JPS5930459B2 - Catalyst for exhaust gas treatment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a catalyst for purifying exhaust gas from an internal combustion engine.

Catalytic converters are used to purify harmful components such as nitrogen oxides (NOx), hydrocarbons (HC), and carbon monoxide (CO) contained in the exhaust gas of internal combustion engines. is proposed.

Nitrogen oxides are treated by a reduction reaction, and hydrocarbons and carbon monoxide are treated by an oxidation reaction.Therefore, there is no suitable catalyst that can satisfy both reactions, so a combination of a reducing catalyst and an oxidizing catalyst is used. is common.

As a reducing catalyst, ruthenium is an excellent catalyst because it has the highest activity for purifying NOx in a reducing atmosphere, produces less ammonia due to reduction action, and has a high reduction rate to nitrogen, but it has poor oxidation performance against HClC0. is not enough.

Therefore, when a rich mixture is used as a warm-up measure during a cold start, an oxidizing performance catalyst such as platinum or palladium is used in combination with the above ruthenium to treat HC and CO that are contained in large amounts in the exhaust gas. ing.

Furthermore, when ruthenium is used in an oxidizing atmosphere, it changes into an oxide and evaporates, so as a countermeasure, it is known that oxides of alkaline earth metals and other base metals are used as stabilizers. It is being

Based on the above findings, a noble metal catalyst in which 0.1 to 3% of a noble metal such as platinum or palladium is supported on a support such as alumina, 35 to 60 mol% of ferric oxide, manganese dioxide,
A mixture of 65 to 40 mol% of a metal oxide selected from cupric oxide, chromium oxide, molybdenum oxide, etc. and a metal oxide sintered catalyst containing ruthenium and partially having a spinel structure has been proposed. (Unexamined Japanese Patent Publication No. 50-131
(See Publication No. 668).

However, in the catalyst proposed above, the stability of ruthenium is still insufficient, and the activity of ruthenium decreases due to the addition of a stabilizer, and furthermore, the addition of a noble metal catalyst such as platinum or palladium results in the nitrogen reduction of NOx, which is a characteristic of ruthenium. There are problems such as lowering the rate and producing ammonia.

The present inventors have completed this invention as a result of intensive research to solve the above problems.

That is, the present invention provides iron oxide containing an oxide of at least one metal selected from manganese, copper, cobalt, nickel, chromium, barium, calcium and magnesium for the total catalyst on a granular porous ceramic support. 0.5
~30% by weight in the inner layer, ruthenium 0.001~0
．． 5% by weight as an intermediate layer, platinum or palladium 0.00%
The catalyst for exhaust gas treatment is characterized in that each layer is sequentially impregnated and coated with 1 to 0.5% by weight of the outer layer.

The granular porous ceramic carrier used in this invention is
It is a porous material made of alumina, alumina-silica, mullite copillite, silicon carbide, etc., and its particle size is 2.
~3 mm is preferred.

The iron oxides that form the inner layer of this catalyst include manganese, copper,
It is a sintered body that is a mixture of an oxide of at least one metal selected from cobalt, nickel, chromium, barium, calcium, and magnesium and iron oxide, and partially has a spinel structure.

For sumo wrestlers, the ratio of the metal oxide such as manganese and iron oxide is preferably 20 to 70 mol% for the former and 80 to 30 mol% for the latter.

To support the inner layer on the carrier, the sufficiently dried carrier is immersed in an aqueous solution of the metal salt, and then
After drying at ℃, 600℃ in inert gas or air.
Firing is performed at ~1300°C.

The type of metal salt, the concentration of the aqueous solution, and the drying and firing conditions are appropriately selected so that the oxide crystals after firing partially have a spinel structure.

To coat the inner layer of ruthenium on the inner layer impregnated on the carrier, the carrier coated with the inner layer is immersed in an aqueous solution of a halide such as ruthenium chloride, or a water-soluble salt. After drying at 100-200℃, drying at 500-200℃ in a stream of inert gas or reducing gas.
Heat treatment is performed at 800°C.

□Then, the outer layer of platinum or palladium is impregnated onto the intermediate layer in the same manner as the impregnation coating of the intermediate layer described above.

The amount of each layer sequentially impregnated and coated on the carrier as described above is 0.5 to 30% by weight for the inner layer and 0.001 to 0.5% by weight for each of the intermediate layer and the outer layer, based on the total amount of catalyst. %,
Preferably it is 0.02 to 0.2% by weight.

If the content of the inner layer is less than 0.5% by weight, the ruthenium in the intermediate layer will not be sufficiently stabilized, and if it exceeds 30% by weight, the strength of the catalyst particles will be significantly reduced and they will be easily damaged.
In either case, the purification rate after the durability test decreases.

If the content of the intermediate layer is less than 0.001% by weight, the purification performance against NOx will be insufficient, and if it exceeds 0.5% by weight, the purification performance will not increase much and the cost will increase.

If the outer layer contains less than 0.001% by weight, the purification performance against hydrocarbons and carbon monoxide will be insufficient;
Even if it exceeds ruthenium, as with ruthenium, the purification performance will not increase much and the cost will increase.

The catalyst of the present invention has improved NOx purification performance in a reducing atmosphere and improved selective reduction rate from NOx to nitrogen, as well as improved HC and CO removal in an oxidizing atmosphere.
Purification performance has been improved.

What is noteworthy about this catalyst is that the NOx purification performance decreases little after the durability test, and it can be used for a long period of time.

Examples of the present invention will be described below.

In addition, parts and percentages in actual cases are expressed on a weight basis unless otherwise specified.

Example 1 Nitric acid No. 1? Iron (Fe (NO3) 2-6H20) and manganese nitrate (Mn (N03) 2 ・6 H20) were dissolved in deionized water to give 20% Fe (NOa) 2,
An aqueous solution was prepared so that the Mn (NOa) 2 content was 10%, and a sufficiently dried alumina granular carrier (particle size 3, filling specific gravity 0.70) was immersed in this aqueous solution, and the aqueous solution was sufficiently applied to the carrier. After infiltrating the carrier, the carrier was pulled up and heated to 150°C.
, dried for 4 hours, and then fired at 900° C. for 2 hours in a nitrogen stream.

After the above calcination treatment, the cooled carrier was heated to ruthenium chloride (R
After immersion in an aqueous solution of uC13) with a concentration of 0.5%,
Dry at 0°C for 2 hours, then dry at 600°C for 2 hours in a hydrogen stream.
A time reduction treatment was performed to form an intermediate layer.

Next, the carrier impregnated with the above intermediate layer was coated with chloroplatinic acid (
The outer layer was immersed in a solution of H2PtCl4.6H20) with a concentration of 0.52% and subjected to reduction treatment under the same conditions as the intermediate layer.

The inner layer of the obtained catalyst contains 0.9% Fe and 94% Mn.
An X-ray diffraction test confirmed that the intermediate layer was made of 05% RuO and the outer layer was made of 905% PiO, and that both Fe and Mn existed as oxides, and a part of them had a spinel structure. .

Example 2 In the same manner as in Example 1, except that palladium chloride (PdC12) was used instead of chloroplatinic acid in the outer layer in Example 1, Fe0.9%, Mn 0.4%,
A catalyst containing 0.05% Ru and 0.05% Pd was obtained.

Comparative Example 1 A carrier on which an internal layer of FeIMn was formed in the same manner as in Example 1 was impregnated with a mixed aqueous solution of ruthenium chloride and chloroplatinic acid to form a two-layer structure consisting of an internal layer of Fe and Mn and an external layer of a mixture of Ru1Pt. A catalyst was obtained.

Comparative Example 2 In Example 1, the order of coating Ru and PT was reversed to obtain a catalyst including an inner layer of Fe and Mn, an intermediate layer of Pt, and an outer layer of Ru.

Comparative Example 3 In Example 1, a catalyst with an inner layer of Ru, an intermediate layer of FeIMn, and an outer layer of Pt was obtained.

Comparative Example 4 In Example 1, a catalyst with an inner layer of Pt, an intermediate layer of FeIMn, and an outer layer of Ru was obtained.

Evaluation tests for the purification performance of NOx and HClC0 were conducted on each of the catalysts obtained in the above Examples and Comparative Examples using the method described below.

The components of the synthetic exhaust gas used in the test are shown in the table below.

NOx after passing through a catalyst with a bed volume of 24 cc at a space velocity where the volume of the synthetic exhaust gas per hour relative to the catalyst capacity was set to 40,000.

The purification rate was calculated by measuring the concentrations of HC and CO.

In order to evaluate the durability of the above catalyst, air and nitrogen gas containing 5% hydrogen were alternately introduced into the catalyst in a 900°C electric furnace in a 15 minute cycle for 12 hours. After this durability test, the catalyst was subjected to a performance evaluation test in the same manner as above.

The results of the above evaluation tests are shown in Tables 1, 2 and 3.

However, M in the inner, middle, and outer layer rows means FeMn.

Note that in Tables 1 and 2, the NOx purification rate in parentheses indicates the selective reduction rate to nitrogen (N2).

As can be seen in Table 1.2 above, compared to the Examples, what each Comparative Example has in common is that the NOx purification rate after the durability test is smaller than the NOx purification rate of the new product.

Comparative Examples 2 and 4 in which ruthenium was used as the outer layer had a low HClC0 purification rate at an air-fuel ratio of 14.0.

Furthermore, in Comparative Example 3, in which ruthenium is used as the inner layer, the NOx purification rate is particularly low.As shown in Table 3, the air-fuel ratio is 16. H in case of O
There is no significant difference in the C and CO purification rates between the Examples and Comparative Examples.

Example 3 FeO, 9%, Mn 0.4% in the inner layer of the catalyst of Example 1
Among them, Mn and Cu and Co in the same amount as Mn.

Ni, Cr, BaXCa or Mg was replaced with the inner layer, the same intermediate layer Rn0.05% and the outer layer Pt0 as in Example 1.
．． 05% and the performance evaluation test of these catalysts was conducted in the same manner as in Table 1 of Example 1. The purification rate (equity) after the durability test is shown in Table 4 below.

As shown in Table 4 above, Mn has the best purification rate after the durability test, but there is no big difference among other metals, and NO
x Purification rate is 70% or more.

Example 4 A performance evaluation test of the catalyst was conducted in the same manner as in Table 1 of Example 1 by changing the weight of the inner layer of Fe0.9% and Mn0.4% of the catalyst of Example 1, and the purification rate after the durability test was (%) is shown in the logarithmic graph of the drawing.

As seen in the drawings, the inner layer is 1-15% by weight of N.
Ox purification rate is 90% or more, and 0.5% by weight or 30%
If the weight % is exceeded, it rapidly becomes smaller than 70%.

[Brief explanation of drawings]

The drawing is a logarithmic graph showing the relationship between the amount of metal oxide in the inner layer and the purification rate after the durability test in Example 4.

Claims (1)

[Scope of Claims] 1. At least one of manganese, copper, cobalt, nickel, chromium, barium, calcium and magnesium, based on the total catalyst, on a granular porous ceramic support.
The inner layer contains 0.5 to 30% by weight of iron oxide containing oxides of various metals, and the intermediate layer contains 0.001 to 0.5% by weight of ruthenium. 1. A catalyst for exhaust gas treatment, characterized in that each outer layer is sequentially impregnated and coated with 0.001 to 0.5% by weight of platinum or palladium.