JPH07251074A - Exhaust gas cleaning catalyst and producing method thereof - Google Patents

Abstract

PURPOSE:To improve the NOx cleaning function of a catalyst in an oxygen excessive atmosphere (thereafter lean atmosphere) in which a conventional catalyst shows no activity, provide an exhaust gas cleaning catalyst which maintains high catalytic function to NOx in an exhaust gas in a wide temperature range from low temperature to high temperature and to provide a producing method of the catalyst. CONSTITUTION:This exhaust gas cleaning catalyst is a catalyst consisting of a multicomponents-compounded oxide containing copper, nickel, and aluminum and has the formula; CuaNibAlOg, wherein (a), (b), and (d) stand for atomic ratios of respective elements and in the case d=2.0, a=-0.01-0.3 and b=0.2-0.8, and (g) stands for the number of oxygen atoms necessary to satisfy the atomic valence of all the elements.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst, and more particularly, it is possible to improve the NO _x purifying ability in an oxygen excess atmosphere (hereinafter referred to as a lean atmosphere), which is not active in conventional catalysts. Moreover, the present invention relates to an exhaust gas purifying catalyst capable of maintaining high performance with respect to NO _X in exhaust gas in a wide temperature range from low temperature to high temperature.

[0002]

2. Description of the Related Art Conventionally, as a catalyst for cleaning exhaust gas emitted from an internal combustion engine of an automobile or the like, activated alumina, cerium oxide or the like is loaded with a noble metal such as platinum (Pt), palladium (Pd) and rhodium (Rh). A monolith carrier coated with this is used. Since this catalyst mainly focuses on improving the exhaust gas purifying ability in stoichiometry, sufficient performance was not obtained even when used for NO _X purification in a lean atmosphere.

On the other hand, many catalysts have been reported which improve the NO _x purification performance in a lean atmosphere. Among them, exhaust gas-purifying catalysts using alumina have been proposed (JP-A-4-284848 and JP-A-4-358).
525). Exhaust gas-purifying catalysts using alumina described in these patent publications can improve catalytic performance by using metal-supported alumina or metal aluminate that is a composite oxide of metal and alumina as a catalyst. In addition to reducing and removing NO _X in exhaust gas in a lean atmosphere, NO _X and C can be efficiently used.
O and HC can be purified.

[0004]

However, in the above-mentioned catalyst containing alumina as a main component, the catalyst cleaning ability of NO _x out of harmful components (HC, CO, NO _x ) in the exhaust gas is particularly high in the exhaust gas composition. Since it is strongly affected by (HC species), temperature, and water contained in exhaust gas, sufficient NO _x purification performance is not exhibited unless in a high temperature range of 500 ° C. or higher. Therefore, improvement of the catalyst activity (NO _x purification performance) from a low temperature range has been a major issue.

Therefore, an object of the present invention is to improve the NO _X purification capacity in a lean atmosphere, which was not active with conventional catalysts, and to purify NO _X in exhaust gas in a wide temperature range from low temperature to high temperature. An object of the present invention is to provide an exhaust gas-purifying catalyst that can be used.

[0006]

The inventor of the present invention has
As a result of diligent study to solve the above problems, copper and nickel
Aluminum, aluminum and, if necessary, an indium component.
When a multi-component catalyst having is coated on the catalyst carrier,
Sufficient NO from low temperature to high temperature even in lean atmosphere
_XThey have found that they have a purifying ability and have reached the present invention.

The above-mentioned object of the present invention has the general formula: Cu _a Ni _b Al _d O _g (where a, b and d represent the atomic ratio of each element, and d =
When 2.0, a = 0.01 to 0.3, b = 0.2 to
0.8, and g 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 copper, nickel and aluminum. It was achieved by the exhaust gas purifying catalyst.

Further, the above object of the present invention is to provide a compound represented by the general formula: Cu _a Ni _b In _c Al _d O _g (wherein a, b, c and d represent atomic ratios of respective elements,
When d = 2.0, a = 0.01 to 0.3, b = 0.2
Is 0.8, c = 0.01 to 0.3, and g is the number of oxygen atoms required to satisfy the valences of the above components.)
It was achieved by an exhaust gas purifying catalyst comprising a multi-component composite oxide containing copper, nickel, indium and aluminum represented by

Further, the above-mentioned object of the present invention has the general formula: Cu _a Ni _b In _c Al _d X _e O _g (where x is chromium, manganese, iron, cobalt, zinc,
At least one element selected from the group consisting of tin, gallium, magnesium, cerium, silicon, silver, lanthanum, strontium, and zirconium, a, b, c,
d and e represent the atomic ratio of each element, and when d = 2.0, a = 0.01 to 0.3, b = 0.2 to 0.8, c =
0.01 to 0.3, e = 0 to 0.2, and g is the number of oxygen atoms required to satisfy the valences of the above components), copper, nickel, indium and aluminum It was achieved by an exhaust gas purifying catalyst characterized by comprising a multi-component complex oxide containing Hereinafter, the present invention will be described in more detail.

In the present invention, alumina (Al
₂ O ₃ ) is a nickel aluminate (hereinafter referred to as a nickel-aluminum composite oxide) in which a specific composition ratio of nickel is added, whereby a catalytic activity (compared to a stoichiometric ratio of nickel-aluminum composite oxide) ( HC and NO _x
Both activities) can be significantly improved. The optimum composition of nickel is b =
It is in the range of 0.2 to 0.8. When b is smaller than 0.2, the catalytic activity for both HC and NO _x decreases, and b =
When it exceeds 0.8, the NO _x purification capacity decreases.

Further, in the present invention, copper is d = 2.0.
On the other hand, by setting the composition in the range of a = 0.01 to 0.3, a remarkable effect is shown in improving the activity of the composition-limited nickel-aluminum composite oxide. In particular, high activity from a low temperature range can be obtained without lowering the NO conversion performance (selectivity from NO to N ₂ ). However, the composition of copper is d = 2.0
On the other hand, if a = 0.01 or less, the original effect of the catalyst is not exhibited, and conversely, if a = 0.3 or more, the NO conversion performance deteriorates. It is considered that copper enters the crystal structure of alumina like nickel and forms a spinel structure.

Further, in the present invention, indium is d
= 2.0, the composition of c = 0.01 to 0.3 exhibits a remarkable effect in improving the selectivity of the copper-nickel-aluminum composite oxide. In particular, HC
High selectivity can be obtained in the low temperature range without lowering the oxidation activity. However, when the composition of indium is d = 2.0, c =
If it is less than 0.01, the original effect of the catalyst is not exhibited, and conversely, if it exceeds a = 0.3, the HC and NO conversion performance deteriorates. Indium is considered to be dispersed in the form of oxide (In ₂ O ₃ ) on the surface of the copper-nickel-aluminum composite oxide.

The component X is used as necessary when it is desired to further improve the activity, selectivity and durability of the indium-copper-nickel-aluminum composite oxide. The composition of this X component is in the range of e = 0 to 0.2 for d = 2.0. The component X can be used as it is as the indium-copper-nickel-aluminum composite oxide as long as sufficient performance can be obtained under the use conditions, and it is not particularly necessary to add it. Therefore, the X component may be added when it is necessary to improve the catalyst performance, but the addition amount is d
= 2.0, when e = 0.2 is exceeded, the catalytic performance of the indium-copper-nickel-aluminum composite oxide, which is the basic composition, rather deteriorates.

Regarding the number of oxygen atoms, it is necessary to identify the valences of all elements, but in a multi-component system the valences of the elements differ depending on the structure and coordination state of the oxide formed, so it is not possible to specify it. Very difficult.

As the raw material compound for preparing the catalyst used in the present invention, nitrates, carbonates, ammonium salts, acetates, halides, oxides and the like of each element can be used in any combination. It is preferable to use the organic salt from the viewpoint of improving the catalyst performance.

The method for producing the exhaust gas purifying catalyst according to the present invention will be described below. When manufacturing the exhaust gas purifying catalyst according to the present invention, first, a catalyst raw material containing copper, nickel, indium and aluminum components is added to pure water and stirred. At this time, a liquid in which each catalyst raw material is dissolved simultaneously or separately may be added. Then, an aqueous solution of at least one compound selected from the group consisting of aqueous ammonia, ammonium carbonate, ammonium hydrogen carbonate, ammonium sulfate and ammonium hydrogen sulfate is gradually added to the mixed solution containing the catalyst raw material to adjust the pH of the solution. After preparing it in the range of 7.0 to 9.0, water is removed and the residue is heat-treated to obtain the desired catalyst.

The method for preparing the catalyst is not limited to a special method and may be appropriately selected from known methods as long as it does not cause the uneven distribution of the components. In particular, aqueous ammonia and ammonium carbonate are used. It is preferable to use a precipitation method in which an aqueous solution of at least one compound selected from the group consisting of ammonium hydrogencarbonate, ammonium sulfate and ammonium hydrogensulfate is added as a precipitation agent.

In the exhaust gas purifying catalyst according to the present invention, the fine pore structure and large surface area of the oxide catalyst obtained by the precipitation method play an important role in exhibiting low temperature activity. On the other hand, the catalyst obtained without using the above-mentioned precipitant lacks a fine pore structure, and the surface area effective for the reaction becomes small, so that the catalytic activity decreases. If the above-mentioned aqueous ammonia or ammonium compound is used as the precipitant used in this precipitation method, no metal element remains even if the washing is insufficient, and the ammonium compound (mainly ammonium nitrate after dropping)
Even if it remains, it can be easily decomposed and removed by subsequent firing. On the other hand, when a metal salt such as sodium hydroxide or sodium carbonate is used, metal elements such as sodium remain in the obtained precipitate, and these residual metal elements adversely affect the catalytic performance. Therefore, a cleaning process is required.

When carrying out the above-mentioned precipitation method, by adjusting the pH of the solution to a range of 7.0 to 9.0, it is possible to form precipitates on various metal salts. pH is 7.
When it is lower than 0, various elements do not form a precipitate sufficiently, and conversely p
When H is higher than 9.0, some of the precipitated components may be redissolved.

Water can be removed by appropriately selecting from known methods such as filtration and evaporation to dryness.
The heat treatment is not particularly limited, but is, for example, 500 to 100.
It is preferable to carry out at a temperature in the range of 0 ° C. in air and / or under air flow.

The thus obtained exhaust gas-purifying catalyst according to the present invention can be effectively used without a carrier,
400 ~
It is preferable to use it after firing at 900 ° C. The catalyst carrier can be appropriately selected and used from known catalyst carriers, and examples thereof include a monolith carrier and a metal carrier.

The shape of this catalyst carrier is not particularly limited, but it is usually preferable to use it in a honeycomb shape, and the catalyst powder is applied to various honeycomb-shaped base materials and used.
As the honeycomb material, a cordierite material is generally used, but a honeycomb made of a metal material can be used, and the catalyst powder itself may be formed into a honeycomb shape. By making the shape of the catalyst honeycomb, the contact area between the catalyst and the exhaust gas becomes large and the pressure loss can be suppressed, which is extremely advantageous when used for automobiles.

[0023]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. Unless otherwise specified in the examples, parts and% refer to parts by weight and% by weight, respectively.

Example 1 1.6 parts of copper nitrate, 9.7 parts of nickel nitrate and 50 parts of aluminum nitrate were added to 400 parts of pure water and stirred and dissolved.
Next, while stirring the solution, 5% ammonia water was gradually added dropwise so that the pH of the solution was in the range of 7.0 to 9.0. The precipitate formed is filtered off and washed at 150 ° C.
After drying for 2 hours, it was baked in air at 800 ° C. for 2 hours. 500 parts of the powder 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). The adhesion amount at this time was set to 200 g / L. The composition of the components other than oxygen of the obtained catalyst (hereinafter the same) is Cu
_{It was 0.1} Ni _0.5 Al _2.0 .

Example 2 The composition was changed to C by the same method as in Example 1 except that 5% ammonium carbonate aqueous solution was used instead of 5% ammonia water.
A catalyst of u _0.1 Ni _0.5 Al _2.0 was prepared.

Example 3 A catalyst having a composition of Cu _0.1 Ni _0.5 Al _2.0 was prepared in exactly the same manner as in Example 1, except that 5% ammonium hydrogen carbonate aqueous solution was used instead of 5% ammonia water.

Example 4 The composition was changed to C by the same method as in Example 1 except that 5% ammonium sulfate aqueous solution was used instead of 5% ammonia water.
A catalyst of u _0.1 Ni _0.5 Al _2.0 was prepared.

Example 5 A catalyst having a composition of Cu _0.1 Ni _0.5 Al _2.0 was prepared in the same manner as in Example 1 except that 5% ammonium hydrogensulfate aqueous solution was used instead of 5% ammonia water.

Example 6 A catalyst having a composition of Cu _0.05 Ni _0.5 Al _2.0 was prepared in exactly the same manner as in Example 1 except that copper nitrate was changed to 0.8 part.

Example 7 A catalyst having a composition of Cu _0.15 Ni _0.5 Al _2.0 was prepared in exactly the same manner as in Example 1 except that the copper nitrate was changed to 2.4 parts.

Example 8 A catalyst having a composition of Cu _0.1 Ni _0.3 Al _2.0 was prepared in exactly the same manner as in Example 1 except that nickel nitrate was replaced by 5.9 parts.

Example 9 A catalyst having a composition of Cu _0.1 Ni _0.7 Al _2.0 was prepared in exactly the same manner as in Example 1 except that nickel nitrate was replaced by 13.6 parts.

Example 10 The composition was In _0.1 Cu _0.1 Ni _0.5 Al _{2.0 in the same} manner as in Example 1 except that 2.4 parts of indium nitrate was added.
Was prepared.

Example 11 A catalyst having a composition of In _0.1 Cu _0.1 Ni _0.5 Al _2.0 was prepared in exactly the same manner as in Example 10 except that 5% aqueous ammonium carbonate solution was used instead of 5% ammonia water.

Example 12 A catalyst having a composition of In _0.1 Cu _0.1 Ni _0.5 Al _2.0 was prepared in exactly the same manner as in Example 10 except that 5% ammonium hydrogen carbonate aqueous solution was used instead of 5% ammonia water.

Example 13 A catalyst having a composition of In _0.1 Cu _0.1 Ni _0.5 Al _2.0 was prepared in exactly the same manner as in Example 10 except that 5% ammonium sulfate aqueous solution was used instead of 5% ammonia water.

Example 14 A catalyst having a composition of In _0.1 Cu _0.1 Ni _0.5 Al _2.0 was prepared in exactly the same manner as in Example 10 except that 5% ammonium hydrogensulfate aqueous solution was used instead of 5% ammonia water.

Example 15 The composition was In _0.1 Cu _0.1 Ni _0.3 Al _{2.0 in the same} manner as in Example 10 except that 5.9 parts of nickel nitrate was used.
Was prepared.

Example 16 The composition was In _0.1 Cu _0.1 Ni _0.7 Al in the same manner as in Example 10 except that 13.6 parts of nickel nitrate was used.
_{A 2.0} catalyst was prepared.

Example 17 A catalyst having a composition of In _0.1 Cu _0.05 Ni _0.5 Al _2.0 was prepared in the same manner as in Example 10 except that 0.8 part of copper nitrate was used.

Example 18 A catalyst having a composition of In _0.1 Cu _0.15 Ni _0.5 Al _2.0 was prepared in exactly the same manner as in Example 10 except that 2.4 parts of copper nitrate was used.

Example 19 The composition was In _0.05 Cu _0.1 Ni _0.5 Al in the same manner as in Example 10 except that 1.6 parts of indium nitrate was used.
_{A 2.0} catalyst was prepared.

Example 20 The composition was In _0.2 Cu _0.1 Ni _0.5 Al in the same manner as in Example 10 except that 4.8 parts of indium nitrate was used.
_{A 2.0} catalyst was prepared.

Example 21 The composition was Zn _0.01 In _0.1 Cu _0.1 Ni _0.5 Al in the same manner as in Example 10 except that 0.2 part of zinc nitrate was added.
_{A 2.0} catalyst was prepared.

[0045] Another plus Example 22 Silver nitrate 0.11 part, the composition in exactly the same manner as in Example _{10 Ag 0.01 In 0.1 Cu 0.1 Ni} 0.5 Al
_{A 2.0} catalyst was prepared.

Example 23 The composition of Cr was the same as in Example 10 except that 0.27 part of chromium nitrate and 0.19 part of manganese nitrate were added.
A catalyst of _0.01 Mn _0.01 In _0.1 Cu _0.1 Ni _0.5 Al _2.0 was prepared.

Example 24 The composition was Fe _0.01 C in the same manner as in Example 10 except that 0.27 part of iron nitrate and 0.19 part of cobalt nitrate were added.
A catalyst of _0.01 In _0.1 Cu _0.1 Ni _0.5 Al _2.0 was prepared.

Example 25 The composition was Sn _0.01 Ga _0.01 Mg _0.01 In in the same manner as in Example 10 except that 0.17 part of tin nitrate, 0.27 part of gallium nitrate and 0.17 part of magnesium nitrate were added. _0.1
A catalyst of Cu _0.1 Ni _0.5 Al _2.0 was prepared.

Example 26 The composition was Ce _0.01 Si _0.01 La _{0.01 in the same} manner as in Example 10 except that 0.29 part of cerium nitrate, 0.2 part of 20% silica sol and 0.29 part of lanthanum nitrate were added. In
A catalyst of _0.1 Cu _0.1 Ni _0.5 Al _2.0 was prepared.

Example 27 The composition was Sr _0.01 Zr _0.01 In _0.1 Cu _0.1 Ni _0.5 A in the same manner as in Example 10 except that 0.15 part of strontium nitrate and 0.18 part of zirconium nitrate were added.
A catalyst of l _2.0 was prepared.

Comparative Example 1 Example 1 was repeated except that copper nitrate and nickel nitrate were not added.
A catalyst having a composition of Al _2.0 was prepared in exactly the same manner as in.

Comparative Example 2 A catalyst having a composition of Cu _0.1 Ni _0.5 Al _2.0 was prepared in exactly the same manner as in Example 1 except that 5% ammonia water was not used.

Comparative Example 3 A catalyst having a composition of Cu _0.1 Ni _0.05 Al _2.0 was prepared in exactly the same manner as in Example 1 except that 0.97 part of nickel nitrate was used.

Comparative Example 4 A catalyst having a composition of Cu _0.1 Ni _1.0 Al _2.0 was prepared in the same manner as in Example 1 except that 19.4 parts of nickel nitrate was used.

Comparative Example 5 A catalyst having a composition of Cu _0.001 Ni _0.5 Al _2.0 was prepared in exactly the same manner as in Example 1 except that 0.016 part of copper nitrate was used.

Comparative Example 6 A catalyst having a composition of Cu _0.5 Ni _0.5 Al _2.0 was prepared in the same manner as in Example 1 except that 8.1 parts of copper nitrate was used.

Comparative Example 7 The composition was Al _{2.0 in the same} manner as in Example 10 except that copper nitrate, nickel nitrate and indium nitrate were not added.
Was prepared.

Comparative Example 8 The composition was Cu _0.1 Ni _0.5 In _0.1 Al _{2.0 in the same} manner as in Example 1 except that 5% aqueous ammonia was not used.
Was prepared.

Comparative Example 9 The composition was Cu _0.1 Ni _0.05 In _0.1 Al in the same manner as in Example 10 except that 0.97 part of nickel nitrate was added.
_{A 2.0} catalyst was prepared.

Comparative Example 10 The composition was Cu _0.1 Ni _1.0 In _0.1 Al in the same manner as in Example 10 except that 19.4 parts of nickel nitrate was added.
_{A 2.0} catalyst was prepared.

Comparative Example 11 The composition was Cu _0.001 Ni _0.5 In _0.1 Al _{2.0 by the} same method as in Example 10 except that 0.016 parts of copper nitrate was added.
Was prepared.

Comparative Example 12 A catalyst having a composition of Cu _0.5 Ni _0.5 In _0.1 Al _2.0 was prepared in exactly the same manner as in Example 10 except that 8.1 parts of copper nitrate was added.

Comparative Example 13 Example 10 except that 0.024 part of indium nitrate was added.
And the composition is Cu _0.1 Ni _0.5 In _0.001
An Al _2.0 catalyst was prepared.

Comparative Example 14 The composition was Cu _0.1 Ni _0.5 In _0.5 Al in the same manner as in Example 10 except that 11.8 parts of indium nitrate was added.
_{A 2.0} catalyst was prepared.

Test Example 1 The catalysts of Examples 1 to 26 and Comparative Examples 1 to 14 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 600 ° C. Temperature rising rate 30 ° C./min Space velocity Approx. 10,000 H ⁻¹ Inlet gas composition Average air-fuel ratio equivalent to 18.0 Model gas composition of CO 0.2% C ₃ H ₆ 5000 ppm C NO 500 ppm O ₂ 4.50% CO ₂ 10.0% H ₂ O 10.0% N ₂ balance A / F No amplitude Evaluation results are shown in Table 1. , Table 2, Table 3, Table 4 and Table 5. The catalytic activity of the example was higher than that of the comparative example, and the effect of the present invention could be confirmed.

[0066]

[Table 1]

[0067]

[Table 2] In Tables 1 and 2, C300 indicates the NO _X conversion rate (%) at 300 ° C, C400 indicates the NO _X conversion rate (%) at 400 ° C, and C500 indicates the NO _X conversion rate (%) at 500 ° C.

[0068]

[Table 3]

[0069]

[Table 4] In Table 4, C300 shows the NO _x conversion rate (%) at 300 ° C., C400 shows the NO _x conversion rate (%) at 400 ° C., and C500 shows the NO _x conversion rate (%) at 500 ° C.

[0070]

[Table 5]

[0071]

The exhaust gas-purifying catalyst of the present invention uses a multi-component catalyst containing copper, nickel, indium and aluminum as the main components, whereby NO _x in an oxygen excess atmosphere, which is not active in conventional catalysts, is used. The purifying ability can be improved, and high performance can be maintained with respect to NO _X in the exhaust gas in a wide temperature range from low temperature to high temperature.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location B01J 23/74 ZAB 23/835 ZAB 23/84 ZAB 23/889 23/85 ZAB A 23/89 ZAB A B01D 53/36 102 B 102 H B01J 23/82 ZAB A 23/84 311 A

Claims (6)

[Claims] 1. A general formula: Cu _a Ni _b Al _d O _g (where a, b and d represent the atomic ratio of each element, and d =
When 2.0, a = 0.01 to 0.3, b = 0.2 to
0.8, and g 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 copper, nickel and aluminum. Exhaust gas purification catalyst. 2. A general formula: Cu _a Ni _b In _c Al _d O _g (wherein a, b, c and d represent atomic ratios of respective elements,
When d = 2.0, a = 0.01 to 0.3, b = 0.2
Is 0.8, c = 0.01 to 0.3, and g is the number of oxygen atoms required to satisfy the valences of the above components.)
An exhaust gas-purifying catalyst comprising a multi-component composite oxide containing copper, nickel, indium and aluminum represented by: 3. A general formula: Cu _a Ni _b In _c Al _d X _e O _g (where x is chromium, manganese, iron, cobalt, zinc,
At least one element selected from the group consisting of tin, gallium, magnesium, cerium, silicon, silver, lanthanum, strontium, and zirconium, a, b, c,
d and e represent the atomic ratio of each element, and when d = 2.0, a = 0.01 to 0.3, b = 0.2 to 0.8, c =
0.01 to 0.3, e = 0 to 0.2, and g is the number of oxygen atoms required to satisfy the valences of the above components), copper, nickel, indium and aluminum An exhaust gas purifying catalyst comprising a multi-component complex oxide containing 4. An exhaust gas purifying catalyst comprising the catalyst carrier according to claim 1, 2 or 3 as a coat layer on a catalyst carrier. 5. The exhaust gas purifying catalyst according to claim 1, 2, 3 or 4, wherein the catalyst carrier is a honeycomb-shaped monolith carrier substrate. 6. In producing the catalyst according to claim 1, 2 or 3, an aqueous solution or an aqueous dispersion containing each metal compound constituting the catalyst is added to aqueous ammonia, ammonium carbonate, ammonium hydrogen carbonate, ammonium sulfate, and At least one selected from the group consisting of ammonium hydrogen sulfate
A method for producing an exhaust gas purifying catalyst, which comprises adding an aqueous solution of seeds and adjusting the pH of the solution to a range of 7.0 to 9.0, removing water, and heat-treating the residue.