DE2158877A1 - METHOD AND CATALYST FOR DETOXIFYING CAR EXHAUST GASES IN CATALYTIC TWO BED REACTORS - Google Patents

Description

Kali-Chemie Hanover, November 2, 1971

Stock corporation Z 3 - PA. M H / M e

Patent application

Process and catalyst for the detoxification of

Car exhaust in catalytic twin bed reactors

The toxins contained in car exhaust fumes carbon monoxide, hydrocarbons and nitrogen oxides contribute significantly to environmental pollution.

Processes for catalytic car exhaust gas cleaning are difficult to carry out, because after the addition of secondary air to the exhaust gas on an Oxydati onskatalysator Although carbon monoxide and hydrocarbons are oxidized, the nitrogen oxide content remains almost unchanged.

For the thermodynamically possible decomposition reaction of nitrogen oxides No catalyst has yet been found for nitrogen and oxygen which accelerates the reaction rate so that in the case of the short residence time of the exhaust gases in the exhaust system of the motor vehicle, a sufficient reduction in nitrogen oxides can be determined could.

In the work of R. M. Campau "Low Emission Concept Vehicles" SAE Paper Sp. 361 (1971) JNTr. 710 294 was therefore proposed that the carry out catalytic car exhaust gas cleaning in two catalyst beds, the nitrogen oxides in the first catalyst bed in the absence of oxygen

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ORIGINAL INSPECTED

reduced and after the addition of air in the second catalyst bed carbon oxide and hydrocarbons are oxidized.

Known catalysts that reduce nitrogen oxides by the reducing components present in the exhaust gases carbon monoxide, Accelerate hydrogen and various hydrocarbons sufficiently generally have the disadvantage that, in addition to nitrogen, due to the presence of hydrogen, there is always more or less ammonia to build.

The free hydrogen arises z. Partly by cracking the hydrocarbons, to a large extent, however, due to the so-called water gas reaction on the catalyst surface. Since it is known that 1 - 4% carbon monoxide and 13 - 14% water vapor are present in the car exhaust, in an equilibrium reaction of carbon monoxide and water vapor accelerated by the catalyst, equivalent amounts of carbon dioxide and hydrogen.

Now meet nitrogen oxide, carbon monoxide and hydrogen when there is a lack of oxygen In the exhaust gas on the catalytic converter, the nitrogen oxide reacts almost exclusively with the hydrogen and is in a wide range Temperature range significantly reduced to ammonia. The formation of ammonia is highly undesirable because in the subsequent oxidation catalyst part after the addition of secondary air in addition to the Combustion of the carbon monoxide and the hydrocarbons also oxidize the ammonia, whereby in some cases nitrogen oxides are formed again. This reaction only achieves a partial elimination of nitrogen oxides from the engine exhaust gases with the catalysts known to date, even with the double catalyst bed.

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Another disadvantage of the double catalyst bed system is that it is relative slow warming-up speed of the catalyst beds during a cold start, since the exothermicity occurring in the reduction bed is only slight is. On the other hand, the formation of nitrogen oxides in the engine in the cold start phase is of minor importance - so that in this period their implementation can be dispensed with.

There has now been a method of detoxifying car exhaust in catalytic Two-bed reactors found, with a reduction of nitrogen oxides in the first catalyst bed and an oxidation in the second catalyst bed the exhaust gases takes place, which is characterized in that the exhaust gases in the cold start phase by switching on secondary air to the ™ first catalyst bed are first brought into contact with a catalyst under oxidizing conditions, which is on a at at least 1000 C annealed carrier contains a maximum of 1 percent by weight of rhodium in combination with iridium or palladium and after Warming up of the reactor with switching of the secondary air to the second catalyst bed in the first bed under reducing conditions be brought into contact with the same catalyst and then with an oxidation catalyst.

By switching the secondary air to the first catalyst bed

in the cold start phase it is achieved that this acts as an oxidation catalyst ™

works and is therefore heated up as a result of the exothermic reactions.

After the optimum working temperature has been reached, the additional air switched to the second catalyst bed, the actual oxidation catalyst, so that reducing conditions in the first catalyst bed

to rule.

However, this procedure requires that the catalyst des first bed optimal oxidation and reduction properties in itself

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united. Catalysts of this type were not previously known since Operation in an oxidizing medium changed the catalysts in such a way that their reducing activity was irreversibly reduced.

A very effective catalyst has now been developed that is 0.001% to 1%, preferably 0.005 to 0.05% rhodium and 0.001% to 1%, preferably 0.005% to 0.05% iridium on a highly heat-resistant Includes carrier. The ratio of rhodium and iridium can vary within wide limits. Ratios of 2: 1 to 1: 2 have proven to be useful proven. This catalyst does not experience any loss of activity if it is operated alternately under oxidizing and reducing conditions will. It is also characterized by the fact that in the reduction the nitrogen oxides the ammonia formation is largely suppressed. One that is also sufficient for the conditions of the first catalyst bed The catalyst consists of a support that has been annealed at at least 1000 ° C and contains a maximum of 1 percent by weight each of palladium and rhodium. He is described in patent application P 21 40 852.

The he inventive rhodium / iridium catalyst and also the rhodium / Palladium catalysts eliminate nitrogen oxides in car exhaust while reducing Atmosphere in a wide temperature range from 200 to 1000 C completely, whereby the ammonia formation is so strongly suppressed is that it is between 0 and a maximum of 2% of the converted amount of nitrogen oxide. In addition, these catalysts eliminate in oxidizing Atmosphere in the same temperature range the carbon monoxide and the hydrocarbons. The catalytic converters are in alternating operation can be used under oxidizing and reducing conditions without affecting their activity and selectivity for both reactions will.

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For the production of the rhodium / iridium catalyst according to the invention Carriers made of aluminum oxides or Alumo silicates are suitable, the processed into moldings of high heat resistance and abrasion resistance will. Your sodium oxide content should be below 0.1% and the content of Anions such as Cl 'or SO "are below 0.2%.

Before being processed into catalysts, the carrier material is 10 to Annealed for 120 minutes between 1000 and 1500 ° C.

Honeycomb bodies or corrugated ceramic bodies are also suitable as carriers, which consist of refractory materials such as cordierite, ß-spodumene, mullite, o (-Al O or combinations of these substances, and optionally are coated with aluminum oxide.

The carrier material is after annealing with salts of iridium and Rhodium in a joint solution or soaked separately. The impregnation can be carried out in an acidic or alkaline solution, with in the latter case, iridium hexammine hydroxide and rhodium hexammine hydroxide are preferably used as salts.

It has been found advantageous to use the first bed catalyst reduce after being at temperatures between about 100 and 200 C dried and in an inert or oxidizing atmosphere at 700 to 900 C. has been annealed. The reduction can be carried out in a hydrogen stream at 400 to 600.degree or in an aqueous hydrazine hydrochloride solution.

Oxidation catalysts are suitable for the second catalyst bed Based on platinum metals and base metal oxides. The rhodium / iridium catalyst according to the invention and that in FIG Patent application P 21 40 852 described rhodium / palladium catalyst.

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The rhodium / iridium catalyst according to the invention can of course even under steadily reducing conditions in car exhaust gas cleaning and also in the cleaning of nitrogen oxide-containing exhaust gases Industrial plants and furnaces are used.

example 1

An aluminum hydroxide that is essentially! made of pseudo-boehmite with parts consists of amorphous hydroxide, is dried, ground, in a known manner to extrusions of 2, 5 mm in diameter or Balls 2 to 4 mm in diameter are deformed and then under

gradually

annealed.

Gradual increase in temperature for 15 minutes in a rotary kiln at 1150 ° C

The moldings are impregnated in the first stage with a solution of rhodium (III) nitrate which contains so much rhodium that the Catalyst after drying at 120 ° C. and calcination at 800 ° C. 0.1 percent by weight Has rhodium. In the second stage, the catalyst is impregnated with a solution of iridium (IV) chloride hydrate Concentration is adjusted so that the iridium uptake, based on the finished catalyst, is 0.1%. After drying again at 120 ° C, annealing at 800 ° C and reduction in the hydrogen stream at 500 C, the finished catalyst no. 1 contains 0.1 percent by weight Rhodium and 0.1 weight percent iridium.

Catalysts 2 to 9 were prepared in the same way Method whereby only the amount and concentration of the impregnation solutions were varied so that the finished catalysts had the rhodium and iridium contents listed in Table 1 below.

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Table 1

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salary at Ir (wt%) Catalyst no. Rh (wt.%) 0.100 1 0.100 0.025 2 0, 025 0.005 3 0.005 0.001 4th 0.001 0.050 5 0.025 0.020 6th 0.010 0.025 7th 0.050 0.010 8th 0.020 0.005 G 0.010

Example 2

A carrier prepared according to Example 1 is impregnated with a solution containing as much rhodium nitrate and iridium (IV) chloride hydrate. includes, that the finished catalyst no. 10 after drying at 120 C, annealing at 800 ° C and reducing material in the water flow at 500 ° C 0 having 025 percent by weight of rhodium and 0, 025 percent by weight of iridium.

Example 3

A carrier produced according to Example 1 is coated with a rhodium-iridium solution impregnated that contains as much rhodium hexammine hydroxide

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and iridium hexammine hydroxide that the finished catalyst No. after drying at 120 ° C., annealing at 800 ° C. and reduction in a stream of hydrogen at 500 ° C, 0.025 percent by weight rhodium and 0.025 percent by weight Having iridium.

Example 4

An aluminum oxide is used in place of the carrier mentioned in Example 1 with an SiO content of 3%, which is used for 1 hour in the muffle furnace had been annealed at 1150 C. The impregnation and final treatment takes place according to Example 1, catalyst no. 2, so that the finished catalyst no. 12 is 0.025 percent by weight rhodium and 0.025 percent by weight Contains iridium.

Example 5

80 parts of aluminum hydroxide are mixed with 20 parts of a kaolinite clay mixed, shaped in a known manner and after drying with a gradual increase in temperature for 30 minutes at 1300 C in a muffle furnace annealed. The impregnation and subsequent treatment are carried out as described in Example 1 for catalyst # 2; the finished catalyst no. 13 contains 0.025 percent by weight rhodium and 0.025 percent by weight Iridium.

Example 6

Instead of the carrier mentioned in Example 1, a honeycomb body is used from a cordierite composition used with active aluminum oxide is coated. The impregnation, drying, and annealing

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Reduction is carried out according to Example 1, catalyst no. 9, so that the finished Catalyst # 14 0.01 weight percent rhodium and 0.005 weight percent Contains iridium.

Example 7

Instead of the carrier mentioned in Example 1, a honeycomb body is used used from a cordierite composition. The impregnation, drying, Annealing and reduction are carried out according to Example 1, catalyst no. 9, see above that the finished catalyst No. 15 0, 01 percent by weight rhodium and Contains 0.05 percent by weight iridium.

Example 8

To test the reducing activity, those according to Examples 1 1 to 7 prepared catalysts No. 1 to 15 and a catalyst No. 16 containing 0.05% rhodium and 0.025% palladium on a calcined at 1150 ° C Contains aluminum oxide carrier, tested with a gas mixture that is close to car exhaust in its composition. It contained

10 Vol.% ^CO 2 14th Vol.% H ₂ O 1 Vol.% CO 500 ppm ^C 6 ^H 14 500 ppm NO 0-0.6 Vol.% ° 2 rest ^N 2

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The oxygen content was varied between 0 and 0.6% by volume. the at a space velocity of 25,000 v / v. h and temperatures between 500 and 700 C are shown in Table 2. 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, 4% by volume of O and

95% by volume N or 500 ppm CH _1. , 4% O and 95, 95% N ₀ . At a

Ct O J-4 ■ Ct Ct

Space velocity of 25,000 v / v. h was the gas flow before entry heated in the catalyst bed from room temperature to 550 C and the conversion measured and recorded as a function of the temperature. The amount required to convert 50% of the amount of CO or n-hexane used required temperature served as the activity index and is referred to as half value.

The reduction and oxidation properties of all catalysts were Measured when fresh and after aging for 200 hours at 800 ° C. In order to provide evidence that the catalytic converters have their reduction properties even after operation in an oxidizing atmosphere do not lose, the aging took place alternately in an oxidizing and reducing atmosphere.

The results show that in the temperature range of engine exhaust gases between 500 and 700 C, the nitrogen oxides are completely removed while suppressing the formation of ammonia, so that practically the nitrogen oxide originally present in the exhaust gas is eliminated is. After aging for 200 hours at 800 ° C., which took place partly in an oxidizing and partly in a reducing atmosphere, there was no decrease in activity to be established. The oxidation activity of the rhodium / iridium or rhodium / palladium catalysts is sufficient to with the addition of secondary air, a rapid start of the reaction in the

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To ensure cold start phase, so that the converter in a short Time is heated to the optimal working temperature.

Particularly noteworthy is the fact that the catalysts use minimal concentrations of the noble metal components (up to 0.001 percent by weight) can still achieve full activity, something for the Economics of the process is of considerable importance.

The process according to the invention is also useful from a technical point of view considerable advantages, since the technically very complex and a higher one Exhaust gas recirculation causing fuel consumption is no longer required for the purpose of reducing the nitrogen oxide content.

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Table 2

'CO "• Ο

i Aging number 1 "" 3 No. ί NH ₃ No. 3 No.4 3 No. i ■ rf 3 No. 6th Temp. O ₂ NO PPmJ NO PPm] NO NH ₃ NO [ppmj NO ppm] NO NH ₅ ⁰ C Io fresh -ppm] 100 JPP ¹ IJ SO ΐΡΡώ] [ppm] Jjpm] 100 [PP.m] 70 LPPmj CPPf! 500 ° ο, ο 0 30th 0 20th 0 110 0 40 0 25th 0 70 0.2 0 7th 0 4th 0 35 0 5 0 π 0 14th 0.4 0 - 0 - 0 10 0 - 0 - 0 5 0.6 500 18th 500 15th 500 - 500 10 500 30th 500 - 700 ° 0.0 0 13th 0 12th 0 15th 10 14th 0 7th 0 45 0.2 ¹ O 3 0 2 0 15th 5 3 0 6th 0 20th 0.4 0 - 0 - 0 5 0 - 0 - 0 8th 0.6 200 h at 500 110 500 90 500 - 500 80 500 80 500 - 500 ° 0.0 800 ° G 0 30th 0 25th 0 90 0 15th 0 30th 0 80 0.2 0 9 0 4th 0 15th 0 2 0 3 0 35 0.4 0 - 0 - 0 5 0 - 0 - 0 3 0.6 500 12th 500 15th 500 - 500 4th 500 13th 500 - 700 ° 0.0 0 12th 0 10 0 12th 20th 0 0 10 0 15th 0.2 0 0 0 0 0 10 20th 0 0 10 0 10 0.4 0 - 0 - 0 0 10 - 0 - 0 10 0.6 500 Hexane 500 Hexane 500 - 500 Hexane 500 Hexane 500 - GO- HW * CO- HW * GO- Hexane CO- HW * CO- HW * CO- Hexane Shark HW * HW * HW * HW * HW * HW * HW * "value Pci Pci Co] C ⁰ Gj fresh 'E ° c ~ ] 381 402 f * \ I
\ J 1 ~ ° PDO L ° c3 449 il ° c] 397 pci Pc "" 200 h at
800 ⁰ G 197 " 400 205 413 ~ 223 419 281 464 203 412 208 405 201 223 242 445 304 218 232 419

* β half value

Table 2 (port setting)

Aging No.' 7th NH ₃ No. ί NH ₃ No. 9 No. 10 No. 11 No. 12th Temp. O ₂
⁰ C fo fresh NO 100 NO
Ppm] 100 NO NH ₃
[PPmJ NO NH ₃
[ppm] NO NH ₃
I]) Pm] NO [ppm] 500 ° ο, ο 0 48 0 50 0 120 0 100 0 90 10 60 0.2 0 3 0 8th 0 60 0 25th 0 40 5 25th 0.4 * 0 0 - 0 5 0 8th 0 12th 0 10 0.6 500 20th 500 17th 500 - 500 - 500 - 500 - 700 ° 0.0 0 5 0 6th 0 15th 0 15th 0 20th 5 15th 0.2 0 5 0 4th 0 5 0 8th 0 7th 5 10 0.4 0 - 0 - 0 3 0 5 0 0 0 5 0.6 200 h at - 120 500 120 500 - 500 - 500 - 500 500 ° 0.0 SOO ⁰ G 0 50 0 40 . 0 120 0 110 0 80 15th 55 0.2 '0 10 0 10 0 30th 0 30th 0 35 10 30th 0.4 0 - 0 - 0 5 0 5 0 15th 7th 10 0.6 ι 500 20th 500 25th 500 500 500 500 _ - 700 ° 0.0 0 12th 0 7th 0 20th 0 20th 0 18th 10 5 0.2 0 6th 0 6th 0 5 0 10 0 10 8th 5 • * o, 4 0 - 0 - 0 5 0 2 0 5 3 0 0.6 500 Hexane 500 Hexane 500 - 500 - 500 500 - GO- HW * CO- HW * CO- Hexar CO- Hexane CO- Hexar CO- Hexar HW * [° cC HW * Qo ₀ ZI HW * EW * HW * HW * HW * HW * SW * .sw * fresh [Μ 412 Pell 43 6 ~ pcj L ⁰ Q] ... Col, CqI Ed Fc] Cc] Co] 200 h at
SOO ⁰ G 209 420 210 451 "220 '417 206 401 205 403 209 412 221 229 236 438 221 414 227 412 228 430

* s half value

Table 2 (continued)

ca to ro

Aging No. 13th No. 14th No. 15th No. 16 Temp. O ₂ NO NH ₃ NO NH " NO NH ₃ NO NH ₃ ⁰ C % fresh [ppm] jfpPm / ^ ppmj / " ^pp m? / pPm / ^ pmj 500 ° ο, ο 15th 50 0 8th 0 50 0 90 0.2 10 • 30 0 2 0 8th 0 30th 0.4 0 10 0 1 0 1 0 0 ο ° ' ⁶ 500 - 500 - 500 - 500 - 700 0.0 10 20th 0 5 0 15th 20th 150 0.2 8th 10 0 3 0 10 20th 50 0.4 5 12th 0 0 0 2 20th 40 ο ° ' ⁶ 200 h at 500 - 500 - 500 - 500 - 500 0.0 800 ⁰ C 20th 30th 8th 10 0 55 0 80 0.2 12th 15th 5 2 0 7th 0 35 0.4 5 10 0 0 0 4th 0 5 ο ° ' ⁶ 500 - 500 500 - 500 .700 0.0 15th 10 0 5 0 20th 15th 50 0.2 12th 8th 0 5 0 8th 10 20th 0.4 8th 5 0 2 0 5 8th 13th 0.6 500 - 500 - 500 - 500 - CO- Hexane co- Hexane CO- Hexane CO- Hexane HW * mi * HW * HW * HW * HW * HW * fresh pc] [M L ⁰ J M. (° cj f ° c7 N 200 h at 210 414 218 422 220 419 19 ^ 388 800 ⁰ C 227 432 229 436 235 431 206 401

* = Half value

cn co oo

Claims (2)

Claims 1. Process for the detoxification of car exhaust gases in catalytic twin-bed reactors, wherein the nitrogen oxides are reduced in the first catalyst bed and the exhaust gases are oxidized in the second catalyst bed, characterized in that the exhaust gases through in the cold start phase Switching on secondary air to the first catalyst bed initially in contact with a catalyst under oxidizing conditions are brought, which is on a carrier annealed at at least 1000 C a maximum of 1 percent by weight of rhodium in combination with Contains iridium or palladium and after the reactor has been warmed up while switching the secondary air to the second catalyst bed Λ in the first bed under reducing conditions with the same catalyst and then with an oxidation catalyst in Be brought into contact. 2. The method according to claim 1, characterized in that the Catalyst of the first bed before use in a hydrogen stream at temperatures between 400 and 1000 C, preferably at 400 to 600 ° C. 3. The method according to claim 1, characterized in that the catalyst of the first bed is reduced in aqueous hydrazine hydrochloride A solution. 4. Catalyst for carrying out the process according to claim 1, characterized in that it consists of a 1000-1500 C annealed aluminum oxide support, which can also _{contain SiO 0} , and in each case 0.001 to 1, preferably 0.005 to 0.05 percent by weight of rhodium and iridium . 309822/0639 5. Catalyst according to claim 4, characterized in that the carrier consists of a refractory ceramic material which is optionally coated with aluminum oxide. 6. Catalyst according to claims 4 and 5, characterized in that that the catalyst rhodium and iridium in proportion Contains 2: 1 to 1: 2. 309822 / 0S39