DE2227877A1 - PROCESS FOR THE CATALYTIC REDUCTION OF NITROGEN OXIDES IN EXHAUST GASES - Google Patents

Description

Kali-Chemie Hanover, June 7, 1972

Aktiengesellschaft Z 3-PA / MH / U1

Patent application

Process for the catalytic reduction of

Nitrogen oxides in exhaust gases

The present invention relates to a method for reducing nitrogen oxides in car exhaust gases with high levels of carbon monoxide and Hydrogen content while avoiding ammonia formation in catalytic two-bed reactors.

Since it has not yet been possible to find a catalyst for the thermodynamically possible decomposition reaction of nitrogen oxides, which in addition to carbon monoxide and unburned hydrocarbons contribute significantly to environmental pollution, which accelerates the reaction rate so that, given the short residence time of the exhaust gases in the exhaust gas cleaning system of the motor vehicle, a sufficient reduction the nitrogen oxide content could be determined, it was proposed to carry out the catalytic car exhaust gas cleaning in two catalyst beds (RMCampau "Low Emission Concept Vehicles ¹¹ , SAE Paper Sp. 361 (1971) No. 710 294), the nitrogen oxides being reduced in the first catalyst bed under a lack of oxygen and after The addition of air in the second catalyst bed oxidizes carbon monoxide and hydrocarbons.

Known catalysts, such as the oxides of copper, copper / chromium, nickel and iron on Al ₂ O / SiO ₂ as carriers, which reduce the nitrogen oxides by the reducing components present in the exhaust gases, carbon monoxide, hydrogen and various

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Accelerate hydrocarbons enough, quite generally the disadvantage of always forming more or less ammonia in addition to nitrogen due to the presence of hydrogen, since the Nitrogen oxide on the catalytic converter usually reacts almost exclusively with the hydrogen and over a wide temperature range is reduced to a considerable extent to ammonia (Shelef c.s. Ind.Eng.Chem.Prod.Res.DeV.ΓΙ, 1972, pp. 2-11). The education the ammonia is highly undesirable because in the subsequent oxidation catalyst part after the addition of secondary air in addition to Combustion of carbon monoxide and hydrocarbons too the ammonia is oxidized, with the formation of nitrogen oxides again in some cases.

The formation of ammonia depends on the composition of the exhaust gas and is favored by high carbon monoxide and hydrogen contents, whereby the hydrogen primarily present in the exhaust gas, caused by the cracking of hydrocarbons in the engine, the reaction is more strongly influenced than that caused by the so-called water gas reaction of carbon monoxide and water vapor on the surface of the catalyst formed hydrogen content.

In this context is the ratio of what is present in the exhaust gas Residual oxygen to the amount of carbon monoxide and hydrogen is of particular importance. If the ratio Op / CO + Hg at the equivalence point according to the reaction equations

CO + 1/2 O ₂ = CO ₂ H ₂ + 1/2 O ₂ = H ₂ O

equals 0.5 »for example with a CO content of 4.5% by volume, an Hg content of 0.5% by volume and an Og content of 0.1% by volume the ratio of 0.02.

Our own studies have shown that in the optimal working range with the known catalysts at Og / co + Hg ratios between 0.00 and 0.10 the most unfavorable results can be achieved, since the ammonia formation reaches a maximum here and only falls above this ratio to values that

309881/0598 " ⁵ ~

satisfactory results of NO elimination in the catalytic Ensure double bed installation.

However, Oo / CO + Hg ratios between 0.00 and 0.10 are used in often occur in practice, as it is not always possible for design reasons to determine the exhaust gas composition in certain Change operating phases by engine measures so that the most favorable working range of the catalytic converter is achieved.

Space velocity is another criterion for ammonia formation When using known catalysts, the ammonia content of the converted nitrogen oxides increases with increasing Space velocity, as our own experiments have shown. However, high space velocities are advantageous, since the required converter then has a smaller dimension and mass can, so it takes up less space and is heated more quickly to reaction temperature.

A method for the catalytic reduction of nitrogen oxides in exhaust gases with high carbon monoxide and hydrogen and low residual oxygen contents has now been found, which is carried out at high space velocities with extensive suppression of ammonia formation, and which is characterized in that the exhaust gases under reducing conditions with a Catalyst are brought into contact, which contains a maximum of 0.5 wt .-% ruthenium in combination with rhodium and / or platinum ^{on a support annealed at at least 1000 0 C.}

The ruthenium and the rhodium and / or platinum content of the catalyst can vary between 0.001 and 0.5 _s wt .-%, and preferably 0.005 to 0.05 wt .-% on a highly heat-resistant support. The ratio of ruthenium to rhodium or platinum is advantageously set between 1: 3 and 1: 0.15. The combination of ruthenium, rhodium, platinum is preferably used in a ratio of 1: 1: 3 to 1: 0.15: 0.15. This catalyst does not experience any loss of activity if it alternates under

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_ 4 -

oxidizing and reducing conditions is operated. It eliminates nitrogen oxides in a reducing atmosphere in a wide temperature range between 300 and 1000 C at space velocities of up to 200,000 v / vh almost quantitatively and largely suppresses the formation of ammonia even at 0 _D / C0 + Ho ratios between 0.00 and 0.10. In addition, this catalyst eliminates carbon monoxide and hydrocarbons in an oxidizing atmosphere in the same temperature range.

For producing the ruthenium / rhodium or ruthenium / platinum or ruthenium / platinum / rhodium catalyst according to the invention carriers made of aluminum oxides or aluminosilicates are suitable, leading to moldings of high heat resistance and abrasion resistance are processed. It is advantageous to have the sodium oxide content below 0.1% and the content of anions such as Cl 'or

keep j below 0.2 fo.

Before processing to catalysts, the support material is annealed for 10 to 120 minutes between 1000 ° and 1500 ⁰ C.

Honeycomb bodies or bodies made of corrugated ceramics, which are made of refractory materials such as cordierite, β-spodumene, mullite, ^ - Al ₂ O or combinations of these substances and are optionally coated with aluminum oxide, are also suitable as supports.

The carrier material is after annealing with salts of ruthenium and rhodium and / or platinum in a joint solution or also impregnated separately. The impregnation can be acidic or ammoniacal Solution to be carried out. Ammonium hexachlororuthenate is the preferred salt in acidic solution or the hydrate of ruthenium (III) chloride and rhodium nitrate and / or hexachloroplatinic acid are used, while in ammoniacal Solution the ruthenium hexammine hydroxide and rhodium hexammine hydroxide and / or platinum tetrammine hydroxide can be used.

It has proved advantageous to reduce the catalyst before use, after being dried at temperatures between 100 ° and 200 ⁰ C and in an inert or oxidizing

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Atmosphere at 700 ° to 900 ⁰ C was annealed. The reduction can be carried out in a stream of hydrogen at 400 ° to 600 ° C. or in an aqueous hydrazine hydrate solution.

The inventive ruthenium / rhodium or ruthenium / platinum or ruthenium / rhodium / platinum catalyst can also be used in the cleaning of nitrogen oxide-containing exhaust gases from industrial plants and furnaces are used.

example 1

An aluminum hydroxide, which consists essentially of pseudoboehmite with proportions of amorphous hydroxide and whose Na ₂ O content is 0.01% and anions 0.02 % , is dried, ground, in a known manner to give extrusions of 2.5 mm Deformed diameter or balls of 2 to k mm diameter and then annealed with a gradual increase in temperature for 15 minutes in the rotary kiln at 1150 ° C.

In the first stage, the moldings are impregnated with a solution of rhodium (III) nitrate which contains so much rhodium that the catalyst has 0.02 percent by weight rhodium after drying at 120.degree. C. and calcining at 800.degree. In the second stage, the catalyst is impregnated with a solution of ammonium hexachlororuthenate, the concentration of which is set so that the ruthenium uptake, based on the finished catalyst, is 0.02 percent by weight. After renewed drying at 120 ^° C., annealing at 800 ^° C. and reduction in a hydrogen stream at 500 ^° C., the finished catalyst no. 1 contains 0.02 percent by weight of rhodium and 0.02 percent by weight of ruthenium.

Catalysts 2 to k are produced by the same process, only the amount and concentration of the impregnation solutions being varied so that the finished catalysts have the rhodium and ruthenium contents listed in Table 1 below.

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Table 1

Catalyst content of

No. . Ru (wt%) Rh (wt%)

1 0.020 0.020

2 0.020 0.010

3 0.020 0.005 k 0.030 0.005

Example 2

Catalyst Nos. 5 and 6 each contain 0.02 percent by weight Ruthenium and 0.01 percent by weight rhodium. They are only produced in a manner analogous to that described in Example 1 with the difference that the impregnation is not done by soaking twice, but by soaking once with a Solution containing both a rhodium and a ruthenium compound is made.

The impregnation solution for catalyst no. 5 contains rhodium (III) nitrate and ammonium chlororuthenate, those for Catalyst No. 6 ruthenium hexammine hydroxide and rhodium hexammine hydroxide.

Example 3

The preparation of the catalyst no. 2, as described in Example 1 was repeated, except that has been annealed as a carrier, an alumina with a SiOg content of 3%, the 1 hour in muffle furnace at 1150 ⁰ C, is used. The Na 2 O content of the carrier is 0.3 percent by weight and the anions 0.2 percent by weight.

The finished catalyst # 7 contains 0.02 percent by weight Ruthenium and 0.01 percent by weight rhodium.

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222787?

Example 4

80 parts of aluminum hydroxide are mixed with 20 parts of a kaolinite clay, shaped in a known manner and, after drying, calcined with a gradual increase in temperature for 30 minutes at 1300 ° C. in a muffle furnace. The carrier contains 0.2 percent by weight Na ₂ O and 0.2 percent by weight anions. The impregnation and subsequent treatment are carried out as described in Example 1 for catalyst no. The finished catalyst # 8 contains 0.02 percent by weight ruthenium and 0.01 percent by weight rhodium.

Example 5

Instead of the carrier mentioned in Example 1, a honeycomb body made of a cordierite composition is used, which is coated with active aluminum oxide. The aluminum oxide contains 0.01 percent by weight Na ₂ O and 0.015 ^ anions. The pretreatment, impregnation, drying, calcination and reduction are carried out according to Example 1, catalyst no. 3, so that the finished catalyst no. 9 contains 0.02 percent by weight of ruthenium and 0.005 percent by weight of rhodium.

Example 6

Instead of the carrier mentioned in Example 1, a honeycomb body is used used from a cordierite composition. The pretreatment, impregnation, drying, annealing and reduction takes place according to example 1, catalyst no. 3, so that the finished catalyst no. 10 0.02 percent by weight ruthenium and 0.005 percent by weight Contains rhodium.

Example 7

The carrier mentioned in Example 1 is made according to the same procedure prepared, whereby instead of impregnation with rhodium nitrate solution, an impregnation with platinum tetrammine hydroxide solution

309881/0598 " ⁸ "

takes place so that the finished catalyst no. 11, after drying at 120 ^° C. and annealing at 800 ^° C., contains 0.02 percent by weight ruthenium and 0.02 percent by weight platinum.

The preparation of the catalysts No. 12-14 takes place after
same process, only the amounts and concentrations of the impregnation solutions being varied, so that the finished catalysts are those listed in Table 2 below
Have contents of ruthenium and platinum.

Table 2

catalyst
No. salary
Ru (wt%) at
Pt (wt%) 11 0.02 0.020 12th 0.02 0.010 13th 0.02 0.005 Ik 0.03 0.005

Example 8

The preparation of the catalyst is carried out in accordance with Example 2, in place of the Rhodiumhexamminhydroxidlösung a solution of Platintetramminhydroxid is used so that the final catalyst no. 15 after drying at 120 ° C, annealing at 800 ⁰ C and reduction in a hydrogen stream at 500 ° C 0 .02 percent by weight ruthenium and 0.01 percent by weight platinum.

Example 9

The support materials mentioned in Examples 3 and k are treated according to the procedure described in the relevant examples, the impregnation taking place according to Example 7, catalyst 12, so that the finished catalysts
Nos. 16 and No. 17 after drying at 120 ° C, annealing at 800 ⁰ C.

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and reduction in a hydrogen stream at 50O ⁰ C have 0.02 percent by weight ruthenium and 0.01 percent by weight platinum.

Example 10

The honeycomb supports mentioned in Examples 5 and 6 are prepared according to the same procedure, but instead of being impregnated with rhodium nitrate solution, they are impregnated with titanium tetrammine hydroxide solution, so that the finished catalysts No. 18 and No. 19 after drying at 120 ° C., annealing at 800 ⁰ C and reduction in the hydrogen stream at 500 ⁰ C contain 0.02 percent by weight ruthenium and 0.005 percent by weight platinum.

Example 11

A honeycomb body made of a cordierite composition coated with active aluminum oxide is impregnated in the first stage with a solution of rhodium (III) nitrate which contains enough rhodium that the catalyst, after drying at 120 ° ^{C. and annealing at 800 °} C., is 0.005 Has percent rhodium by weight. In the second stage, the honeycomb body is impregnated with a solution of platinum tetrammine hydroxide, the concentration of which is set so that the platinum uptake, based on the finished catalyst, is 0.005 percent by weight of platinum. After renewed drying at 120 ° C. and annealing at 800 ° C., the honeycomb body is impregnated in the third stage with a solution of ammonium hexachlororuthenate that contains so much ruthenium that the ruthenium uptake, based on the finished catalyst, is 0.03 percent by weight. After further drying at 120 ^° C., annealing at 800 ^° C. and reduction with hydrazine hydrate solution and final ^{drying at 200 °} C., the finished catalyst no. 20 contains 0.03 percent by weight ruthenium, 0.005 percent by weight rhodium and 0.005 percent by weight platinum.

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309881/0598

Example 12

To test the reducing activity, those according to the examples Catalysts No. 1-20 manufactured 1-11 were tested with a gas mixture that has a car exhaust gas composition comes close.

It contained:

10 5 Vo 1.-7 " co ₂ lh Vo \ .-% H ₂ O k Vo1 .-% CO ο, 3 Vo 1 .-% H ₂ 500 ppm 1000 ppm NO 0-2, Vol.-fo ° 2 rest N "

The oxygen content was varied from 0 to 2.3 VoI .-% 0, "The v at space velocities of 50 000 and 200 000 / vh and temperatures between 500 ° and ⁰ 70o C results obtained are summarized in Table 3 below. This table also contains the results of the oxidation test, which was carried out under the following conditions.

The gas mixture contained either 1% by volume of CO, k % by volume of O ₂ and 95% by volume of N ₂ or 500 ppm of C ₅ H ₁₄ , k% of O ₂ and 95.95 % of N ₂ . At a space velocity of 50,000 v / vh, the gas stream prior to entry into the catalyst bed of Eaumtemperatur to 55O ⁰ C was heated and the conversion measured as a function of the temperature and recorded. The temperature required to convert 50% of the amount of CO or n-hexane used served as an activity index and is referred to as the half-value.

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Table 3/6

t 50,000 No. 11 NH ₃ - No. 12th No NO-Um .13 No.14 NH3- Number 1: NH ₃ - Temp. Room- Og / CO + I ^ NO-Um Bldg. NO-Um NH ₃ - sentence NH3- NO-Um Bldg. NO-Um 31dg. T ν / ν.h) sentence (ppm) sentence Bldg. (Vol.-96) BMg. sentence sentence (m> m) 700 ^u 50,000 0.00 (Vol.-96 *) 60 (Vol.-96) 94 (ppm) (Vol.-90 27 (Vol.-Sun) 35 0.02 94 30th 96 56 94 28 95 25th 96 28 0.05 95 30th 96 31 94 • 25 95 25th 96 28 0.07 95 30th 96 28 94 20th 95 14th 96 19th i * 0.10 95 28 96 28 94 20th 95 14th If 15th ö '0.15 95 17th 96 28 94 20th 95 10 06 10 39 x 0.25 95 15th 96 23 94 20th 95 3 Q6 1 '0.40 95 13th 96 20th 95 20th 95 0 97 1 -. * Ν 0.51 95 - 96 2 0 20th 95 - 97 - J. 200,000 0.00 0 58 0 - 89 - 0 23 O 30th e 0.02 91 42 90 40 90 18th 91 20th 91 30th »0.05 91 30th 90 35 90 15th 91 20th 91 28 0.07 91 19th 90 35 90 10 92 15th 91 25th 0.10 91 19th 90 27 90 11 92 10 92. - 25th 0.15 91 15th 90 27 90 10 92 5 92 20th 0.25 91 15th 91 19th 91 10 92 3 92 15th 0.40 91 8th 91 18th 91 9 92 1 92 ' 15th 0.51 91 - 92 18th 0 9 92 - 92 - .0 Hexane 0 - CO-HW - 0 Hexane O Hexane CO-HW * HW CO-HW Hexane Fexan CO-HW HIV CO-HlV HIV (° c) HW (° c) HlV ( ⁰ C) ( ⁰ C) (° C) 342 ° ( ⁰ C) (° c) 264 ° (° c) ( ⁰ O 368 ° (° c) } kb 224 ° 230 ° 345 ° 371 ° 261 ° 228 °

* Half value

ÖO

-it ··

Q) ι — Ι ι — I Q) X! OJ

t 1 = 0 r-i r-l CJ 1 a O IfN GN m in in O I ^s ·· CN ON Oil t-- O I. . O O in O O oi m m O tn I. O W. CQ pq Y P < in-er ¹ ON Oil •H GN GN I. O -T m Oil ON Oil -H I. Oil O 3 Xi * ^ - ' O O r- in O Vi P. (Tt N O O > · - "^ - •he O O O) in _t ■ · ■ . ' I.
O N ω P.
cj Q) > Γ t ^ - •H O IfN I ^ O •H Oil oi Oil Cl Oil Oil Oil OJ O Vi +3
EJ to -M I. bO »- f-l ON ON ON ON GN GN in ON ON ON ON GN ON GN H ON - ω "N Ό
. I. S. ^ o O ON £ Q U) «J m O ti) "N -" Ο oi O "ir O O ON m CO m CO m I. m O in a \ in O O CO O I. ON m ό O Pl mm tn ■ H CNGN C \ ■ H G\ I. m in-τ tn Oil -H tn • Η N H ft P < ^: • P.
«J a O O O O !
a Oil Q) Gn ■ H m P. I. ' in m tn m O) m O O O O O O O O O 1 bß -P (H GN ON ON ^; - * ON ON GN ON ON ON ON ON Vl tn ό rj
Oil O ^ - m mm m O I. O O m co in tn O) O I. ω V Vl 1 VO -i ¹ Oil ON GN I. VO • N ¹ Oil •H CN I. • Η Vl I. P. ON O ON U a 1Λ ■ H Vl I. Co " m CN O m P. I. Γ in in m [- ■ H m O O O m O O O O Cl -H O I.
O r-l ON ON ω ON ON GN -a * CN GN GNGN O GN Jn. _Ο O I. - •H I. tr.)] O O O m O I. O O m σ) m O I. Γ- Ά Oil •H . ^ * ON Ή 1 O CO m -H I. τ-ΐ V Ά ■ H t4 C-. G-. ■ H • I. ·· U I. in GN P. ^ r ρ •H m I. -ΐ ¹ O O O O •H τ ( • cH Ή O O GN C-. CN Cn CN m GN GN ON CN O O O VO 's O O m I. m in m O O tn I. -rl Ps O I. CT. -μ * f) I. Pj ■> -i H mm ■ · IP ₁ • N ^ CN ON ¹ H. Γ m m a m m O Cl m -H -H τ ~ λ -r-l ■ H Cl O .-H CN O O Cl ON CN GN CN GN O
κ.
■ - O Oil O C. C) O O •H ^ ⁵ O O O O •H r ¹ m O O O C. O O O O O O O O O O O O O d * O CVl - O O O IA

-vr-

ο ♦ Table 3/8 50,000 Number 1 6th NH ₃ No.17 NH ₃ Number 1 8th NH ₃ No. 1 c NH,
j ι -
'''Ico
-I No. 20 NH-, < % 30th
G3 * Half-ended NO-Um- Bldg. NO-Um- Bldg. NO-Um- Bldg. NO-Um- Bldg. NO-Um- Bldg. r sentence (ppm) sentence (ppm) sentence (ppm) sentence (ppm) sentence (ppm) r ~ Temp. Room- 0 ₉ / C0 + N ₉ (Vol.-96) 65 (Vol. %) 60 (Vol.-96! 37 (Vol.-96) 28 (Vol.-96) 16 O ^ \ speed 96 40 95 35 95 25th 95 25th 97 15th m
D. ^C) ? V / vh) 96 40 95 30th 95 20th 95 25th 97 15th / 00 ° 50,000 0.00 96 28 95 25th 95 20th 95 20th 97 10 0.02 96 25th 95 25th 95 20th 95 15th 97 10 co 0.05 96 20th 95 18th 95 20th 95 5 97 5 O 0.07 96 15th 95 10 96 15th 95 5 ' 97 ■ ο co 0.10 96 15th 95 5 96 10 95 5 97 2 OO 0.15 96 - 95 96 - 95 -. 97 __ NO 0.25 0 0. 0 0 0 NJ > ^ "" 0.40 50 45 28 20th 10 NJ O 0.51 91 45 91 30th 91 23 90 IS 93 10 CX cn 91 45 91 30th 01 18th 90 18th 93. 8th -J co 200,000 0.00 91 28 91 28 91 18th 90 15th ¹ 93 '. 8th Ou 0.02 91 20th 91 25th 91 18th 90 10 93 ^: 5 0.05 94 20th 91 25th 91 15th 90 10 93 '- 4th 0.07 91 10 91 IS 91 15th 90 8th 93 "3 0, 10 92 10 91 10 91 10 90 8th 93 3 0.15 92 - 91 - 91 91 - 92 - 0.25 0 Hexane 0 Hexane 0 Hexane 0 Hexane 0 Hexane 0.40 CO-HW * HW CO-HW HW CO-HW HW CO-HW HW CO-HIi HW 0.51 ( ⁰ O ( ⁰ O ( ⁰ O ( ⁰ O • ( ⁰ O 34S ° ( ⁰ C) 359 ° ( ⁰ O 344 ° ( ⁰ C) 358 ° ( ⁰ O 331 ° 235 ° 241 ° 228 ° 236 ° 249 °

The results show that in the temperature range leaking Engine exhaust between 500 and 700 C an almost complete reduction of nitrogen oxides occurs, with the formation of ammonia largely suppressed even in the range of low oxygen concentrations and high carbon monoxide and hydrogen contents will. A particular advantage of the catalyst according to the invention is its ability to operate at high space velocities to maintain its effectiveness up to 200,000 v / v.h, so that even under these conditions there is sufficient elimination of the nitrogen oxides originally present in the exhaust gas entry. This makes it possible to get by with small converters that require little space and are inexpensive Have warm-up characteristics.

The oxidation activity of the catalytic converters is also so good that it can also be activated in the cold start phase by adding secondary air can be operated as oxidation catalysts, which means that the reduction converter is heated to reaction temperature is accelerated significantly.

309 8-8 1/0598

Claims (8)

Claims 1. Process for the catalytic reduction of nitrogen oxides !! in exhaust gases with high carbon monoxide and hydrogen contents as well as low residual oxygen content at high space velocity, with extensive suppression of ammonia formation, characterized in that the exhaust gases are brought into contact under reducing conditions with a catalyst which is on a support ^{annealed at at least 1000 0} C at most each Contains 0.5 percent by weight ruthenium and rhodium and / or platinum. 2. The method according to claim 1, characterized in that the ratio of O ₀ : (00 + H ₀ ) in the exhaust gas is between 0.00 and 0.10. 3. The method according to claim 1 and 2, characterized in that the space velocity of the exhaust gases is in the range of 5 © 000 to * 200,000 h " ¹ . k. The method of claim 1, characterized in that the catalyst prior to use in a hydrogen stream at temperatures between 400 ° and 1000 ⁰ C, is preferably reduced at 400 ° to 600 ° C. 5. The method according to claim 1, characterized in that the catalyst prior to its use in aqueous hydrazine hydrate solution is reduced. 6. The method according to claim 1, characterized in that the catalyst ruthenium and rhodium or Pt in a ratio of 1: 3 contains up to 1: 0.15. 7. The method according to claim 1, characterized in that the catalyst ruthenium, rhodium and platinum in a ratio of 1: 1: 3 contains up to 1: 0.15: 0.15. 8. The method according to claim 1, characterized in that the Na ₀ O content of the catalyst support is below 0.1 % and of anions below 0.2 % . 309881/0598