JPH07155604A - Exhaust gas purifying catalyst and method for producing the same - Google Patents

Abstract

(57) [Abstract] [Purpose] It has a high oxidizing activity against harmful components in exhaust gas emitted from internal combustion engines such as automobiles even in a low temperature range, and reduces cold HC emissions emitted immediately after engine startup. An exhaust gas purifying catalyst that can be obtained is obtained. [Configuration] formula _{Pd a Mn b Ce c X d} Y e O f ( at least one element wherein X is selected from the group consisting of potassium, rubidium, cesium and barium, Y is copper,
Magnesium, zinc, germanium, silicon, nickel,
At least one element selected from the group consisting of silver, chromium, lanthanum, strontium and zirconium, a represents weight% of palladium, and a = 0.01 to 3,
b, c, d, e, and f represent the atomic ratio of each element, and b = 1
When 0, c = 0.1-10, d = 0.01-5, e =
0.01 to 5 and f is the number of oxygen atoms required to satisfy the valences of the above components) and is composed of a multi-component composite oxide containing palladium, manganese and cerium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention purifies exhaust gas for purifying hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) in exhaust gas discharged from internal combustion engines such as automobiles. And a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as a catalyst for purifying exhaust gas emitted from an internal combustion engine of an automobile or the like, platinum (Pt) or palladium (Pd) in activated alumina, cerium oxide, etc.,
A structure in which a noble metal such as Rhodim (Rh) is carried and a monolith carrier is coated with this is used.
The catalyst is called a three-way catalyst because it can remove HC, CO and NOx at once. This catalyst is effective only when the internal combustion engine is operated under conditions near the stoichiometric air-fuel ratio (stoichiometric ratio).

[0003]

However, among the harmful components (HC, CO, NOx) in the exhaust gas, especially H
The catalytic purifying ability of C is strongly influenced by the exhaust gas temperature, and is generally purified by the above-mentioned precious metal catalyst at a temperature of 300 ° C. or higher. Therefore, when the exhaust gas temperature is low, such as immediately after the start of the engine, the HC is difficult to be purified by the catalyst. Moreover, a large amount of HC is discharged immediately after the engine is started, and the proportion of the cold HC in the entire hydrocarbon emission is large, and it has been a major problem to suppress the discharge of cold HC. Therefore, an object of the present invention is to provide an exhaust gas purifying catalyst having an excellent effect of suppressing the emission of cold HC immediately after the engine is started, and a method for producing the same.

[0004]

Means for Solving the Problems As a result of various studies to achieve the above object, the present inventor has developed a multi-component composite oxide catalyst containing palladium, manganese and cerium components,
It has been found that by coating a honeycomb carrier having a monolith structure with an exhaust gas purifying catalyst having a sufficient HC purifying ability from a low temperature to a high temperature, the present invention has been accomplished. The catalyst of the present invention have the general formula _{Pd a Mn b Ce c X d} Y e O f ( at least one element wherein X is selected from the group consisting of potassium, rubidium, cesium and barium, Y
Is at least one element selected from the group consisting of copper, magnesium, zinc, germanium, silicon, nickel, silver, chromium, lanthanum, strontium and zirconium, and a represents the weight% of palladium, and a = 0.01 to 3 And b, c, d, e and f represent the atomic ratio of each element,
When b = 10, c = 0.1-10, d = 0.01-
5, e = 0.01 to 5 and f is the number of oxygen atoms required to satisfy the valences of the above components), and a multi-component composite oxide containing palladium, manganese, and cerium. It is characterized by consisting of.

If a in the above general formula is less than 0.01, the performance of the catalyst is hardly exhibited, and even if it exceeds 3.0, the effect of palladium is saturated and no further effect can be obtained. When b = 10, when c is less than 0.1, the effect of combining manganese and cerium is small, and the value of T50 is deteriorated, and when it is more than 10, the purification ability of HC is lowered. Further, the values of d and e are set to 0.01 to 5 in consideration of the overall catalyst performance such as durability of the catalyst, but when d is larger than 5, the catalyst performance deteriorates.

Next, a method for producing the above catalyst of the present invention will be described. In producing the catalyst of the present invention, the metal constituting the catalyst, Pd, Mn, Ce, X and Y compounds are used as catalyst raw materials, and an aqueous solution or aqueous dispersion of these compounds is added with ammonium carbonate, ammonium hydrogen carbonate and It is preferable to add at least one compound selected from the group consisting of aqueous ammonia, remove water, and heat treat the residue. As the raw material compound for catalyst preparation, nitrate, carbonate, ammonium salt, acetate, halide of each element,
An oxide or the like can be used in combination. The method for preparing the catalyst is not limited to a special method, and various known methods such as a dry evaporation method, a precipitation method, and an impregnation method can be used as long as the components are not unevenly distributed. In carrying out the present invention, for example, a catalyst raw material containing manganese and cerium is dissolved or dispersed in water, and then X,
The catalyst raw material of Y is added. At this time, the catalyst raw materials may be added simultaneously or sequentially, or the catalyst raw materials may be separately dissolved and then mixed with these aqueous solutions.

The amount of ammonium carbonate, ammonium hydrogen carbonate and aqueous ammonia used is 1 of the total weight of the catalyst raw material.
-60% by weight, especially 5-50% by weight is preferred. On the other hand, when the mixture of raw salt is evaporated to dryness without adding ammonium carbonate, ammonium hydrogen carbonate and aqueous ammonia, the BET surface area of the obtained powder becomes small. BET
When the surface area is small, the dispersibility of palladium is deteriorated and the activity (T50) is deteriorated. In addition, technically, the synergistic effect existing between palladium and the base oxide (the effect of promoting the desorption of lattice oxygen of the base oxide by palladium) becomes small, and the effect of improving low temperature activity is also small. Become.

The base oxide impregnated with palladium is
Manganese oxide and cerium oxide as main components (however, Mn and Ce do not form a complex oxide), Mn and Ce
Is a mixture of Mn-based and Ce-based composite oxides in which a part of each is replaced with various components, and various oxides (single oxides or composite oxides) as necessary. Therefore, Mn and Ce
On the other hand, if the X and Y components are too much, a completely different oxide (presumably) is formed, or the characteristics of manganese oxide and cerium oxide are lost.

Then, water is removed from the catalyst raw material mixture and the residue is heat-treated to obtain the desired catalyst. The heat treatment is carried out in air and / or at a temperature of 300 to 800 ° C., for example.
Alternatively, it is preferably carried out under air circulation. This heat treatment is necessary to decompose the raw material salt and the raw material intermediate (some oxides pass through ammonium salt, carbonate, etc. during the preparation) to obtain the desired oxide. In the present invention, the palladium raw material may be added when the other catalyst raw material is added,
In particular, good results are obtained when water is removed from the mixture containing all the other raw materials, the residue is heat-treated, and then the palladium raw material diluted in water is added. The shape of the catalyst of the present invention is arbitrary, and it is effective even without a carrier, but it is pulverized / slurried to coat a honeycomb carrier having a monolith structure,
For example, it is preferable to use by firing at a temperature of 400 to 650 ° C. As the honeycomb material, generally, a cordierite material is often used, but a honeycomb made of a metal material can also be used.

[0010]

The present invention will be described with reference to the following examples, comparative examples and test examples. The parts in the examples are parts by weight unless otherwise specified. Example 1 1000 parts of manganese nitrate and 380 parts of cerium nitrate were added to 2500 parts of pure water and stirred and mixed. To this, 10 parts of barium acetate and 30 parts of zirconium nitrate were added, and ammonium carbonate 550 was further dissolved in 1500 parts of pure water.
After adding parts, the mixture was evaporated to dryness while heating.
The obtained solid was dried at 150 ° C. for 12 hours, pulverized, and heat-treated in air at 400 ° C. for 2 hours. The powder thus obtained was impregnated with a solution of palladium nitrate diluted with pure water, dried, and then heat-treated at 400 ° C. for 2 hours. The carrier concentration of palladium was 1.00% by weight. 400 parts of the catalyst thus obtained and 1000 parts of pure water were mixed and pulverized by a ball mill, and the resulting slurry was adhered to a monolith carrier substrate and baked (at 400 ° C. for 1 hour). At this time, the attached amount is 120 g / L, and the palladium amount is 1.06 g / L
It was set to (30 g / cf). The composition of components other than oxygen of the obtained catalyst was Pd _1.0 Mn ₁₀ Ce _2.5 Ba _0.1 Zr _0.2 (a = 1.
0, b = 10, c = 2.5, d = 0.1, e = 0.2)
Met.

Example 2 To 1000 parts of manganese nitrate, potassium nitrate, silica sol and zirconium nitrate were used, 500 parts of ammonium carbonate and 100 parts of ammonium hydrogen carbonate were added in place of ammonium carbonate, and the composition was the same as in Example 1. Pd _1.0 Mn ₁₀ Ce _2.5 K _0.1 Si _0.2 Zr _0.7 (a =
1.0, b = 10, c = 2.5, d = 0.1, e = 1.
The catalyst of 0) was prepared.

Example 3 Cesium nitrate, germanium nitrate and chromium nitrate were used for 1000 parts of manganese nitrate, and 500 parts of ammonium carbonate and 5 parts of ammonia water were used instead of ammonium carbonate.
0 parts was added, and the other components were the same as in Example 1 except that the composition was Pd _1.0 Mn ₁₀ Ce _2.5 Cs _0.1 Ge _0.2 Cr _0.1 (a
= 1.0, b = 10, c = 2.5, d = 0.1, e =
The catalyst of 0.3) was prepared.

Example 4 Rubidium acetate, cesium nitrate, zinc nitrate, silver nitrate and zirconium nitrate were used for 1000 parts of manganese nitrate, and the composition was Pd _1.0 Mn ₁₀ Ce _2.5 Rb _0.1 Cs _0.1 Zn _{0.2 in the same} manner as in Example 1. Ag
_0.2 Zr _0.5 (a = 1.0, b = 10, c = 2.5, d
= 0.2, e = 0.9) was prepared.

Example 5 To 1000 parts of manganese nitrate, barium acetate, copper nitrate,
Magnesium nitrate, with nickel nitrate and zirconium nitrate, others composition according to Example _{1 Pd 1.0 Mn 10 Ce 2.5 Ba} 0.1 Cu 0.1 Mg 0.1 Ni
_0.1 Zr _0.8 (a = 1.0, b = 10, c = 2.5, d
= 0.1, e = 1.0) was prepared.

Example 6 Barium acetate, potassium carbonate, lanthanum nitrate, strontium nitrate and zirconium nitrate were used for 1000 parts of manganese nitrate, and the composition was Pd _1.0 Mn ₁₀ Ce _2.5 Ba _0.1 K _0.1 La in the same manner as in Example 1. _0.1 Sr
_0.2 Zr _0.5 (a = 1.0, b = 10, c = 2.5, d
= 0.2, e = 0.8) was prepared.

Example 7 Barium acetate, rubidium acetate, zinc nitrate, chromium nitrate and zirconium nitrate were used for 1000 parts of manganese nitrate, and the composition was Pd _1.0 Mn ₁₀ Ce _2.5 Ba _0.1 Rb _0.1 Zn in the same manner as in Example 1. _0.1 Cr
_0.1 Zr _0.7 (a = 1.0, b = 10, c = 2.5, d
= 0.2, e = 0.9) was prepared.

Example 8 Barium nitrate, potassium nitrate, strontium nitrate and lanthanum nitrate were used for 400 parts of manganese carbonate, and the composition was Pd _1.0 Mn ₁₀ Ce _2.5 Ba _0.1 K _0.1 Sr _0.1 La in the same manner as in Example 1.
_0.2 (a = 1.0, b = 10, c = 2.5, d = 0.
2, e = 0.3) was prepared.

Example 9 Cesium nitrate, potassium carbonate, barium acetate, lanthanum nitrate, strontium nitrate and zirconium nitrate were used for 400 parts of manganese carbonate, and the composition was Pd _1.0 Mn ₁₀ Ce _2.5 Cs _{0.1 in the same} manner as in Example 1. K _0.1 Ba _0.1 La
_0.2 Sr _0.1 Zr _0.4 (a = 1.0, b = 10, c =
A catalyst of 2.5, d = 0.3, e = 0.7) was prepared.

Example 10 Cesium nitrate, rubidium acetate, barium acetate, zinc nitrate, copper nitrate and zirconium nitrate were used for 400 parts of manganese carbonate, and the composition was Pd _1.0 Mn ₁₀ Ce _2.5 Cs _{0.1 in the same} manner as in Example 1. Rb _0.1 Ba _0.1 Zn
_0.2 Cu _0.1 Zr _0.3 (a = 1.0, b = 10, c =
2.5, d = 0.3, e = 0.6) was prepared.

Comparative Example 1 Alumina was impregnated with an aqueous palladium nitrate solution, dried and then heat-treated at 600 ° C. for 2 hours to obtain a palladium-supported activated alumina powder. The supported palladium concentration is 1.00% by weight. According to Example 1, this powder was adhered to a monolith carrier substrate and fired to prepare a catalyst. Comparative Example 2 A catalyst having the same composition as in Example 1 was prepared in the same manner except that cerium nitrate was not added to obtain a catalyst of Comparative Example 2. Comparative Example 3 A catalyst was prepared in the same manner as in Example 1 except that ammonium carbonate was not added. Comparative Example 4 A catalyst was prepared in the same manner as in Example 2 except that cerium nitrate was not added. Comparative Example 5 A catalyst was prepared in the same manner as in Example 2 except that ammonium carbonate and ammonium hydrogen carbonate were not added.

Example 11 According to Example 1, the composition was Pd _0.01 Mn ₁₀ Ce _2.5 Ba _0.1 Zr _0.2 (a = 0.0
1, b = 10, c = 2.5, d = 0.1, e = 0.2)
Was prepared. Example 12 According to Example 1, the composition was Pd _3.0 Mn ₁₀ Ce _2.5 Ba _0.1 Zr _0.2 (a = 3.
0, b = 10, c = 2.5, d = 0.1, e = 0.2)
Was prepared.

Comparative Example 6 The composition of Mn ₁₀ Ce _2.5 Ba _0.1 Zr _0.2 (a = 0, b = 10) was the same as in Example 1 except that palladium was not added.
A catalyst of c = 2.5, d = 0.1, e = 0.2) was prepared. Comparative Example 7 According to Example 1, the composition was Pd _5.0 Mn ₁₀ Ce _2.5 Ba _0.1 Zr _0.2 (a = 5.
0, b = 10, c = 2.5, d = 0.1, e = 0.2)
Was prepared.

Example 13 According to Example 1, the composition was Pd _1.0 Mn ₁₀ Ce _0.2 Ba _0.1 Zr _0.2 (a = 1.
0, b = 10, c = 0.2, d = 0.1, e = 0.2)
Was prepared. Example 14 According to Example 1, the composition was Pd _1.0 Mn ₁₀ Ce _2.5 Ba _0.01 Zr _0.01 (a = 1.
0, b = 10, c = 2.5, d = 0.01, e = 0.0
The catalyst of 1) was prepared. Example 15 According to Example 1, the composition was Pd _1.0 Mn ₁₀ Ce _2.5 Ba _3.0 Zr _0.2 (a = 1.
0, b = 10, c = 2.5, d = 3.0, e = 0.2)
Was prepared.

Comparative Example 8 According to Example 1, the composition was Pd _1.0 Mn ₁₀ Ce _2.5 Cs _6.0 Zr _0.2 (a = 1.
0, b = 10, c = 2.5, d = 6.0, e = 0.2)
Was prepared.

Test Example The catalysts of Examples 1 to 15 and Comparative Examples 1 to 8 were evaluated for activity under the following conditions. For the activity evaluation, an automatic evaluation device using a model gas imitating automobile exhaust gas was used.

Evaluation conditions Catalyst Monolith type multi-component precious metal catalyst Total gas flow rate 40 L / min Catalyst inlet gas temperature 100 to 550 ° C. Temperature rising rate 30 ° C./min Space velocity Approximately 20000 H ⁻¹ Inlet gas composition average value Rich Lee H ₂ 0.2% 0.85% 0.2% CO 0.6% 2.53% 0.6% HC 1665 ppm 1665ppm 1665ppm NC 1000 ppm 1000ppm 1000ppm O ₂ 0.6% 0.6% 1.85% CO ₂ 14.0% 14% 14.0% H ₂ O 10.0% 10.0% 10.0% N ₂ 74.44% 74.44% 74.44% A / F amplitude ± 1.0 equivalent The evaluation results are shown in Table 1. The catalytic activity of the example was higher than that of the comparative example, confirming the effect of the present invention.

[0027]

[Table 1]

[0028]

As described above, the catalyst of the present invention is composed of a multi-component composite oxide containing palladium, manganese and cerium components, so that it can be used in a low temperature range where conventional catalysts are not active. Also has a high oxidation activity for HC, CO, and NOx in the exhaust gas and can maintain high performance. Therefore, since the catalyst exhibits higher activity in a low temperature range than the conventional catalyst, it is possible to reduce the emission of cold HC, which is emitted immediately after the engine is started and occupies a large proportion of the entire hydrocarbon emission.

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[Procedure amendment]

[Submission date] December 27, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction content]

Evaluation conditions Catalyst Monolith type multi-component noble metal catalyst Total gas flow rate 40 L / min Catalyst inlet gas temperature 100 to 550 ° C. Temperature rising rate 30 ° C./min Space velocity Approx. 20000 H ⁻¹ Average inlet gas composition Rich lean H ₂ 0.2% 0.85% 0.2% CO 0.6% 2.53% 0.6% HC 1665 ppm 1665ppm 1665ppm NC 1000 ppm 1000ppm 1000ppm O ₂ 0.6% 0.6% 1.85% CO ₂ 14.0% 14% 14.0% H ₂ O 10.0% 10.0% 10.0% N ₂ 74.44% 74.44% 74.44% A / F amplitude ± 1.0 equivalent The evaluation results are shown in Table 1. The catalytic activity of the example was higher than that of the comparative example, confirming the effect of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/64 ZAB 9342-4G 23/656 23/68 ZAB A 9342-4G C01B 13/18 C01G 55 / 00 9342-4G B01J 23/64 104 A

Claims (3)

[Claims] 1. A following general formula _{Pd a Mn b Ce c X d} Y e O f ( at least one element wherein X is selected from the group consisting of potassium, rubidium, cesium and barium, Y
Is at least one element selected from the group consisting of copper, magnesium, zinc, germanium, silicon, nickel, silver, chromium, lanthanum, strontium and zirconium, and a represents the weight% of palladium, and a = 0.01 to 3 And b, c, d, e and f represent the atomic ratio of each element,
When b = 10, c = 0.1-10, d = 0.01-
5, e = 0.01 to 5 and f is the number of oxygen atoms required to satisfy the valences of the above components), and a multi-component composite oxide containing palladium, manganese, and cerium. An exhaust gas purifying catalyst comprising: 2. An exhaust gas purifying catalyst comprising the catalyst according to claim 1 as a coat layer on a honeycomb-shaped monolith carrier substrate. 3. In producing the catalyst according to claim 1,
At least one compound selected from the group consisting of ammonium carbonate, ammonium hydrogen carbonate and aqueous ammonia is added to an aqueous solution or an aqueous dispersion of each metal compound constituting the catalyst, and then water is removed to remove the residue. A method for producing an exhaust gas purifying catalyst, characterized by heat treatment.