DE2233187A1 - EMISSION DETOXIFICATION CATALYST - Google Patents

Description

The invention relates to exhaust gas decontamination catalysts for internal combustion engines. - ■

The problems of air pollution are not new as such, but in recent years air pollution has become one assumed ever greater proportions. A significant part of air pollution comes from the exhaust gases from internal combustion engines and consists of unburned or partially burned hydrocarbons and nitrogen oxides. When acting of sunlight a measurable amount of ozone is created from the nitrogen oxides by a photolysis reaction, which in turn with numerous organic compounds from the exhaust gases reacts to form more or less toxic compounds, which the Cause of health damage from smog such as eye irritation; or deterioration in eyesight and plant

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Injuries are. The toxic carbon monoxide also comes from it
mainly from exhaust gases.

Numerous devices and filters with catalytically active compounds have already been proposed for detoxifying the exhaust gases, but none of them work completely satisfactorily. A particular difficulty lies in the fact that most cleaning systems are effective initially, but then after a short time
Operating time lose their catalytic activity and become useless as a result.

To detoxify the exhaust gases or to reduce the content of Hydrocarbons and carbon monoxide have proven to be the only useful method, the oxidation of the hydrocarbons to carbon dioxide and water and the oxidation of carbon monoxide to carbon dioxide. The nitrogen oxides contained in the exhaust gases NO are preferably reduced to elemental nitrogen. The exhaust gas decontamination catalyst must be the undesirable or toxic compounds in the exhaust gases can oxidize and reduce.

There are already numerous oxide reduction catalysts of different types chemical and physical structure known;

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in addition, the ability of numerous metals and metal oxides, either as a single compound or in combination, to found complete catalytic oxidation of hydrocarbons and carbon monoxide.

In order to effectively remove hydrocarbons and carbon monoxide from exhaust gases, a catalytic converter must become active within minutes of the engine being started and must maintain its efficiency during the various workloads of the engine. In addition, the problems which arise due to extremely high temperatures and which often arise when the contaminating compounds are oxidized must be solved, temperatures of 98O ⁰ C or above being detectable. The catalytic systems customary up to now cannot withstand prolonged exposure at these temperatures without thermal or thermochemical decomposition of the catalyst.

It is known that the catalytic activity is influenced to a considerable extent by the total surface area of the catalyst support, the total surface in turn being influenced by the temperature of the catalyst system. That Ratio of total surface area and temperature depends primarily on the chemical and physical properties of the

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Catalyst support material from. The previously common catalyst support materials such as silicon dioxide, silicon dioxide-aluminum oxide, aluminum oxide or clays do not have a particularly favorable ratio of total surface area to temperature, since these materials can be produced in catalytically active form with a large total surface area, but when exposed to temperatures of about 980 to 1095 ° C lose about 90% or more of their surface activity.

The invention is therefore based on the object of exhaust gas decontamination catalysts to develop that oxidize hydrocarbons and carbon monoxide and reduce nitrogen oxides from exhaust gases and which are thermally and chemically stable at the same time.

To solve the problem, exhaust gas decontamination catalysts are used to convert polluting compounds from the exhaust gases of internal combustion engines that have catalytically active components on a catalyst carrier for oxidizing Carbon monoxide and hydrocarbons and / or to reduce nitrogen oxides, proposed that are characterized sindj that they use a spinel as a catalyst support

p with a total surface area of 7 to 200 m / g.

The exhaust gas decontamination catalysts according to the invention therefore contain for the catalytic oxidation of carbon monoxide and carbon

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Hydrogen and / or compounds capable of reducing nitrogen oxides on a catalyst support made from a spinel with a total surface area of 7 to 20 O and preferably 20 to 120 m ² / g.

The spinel used as a catalyst support according to the invention, magnesium aluminate, has excellent physical properties and chemical stability and maintains even at elevated operating temperatures a large total surface.

The spinel can be used in particle form, as a monolithic structure or as a coating on a monolithic structure will. After impregnation with catalytically active compounds such as copper, chromium, manganese, Iron, cobalt, nickel, platinum and / or palladium have excellent thermal stability even at temperatures above 98O C. on. The spinels used according to the invention can be prepared according to the methods described in Italian patent specification No. 879 087 method described are prepared by adding magnesium aluminate MgAIpOj. by thermal decomposition of decomposable Salts, solutions of decomposable salts or aqueous ammoniacal slurries of the hydroxides or oxides in a jet mill operated at high temperature is obtained. By using the jet mill, the decomposable

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Compounds converted into magnesium aluminate, being in addition the otherwise usual expensive washing processes can be avoided. The rapid thermal decomposition in the jet mill results to an extensive elimination of volatile constituents without increasing the crystal size.

The spinels produced in this way can be cold-pressed after calcination and sintered to about 97 to 99% of the theoretical density, so that mechanically resistant moldings can be produced from the finely divided spinel powders. When produced from microcrystalline spinel powders, these shaped pieces made of spinel have a very fine grain size, excellent mechanical properties and excellent surface shaping.

The very small spinel crystallite size (only a few 100 Å such as 100 to 250 8) is achieved by the very rapid thermal treatment in the jet mill. The product obtained from the jet mill or after grinding in the jet mill with subsequent mild calcination consists of a magnesium aluminate MgAl ₃ O ₁ ^ present in a crystalline phase and not of MgAl ₂ O ^ Al ₂ O, + MgOj the purity of the product is explained from the homogeneous mixing of the feedstock and the instantaneous co-precipitation as soon as the mixed salt solution decomposes

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will. Since the compounds used to form the spinel are in a homogeneous mixture, the diffusion paths are very large short, so that there is no need for strong calcination for thermal diffusion to form the spinel phase.

To produce the spinels used according to the invention, suitable magnesium and aluminum compounds, namely mostly magnesium nitrates and aluminum nitrates, preferably Mg _{(NO,) p} «6H _p 0 and Al (NO,), 9H ₉ O are selected. However, suitable spinels can also be produced from other decomposable magnesium or aluminum salts or compounds, such as, for example, from magnesium formate, acetate or nitrite, aluminum formate, acetate or nitrite, or from hydroxides or hydrous oxides and from jointly precipitated hydroxides or oxides.

To produce a spinel from a stoichiometric magnesium aluminate, the ratio of MgOrAl ₂ O must be as close as possible to the value 1 (for example 1.00-0.01). These molar ratios are preferred for the production of ceramic moldings for use as a catalyst carrier, but molar ratios of about 0.95: 1 to 1.2: 1 can also be used, where particularly when using a molar excess of magnesium oxide, ver -

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reversible catalyst carrier for later impregnation Metal oxides are obtained. The composition of the input material depends on the type of final composition required, by generally dissolving magnesium nitrate and aluminum nitrate in water. These salts can be added by adding precipitated by ammonia as hydrous oxides and then fed into the jet mill. In these cases it will the pH of the slurry is adjusted to about 9-10.5. However, suitable spinels can also be produced if Magnesium nitrate hexahydrate and aluminum nitrate nonahydrate dry mixed in the appropriate amounts and the dry one Mixture is fed into the jet mill. During dry grinding of aluminum oxide trihydrate and magnesium nitrate hexahydrate a suitable spinel containing very small amounts of alumina is also obtained.

The solution, slurry or dry mixture of the starting compounds is then fed into the jet mill, the working temperature of which depends on the type of mill and the type desired Reaction depends. The jet mill can be operated in the presence of steam or air Presence of water vapor is the pressure of the fed

2 water vapor generally between about J >> 5 to 12.25 kg / cm

Overpressure.

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To produce the ceramic shaped pieces, the powder removed from the jet mill is calcined and sintered. The calcination is generally carried out at about 650 to 1,100 ^{° C. for one or two hours.} The calcined product is in the desired manner, as for example, into pellets, molded and then sintered one to two hours at temperatures of for example 50 to 1. ^ ⁰ 1.65O C.

The spinels used as catalyst supports according to the invention can be compressed, pelletized or, if appropriate, monolithic Structures can be formed or applied as a coating on monolithic structures.

The invention is explained in more detail below with the aid of the examples. All parts and percentages relate, if any not otherwise specified, based on weight.

example 1

This example shows the manufacture of a catalyst support suitable spinels.

30 parts of aluminum nitrate nonahydrate Al (NO,) - 9H ₃ O were dissolved in a vessel in HO parts of deionized water with stirring. In another vessel, 15 parts of magnesium nitrate

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- ίο -

Hexahydrate Mg (NO,) ,, '6H ₃ O dissolved in 13.5 parts of deionized water with stirring. The solutions were then mixed together in amounts such that a mixed nitrate solution was formed having a ratio of magnesia to alumina as determined by chemical analysis of 1.01: 1.

This nitrate solution was then fed at a rate of 150 g / min into a jet mill whose inlet temperature 750 C and the outlet temperature were 500 ⁰ C. The steam used as a grinding medium has been supplied to the mill during the grinding of a steam heater having a temperature of 83O ⁰ C so that during the grinding process, a pressure of 8.4 kg / cm gauge pressure prevailed. The nitrate solution momentarily decomposed in the jet mill to form a magnesium aluminate powder, which was collected in a permanently attached cyclone collector. The powder was then calcined at a temperature of 800 ^{° C. for three hours.} After calcination, this powder was found to be spinel with a total surface area of 80 m 2 / g when measured by the BET (Brunauer-Emmett-Teller) method.

Example 2

In this example, a different process for the production of a spinel powder suitable as a catalyst support is given.

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- ii -

A magnesium-aluminum-nitrate solution with a ratio of MgO: Al ₂ O of 1.01: 1.00 was prepared from analytically pure magnesium nitrate, aluminum oxide monohydrate and nitric acid. This solution was fed to a steam-operated (790 ⁰ C) Heat reactor outlet dessert * Ι00 ° Ο was. The pulverulent magnesium aluminate formed was collected in two separate containers according to the particle size and then separately calcined at a temperature of 800 ° C., after which total surface areas of 73 to 96 m / g could be determined. The X-ray diffraction spectra of the powder corresponded to those of the spinel MgAlpOh.

Example 3

Usable pellets were made from the spinel powder prepared in Example 2 as a catalyst support by the two powder fractions are mixed and blended with 2 wt.% Polyvinyl alcohol, 2 wt.% "Sterotex" and 6 wt.% Water and

2 were then pressed in a press with an excess pressure of about 7 kg / cm. The press cake was crushed and sieved. The fraction, which had an average size of about 0.2 to 0.119 mm, was used to produce pellets with a diameter of about 0.1 cm in a conventional granulating machine. ^{The pellets were heated to 76O 0} C to burn off the organic constituents and then showed a total surface area of 58 m 2 / g.

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Example 4

The procedure described in Example 3 was repeated, but the final calcination was carried out at 1.004 C and a granulated product with a total surface area of
28 m / g was obtained.

Example 5

Example 3 was again repeated, but the final calcination performed at about 1,107 ⁰ C and a granulating

2
tes product was obtained with a total surface area of 7 m / g,

Example 6

^ 3 * 09 β of the spinel pellets produced in Example 3 with a surface area of 58 m ^ / g were mixed with 16.5 ml of a solution containing 11.82 g of Cu (NO.) ₂ '3H ₂ O and 4.89 g CrO, in one
impregnated rotating mixer. The pellets were then dried at a temperature of 110 ° C. and then impregnated with a palladium tetrammine dinitrate solution containing 0.0101 g of palladium. The pellets were then initially dried at 110 ° C. and then at 200 ^° C. for several hours and finally
Calcined for three hours at 76O ° C. The finished catalyst
("Catalyst 1") had a content of 7.7 % CuO, 7.3 % Cr ₂ O and 0.02 % Pd on spinel pellets as a carrier.

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Example 7

16.09 g of Co (NO,) ₂ «6H ₂ 0 and 11.98 g of Ni (NO ₃ ) ^ oH ₂ O were dissolved in 22.3 ml of aqueous solution and then 40.68 g of the in example were impregnated twice 4 produced spinel pellets with a surface area of 28 m / g are used. The pellets were dried at 110 ° C. and then ^{impregnated with 1} J, 8 ml of a palladium tetrammine dinitrate solution containing 0.005 g of Pd per ml. After the final three-hour calcination at a temperature of 760 ° C., the catalyst ("catalyst 2") with spinel pellets as a carrier had a content of 8.6 % CoO, 6.4 % NiO and 0.02 % Pd.

Example 8

A monolith of cordierite from American Lava Company was coated with 15 wt.% Magnesium aluminate spinel MgAIpOj ,,. The coated monolith was immersed for 40 minutes in a platinum tetrammine dinitrate solution with a platinum content of 0.013 g Pt per ml. The monolith was then treated with compressed air to remove the excess solution and then dried in a moist state at a temperature of 65 ° C. in vacuo. The dried monolith was then reduced in a stream of hydrogen at 320 ° C. for 3 hours. This referred to as "catalyst 3" catalyst had a content of 0.5 wt.% To Platinrnetall.

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Example 9

The catalysts from Examples 6, 7 and 8 were run at various temperatures in a standard laboratory procedure on their effectiveness in converting carbon monoxide, hydrocarbons and nitrogen oxides into non-toxic products examined.

The test results are compiled in Table 1. It can be seen from the data that there is a high conversion in all cases of carbon monoxide, hydrocarbons (HC) and nitrogen oxides takes place.

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Table 1

Temperature in C when converted to %

O CO 00 CO catalyst

Throughput speed

t η

10 %

CO HC NO

50 %

CO HC NO

Catalyst 1 14,000 hours

-1

Catalyst 2 14,000 hours

Catalyst 3 26,000 hours

on Λ 90 %

CO HC NO

0.5 186 233 292 237 '307 346 362.478 422 0.5 199 228 271 265 295 311 341 286 362 2.0 237 240 ---. 259 269 287 309 -

Example 10

In this example, the stability of an exhaust gas decontamination catalyst investigated for internal combustion engines with spinel as a carrier.

According to the method described in Example 7, spinel ^{pellets 1} were impregnated with an aqueous nitrate solution containing cobalt, nickel and palladium. After three hours' calcination at 76o ° C the catalyst had Spinellpellets with as carrier a content of 8.6 wt.% CoO, 6.4 wt.% NiO and 0.02 wt.? Pd on.

The catalytic activity and the aging properties were examined by determining the activity of the fresh catalyst and the activity of the catalyst after 17.5 hours of operation simulated exhaust conditions were measured at a temperature of 790 ° C. From the following table 2 it can be seen that there is only a slight change in effectiveness:

Table 2

Catalytic activity of fresh and aged catalyst (14,000 h " ¹ , 0.5 % O ₂ )

Temperature in ° C when converting

10% 50 % 90 %

P_2 ίί2 Ü2 co HC no co hg no

Fresher

Catalyst 199 228 ? '[1 265 239 311 3 ¹ Il 342 362

aged

Catalyst 213 P ¹ Ii 277 283 302 322 351 342

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Claims (7)

Claims 1. Exhaust gas decontamination catalyst to remove pollutants Compounds from the exhaust gases of internal combustion engines, in which on a carrier for the oxidation of carbon monoxide and Hydrocarbons and / or capable of reducing nitrogen oxides, catalytically active components are thereby present characterized in that the carrier contains a spinel with a surface area of 7 to 200 m / g. 2. exhaust gas decontamination catalyst according to claim 1, characterized> characterized that the spinel is in particulate form. 3. exhaust gas decontamination catalyst according to claim 1, characterized in that that the spinel is present as a coating on a monolithic structure. H. Exhaust gas decontamination catalyst according to claim 1, characterized in that the spinel is in a monolithic form. 5. exhaust gas decontamination catalyst according to claim 1 to 4, characterized characterized in that the catalytically active components are oxides of copper, chromium, manganese, iron, cobalt and / or Nickel and / or platinum and / or palladium are included. 2098B6 / 1129 6. exhaust gas decontamination catalyst according to claim 1 to 5, characterized in that the spinel has a ratio of magnesium oxide to aluminum oxide of 0.95: l '~ to 1.2: 1. 7. Process for detoxifying exhaust gases from internal combustion engines, in which the exhaust gases are passed through a catalytic converter to remove the polluting compounds , characterized in that a catalyst according to claims 1 to 6 is used. si: kö 209886/1129 y