and also in the laboratory. In the test cell, the hydrocarbon and carbon monoxide conversions were measured in the equilibrium state at around 570 ° C and a volume velocity of 115,000 h ~ (STP). » The CO and propylene conversions were determined as a function of temperature in a laboratory reactor system. The laboratory reactor consisted of a pipe made of stainless steel with a diameter of 19 mm, which was heated in an electric furnace. An inert filling made of silicon carbide (SiC) was used for preheating. A 10 cm catalyst sample and a volume velocity of 85,000 h "(STP) was used. The feed stream in the laboratory consisted of 0.3 % CO, 0.025 % propylene, 1.5 % _0.1 and 10 % H ₂ O in nitrogen The programmed heating rate was 10 ° C./min.

The conversion of hydrocarbons was made as a function of Exposure time observed during the accelerated poisoning tests on the dynamometer and is shown in FIG. 5.

In performing the durability test, it was first necessary to stabilize the catalysts with an indoline clear fuel for about 15 minutes in order to obtain an initial efficiency reading. As can be seen from Figure 5, the initial conversion values for hydrocarbons depended on the catalytically active material and on its relative location on the support. For both hydrocarbons and carbon monoxide, the Pt / Pd catalyst gave the best initial high temperature efficiency, while the other catalyst designs were significantly inferior. Similar Umwan_dlungstests _s such as those shown in Fig. 5, were performed for CO.

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Exposing the catalysts to the poison-containing exhaust gas by switching to the poison-containing fuel resulted in an almost instantaneous drop in activities, as shown in FIG. Previous work has shown that this rapid drop in activity was largely associated with the halogen cleaners in the additive that was used as the lead source in the test fuel. The decrease in activity was between 5 and 7 % hydrocarbon conversion under the test conditions. The smallest drop occurred with the catalyst type Pt and the largest decrease with the catalyst type Pd.

As shown in Fig. 5, the efficiencies of the five types of catalyst were listed in the order of decreasing activity after about the first hour of exposure to the Exhaust gases from the fuel containing poison have the following:

Hydrocarbons: Pt / Pd, Pt, Pt-Pd, Pd / Pt and Pd.

On the basis of similar experiments, the following resulted Effect sequence with decreasing effectiveness for CO conversion:

Carbon monoxide: Pt / Pd, Pt, Pt-Pd, Pd and Pd / Pt.

In both cases, the Pt / Pd type of catalyst gives the best effectiveness against hydrocarbons and carbon monoxide both the indoline clear fuel and the halogen-containing fuel. This attribute is very indicative as it states that both hydrocarbon and carbon monoxide conversion occur through the same type of catalyst, i.e. the layered catalyst with an outer or first platinum layer and an inner or second layer Palladium layer, has been improved. When the catalysts were poisoned with phosphorus and lead, the differences occurred

809885/0829

the conversion efficiency even more. After 40 hours The following sequence of effectiveness was observed based on smoothed time curves (Fg 5):

Hydrocarbons: Pt / Pd, Pt, Pt-Pd, Pd / Pt, Pd. It can be seen that the catalyst type Pt / Pd in addition to The best initial effectiveness is also found in the resistance to poisoning for hydrocarbons and, on the basis of a like Trying for carbon monoxide proves superior. As can be clearly seen from Fig. 5, the types of catalysts that Palladium contained as the only catalyst substance or as the first layer on the carrier, the strongest deactivation for hydrocarbon and, based on a similar series of experiments, for carbon monoxide conversion.

It is noteworthy to observe the influence of an inner layer of palladium beneath the outer layer of platinum. The higher hydrocarbon activity of the Pt / Pd catalyst results, as is assumed, from the oxidation of the hydrocarbon species, which are normally difficult to oxidize, inside the catalyst support. For a balance s carbon monoxide oxidation, the inner areas seem to be less important.

In determining the effect of the catalyst type on the temperature profile of the conversion capacity, the previously described temperature programmed laboratory reactor was used to generate conversion inlet temperature curves for fresh and for poisoned catalysts. Figures 6 and 7 show the temperatures required for 50% conversion. As is known, the lower the temperature required, the better or more useful the catalyst.

The laboratory reactor was filled with catalysts,

80988S / 0829

taken from the inlet trough of the test cell reactor, and so the poison loads of the catalysts shown in Figures 6 and 7 correspond to the inlet poison load values discussed above. Since these inlet toxicity values are higher than the toxicity values according to the integral average, the equivalent "age" of the catalyst samples used in the conversion temperature tests corresponds more to a catalyst after 80,000 km exposure. Only the results of attempts to induce a state of _equilibrium} have been considered after the first run for each sample of the catalyst.

There is only a relatively small difference in the fresh initial effectiveness of the catalysts for both propylene as well as for carbon monoxide. The order in order of increasing temperature for 50% conversion is:

Propylene: Pt / Pd, Pt-Pd, Pt, Pd / Pt and Pd CO: Pt-Pd, Pt / Pd, Pt, Pd / Pt and Pd.

The sequence is similar to that for high temperature behavior observed according to FIG. The catalysts with only palladium result in the worst starting conversion. It is noteworthy that the value of the initial effectiveness of the palladium catalyst is considerably improved when platinum is added (Pd / Pt, Pt-Pd).

The initial transformation after poisoning is also shown in FIGS. The order ₅ in increasing temperature for 50% conversion is as follows:

Propylene: Pt / Pd, Pt-Pd, Pd / Pt, Pt and Pd CO: Pt / Pd, Pt-Pd, Pd / Pt, Pt and Pd.

The starting temperatures increased with the aging to between

809885/0829

20 and 90 ° C. The differences in the initial conversion of the various types of poisoned catalyst are very large, for example, is the starting temperature of the Pd catalyst for propylene about 90 ° C higher than that for the Pt / Pd catalyst. Again, the Pt / Pd catalyst type shows the best Behavior and the jointly impregnated Pt / Pd catalysts follow closely behind. It's interesting too it should be noted that the deterioration in starting activity for propylene is somewhat greater than that for carbon monoxide with all types of catalyst.

According to Table I, the Pt catalysts experienced the greatest loss in metal dispersion (from 68 % to 3 %) after sintering for 7 hours at 870 ° C. in air, while the Pd catalysts suffered the lowest loss (from 53 % to 39 %) . The three catalysts containing Pt and Pd had dispersion losses between 8 and 15 % on sintering.

The Pd catalyst showed after sintering (Fig. 8 and 9) neither a deterioration in the propylene starting temperature nor the CO start temperature. In contrast, the suffered Pt catalyst caused the greatest loss of starting activity. However, after sintering, the Pt / Pd catalyst had the largest Starting activity for both propylene and CO. The impregnated together. Pt-Pd catalyst lost a considerable amount of time Starting activity for both propylene and CO. The order of the catalyst types in order of increasing temperature for 50% conversion after sintering is:

Propylene: Pt / Pd, Pt-Pd, Pd / Pt, Pd, Pt; CO: Pt / Pd, Pt-Pd, Pd / Pt, Pd, Pt.

Accordingly, the best configuration for maintaining a startup activity is after sintering clearly the Pt / Pd catalyst,

809885/0829

i.e. the one with platinum as the outer layer on the carrier and palladium as the second layer, the inner boundary of the first platinum layer adjacent layer that extends inward from there.

In a further embodiment of the improved invention Catalyst, the three-way catalyst, the aluminum oxide carrier is provided with a first layer of platinum, which is located on the surface of the wearer and into the body from there penetrates inwards, a second layer of rhodium being adjacent to the inner boundary of the first layer and penetrating the body of the wearer inwardly from that boundary, the greater amount of the rhodium being at the first Layer lies inwardly adjacent to the rhodium from rapid deterioration and failure of the convertibility to protect as a result of poisoning. The present invention uses rhodium, albeit in greater amounts can be used, a use of the rhodium in amounts that are only about 0.002% by weight of the catalyst, since most of it is protected from poisoning by the outer, platinum-coated layer. It's not just because of the lower cost is very significant, but also because a greater consumption of larger amounts of rhodium, for example of 0.018% by weight in automotive converters, the rhodium reserves would exploit very quickly and an economic one Balance of the precious metals platinum, palladium and rhodium, which in South Africa has a natural ratio of platinum to rhodium of about 18: 1 would be disturbed. Since small amounts of rhodium are present in the first or outer platinum layer, the presence of such may be smaller Quantities close to the surface are important to avoid the undesirable formation of ammonia in the fresh or relative avoid fresh catalyst.

809-685 / 0829

When the tests were carried out, it was found that the effectiveness and resistance properties of the noble metal catalysts can be very much influenced by the relative arrangement of the catalyst materials. To this further embodiment of the invention To illustrate in detail, four platinum and bhodium-containing catalysts were prepared with respect to the Poisoning of the catalyst material in the carrier showed three different forms and there were equilibrium conversion tests ridden with a dynamometer. The conversion tests using the three-way layered catalyst constructed according to the invention showed a significantly improved performance compared to the results obtained with both commercial as well as with differently structured catalysts.

The catalysts prepared according to the invention that were investigated had the following structural features:

(1) Outer platinum (Pt) layer, inner bhodium (Eh) layer (Pt / Rh),

(2) Outer Eh layer, inner Pt layer (Bh / Pt),

(3) Pt and Bh simultaneously deposited as a mixture with a maximum Concentrations of both substances on the carrier surface (Pt-Eh).

These catalysts and their properties are listed in Table IV, along with two commercially available catalysts shown.

809885/0829

Pt "to z / vehicle *

Ge vj? 6th
Shift start, ^
-End '^

«Ο Complex

<ο Prep.

OO ΙΌ «Ο

TABLE IV Properties and preparation process of the catalysts used Pt / Rh Pt / Rh Pt-RIi Rh / Pt commercially available Ft *

sample No. -r PL 1 PL P. PL 3 PL Room 5 6th PL 7th Carrier· 3-22-76 3-22-76 5-22-76 5-22-76 Rhone
profile Rht-ne-
Profile 5-22-76

0 ^ 037
0 _; 046

+ _ 24
H ₂ PtBr ₆

0.053

0.041

± 30

K ₀ FtBr.

0.0 ^ 5
0
> 100

H ₀ PtBr, - + RhCl ^ 2 6 ρ

0 _T 02S

0 _r 036
91 - 21
Eins.Bef.

UbschLösg. ^ UbschLösg.- E ^ ns.Bef.

«Eh- tos / vehicle *
Gev ^ i
Max
end
ILo qp lex
BlockMitt.
Prep.

Trο ckenataosph.

Dispersion (%)
Γ. Waterproof

0 _T 0020
0 ^ 0025
65
200

^ -0.0016

^ -0.0020

35

428

0.042 0.047 0 _r 049

0 _r 045 0.047 0.062

** 0 0

** 87 Ji 22 235 ± 25

? ? Pl ₀ PtBr.

2 ο

Spray-on-spray-over-release C?) Hen I ^ J

0.018 0.0025 0

0 _r 019 0 _r 002> -,

KP

Application humid.

HF insert humidified.

air

99

Rh.Pt Pt.Rh

0
32

K ₀ Pt Br r + RhCl ₂ . d. 6 t>

no
Application humid.

Air-

85

at the same time - - Eins_.Bef.

'V 0.0016

t0.0020

EhCl,

Citric acid ~. ~
Application, spray-on, spray-on moistening. hen (?), hen '(?) -

air
78
Pt. Rh

Air 93

K>

-txr

CD CJ) GO G)

Converter of type 260 (4261 cm ⁵ ); '! toz = 31.1 g.
According to the reactivity of the poisoning behavior, these catalysts probably contain Rh and Pt ind. Close to the outer surface of the pellets

to
SnCl2im

Jump la de _m toklen metal

Table V shows the physical properties of the pellet carriers for the samples compiled in Table IV. The, in the samples 1 to 7 used If and slides were prepared according to US-PS 1+ 051,072. The alumina supports used in preparing the catalysts were in the form of spheres 3.2 mm in diameter. It is to be understood, however, that the supports can also take the form of pellets or grains that are not spherical, for example cylindrical pellets, or the extrudates are granular or annular, and that monolithic support shapes can also be used. That is, the carrier can be a continuous aluminum oxide body or a monolithic ceramic body or such a pellet with an aluminum oxide coating. The type and shape of the carrier is not relevant to the invention. In the manner described, this is directed to the formation of the catalyst from the standpoint of the relative arrangement of the layers of the various catalyst materials on the support, either on the aluminum oxide body or on the layer.

TABLE V

Properties of the catalyst supports used

Total pore volume -, 'cnr / g)

3 macro-pore volumeXcm / g)

Micro pore volume (cnr / g) 10 macro pore radius (ηΐφ * Micro pore radius (nm) *

spec, surface area • 2 / - \ according to BET " ^{Cm / s;}

Pellet density - (g / cm ⁵ )

Effective diffusivity (cnL ² / sec) ⁺ 0.0110 0.0126 15 Nominal pellet radius (cm) 0.159 0.159

Integral average. The diffusivity relates to an N ^ pulse in the Eelium-filled pores as? respective. Xat-alyss.-torträ.sers at ^; .-Oocur.d 1 Atr.osphere?

809885/0829

.Rehearse.
5 and 6 . rehearse
1 to Zf and 7 0.595 0.683 0.115 Oj 480
423 ^ 7 mon.omod.al 6.7 96 112 1,135 1.037

As can be seen from Table IV, the amounts of platinum and rhodium were determined in percent by weight based on the total weight of the catalyst for each type of catalyst except for sample Fr. 7 see above selected that same order of magnitude was obtained in order to obtain results that are well comparable with each other and with the commercial one Achieve catalyst sample # 6. Sample No. 5> possesses an amount of rhodium which is about nine times as high as those of the other samples. The term "catalytically active material" is used herein to include both materials in the elemental state as well as in the oxide form, as the materials are likely to be after dry-firing (calcining) are present in both forms, at least to some extent. It should be noted that the properties of the Carrier are not relevant for the invention described here, since the formation of layers in every active aluminum oxide, which is known as a catalyst support material can be carried out. Even if the optimized types of carrier US-PS If 05t O73 are to be used preferably, so is Invention is not limited to the use of such optimized types of carrier, but also with carriers with, for example lower specific surface and specific pore volume applicable.

In the preparation of the catalyst samples Nos. 1 and 2, the Containing a first or outer layer of platinum and a second or inner layer of rhodium is an impregnation of the support with platinum achieved by using an excess of impregnation solution, while the rhodium with the Use humidification technology was applied. It is to be understood that other well known methods of impregnation are also used of the carrier, e.g. spraying or shaking in the solution. The process of creating a layered Catalyst by using successive

Impregnation with the various catalyst solutions, one of which still has a proportion of an acid to block the active sites such as hydrogen fluoride and citric acid in sufficient quantity to block the active sites in the beam to the required depth is described below.

Specifically, is referred to as sample 1 in the production Catalyst with an outer Pt layer and an inner Rh layer an amount of 0.06 ^ 0 g of the rhodium salt (NH, K RhCl, -. 3H-O and 0.72 g of hydrogen fluoride in 560 cm * of distilled (or deionized) water dissolved. This solution was mixed with 1200 cubic centimeters of active alumina beads to make the alumina to be impregnated by the application humidification technology. The impregnated carrier was then air dried and in ambient air Baked (calcined) for ten hours at 550 ° C.

According to FIG. 10, the depth of blocking of the active sites by the hydrofluoric acid and thus the depth of penetration of the catalytically active material for the formation of the layers increases with the amount of hydrogen fluoride used. The variable f is equal to the depth measured from the surface of the support divided by the pellet radius. In the example of Sample 1, the amount of hydrogen fluoride used was so great that it resulted in such stratification that the maximum concentration of rhodium occurred at a depth of about 65 mjh. As described in more detail below, the pH of the impregnation solution influences the depth of penetration of the catalyst material and the blocking of the active sites so that decreasing pH results in greater depth of penetration, a pH range of 2 'to 3 being preferred and a pH -Value up to 5 can be used.

When determining the position of the rhodium in the pellet, a Ion microprobe mass analysis (IMMA) uses that very much

809885/0829

is sensitive to small amounts of rhodium. Fig. 10 shows the relationship between the amount of site blocking agent used and the subsurface placement of the rhodium of the carrier used. For another wearer, this relationship can be established by a single IMMA measurement of the rhodium at a certain amount of the site blocking agent.

Since baking out (calcining) the impregnated carrier drives out the hydrogen fluoride to unblock the sites and decomposes the rhodium salt into elemental metal and metal oxide, the carrier is then prepared for impregnation to form the outer layer of platinum. In this example, 2.25 / fg of H ₂ PtBiV ^ H ₂ O was dissolved in 22,000 cpm of distilled water to form a solution with a pH of 2.92. The aluminum support with an internal rhodium layer was placed in the solution and remained in it for 3 hours at ambient temperature; then the excess solution was poured off and the impregnated support was dried in air and baked (calcined) in ambient air for 1+ hours at 550 ° C. in order to form the catalyst according to the invention. The distribution of rhodium on the support in the sample is shown in FIG. 11; the maximum concentration of rhodium is about G5 / £ ß- below the surface.

In the production of sample 2, the outer layer of platinum was first impregnated on the carrier, ie the reverse process as in the preparation of sample 1 was carried out. An H-PtBiv solution of 2.333 SH ₀ PtBr ^. 9E ₀ Q in 2if00 cnr ^{5 of} distilled H ₅ O with a pH of 2.72. was held in contact with 1200 cnr AlpO for three hours. The solution was then poured off and the catalyst

80988S / 0829

dries and then in air Zj. Heated (calcined) for hours at 550 ° C. The Pt / Al O _x catalyst was then impregnated with a RhCl ^ .3HpO solution (0.0119 g Rh salt in 69O cm H ^ O) containing 15 cm 2% hydrofluoric acid. The pH of the rhodium solution was 2.5. The catalyst was dried in air overnight and then heated (calcined) in air for Zf hours at 550 ° C. The distribution of rhodium in the carrier is shown in Fig. 12; the maximum concentration of rhodium is found at about 88 μm below the surface.

Sample 3 is a catalyst impregnated with platinum and rhodium at the same time. For its production, 1.833 g HpPtBr were -. 9H ₂ O and 0.0320 g of RhCl, .3HpO in 560 cnr ⁵ of distilled water and 1200 cm ^ ALPO beads were impregnated with it. The pH was "bfZZ. The impregnated catalyst was dried in air and baked (calcined) for 2 hours at 535 ° C. in ambient air. The distribution of the rhodium in the support is shown in FIG. 13 and the maximum rhodium concentration appears at the edge or surface of the pellet in contrast to Samples 1 and 2, in which hydrogen fluoride was used to block the active sites in the vicinity and on the surface to form a layered catalyst.

Sample Z ₁ . is a layered catalyst in which the order of the layers is reversed compared to samples 1 and 2, ie the outer layer consists of rhodium and the inner layer of platinum. As can be seen from Fig. 1Zf, the distribution of the rhodium in the support is the same as for the simultaneously impregnated catalyst sample No. 3 "since no site-blocking acid was used to determine the location of the rhodium, but the site-blocking acid together with the platinum was used. Therefore, the maximum concentration of rhodium is on the surface and decreases towards the center. As shown, the acid site blockage along with the platinum impregnation solution results in a distribution of the

809885/0829

Platinum, made visible by SnCl ₂ , which starts at about 91 + ZiJ (j & inside the surface and extends towards the center. In this example, the greater part of the rhodium is located, ie about 80 % after integration of the visible distribution of the surfaces under the curve of Fig. M + in the outer layer, i.e. from the surface to a depth of about 30 i (m,

Sample 4 was prepared in such a way that first 0.855 g of H ₂ PtClg and 1, Q53 S citric acid monohydrate as a site-blocking acid was dissolved in 560 cnr distilled water, resulting in a solution with a pH of 2.18 and thus became 1200 cm Al ₂ O, impregnated. The catalyst was dried in air and in ambient air Zj. Calcined at 535 ° C for hours. A solution of 0.0320 g of RhCl, .3H ^ ₁ O in 560 cnr of distilled

-? 3

Water was then used to impregnate the 1200 cm of the Pt impregnation

ten AIpO, used. The catalyst was air dried and calcined in ambient air at 335 ° C. for four hours.

Samples 5 and 6 were obtained commercially from two different locations; their metal distributions are considered to be with the Information in Table IV was accepted in agreement.

Because of the relatively small amounts of rhodium present in the catalyst, the ion microprobe mass analysis technique has been found to be well suited for determining the relative distribution of rhodium as a function of distance from the support surface. Scanning across the carrier pellet was performed using a 25 / µm λ ^ / µm rectangular probe. Since both rhodium and aluminum ions are sprayed from the carrier, the intensity ratio of rhodium to aluminum was measured in order to determine changes in the amount of aluminum as a result of the variable surface scanned.

809885/0829

structure to be eliminated. Since at the beginning of the scanning from the carrier surface inwards in the V / eise outlined here the probe surface was partially not in contact with the pellet, the measurements of the distance adder the depth in Fig. 11 to 11+ must be the distance of the first relatively sharp break-off point moved to the right in the direction of the ion intensity curve, as this breaking point represents the point at which considerable amounts of aluminum have been removed from the surface. This amount is between 5 and approximately 12 μm for a probe surface of the specified dimension 5, depending on the roughness of the pellet surface. When applied to Fig. 11, the surface of sample 1 is actually at the point indicated about 10 µm of the scale distance and the maximum rhodium concentration is therefore about 75 Å * m less 10 ^ µm or about 65 Å * m. It should also be noted that the data presented in Table IV are based on a single pellet, since such analysis has been shown to be representative of data from other pellets in the same series of catalysts.

As already noted, the platinum in each of the samples 1 is so distributed over the depth of the pellet that the maximum concentration occurs on the surface and the concentration decreases with increasing penetration depth. The depth of penetration the platinum was determined by optical microscope observation after the pellet was treated with an aqueous solution was subjected to by SnCIp. Although the pellet for visualization of the blackening platinum can be soaked as a whole in the solution, preferably the pellet first split in half for rapid development of the color. This procedure is in this field well known and a common solution is made by dissolving 0.1 g of SnClp.2HpO in 20 ml of water and the solution becomes brought to a boil with pellets submerged in it.

8098-85 / 0829

Various platinum and rhodium salts can be used in the manner described, whereby it is only necessary that the salts are water-soluble, in order to impregnate or impregnate by a known application method, for example Spray on, submerge and shake to achieve. Drying and baking (calcining) can be done in a similar way according to temperature and time can be changed, these two values being reversed Relate to each other. Temperatures of only 80 ° can be used for drying and only 200 ° for calcining. The calcining or baking temperatures can be as high as desired provided the substrate will not baked or sintered and the dispersion of the catalyst is not reduced. As also in the description mentioned in the sample preparation, various site-blocking acids can be used to impregnate the impregnation to control the carrier with the catalytically active materials, hydrogen fluoride being preferred, as recognized was found to function as intended regardless of the type of alumina support. As with Samples 1 and 2, the impregnation or application process can also be changed in the manner described below. The amounts of catalytically active material shown in Table IV in samples 1, 2 and Zf correspond approximately to the ratio Platinum to rhodium as it is in the mined ores. Preferably, these materials are used in these relative amounts, namely about 0.036 wt% platinum and 0.002 wt% Rhodium; it is nevertheless to be understood that the amount of material does not represent a fundamental characteristic of the invention and is changed depending on the required efficiency can »It must be borne in mind that changes in the quantities Can change the depth of the layers of catalytically active material. The amount required for processing acidity is easily determined by taking a sample under

809885/0829

Using the proposed method, as described above, is routinely treated and the layer depth is analyzed will. In the preparation of the catalysts according to the invention the depth of the first, the platinum layer is preferably designed in such a way that it allows the penetration depth of the toxins during the desired Life of the catalyst corresponds to; Panel IV shows a depth of about 50 to 130 µm. It should be understood that that this depth depends on the concentration of the poisons in the emission gas stream and on the physical Properties of the Jeiveiligen carrier is changeable.

The tests with catalysts containing platinum and rhodium showed that a correct design of the catalyst one Catalyst with a low rhodium content results, which overall has a better effect than a commercial catalyst with nine times the amount of rhodium. See in particular Figs. 15, 16, 19 and 20 and Table VI.

(G? W%) 0.0025 YT 5 6 (J3ew%) 0 ^ 046 0.019 0.0025 BLACKBOARD (#) * 46 Hours accelerated
high volume velocity 0.045 0.047 Conversion after 39
Poisoning tests with_ (%) ** 56 2 55 26 Sample "1 . (%) ** 56 0.0020 54 27 Hh 0.041 54 27 Pt 56 HC 37 CO 37 NO ₃

* with a stoichiometric air / fuel ratio

** at the CO / NO crossover point (air / fuel ratio, if the NO and CO conversions are the same; Fig. 6-12. Here there is a good correlation with the exhaust gas analysis by the Buttdesprüfungsvorschrift von 1975 ETSA) ₄

809885/0829

- hl -

2830688

In particular, the results of an equilibrium dynamometer test with a converter with a volume of 4261 cm ³ , which was loaded with 1.0263 g (= 0.033 toz) of platinum and O, OZf976 g of rhodium (= 0.0016 toz), showed the effectiveness of a commercially available one Catalyst with 1.3062 g (= 0.0 / f2 toz) platinum and 0.05598g (= 0.018 toz) rhodium under the same conditions. The tests were performed with a 5.7 liter Chevrolet V-8 engine at 1800 rpm, hl kPa intake pressure without EGR and an exhaust gas flow rate of approximately 100,000 cmr / s at 560 ° C and 1 atm. carried out. For the activity test, the air / fuel ratio was kept at set values, the system was stabilized and the CO-NO and hydrocarbon conversions were determined.

The air / fuel ratio was used for the aging process continuously increased from 13 »7 to 15 over 20 seconds and lowered again to the old value by moving the starter auxiliary plate (choke plate) with an electric motor.

A converter with 1000 cnr content was used, which is compatible with

1 D

high volume velocity of about 130,000 h at 22 C and 1 atm. Was operated. This had the advantage that the conversions were reduced from approximately 100% at low volume velocities to a readily measurable range, so that the differences between the catalysts were more pronounced and easier to observe.

The inlet temperature into the converter was between 560 and 570 ° C. The outlet temperatures varied between about 580 ° C and 630 ° C, depending on the conversion rate on the catalyst, whereby the amount of heat generated was determined. The composition the fuels used are shown in Table VII.

98 8 5/0829

⁴⁸ "2830688

17JEL - VII Toxic content of the fuels used

Brennst, a 77 ff ort.

Pb _(e / -l) 0.029 00045 ₁ O

P (g / 1) 0.007 0.00005

β (g / -l) 0 _f 117 0.080

Fuel a contained greater proportions of phosphorus and lead than the typical approved fuels (77 cert.). Since the Time scale of catalyst poisoning experiments based on poison values in the inflow of the catalyst corresponded to fuel a poisoning approximately 80,000 km (48,000 miles) about ^ O hours.

Table VIII shows the effects of poisoning on the respective catalyst samples.

BLACKBOARD

Aging condition
and catalyst analyzes after aging

Probe-Con- BreQn- Integrals through- Integr. Through hon.:. Y,

num- verstoff duration cut. poisoning. poisoning. indring

.Here * ^e ? tUDgsaufnahme - depths

pie (cm3) 1 _ (P weight% Pb weight 6 Γ (JW) Pb (iijn 1 1000 a 39 h. 0 ^ 31 0.06 23 3 ^ 0 2 1000 a 39 h 0 _T 20 O _f 25 20th 4.3 3 '1000 a 39 h. 0 _T 26 0 ^ 25 16 2.7 5 1000 a 39 ti O ₁ IS 11 4th 4261 77
Cert 80,000
km 0 _n !; 5 0 _T 10 6th 1000 a 39 Ix 0.17 0 _r 14 ₈₎ 5 5.8 7th 1000 a 39 h. 0.21 0 _t 15 15th 2.2

809885/0829

When checking the effectiveness curves and Table VI, the catalyst represented by sample 2 proves to be the one that gives the most favorable overall effect over a distance of 80,000 km (if8,000 miles), as represented by 1 + Q test hours. A comparison of Figures 15 and 16 shows that Sample 2 outperforms Sample 1 on the lean side of the stoichiometric air / fuel ratio for hydrocarbon conversion while the two samples are comparable for NO and CO-IT conversion. In this regard, commercial, non-layered catalysts drop sharply in their CO conversion efficiency after about 20 hours of accelerated aging have been reached. As is to be expected and can be seen in iig, 19 and 20, the two commercially available catalyst samples 5 and 6 have the best NO-Tlmw and treatment effect when fresh; this is due to the fact that the rhodium is present in the maximum amount on the surface. As is also to be expected, Sample 5 performs better than Sample 6 because of the considerably higher rhodium content. Note that Sample 4, the layered catalyst with rhodium as the outer or first layer, is essentially as good as the commercial catalyst Sample 5 in nitric oxide conversion after poisoning, even though Sample 5 contains nine times as much rhodium. Although Sample 2, the preferred catalyst, performs worse than Samples 3, kt 5, and 6 in nitric oxide conversion, it is its overall efficiency that is important here and in that regard Sample 2 has better conversion properties on the efficiency curves and Table VI; Here it was important to create a three-way catalytic converter.

As already mentioned at the beginning, the analyzer according to the invention within a narrow air / fuel ratio range in the area of the stoichiometric point, which is

809885/0829

ratio of rf, 65 is located, work. A comparison of the conversion efficiencies for Samples 1-7 is given in Figures 15-21. These curves show the percentages of hydrocarbon, CO and NO conversion at various air / fuel ratios and provide an overview of the effectiveness at actual operating conditions that include a change in the air / fuel ratio around the stoichiometric point. As can be seen, the inventive catalyst samples 1 and 2 outperform the commercial catalysts in essentially the entire air / fuel ratio range. Similar results are shown in Fig. 22, which shows a comparison of the nitric oxide conversion efficiency during ifO hours for Samples 1 to L ± at an air / fuel ratio of 13.8. The overall effectiveness of Samples 1 and 2 is much better than that of Samples 3 and 1 ±; sample 3 in. the arrangement of the catalyst material corresponds to the commercially available samples 5 and 6, d.ii. sample 3 is unlayered and the greatest concentration of both platinum and rhodium is on the surface.

From the foregoing description and from the drawings it can be seen that a layered catalyst having a first Line containing platinum and an outer layer containing a larger proportion of the Ehodiums in the catalyst inner layer gives improved three-way efficiency when operated close to the stoichiometric point. Other Embodiments according to the invention are therefrom for the person skilled in the art easy to remove, i.e. both layers can be closer to the surface, for example.

«09885/0829

Claims (16)

Patent claims: 1. Process for the preparation of a noble metal catalyst with an alumina support, characterized in that the support is coated with a solution containing platinum is soaked in order to form a first layer of platinum on it, which extends from the surface through the body of the wearer extends inwardly to a depth required that the support is then coated with a solution of a catalytically active Material is impregnated, the material being selected from the group consisting of rhodium and palladium, to arrange a second layer adjacent to the first layer, the catalytically active material of the second Layer is at least one of the materials whose catalytic effectiveness for converting vehicle exhaust gases is known and which have a greater susceptibility to poisoning in such exhaust gases than platinum that active sites on the carrier from its surface over the impregnation depth 9885/0829 MAN1T7 · FINSTERWALD · HEYN - MORGAN · 8000 MUNICH 22 ■ ROBERT-KOCH-STRASSE 1 · TEL. (089) 2242 11 ■ TELEX 05-29672 PATMF MANITZ FINSTERWALD ^H = ™ _M ™) ™ ^ 0 STUTTGART50 (BAD CANNSTATT) · SEELBERGSTR. 23/25 TEL. (07 11) 567261 ORIGINAL INSPECTED the first layer by treating the support with one of hydrogen chloride, hydrogen fluoride, sulfur and Citric acid existing group selected acid are blocked, each acid having the ability to block the has active sites in the carrier and is present in sufficient quantity to provide the active sites to the required extent Depth of the platinum layer and block the acid either with the solution of the catalytically active material of the second layer combined for cooperative application on the wearer or on the wearer prior to impregnation with "the" Solution of the catalytically active material is used that the carrier to remove the acid after impregnation with the solution forming the second layer is baked out, if the impregnation with the platinum solution after the acid treatment takes place that the carrier is burned (calcined) with the first layer thereon, if the impregnation with the platinum-containing solution takes place before the acid treatment and that the carrier with thereon first and second layers of platinum or of the catalytically active material are dried and fired (calcined), whereby the resulting catalyst improved conversion efficiency and has greater resistance to poisoning and thermal deterioration. 2. A method for the preparation of a noble metal catalyst, characterized in that the catalyst has a Layered catalyst with an aluminum oxide carrier comprises that the carrier with one of the group consisting of hydrogen chloride, hydrogen fluoride, Sulfuric and citric acid existing group selected acid is treated to active sites in the To block carrier from the surface over a depth required for soaking with platinum, that the amount of acid so is dimensioned that the required blocked depth results that the carrier with a solution at least one 809885/0829 that of the group consisting of rhodium and palladium selected materials is soaked to a second To form a layer within the support body, which consists of a catalytically active material that is Poisoning in vehicle exhaust is more prone than platinum that the carrier is heated to drive off the acid that the support is impregnated with a platinum solution to remove a first layer of catalyst material from the Surface of the support inward to form the depth required for the first layer and that the soaked Catalyst carrier to form a catalyst with improved effectiveness and greater resistance to poisoning and baking (sintering), drying and firing (calcining), the second layer being catalytically active material of the first layer of platinum is adjacent and the amounts of the catalytically active material so large are as necessary to achieve the required catalytic activity. 3. Method of preparing a noble metal catalyst according to claim 2, characterized in that that the acid blocking the active sites with the solution of the catalytically active material for the second . Layer for simultaneous treatment of the support is mixed. k. A method of preparing a noble metal catalyst according to claim 2, characterized in that the acid is hydrofluoric acid. 5 .. Process for the preparation of a noble metal catalyst according to claim 3 »characterized in that that the solution for simultaneous treatment hydrofluoric acid in an aqueous solution of a palladium compound. ". ■ 809885/0829 - * "2830888 6. A method for the preparation of a noble metal catalyst according to claim 3 »characterized in that that the solution for the simultaneous treatment of hydrofluoric acid in an aqueous solution of a rhodium compound contains. 7. A method for the preparation of a noble metal catalyst with an aluminum oxide support, characterized in that the support with an aqueous solution a soluble platinum salt is soaked to the platinum salt in a first layer with a required depth to deposit, the layer starting on the outer surface of the wearer and penetrating into the wearer's body, that the carrier is dried and calcined to decompose the salt, that the carrier with one of the acid selected from the group consisting of hydrochloric, hydrofluoric, sulfuric and citric acids wherein the selected acid has the ability to block active sites in the carrier and the amount of acid sufficient to block the bodies from the surface of the support beyond the depth of the platinum salt soaked layer to achieve that the carrier with a solution of a soluble salt at least one of the catalytically active materials selected from the group consisting of rhodium and palladium is impregnated to the Salt to be deposited in a second layer within the support body, adjacent to the platinum layer, this being catalytically active material of the second layer is present in the first layer with the minimum concentration to the largest Use of the poisoning resistance of the platinum layer against poisoning by lead, phosphorus and sulfur and that the impregnated catalyst carrier to form a catalyst with improved conversion efficiency and improved Resistance to poisoning and caking (sintering) is dried and fired (calcined). 809885/0829 8 «Method for the preparation of a noble metal catalyst according to claim 7> characterized in that for blocking the active sites of the carrier the acid used is hydrofluoric acid. 9. A method for the preparation of a noble metal catalyst according to claim 7, characterized in that the joint impregnation is effected using an aqueous solution of a palladium compound containing hydrofluoric acid. 10. A method for the preparation of a noble metal catalyst according to claim 7 »characterized in that that the joint impregnation using a hydrofluoric acid-containing aqueous solution of a Rhodium compound is effected. 11. Process for the preparation of a noble metal catalyst according to claim 7, characterized in that the carrier prior to impregnation with the second layer forming solution is impregnated with the acid. 12. Precious metal catalyst, characterized in that that the catalyst comprises a layered catalyst that it consists of an alumina support that the latter has a first layer of platinum, the platinum penetrating into the body of the carrier on the surface is arranged and that it has a second inner layer of rhodium or palladium, which is adjacent to the first layer in the wearer's body to beyond the first layer Located depth is arranged, the greater proportion of the total amount of rhodium or palladium on the catalyst is located in the inner layer to have the greatest advantage 809885 / 0.829 to draw part of the poison resistance of platinum to poisoning by lead, phosphorus and sulfur, and that the Amounts of platinum and rhodium or palladium on the support are sufficient to achieve the required catalytic effect are sized. 13. noble metal catalyst according to claim 12, characterized in that g e k e η η draws that the depth of the platinum layer of the penetration depth of the toxins in vehicle exhaust during the required Lifetime of the catalyst. 1if. Noble metal catalyst according to Claim 12 or 13, characterized in that the total depth of the first and second layers is at least II9 Lass . 15. noble metal catalyst according to one of claims 12 to I4, characterized in that the catalytically active material is palladium. 16. Noble metal catalyst according to one of claims 12 to \ h _ti, characterized in that the catalytically active material is rhodium in a low total amount of 0.002 Ge wt%. 809885/0829