DE102007043531A1 - New catalyst material comprising silver useful for the treatment of combustion exhausts gases, for catalytic conversion of carbon containing particle, and in the exhaust gas after treatment device - Google Patents

Abstract

Catalyst material for the treatment of combustion exhaust gases or catalytic conversion of carbon containing particles, is new, where the material comprises silver (5-90 mol.% relative to the total content of the catalytically active components). Independent claims are included for: (1) an exhaust gas after treatment device, preferably diesel particle filter or oxidation catalyst, comprising ceramic or metallic carrier coated with the catalyst material; and (2) a process for preparing the device comprising applying the catalyst material on a carrier, using sol-gel process.

Description

The The present invention relates to a catalyst material, an exhaust aftertreatment device and a method to their preparation according to the preamble of the independent Claims.

State of the art

For the post-treatment of combustion exhaust gases, which, for example in industrial processes or in engine combustion from Z. B. arise fossil fuels, catalysts are used. These serve to eliminate particulate as well gaseous or liquid components of the combustion gases.

About that In addition, for example, in the treatment of exhaust gases, which at A combustion of diesel fuel, so-called diesel particulate filter for use. In particular, with a diesel particulate filter Soot particles filtered out of the exhaust stream. Does the Diesel particulate filter on catalytically active components, so can at least in a regeneration phase of the diesel particulate filter separated soot particles oxidized and possibly unburned Hydrocarbons (HC) and carbon monoxide (CO) reacted with oxygen become. Ideally, the abovementioned exhaust gas ingredients become too Carbon dioxide and water oxidizes.

In particular, for a complete reduction of soot particles, specific requirements are to be placed on a corresponding catalytically active component of the exhaust gas particulate filter. For example, catalytically active metals such as, inter alia, platinum, palladium, vanadium or iron are used, which serve in particular to reduce the so-called Rußabbrandtemperatur. A device for exhaust aftertreatment, which has such a catalytic coating is, for example, from DE 196 30 250 C1 known.

Disclosure of the invention

Purpose and advantages of the invention

task The invention is a catalyst material and a device containing this ready for the aftertreatment of combustion exhaust gases to ask, with which the catalytic reaction in particular of carbonaceous particles can be improved.

These Task is by a catalyst material or a device containing it with the characterizing features of the independent ones Claims solved in an advantageous manner.

This is based in particular on the fact that the catalyst material is silver as a component. An appreciable content of silver in the catalyst material results in a comparison with other catalyst material compositions significant lowering of the temperature at which soot or carbonaceous particles to a significant extent thermally too Carbon dioxide or monoxide can be implemented. Especially the cold start behavior of diesel particulate filters is thereby improved, so that in this way an effective measure for Provide fulfillment of statutory environmental protection requirements lets z. B. to reduce the particulate pollution by Car exhaust fumes.

Next the lowering of Rußabbrandtemperatur is with the proposed Catalyst material also achieved that with the Rußabbrand temporarily connected temperature peaks comparatively low fail and can be damped. In order to may be the carrier material on which the catalyst material is applied, from heat-related damage Rußabbrand be protected.

Further advantageous embodiments of the present device emerge from the dependent claims.

So it is advantageous if the catalyst material in addition to silver at least another catalyst component such as preferably cerium, because in this way the catalytic conversion of carbonaceous Particles can be realized particularly effectively and a catalytic effective degradation effect z. B. also for non-particulate Combustion products such as unburned hydrocarbons or carbon monoxide can be achieved.

In a particularly preferred embodiment of the present invention, the catalyst material composition Ag _(45-65) Ce _(35-55) , since catalyst materials of said composition show a relatively significant reduction in the burning temperature of carbonaceous particles.

figure description

The Invention is based on the single shown in the drawing Figure explained in more detail. It shows

1 a plot of the relative mass loss of carbon black as a function of the prevailing ambient temperature for soot without catalytically active admixtures and for mixtures of carbon black with selected catalyst materials.

The The invention is based on a catalyst material for treatment of combustion gases, the gaseous, liquid and / or solid pollutants. In this case, the catalyst material in particular for a thermal conversion of carbonaceous Particles at relatively low ambient temperatures trained on regular exhaust gas temperatures. The catalyst material is preferably on a ceramic support such as. Particles or fibers of alumina, silicon carbide, titanium dioxide or cordierite applied or on a metallic support, the example. Is made of a sintered metal. The catalyst material contains silver as an ingredient. In addition, can provided at least one further catalytically active component be, in particular Cer. The catalyst material contains silver to more than 5 and less than 90 mol%, preferably more than 30 and less than 80 mol% and especially more than 40 and less than 70 mole%, based on the total amount of catalytic active components in the catalyst material. Under catalyst components are in the meaning of the invention in addition to silver in principle in particular to understand the constituents of the catalyst material, which catalytically with respect to the degradation of combustion products are effective and in particular the thermal conversion of exhaust components catalyze. These are usually not as support materials or as filling or supporting materials in the catalytic Layer used substances that no or almost no catalytic Have function.

Regularly Silver is in the finished state of the catalyst material exist as an oxide, but it is also conceivable that silver or further catalytically active components of the catalyst material in elemental form or as alloys, mixed oxides or in the form of complex compounds.

Preferably is the catalyst material formed as a binary compound, the next silver with a share of more than 5 and less than Contains 90 mol% as further catalytically active component cerium.

For checking the catalytic function of corresponding silver and cerium containing Catalyst materials was the thermal conversion of carbon black for Catalyst materials of different compositions experimentally checked. These were comparative experiments based on a differential thermal analysis (DTA), wherein the respective catalyst materials mixed with carbon black in a ratio of 1: 4 and synthetic air containing 20% by volume of oxygen and 80 vol.% of nitrogen were exposed. It was starting heated from room temperature to a temperature of about 700 ° C. The heating rate was 10 Kelvin per minute; the volume flow Synthetic air was adjusted to about 100 milliliters per minute.

To assess the catalytic effect of the different catalyst components in particular the temperature is determined in addition to the entire curve to complete combustion of the soot, in which a mass loss of the carbon black compared to the Ausgangsrußmenge of 50% is observed. The following Table 1 shows the measured temperatures T ₅₀ in ° C for pure carbon black or the individual investigated mixtures of carbon black with different, silver and cerium-containing catalyst materials. As a reference, a sample was measured containing soot without catalytically active additives. Table 1 Ag (mol%) Ce (mol%) T ₅₀ (° C) 5 95 488.66 10 90 443.01 15 85 445.08 25 75 445.97 30 70 455.01 35 65 442.26 40 60 448.27 45 55 436.74 50 50 421.82 55 45 432.93 60 40 410.66 65 35 423.86 70 30 441.94 75 25 445.97 80 20 429.09 90 10 465.67 95 5 482.15 soot 607

It is recognizable that containing binary, silver and cerium Catalyst materials in all according to the above table experimentally recorded mixing ratios to a noticeable reduction of the respective soot oxidation temperature to lead. However, this applies in particular to catalyst materials, the silver in a proportion of more than 5 and less than 90 mol% and cerium in a proportion of 10 to 95 mol% and in particular Measures for catalyst materials containing silver too more than 30 and less than 80 mol% and especially more than 40 mole% and less than 70 mole%.

1 shows a plot of the relative mass loss of carbon black depending on the prevailing ambient temperature and the catalyst material used. The test conditions correspond to the abovementioned conditions for the determination of the measurement results listed in Table 1. The starting amount of carbon black or carbon black / catalyst mixture corresponds to an ordinate value of 1. In the graph according to 1 the reference temperatures T ₅₀ in ° C are to be determined by the intersections of the individual measuring curves with an ordinate value of 0.5. This shows curve 1 the thermal behavior of pure soot, curve 2 the thermal behavior of a carbon black sample containing a catalyst material of composition Ag ₅₀ Ce ₅₀ and curve 3 the thermal behavior of a carbon black sample containing a catalyst material of composition Ag ₆₀ Ce ₄₀ .

Below are listed in Table 2, the temperatures determined T ₅₀ in ° C for pure carbon black or for the individual investigated mixtures of carbon black with said different catalyst materials. Table 2 connection type measured connection T T ₅₀ [° C] soot 607 Ag _(45-65) Ce _(35-55) Ag ₅₀ Ce ₅₀ 422 Ag _(45-65) Ce _(35-55) Ag ₆₀ Ce ₄₀ 411

According to a further essential aspect of the invention, a method for producing a Catalyst material proposed on a support, in particular for one of the catalyst materials listed above, which is characterized in that a sol-gel process for forming the catalyst components is used on the support. With a so-called sol-gel process, in particular metallic materials z. B. in the form of complex compounds are homogeneously distributed on a surface structure. A doping of ceramic materials with catalytically active components can also be achieved in this way. Thus, for example, by thermolytic decomposition of metal complexes or by treating them in an oxygen plasma fumed metal oxide or metal particles can be produced, which can be used inter alia as heterogeneous catalyst materials. They are characterized by very small, homogeneously distributed and non-agglomerated particles, a narrow particle size distribution and a very variable degree of loading.

When Complex compounds are particularly suitable soluble organometallic Compounds such as metal alkoxides, alcoholates or propionates, which for example, by a condensation step under water or Alcohol elimination to form a gel. Becomes an alcoholic solution hydrolyzable alcoholates of polyvalent metal ions on a surface applied, so it forms in the presence of moisture already during the evaporation of the solvent at room temperature Metal hydroxide network out. This is hydrophilic and antistatic. When increasing the temperature to, for example, 400 to about 800 ° C. The metal hydroxides react with dehydration to metal oxides and the coated surface becomes very stable mechanically. An advantage of the sol-gel process is that z. B. good ceramic or metal oxide coatings can produce, for example, with ceramic fibers, particles or ceramic carrier can coat.

In an alternative method, a representation based on a metal salt solution of corresponding metal nitrates, acetates, citrates or carbonates take place. The solutions will be evaporated and then at temperatures of about 400 calcined to about 800 ° C, with the corresponding anions thermally decomposed and the corresponding metal oxides are formed.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• - DE 19630250 C1 [0004]

Claims (8)

Catalyst material for the treatment of combustion exhaust gases or for the catalytic conversion of carbonaceous particles, characterized in that the catalyst material based on the total content of catalytically active components contains more than 5 and less than 90 mol% of silver. Catalyst material according to claim 1, characterized in that the catalyst material is a binary mixed oxide Catalyst material according to claim 2, characterized in that that the catalyst material in addition to silver as a second component Contains cerium. Catalyst material according to any one of claims 1 to 3, characterized in that the catalyst material based on the total content of catalytically active components more than Contains 35 and less than 75 mol% of silver. Catalyst material according to claim 4, characterized in that the catalyst material is a binary mixed oxide of composition Ag _(45-65) Ce _(35-55) . Exhaust after-treatment device, in particular diesel particulate filter or oxidation catalyst, characterized by one with a Catalyst material according to one of the preceding Claims coated ceramic or metallic carrier. Method for producing an exhaust aftertreatment device according to claim 6, characterized in that the catalyst material Applied to the carrier by means of a sol-gel process becomes. Method according to claim 7, characterized in that that as starting materials of the sol-gel process alcoholates a catalytically active component can be used.