JPH07213907A - Exhaust gas purifying catalyst and method for producing the same - Google Patents

Abstract

(57) [Summary] [Purpose] The emission of cold HC emitted immediately after the engine is started, which 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. An exhaust gas purifying catalyst that can be reduced is obtained. [Structure] General formula Pd _a Co _b Ce _c X _d Y _e O
_f (X in the formula is at least one element 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, a represents the weight% of palladium, and a = 0.01 to 3 Yes, 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 is composed of a multi-component composite oxide containing palladium, cobalt and cerium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention purifies hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) in exhaust gas discharged from internal combustion engines such as automobiles. The present invention relates to a purification catalyst and a method for manufacturing 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 rhodium (Rh) is supported and is coated on a monolith carrier is used. The catalyst is called a three-way catalyst because it can remove HC, CO and NO _x at once. This catalyst is effective only when the internal combustion engine is operated under conditions near the stoichiometric air-fuel ratio.

[0003]

However, of the harmful components (HC, CO, NOx) in the exhaust gas, especially H
The catalyst purifying ability of C is strongly influenced by the exhaust gas temperature, and is generally purified by the noble 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, so that suppressing the discharge of cold HC has been a major issue. 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]

As a result of various studies aimed at achieving the above object, the present inventor has found that a multi-component composite oxide catalyst itself containing palladium, cobalt and cerium components or a honeycomb having this catalyst in a monolith structure. It has been found that by coating a carrier, an exhaust gas purifying catalyst having a sufficient HC purifying ability from a low temperature to a high temperature can be provided, and the present invention has been accomplished. The catalyst of the present invention have the general formula _{Pd a Co 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 At least one element selected from the group consisting of magnesium, zinc, germanium, silicon, nickel, silver, chromium, lanthanum, strontium and zirconium,
a represents the 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 to 10, d = 0.01 to 5, e = 0.01
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, cobalt and cerium. .

When a in the above general formula is less than 0.01, the performance of the catalyst is hardly exhibited, and even when it exceeds 3.0, the effect of palladium is saturated and no further effect can be obtained. b
= 10, when c is less than 0.1, the effect of combining cobalt and cerium becomes small, and the value of T50 deteriorates.
If it is larger than 10, the purification ability of HC decreases. The values of d and e are set to 0.01 to 5 in consideration of the overall catalyst performance such as the durability of the catalyst, but if 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, a metal constituting the catalyst, a compound of Pd, Co, Ce, X, and Y is used as a catalyst raw material, and ammonium carbonate is added to an aqueous solution or dispersion of the compound of the catalyst raw material. It is preferable to add at least one compound selected from the group consisting of ammonium hydrogen carbonate and aqueous ammonia, remove the water, and heat treat the residue.

As a raw material compound for catalyst preparation, nitrates, carbonates, ammonium salts, acetates, halides, oxides and the like of each element can be used in combination.
The method for preparing the catalyst does not have to be 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 cobalt and cerium is dissolved or dispersed in water, and then X, Y catalyst raw materials are 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 hydrogencarbonate and / or ammonia water used is 1 to 6 of the total weight of the catalyst raw material.
0% by weight, especially 5 to 50% by weight is preferred.

On the other hand, when the mixture of the raw salt is evaporated to dryness without adding ammonium carbonate, ammonium hydrogen carbonate and aqueous ammonia, the powder obtained has a small BET surface area. When the BET surface area is small, the dispersibility of palladium is deteriorated and the activity (T50) is deteriorated. And technically,
The synergistic effect existing between palladium and the base oxide (the effect of promoting the desorption of lattice oxygen from the base oxide by palladium) becomes small, and the effect of improving the low temperature activity also becomes small.

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

Next, water is removed from this catalyst raw material mixture and the residue is heat-treated to obtain the desired catalyst. The heat treatment is preferably performed in air and / or air circulation at a temperature of 300 to 800 ° C., for example. This heat treatment is necessary in order to decompose the raw material salt and the raw material intermediate (some oxides pass through ammonium salt, carbonate, etc. at the time of preparation) and 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, the water is removed from the mixture containing all the other raw materials, and the residue is heat treated, and then water is added. Good results are obtained when a palladium raw material diluted with is added.

The catalyst of the present invention may have any shape, and it is effective even without a carrier, but it is pulverized and slurried and coated on a honeycomb carrier having a monolith structure, for example, 400 to 6
It is preferable to use it after firing at a temperature of 50 ° C.

[0014]

EXAMPLES 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 1 500 parts of cobalt nitrate and 750 parts of cerium nitrate were added to 1500 parts of pure water and stirred and mixed. To this, 5 parts of barium acetate and 15 parts of zirconium nitrate were added, and further 600 parts of ammonium carbonate dissolved in 1500 parts of pure water was added, and then 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 600 ° C. for 2 hours. The supported concentration of palladium was 1.00% by weight. 400 parts of the catalyst thus obtained and 1000 parts of pure water were mixed by a ball mill and pulverized, and the obtained slurry was adhered to a monolith carrier substrate and baked (at 400 ° C. for 1 hour). The adhesion amount at this time is 120
The g / L and palladium amount were set to 1.06 g / L (30 g / cf). The composition of the components other than oxygen of the obtained catalyst was Pd.
_1.0 Co ₁₀ Ce ₁₀ Ba _0.1 Zr _0.2 (a = 1.0, b = 1
0, c = 10, d = 0.1, e = 0.2).

Example 2 To 500 parts of cobalt nitrate, potassium nitrate, silica sol and zirconium nitrate were used. Instead of ammonium carbonate, 500 parts of ammonium carbonate and 100 parts of ammonium hydrogencarbonate were added, and the other components were the same as in Example 1. P
d _1.0 Co ₁₀ Ce ₁₀ K _0.1 Si _0.1 Zr _0.7 (a = 1.0
, B = 10, c = 10, d = 0.1, e = 0.8).

Example 3 Rubidium acetate, germanium nitrate, and chromium nitrate were used with respect to 500 parts of cobalt nitrate, and instead of ammonium carbonate, 500 parts of ammonium carbonate and 15 parts of ammonia water.
0 parts were added, and the composition was Pd _1.0
Co ₁₀ Ce ₁₀ Rb _0.1 Ge _0.1 Cr _0.2 (a = 1.0, b
= 10, c = 10, d = 0.1, e = 0.3).

Example 4 Cesium nitrate, zinc nitrate, 500 parts of cobalt nitrate,
Example 1 was used except that silver nitrate and zirconium nitrate were used.
The composition is Pd _1.0 Co ₁₀ Ce ₁₀ Cs _0.1 Zn _0.1
Ag _0.1 Zr ₃ (a = 1.0, b = 10, c = 10, d =
A catalyst of 0.1, e = 3.2) was prepared.

Example 5 Barium acetate, copper nitrate, magnesium nitrate, nickel nitrate and zirconium nitrate were used for 500 parts of cobalt nitrate, and the composition was Pd _1.0 Co _{10 in the same} manner as in Example 1.
Ce ₁₀ Ba _0.1 Cu _0.1 Mg _0.15 Ni _0.1 Zr ₂ (a =
A catalyst of 1.0, b = 10, c = 10, d = 0.1, e = 2.35) was prepared.

Example 6 Barium acetate, potassium carbonate, nickel nitrate, lanthanum nitrate, strontium nitrate and zirconium nitrate were used with respect to 500 parts of cobalt nitrate, and the composition was Pd _1.0 Co ₁₀ Ce ₁₀ Ba _0.1 K _0.1 Ni _0.2
La _0.1 Sr _0.2 Zr ₅ (a = 1.0, b = 10, c = 1
A catalyst of 0, d = 0.2, e = 5.5) was prepared.

Example 7 Barium acetate, rubidium acetate, zinc nitrate, chromium nitrate and zirconium nitrate were used for 500 parts of cobalt nitrate, and the composition was Pd _1.0 Co ₁₀ C in accordance with Example 1 except for the above.
e ₁₀ Ba _0.1 Rb _0.1 Zn _0.1 Cr _0.1 Zr ₃ (a = 1.
A catalyst of 0, b = 10, c = 10, d = 0.2, e = 3.2) was prepared.

Example 8 Barium acetate, potassium carbonate, strontium nitrate and lanthanum nitrate were used for 250 parts of cobalt carbonate, and the composition was Pd _1.0 Co ₁₀ Ce ₁₀ Ba according to Example 1 except for the above.
_0.1 K _0.1 Sr _0.1 La _0.2 (a = 1.0, b = 10, c
= 10, d = 0.2, e = 0.3).

[0022] Example 9 of cesium nitrate to cobalt carbonate 250 parts of potassium nitrate, barium acetate, lanthanum nitrate, using strontium nitrate and zirconium nitrate, other Pd _1.0 is the composition according to Example 1 Co ₁₀ Ce ₁₀ Cs _0.1 K _0.1 Ba _0.1
La _0.2 Sr _0.1 Zr ₄ (a = 1.0, b = 10, c = 1
A catalyst of 0, d = 0.3, e = 4.3) was prepared.

Example 10 Cesium nitrate, rubidium acetate, barium acetate, zinc nitrate, copper nitrate, chromium nitrate and zirconium nitrate were used for 250 parts of cobalt carbonate, and the composition was Pd _1.0 Co ₁₀ Ce in the same manner as in Example 1. ₁₀ Cs _0.1 Rb _0.1 Ba _0.1
Zn _0.2 Cu _0.1 Cr _0.1 Zr ₄ (a = 1.0, b = 1
A catalyst of 0, c = 10, d = 0.3, e = 4.4) was prepared.

Comparative Example 1 Palladium-supported activated alumina powder was obtained by impregnating alumina with an aqueous palladium nitrate solution, drying and heat treating at 600 ° C. for 2 hours. 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. 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 Co ₁₀ Ce ₁₀ Ba _0.1.
Zr _0.2 (a = 0.01, b = 10, c = 10, d = 0.1,
A catalyst of e = 0.2) was prepared. Example 12 According to Example 1, the composition was Pd _3.0 Co ₁₀ Ce ₁₀ Ba _0.1.
Zr _0.2 (a = 3.0, b = 10, c = 10, d = 0.1,
A catalyst of e = 0.2) was prepared.

[0026] Comparative Example 6 except that palladium was not added to the Example 1 composition in the same manner as the _{Co 10 Ce 10 Ba 0. 1 Zr} 0.2 (a = 0, b = 10,
A catalyst of c = 10, d = 0.1, e = 0.2) was prepared. Comparative Example 7 According to Example 1, the composition was Pd _5.0 Co ₁₀ Ce ₁₀ Ba _0.1.
Zr _0.2 (a = 5.0, b = 10, c = 10, d = 0.1,
A catalyst of e = 0.2) was prepared.

Example 13 According to Example 1, the composition was Pd _1.0 Co 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 Co ₁₀ Ce ₁₀ Ba _0.01.
Zr _0.01 (a = 1.0, b = 10, c = 10, d = 0.01,
A catalyst of e = 0.01) was prepared. Example 15 The composition was Pd _1.0 Co ₁₀ Ce ₁₀ Ba _3.0 in accordance with Example 1.
Zr _0.2 (a = 1.0, b = 10, c = 10, d = 3.0,
A catalyst of e = 0.2) was prepared. Example 16 Instead of ammonium carbonate, ammonium hydrogen carbonate 5
00 parts were added, and the composition was Pd in the same manner as in Example 1 except for the above.
_1.0 Co ₁₀ Ce ₁₀ Ba _0.1 Zr _0.2 (a = 1.0, b = 1
A catalyst of 0, c = 10, d = 0.1, e = 0.2) was prepared. Example 17 Instead of ammonium carbonate, 500 parts of aqueous ammonia was added, and the other components were the same as in Example 1 except that the composition was Pd _1.0 Co _10.
Ce ₁₀ Ba _0.1 Zr _0.2 (a = 1.0, b = 10, c = 1
0, d = 0.1, e = 0.2) was prepared.

Comparative Example 8 According to Example 1, the composition was Pd _1.0 Co ₁₀ Ce ₁₀ Cs _6.0.
Zr _0.2 (a = 1.0, b = 10, c = 10, d = 6.0,
A catalyst of e = 0.2) was prepared.

Test Example Regarding the catalysts of Examples 1 to 15 and Comparative Examples 1 to 8,
The activity was evaluated 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 Approx. 20000H ^-1 Inlet gas composition average value Rich lean H ₂ 0.2% 0.85% 0.2% CO 0.6% 2.53% 0.6% HC 1665 ppm 1665 ppm 1665 ppm NO 1000 ppm 1000 ppm 1000 ppm O ₂ 0.6% 0.6% 1.85% CO ₂ 14.0% 14.0% 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 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.

[0030]

[Table 1]

[0031]

As described above, the catalyst of the present invention is composed of a multi-component composite oxide containing palladium, cobalt and cerium components, so that it is not active in conventional catalysts in the low temperature range. Also in this case, it 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 that of 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.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C01B 13/18 C01G 55/00

Claims (3)

[Claims] 1. A following general formula _{Pd a Co 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, At least one element selected from the group consisting of magnesium, zinc, germanium, silicon, nickel, silver, chromium, lanthanum, strontium and zirconium,
a represents the 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 to 10, d = 0.01 to 5, e = 0.0
1 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, cobalt and cerium. Exhaust gas purification catalyst. 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 aqueous dispersion of each metal compound constituting the catalyst, water is removed, and the residue is heat treated. A method for producing an exhaust gas purifying catalyst, comprising: