DE2744868C3 - Catalyst carrier for car exhaust gas detoxification systems and processes for their production - Google Patents

Description

The present invention relates to a catalyst carrier and to a method for the same Production according to the preamble of claim 1 or that of claim 4.

In such a catalyst support, as it has become known from DE-OS 26 10 244, is as Main component of the porous, heat-resistant carrier material also uses «-aluminium oxide, that is crushed, mixed with a sintering agent, processed into grains that are sintered together Bearer surrender. However, like zirconium, cordierite or mullite, this material is adequate mechanical strength and thermal resistance and a correspondingly large average Pore diameter in order to enable rapid diffusion of the exhaust gases, however, it still has to be Proven to be of little use, because a catalyst with such a support material is lower because of it specific surface does not have sufficient exhaust gas detoxification properties, in particular what the As for initial rates of detoxification.

There are also catalyst supports made of a transition aluminum oxide, known as y-aluminum oxide, which has quite a high value in terms of specificity Surface area, but an extremely low value in terms of pore volume and especially the have average pore diameter. The disadvantage here is that the car exhaust with an extremely carried out at high speed and the reaction mainly near the surface of the catalyst takes place. In addition, these have catalyst supports

Ίο the disadvantage that, since the transition aluminum oxide ^{crystallizes at around 900 0} C and is mechanically very weak as a result, the catalyst carrier breaks, with the result that the catalyst characteristics are changed by vehicle vibration or thermal shock

r> stress significantly worsened, because the mechanical strength of the transition aluminum oxide falls in accordance with the hysteresis when it is exposed ^{to car exhaust fumes of around 1000 ° C.} It can then happen that the crumbled powder

■ 'blocked in the passage, reducing the output or a large reduction in the volume of the catalyst due to thermal contraction Forms exhaust gas passage which is not adapted to the purification reaction, thereby reducing the catalyst durability

■ i5 is significantly reduced.

Thus, the catalyst carrier made of transition alumina was used for cleaning or detoxifying Car exhaust is not always felt to be sufficient. This fact refutes the validity of the traditional

w) len conception that a catalyst support that has fine pores and accordingly has a large specific surface area in the detoxification of the Car exhaust brings the best performance or efficiency.

The object of the present invention is therefore to ! ion catalyst carrier for car exhaust gas detoxification systems to create of the type mentioned, which leads to a catalyst with improved detoxification

stocks leads

According to the invention, this object is achieved with regard to the catalyst support itself by the characteristics of the Claim 1 and with regard to the method for its production by in the characterizing part of claim 4 specified features solved.

The catalyst support according to the invention is not only mechanically and thermally very resistant, but also allows for improved detoxification, especially in the early stages, as he is with a optimal range of values of total pore volume, average pore diameter and more specific Surface is provided and because it is also loaded with an active aluminum oxide. that to the Pore inner surfaces of the carrier material is deposited.

From US-PS 34 37 605 a catalyst support for gas cleaning processes has become known, the loaded with alumina. However, the substrate of the carrier is neither a porous nor a heat-resistant one Material in the form of -aluminium oxide, but almost any other material. Also takes place loading with alumina in such a way that suspended in an organic solvent or Applied dispersed aluminum powder, which is then calcined in, for example, aluminum oxide is converted, which forms the actual catalyst carrier with or without a substrate and then with is impregnated with a catalyst metal. In contrast, the invention is a carrier material made of -aluminum oxide crushed and then by immersion in an aqueous solution of, for example, aluminum nitrate and subsequent drying, which process can be repeated, and a subsequent heat treatment loaded with, for example, ^ -alumina. r,

Further details and configurations of the invention can be found in the following description, in which the invention is described and explained in more detail with reference to the characteristic curves shown in the figures will. It shows 4 (1

Fig. 1 shows the relationship between the purification rate of HC and CO in the exhaust gas and the running distance or the Mileage as a comparison between a conventional catalyst and the catalyst according to the invention,

Fig. 2 shows the relationship between the average pore diameter and the HC cleaning start temperature in the case of a catalytic converter with a catalytic converter carrier according to an exemplary embodiment the present invention,

F i g. 3 the relationship between the total pore volume-> o lumen and the compressive strength of the catalyst support according to the invention,

F i g. 4 the relationship between the total pore volume and the HC cleaning start temperature in a catalyst with the catalyst support according to the invention,

Fig. 5 shows the relationship between the specific surface area and the HC cleaning start temperature in a catalyst with a catalyst support according to the invention and t> o

Fig. 6 shows the relationship between the specific surface area and the rate of volume decrease.

The catalyst support according to the present invention is, as described above, free from the disadvantages mentioned above and suitable for cleaning or detoxifying car exhaust gases. After considerable efforts in research and development, the optimal values for the total pore volume, the average pore diameter and the specific surface area for the catalyst support were found. These lead, in particular, to a catalyst carrier made of a porous, heat-resistant or high-temperature resistant material, such as aluminum oxide, zirconium, mullite or cordierite, preferably in particle form with a higher pore density in the core than near the surface exists, on whose inner pore surface active aluminum oxide is deposited or deposited and whose total pore volume is 0.05 to 0.50 cmVg, whose average pore diameter is 0.05 to 5.0 μm and whose specific surface area is 3 to 60 cm ² / g.

The catalyst carrier according to the present invention is characterized in a remarkable way from that its base material is mechanically strong and highly resistant at high temperatures, that it is provided with a large average pore diameter having a double structure with a deposited active aluminum oxide and large specific surface area on the pore inner surfaces possesses, and that by the multiple effect of the optimized total pore volume, average Pore diameter and specific surface area an unprecedented high performance exhaust gas detoxification achieved.

The catalyst support according to the invention is obtained as follows: the material, such as, for example, aluminum oxide, zirconium, mullite or cordierite or a compound which produces such a substance when heated or fired, is comminuted; _{at least one of SiO 2} , TiO ₂ , ZrO ₂ , CaO, MgO is used as a sintering agent from a total of less than 20% to preferably more than 80% of such a material. B ₂ O ₃ , MnO ₂ , Cr ₂ Oj and CuO added. This is done with a conventional organic materia! mixed, such as starch, polyvinyl alcohol, or water-soluble cellulose; the resulting thin slurry is dried in a spray dryer and turned into highly fluid granules; then these granules are molded into a desired shape and size in a press or an extruder. After drying, the molded product is fired at 1000 to 1650 ° C, resulting in a porous fabric that is resistant to high temperatures and forms the carrier. The average pore diameter and the total pore volume of the carrier material are brought to the prescribed values or to slightly larger values by controlling the particle size of the material, the type and added volume of the sintering agent and the firing conditions.

The carrier material obtained in this way is immersed in an aqueous solution of aluminum salt, the The process of dipping and drying is repeated until the specific surface area is in falls within a certain or prescribed range of values. This is followed by post-heat treatment and gradually the deposition of the active alumina on the inner surface of the pores results in that of the invention Catalyst carrier. The catalyst is obtained therefrom by, for example, the The effect of the immersion process is that the catalyst is held on the catalyst support. As a material that Provides alumina, any compound such as aluminum salts, e.g. B. aluminum nitrate or aluminum hydroxide, be used for this purpose, the one

is water-soluble or water-dispersible compound and at the same time by heat treatment aluminum oxide results.

In the catalyst reaction for exhaust gas detoxification, the CO purification can take place with relative ease and at a higher rate than the HC purification. Thus, the most important factor in detoxification is the initial temperature of HC cleaning, which is considered difficult to perform. For HC cleaning or detoxification, the lower the initial temperature, the better: however, as far as exhaust gas detoxification is concerned immediately after the engine has been started, a temperature of less than 260 ^° C. is desirable; this temperature of below 260 ^° C. is practicable. From Fig. 2. the average pore diameter of the catalyst support according to the present invention as a function of the HC cleaning initial temperature of a catalyst held by this support shows that the upper limit of the average pore diameter should be 5.0 μίτι. If the diameter is less than 5.0 μm, the HC cleaning start temperature is sufficient; in particular, the range from 0.08 to 0.35 μm is most preferred.

A carrier made of a conventional active alumina has an average Pore diameter of less than 0.05 μm. If such a carrier is designed in such a way, that he carries a noble metal as a catalyst by, for example, the immersion process, then one results Relationship between the pore structure and the cleaning performance of this catalyst, as shown in the Cases a, b is shown in Table 1. This relationship of the same noble metal catalyst, however on the carrier of the present invention having an average diameter in the range of 0.05 to 5.0 μιτι is held, has values as in the Cases c, d, e and f are shown in Table 1.

Tabel 1 Pore structure of the wearer More specific
Surface
inhall Life of the catalyst 73 lall By
more cut
l'oren-
diameter overall
porcnum volume (no / g) Cleaning rate (%)
HC CO 75 (/.■ml (cnrVg) 70 93 0.01 0.62 90 61 98 a 0.03 1.05 55 65 99 b 0.08 0.50 20th 82 90 C. 0.25 0.23 4th 95 d 1.20 0.12 11th 93 C. 3.50 0.30 84

The cleaning rate in Table 1 is a value obtained from 10 values of stationary simulated 30,000 km corresponding running distance was derived, which corresponds to a prescribed service life test pattern was carried out.

As can be seen from this table. the rate of purification of that catalyst drops that of conventional Carriers a. b is held. in the case of HC to about 60 ° o and in the case of CO to about 70%. In contrast is in cases c to f. in which a carrier according to the invention is used, both the HC and the CO purification performance always kept at the same high level, which is due to the excellent Indicates durability of the catalyst held by this carrier. The average pore diameter is so to a range of 0.05 to 5.0 μm or preferably 0.1 to 2.0 μίτι from the point of view of Durability and mechanical strength limited or limited

Like F i g. 3 shows, as the total pore volume increases, the carrier becomes more porous and consequently falls its strength decreases: but if the total pore volume exceeds 030 cm Vg, there is no deterioration in strength rapidly increasing. If, however, the total pore volume in the pore structure of the carrier

is brought less than 0.50 cmVg, the wearer can Maintain the fracture strength necessary for automobile emission control catalysts and is therefore practical applicable.

In Fig. 4 shows the total pore volume of the catalyst carrier according to the present invention as a function of the HC cleaning start temperature of a catalyst held on this carrier; from this, it can be seen that with a decrease in the total pore volume, the carrier becomes dense with loss of its porosity, and accordingly, with the decreased reactivity at low temperature, the HC purification starting temperature increases. If the total pore volume is close to 0.05 cmVg, then the HC cleaning start temperature reaches about 260 "C: if this volume is below 0.05 cmVg, the reactivity at low temperature is reduced, which makes the catalyst unsuitable for car exhaust gas cleaning For this reason, the total pore volume should be greater than 0.05 cmVg. Considering the cleaning performance and mechanical strength of the catalyst, the practical range of total pore volume for the catalyst carrier is preferably 0.05 to 0.50 cm ³ / g , or especially at 0.10 to 035 cm Vg.

5 shows the specific surface area of the catalyst carrier according to the present invention as a function of the HC cleaning start temperature of a catalyst held by this carrier. It follows from this that if the HC cleaning start temperature is to be below its practical value of 260 ^° C., then the specific surface area should be greater than 3 m ² / g; if the specific surface area exceeds 60 m ² / g, its mechanical strength is decreased and the possibility that it will be pulverized by vibration becomes greater, which is because of a large increase in the rate of reduction in volume, as shown in FIG. 6 shows is undesirable. From the point of view of catalyst performance and mechanical strength, the specific surface area should therefore be 3 to 60 m ² / g or preferably 10 to 30 m ² / g.

Since the above porous material is exposed to a reactive fluid having a high space velocity such as automobile exhaust and is used under severe shock and vibration, it must have a sufficiently high breaking strength as a support and at the same time have the ability to clean the catalyst near the outer surface; accordingly, for this purpose ^{it must preferably have a 2 r} > double structure, ie it must be thin near the outer surface and dense in the core so that the surface can have a large average pore diameter and a large total pore volume, while the core to maintain » \ the mechanical wedge can have low values in this regard.

The following are preparation examples of the invention Catalyst carrier described in detail: r>

100 ± 2% of the support materials listed in Table 2 are wet to 35 μm in a ball mill crushed. To 100 parts by weight of each crushed and dried material, 20 parts of starch, Crystal cellulose, the proportions of which are given in part C of the table, and 30 parts of water are added and in completely mixed in a kneading machine. The mixture is poured into a Column about 2.7 mm in diameter pressed, then with a roll granulator to 2.8 to 3.4 mm in size granulated, dried and calcined at a temperature according to Part C of the table for two hours. this then leads to the porous support pattern no. 1 to 10 of the Table 2.

It is also possible that the materials molded and fired at 1550 ⁰ C, which leads to compact Sjntcrprciiukteii. These products "were finely ground to a size of 1.4 to 2.0 mm. The granulate is mixed alternately with the above-mentioned comminuted and dried carrier materials and with a 5% aqueous solution of aluminum oxide so! In a roller granulating machine, resulting in grains of 2.8 to 3.4 mm in size The grains, after they have dried, are ^{fired at 1250 to 1400 °} C., resulting in Patterns Nos. 11-13 with double structure, i.e., dense in the core and thin near the surface (see Tab. 2).

3 1 each carrier material obtained in this way is heated to 50 to 55 ° C then 3 to 5 minutes nitrate in a saturated aqueous solution of aluminum b5 immersed heated to 55 to 6O ⁰ C and the solution is subjected to ultrasonic vibration The carrier material is ^{dried with a hot air jet from 90 to 100 °} C. for 10 to 15 minutes, immediately after it has been washed with water in a water jet for 2 to 3 seconds, while it is kept vibrating. The immersion-drying process is then repeated as often as is indicated in part C of Table 2, whereupon a heat treatment is carried out at 900 ^° C. for one hour, it being arranged within a mullite protective cover. This then leads to the catalyst carrier according to the present invention, in which the ^ -alumina generated by the decomposition of aluminum nitrate is burned and deposited on its pore inner surfaces.

The total pore volume and average pore diameter of each support material and the Carrier, with the y-aluminum oxide on the pore inner surfaces, were determined by the mercury printing process and the specific surface area by the BET method measured.

1 1 of each of these support materials then receives 1 g / l Pt as a catalyst by adding 2 to 3 Is immersed for minutes. The catalyst support in which 1 g / l Pt is kept on the support as a catalyst is obtained by pyrolysis for 1 hour at 900 ° C.

The initial cleaning rate was normal gasoline and the continuous cleaning rate of the catalysts obtained in this way measured from 10 values of a simulated constant run corresponding to 30,000 km; the results for samples 1 to 10 are given in Table 2. The rate of decrease in volume was also measured. the Values for the conventional transition alumina support, i.e. H. a, b in Table 1, are in Table 2 as Specimen 14 and 15 indicated. The continuous cleaning performance for pattern 1, i.e. for the Catalyst according to the present invention, and for example 14, i.e. H. for the conventional catalyst, is shown in Fig. 1.

The composition of the carrier thus obtained after immersion in aluminum nitrate and its Thermal decomposition is shown in Table 3, sample 1 being used as the test example.

An X-ray examination of the catalyst support shows the presence of ^ -alumina.

The fact that active alumina is deposited on the inner pore surfaces of the carrier has been revealed confirmed as follows, again using sample 1 as an investigation example: The Support material and the catalyst support, on the ^ -Alumina is deposited, are in one stainless container with a diameter of 50 mm and a height of 65 mm filled so far that the Container is 90% full with it. The specific surface area of the catalyst support, which one 1 hour wear resistance test with vertical vibration 5 G (at a vibration frequency of 1500 cpm and an amplitude of 4 mm) is shown in Table 4.

From these data in Table 4 it can be seen that γ-aluminum oxide on the inner pore surfaces of the Support material is deposited.

The amount of active alumina deposited is from 15 g (test example is sample 4) to 238 g (test example is sample 5) per 1 liter of carrier. The optimum amount of active alumina deposited is 60 to 140 g / l of carrier in terms of HC inlet cleaning temperature and mechanical strength.

IO

Table 2 (part Λ)

template
No. Carrier Motherhood Higmaflcn «-Alumina ^ -Alumina Ciesamt-
porcn
volume liruchfcsligkcit By
more cut
l'orcn-
penetrate density
ig / cnv ') {ate (%) core Kutalysalnrträgur-
^{| ::} .- 'shafts continuous Ciesaml-
porcn
volume description (7-aluminum oxide ("-Alumina (cnvVg) (kg / particle) (lim) vicinity
Oberlliiche initially permanent More specific
Surface
contents (cnvVg) «-Alumina > (Part B) 3.03 (cnr / g) Invention product «-Alumina 0.18 0.35 3.03 "> TO 0.15 1 «-Alumina 0.25 0.30 2.78 3.15 10 0.2! i Z. «-Alumina 0.15 0.35 3.15 3.44 7.5 0.14 3 «-Alumina 0.07 0.55 3.44 1.70 9 0.06 ,; 4th Zircon 0.54 0.06 1.70 2.71 3 0.50 ) 5 Mullite 0.27 0.25 2.71 2.75 58 0.23 6th Cordierite 0.14 1.2 2.75 2.96 27 0.12 j 7th «-Alumina 0.20 0.55 2.96 2.41 8th 0.18 8th «-Alumina 0.17 0.80 2.41 1.83 18th 0.15 ι 9 Mullite 0.28 4.8 1.83 3.75 15th 0.23 ι 10 Sales product 0.08 0.33 3.01 3.75 30th 0.06 Il 14th 0.10 0.08 2.87 2.81 10 0.08 I. 12th 15th 0.06 0.80 2.11 48 0.05 ί 13th Tabel . - 13th ΐ template
No. - - - - 0.62 - - 70 1.05 I. 90 I. Catalyst schools Cleansing facilities volume
acceptance*) Average
l'ore diameter CO cleaning oil Rate (%) ι
I. (, .m) 1 IC cleaning rate (%) at first

According to the product 0.35 31 1 0.30 23 2 0.35 31 3 0.54 34 4th 0.06 IC 5 0.25 21 6th 1.2 34 7th 0.55 25th 8th 0.80 35 9 4.8 20th 10 0.33 42 11th 0.08 46 12th 0.80 45 13th Product Sales I. 0.01 7th 14th 0.03 2.5 15th

97
97
96
89
95
97
95
95
93
87
93
96
93

95
96

94 93 86 83 93 89 84 84 85 85 87 85 86

73 75

95 96 95 87 95 96 90 92 90 86 90 94 91

90 93

93 90 83 80 89 85 80 81 82 82 80 83 81

61 65

13 30

') Volume decreaseitc

There is also volume in the stationary endurance test.

27 (Part C) 44 868 - Table 2 Crystal- Musler / ellulosc Sinlcr- To / iihl the No. Tcmperauir Repetitions of the back (Ciew .- "..> Remedial 3 Process 1 5 1300 2 2 3 1300 2 3 2 1300 2 4th 3 1300 1 5 3 1300 4th 6th 3 1250 3 7th 3 1300 2 8th 3 1400 3 9 3 1250 3 10 1250 3

Table 3

Al, O,

SiO,

Carrier material
Catalyst carrier

Table 4

98.15% 1.04 '· ,,

98.32 "/, 0.96%

Spe /.

wear and tear

OherllÜLhen content (nr '/ p) (41

Carrier material 2.0

Catalyst carrier 10

After the 9.8 wear strength test

2.3

As shown in Table 2 and F i g. I emerge, he suffers The catalyst of the present invention has a far less large deterioration in the purification rate

CiO MgO le.O; Κ, Ο / Na..O 0.04% 0.05'V ₁ , 0.03 "µ 0.17% 0.03% 0.04% 0.02% 0.15%

after an endurance test than the conventional catalyst. That way it is excellent Behavior of the catalyst according to the present invention with regard to its durability or service life proven. As for the mechanical strength, the product of the present invention exceeds with regard to the breaking strength considerably. Own it! also has a very low rate of volume decrease and is least exposed to cracking and surface abrasion.

The product according to the invention with such a large specific surface area of the catalyst support gave excellent results in the cold start test. as one of the points in the Auio exhaust measurement is prescribed.

ilier / ii (i sheet of drawings

Claims (5)

Patent claims: 1. Catalyst support for car exhaust gas detoxification systems, consisting of a porous, heat-resistant material, such as aluminum oxide, zirconium, mullite, cordierite, whereby a total pore volume of 0 is achieved by controlling the particle size of the support material, the type and added volume of the sintering agent and the firing conditions , 05-030 cmVg and an average pore diameter of 0.05-5.0 μm is achieved, characterized in that the grains produced from the finely ground carrier material after drying and firing at 1250-1400 ° C in a saturated aqueous solution of aluminum salt immersed, rinsed with water and dried, this process being repeated until a specific surface area of 3 - 60 m ² / g is reached, and after which the grains are heated in γ- aluminum oxide to convert the aluminum deposited on the inner surfaces of the pores . 2. Catalyst support according to claim 1, characterized in that the grains by mixing the finely ground carrier material with a solution j> can be made from alumina sol. 3. Catalyst support according to claim 1 or 2, characterized in that its specific Surface area is 10 to 30 i-2'g 4. Procedure for. . .- ■ serve as a catalyst carrier for car exhaust gas detoxification systems, consisting of a porous, heat-resistant material such as »-aluminium oxide, zirconium, mullite, cordierite, in which by controlling the particle size of the carrier material, the type and added volume of the sintering agent and the burning conditions a total pore volume of 0.05-0.50 cmVg and an average pore diameter of 0.05-5.0 μm is achieved, characterized in that the grains produced from the finely ground carrier material after drying and firing at 1250- HOO ⁰ C immersed in a saturated aqueous solution as aluminum salt, rinsed with water and dried, and this process is repeated until a specific surface area of 3 - 60 m ² / g has been reached, and then the grains for topping of the aluminum deposited on the pore inner surfaces are heated in j'-aluminum oxide. 5. The method according to claim 4, characterized in that the grains by mixing the finely ground carrier material can be produced with a solution of aluminum oxide sol.