DE69633831T2 - PROCESS FOR THE PRODUCTION OF A CATALYST FOR EXHAUST GAS CLEANING - Google Patents

Description

Background of the invention

Field of the invention

The The present invention relates to a process for producing a Catalyst, especially useful is for the removal of nitrogen oxides from portable combustion engines, be dispensed, like those in gasoline-powered automobiles and diesel-powered automobiles are used; stationary combustion engines like those used in heating plants; combustion chambers, like those used in boilers; furnaces factories, etc. by reducing nitrogen oxides to harmless gases.

State of technology

In general, the exhaust gases emitted by factories from portable or stationary internal combustion engines, combustion chambers or furnaces contain a large amount of nitrogen oxides (NO _x ) such as NO or NO ₂ . It is believed that these nitrogen oxides (NO _x ) cause not only photochemical smog but also damage to the human respiratory system.

Conventionally, a method for reducing the NO _x content in the exhaust gas has been widely known, wherein NO _x is removed by reduction using a catalyst with carbon monoxide or hydrocarbons contained in the exhaust gas.

Usually for such Catalysts used include those obtained by Incorporation of metals by ion exchange, impregnation etc, into a zeolite-formed support such as crystalline aluminosilicate getting produced.

In particular, even under the conditions of high gas hourly space velocity (GHSV), a crystalline aluminosilicate catalyst carrying copper as a metal component can efficiently remove nitrogen oxides (NO _x ) from exhaust gases, which is a large amount Contain oxygen by using a hydrocarbon as a reducing agent. Therefore, this type of catalyst is considered to be a promising catalyst for purifying exhaust gases from portable or stationary internal combustion engines.

Of the However, copper-on-crystalline aluminosilicate catalyst has one poor durability compared Heat and Steam; i.e. the valence, the oxidation state and the dispersion state of the copper present in the catalyst undergo a change, when the catalyst undergoes treatment with heat and steam. Therefore The disadvantage remains that a constant cleaning performance during a long time at temperatures of 600 ° C or more, or if the exhaust gas contains a large amount of moisture, not is achieved.

Around overcome this disadvantage disclosed in Japanese Laid-Open Patent Application (Kokai) No. 6-134314 and in EP-A-0 585 025 the inventors as a catalyst for cleaning exhaust gases, which a significantly increased durability comprising a catalyst comprising a crystalline aluminosilicate catalyst support from Pentasil type that carried a copper component and a phosphorus component.

With an ion exchange method that is suitable for the homogeneous Incorporation of the copper component and the phosphorus component, The pH ranges of the mother solution differ from each other, which are for the Incorporation of the respective components in the required quantities are suitable. Accordingly, the pH range in which both components are simultaneous be incorporated in appropriate amounts, too narrow to satisfactory to be maintained by industrial equipment.

Even though the respective components sequentially within pH range, the for the respective components are suitable, can be incorporated, is an increased Number of training steps industrially not at all advantageous,

Summary the invention

The The present invention has been made in light of the foregoing and an object of the present invention is the provision a process for the preparation of a catalyst for the purification of Exhaust gas, within a wide pH range and in a stable manner, wherein the catalyst has excellent durability, a Copper component that contains a phosphorus component and is suitable for cleaning of exhaust gas with high efficiency.

The Inventors have done eager studies and have found that efficiently solved the above task is determined by the pH of a the incorporation of the copper component and the phosphorus component during a Initial step of incorporation of the solution used is increased and the pH in the course of the training step is lowered. The present invention was completed based on this finding.

Accordingly The present invention provides the following.

• (1) Method for producing a catalyst for purifying exhaust gas, wherein the catalyst is a crystalline Aluminosilicate catalyst support from Pentasil type or zeolite catalyst support selected from ferrierite and mordenite includes, which is supported has at least one copper component and one phosphorus component, the process being characterized in that the catalyst support is in a solution which is at least one copper component, a phosphorus component, Contains ammonia and a buffer and having a pH of 8.0 or more, and then adding an acid to the solution for adjusting the pH of the solution to 7.0 or less, resulting in at least the copper component and incorporating the phosphorus component into the catalyst carrier become.
• (2) Method for producing a catalyst for purification exhaust gas as described in (1), wherein the pH of the solution before the addition of the catalyst carrier 8.0 to 12.0.
• (3) Method for producing a catalyst for purification exhaust gas, the catalyst comprising a crystalline aluminosilicate catalyst support from Pentasil type or zeolite catalyst support selected from ferrierite and mordenite includes, who carried on it has at least one copper component and one phosphorus component, the process being characterized in that the catalyst support is in a solution is given, the at least one copper component, a phosphorus component and ammonia and having a pH of 9.0 or more, and then adding an acid to the resulting solution for adjusting the pH of the solution to 7.0 or less, thereby at least the copper component and incorporating the phosphorus component into the catalyst support.
• (4) Method for producing a catalyst for purification exhaust gas as described in (1), wherein the pH of the solution before the addition of the catalyst carrier 9.0 to 12.0.
• (5) Method for producing a catalyst for purification exhaust gas as described in any one of (1) to (4), wherein the crystalline Aluminosilicate of the pentasil type has an MFI structure.
• (6) Method for producing a catalyst for purification exhaust gas as described in (1) or (2), wherein the buffer is at least a species is chosen is made from ammonium nitrate, ammonium chloride, ammonium acetate and sodium acetate.
• (7) Method for producing a catalyst for purification exhaust gas as described in any one of (1) to (6), wherein the acid is at least a species is chosen is made from nitric acid, hydrochloric acid and sulfuric acid.

preferred embodiments the invention

The preferred embodiments The present invention will next be described in detail.

When First, the catalyst for purifying exhaust gas, which is produced according to the invention is described.

According to the present invention, a catalyst for purifying exhaust gas is prepared by incorporating a specific component in a catalyst carrier comprising crystalline pentasil type aluminosilicate or zeolite selected from ferrierite and mordenite. Crystalline aluminosilicate of the pentasil type is used as the catalyst carrier in the present invention, since crystalline aluminosilicates, except for crystalline pentasil type aluminosilicate, have an inherently poor hydrothermal durability and since the resistance to steam further decreases when a phosphorus component is incorporated, and therefore, such crystalline aluminosilicates are not suitable for catalyst supports requiring long-term stability.

According to the invention crystalline aluminosilicate of the pentasil type zeolite, its structural units an oxygen-5 ring and examples thereof include ZSM-5 and ZSM-11 which has an MFI structure exhibit. As used herein, MFI structure means ZSM-5 or a same structure as ZSM-5, and categorized as MFI structure Close examples ZSM-8, ZSM-11, ζ-1 , ζ-3, NU-4, Nu-5, TZ-1, TPZ-1, ISI-3, ISI-5 and AZ-1. These crystalline ones Each of the pentasil-type aluminosilicates can be replaced by a known one Method be prepared.

Of these pentasil type crystalline aluminosilicates, an aluminosilicate having an MFI structure is preferable from the viewpoint of excellent hydrothermal durability, with ZSM-5 produced by using mordenite as a seed crystal being particularly preferred. Of the above-described crystalline aluminosilicates of the pentasil type, an aluminosilicate having a molar ratio (SiO ₂ / Al ₂ O ₃ ) of 10 to 200 is preferable. When the molar ratio is smaller than 10, the hydrothermal durability of the zeolite itself is low, so that a reduction in the long-term stability of the corresponding catalyst is induced, while when the molar ratio is larger than 200, the ion exchange capacity is limited, so that the amount of active metal which is incorporated is reduced, resulting in poor catalyst activity. In the present invention, these pentasil type crystalline aluminosilicates and zeolite selected from ferrierite and mordenite may be used singly or in combination of two or more kinds to form a catalyst carrier.

To the above-described crystalline aluminosilicates of the pentasil type and the zeolite selected Made of ferrierite and mordenite, can be a variety of compounds how to give an oxide which is common for conventional catalyst carrier Formation of a catalyst carrier is used as long as the compounds are the properties of the catalyst how not to inhibit power to purify exhaust gas. For example, silicon oxide, Alumina, silica-alumina, Magnesium oxide or zirconium oxide incorporated to the dispersibility increase the copper component and the phosphorus component.

in the Catalyst for purifying exhaust gas according to the present invention be at least a copper component and a phosphorus component incorporated in the catalyst support described above.

According to the invention, the amount in the catalyst carrier incorporated copper component preferably 0.8 to 30.0 wt .-%, particularly preferably 2.0 to 15.0% by weight, based on the total weight of the catalyst, reduced to CuO. If the content is lower as 0.8% by weight, the catalyst shows poor activity due to the low copper content while, when the content exceeds 30.0 wt%, copper oxide (CuO), for example, aggregated on the surface of the catalyst support, so that the micro pores of the catalyst support clog up, sometimes may cause a reduction in catalyst activity.

The amount of the incorporated phosphorus component is preferably 0.1 to 5.0 wt .-%, particularly preferably 0.1 to 2.0 wt .-% based on the total weight of the catalyst, reduced to P ₂ O ₅ . When the content is less than 0.1% by weight, the stability of the copper component is not fully ensured, sometimes resulting in failure to obtain a catalyst having excellent hydrothermal stability, while when the content is 5.0 Wt .-%, an improvement in durability is not obtained to the same extent with the addition amount.

According to the invention, others can Components as the copper component and phosphorus component, as long as they have the catalyst activity and durability do not negatively influence. For example, a metal component such as Co, Fe, Ga or In, to further the catalyst activity to increase. A metal component such as a rare earth metal, alkaline earth metal or Zr, or a halogen compound thereof can be incorporated to further increase the durability of the catalyst. Such other components are typically present in an amount of about 0.05 to 10 wt .-% incorporated based on the total amount of the catalyst.

When next discloses a process for preparing a catalyst for purification described by exhaust.

in the first step of the method for producing a catalyst for purifying exhaust gas according to the present invention Invention becomes a solution prepared containing a copper compound and a phosphorus compound, the the copper component and the phosphorus component, which in the Catalyst carrier to be incorporated.

When solvent for the preparation of the solution for incorporation can solvent used, usually for preparing a catalyst by, for example, incorporation an active component in a catalyst carrier, and they are used can suitably from polar solvents such as water or Alcohol (e.g., methanol, ethanol). Of these will in practice, water is preferably used.

None special restriction exists with respect to the copper compound and it can copper compounds such as Salts of inorganic acids, Halides, salts of organic acids and complexes are used. Examples include salts of inorganic acids such as Copper nitrate or copper carbonate; Halides such as copper fluoride, Copper chloride or copper bromide; Salts of organic acids such as Copper acetate or copper oxalate; and complexes such as a copper-amine complex or a copper-cyano complex. Of these copper compounds are salts of inorganic acids to the extent that they are easily incorporated homogeneously into the catalyst support with copper nitrate being particularly preferred. These copper compounds can used singly or in combination of two or more species.

It There is no special restriction for the Phosphorus compound as long as it contains phosphorus and solubility or compatibility with the solvent used and phosphorus compounds such as inorganic phosphoric acid or salts thereof or phosphorochalcogenides. Examples for the inorganic phosphorus acids shut down (a) phosphoric acid with a variety of oxidation numbers of phosphorus such as orthophosphoric acid, metaphosphoric acid, hypophosphorous acid, phosphorous Acid or hypophosphorous acid; and (b) condensed phosphoric acids such as polyphosphoric acids - e.g. Orthopyrophosphoric acid, metapyrophosphoric acid, tripolyphosphoric acid and tetrapolyphosphoric and polymetaphosphoric acids - e.g. Trimetaphosphoric acid, tetrametaphosphoric acid and hexametaphosphoric a, examples of the salts of the above-described inorganic phosphoric acids include alkali metal salts such as lithium salts, sodium salts and potassium salts; and ammonium salts one. These salts close also hydrogen salts such as alkali metal dihydrogen orthophosphates, alkali metal hydrogen orthophosphates, ammonium dihydrogen orthophosphate, Ammonium hydrogen orthophosphate, alkali metal hydrogen phosphite and Ammonium hydrogen phosphite as well as normal salts such as trialkali metal orthophosphates and triammonium orthophosphates. Examples of the Phosphorchalcogenide shut down Phosphorus pentoxide, phosphorus trioxide and phosphorus pentasulfide. From these phosphorus compounds are lithium phosphates, sodium phosphates and ammonium phosphates to the effect preferred that a catalyst having excellent heat resistance it is easily obtained, with ammonium dihydrogen orthophosphate particularly is preferred. These phosphorus compounds can be used individually or in combination used by two or more species.

The Amount of copper component and that of the phosphorus component used in the solution for incorporation are not unequivocally specified, since they are incorporated according to the amounts of the respective carriers incorporated in the catalyst carrier Components or conditions of incorporation such as temperature or pH of the solution vary. Typically, the amount is preferably 0.2 to 2.0 mmol / g-cat for the copper compound or 0.01 to 1.0 mmol / g cat for the phosphorus compound. When the amounts of the copper compound and that of the phosphorus compound so selected to be 2.0 mmol / g-cat or 1, 0 mmol / g-cat or more, aggregate the copper component or the phosphorus component on the surface of the catalyst support, so that sometimes a failure in the production of a catalyst resulting in sufficient exhaust gas purification capability. When in the In contrast, the amounts are chosen to be 0.2 mmol / g cat or less or 0.01 mmol / g-Kat or less, the Copper component or the phosphorus component not incorporated or only a small amount of the component is used in a incorporation process incorporated, allowing many repetitions of the incorporation process are required, which is not practical.

When a further component other than the copper component and the phosphorus component is incorporated, a compound containing the component and easily dissolved in a solvent to be used is suitably selected, and the compound is preferably in a solution which contains the above copper component and phosphorus component for simultaneous incorporation, that is, in a one-step incorporation process. Alternatively, a usual incorporation treatment separately before and after the incorporation of the copper component and the phosphorus component, the According to the invention be carried out.

According to the invention pH of the solution adjusted by adding ammonia after a buffer (or no buffer) to the solution was given.

Of the Purpose of adjusting the pH is the formation of a sufficient Amount of a copper complex in the solution. The pH is determined by use adjusted by ammonia, as a formed copper-amine complex suitable is for the achievement of a homogeneous incorporation of the copper component in the catalyst carrier with regard to the ionic state, the shape and size of the complex.

It There is no special restriction for the used ammonia, and commercially available aqueous ammonia or a Ammonia-containing solution is properly undiluted or with a solvent dilute used that in the solution is used for incorporation. Generally, an ammonia source is preferred used, the ammonia in an amount of 0.5 vol .-% or more contains. If the source, which has an ammonia content of less than 0.5% vol. contains used is a big one Amount of ammonia solution be added to adjust the pH, and the concentration of Copper component or the phosphorus component in the solution to Training varies considerably, so that incorporation at the desired concentration is negative is influenced.

In the embodiments of the invention The pH of the solution to be adjusted varies depending on whether the pH adjustment by using the buffer described below or without use of the buffer.

that is, if no buffer is added, the pH becomes 9.0 or more, preferably 9.0 to 12.0, while if the buffer was previously is added, the pH to 8.0 or more, preferably 8.0 to 12.0 is set. If the pH is less than 9.0 in the first case and less than 8.0 is set in the latter case, none will sufficient amount of a copper-amine complex formed. Therefore, will the copper component not homogeneous in the catalyst support incorporated, resulting in a deterioration of the performance of the catalyst in the purification of exhaust gas results.

As mentioned above, the pH of the solution becomes after addition of a buffer in one embodiment of the present invention Set invention, since the copper-amine complex in a sufficient Amount can be formed at lower pH by adding the buffer can, and a phosphorus compound efficient with high solubility in the catalyst carrier is incorporated.

It There is no special restriction in terms of the invention used Buffers, and commercially available Buffers can suitable to be used. A buffer that adjusts the pH to 7.0 or more, is preferred because ammonia must be added in an amount which is bigger as required to adjust the pH of the solution to 8.0 or more, if a buffer is used, reduce the pH to 7.0 or less established. examples for the preferred buffers include ammonium nitrate, Ammonium chloride, ammonium acetate and sodium acetate. Of these More preferably, a salt is an ionic fragment contains that is also a fragment of the copper compound and the phosphorus compound is that used to make a the copper component and the solution containing phosphorus component is used. If, for example Copper nitrate is used as a copper compound and ammonium dihydrogen phosphate as a phosphorus compound ammonium nitrate is the most preferred buffer. The Amount of buffer used depending on the type of buffer is typically 2 to 6 moles / mole of Cu ions.

According to the invention at least one copper component and one phosphorus component in one Catalyst carrier incorporated, which is a crystalline aluminosilicate of the pentasil type or one of ferrierite and mordenite, by using the above described pH adjusted solution for incorporation. The training method will be next in the Detail described.

What the incorporation method of the present invention is concerned a catalyst carrier, containing crystalline aluminosilicate of the pentasil type or one of Ferrierite or mordenite, to the solution described above Incorporation given to a temperature range of 10 to 50 ° C, preferred 15 to 40 ° C heated or cooled and the mixture is allowed to stand or is preferred while Stirred for 1 to 10 hours, preferably 1 to 5 hours. The copper component or the phosphorus component is reacted with cations of the catalyst support ion-exchanged this step. There are no special restrictions for the for heating, Cool or stirring used equipment, and one usually used apparatus can be used according to the invention.

To the treatment for the time described above, the pH of the solution to 7.0 or less, is preferred 6.5 to 4.0 by adding an acid to the solution set. The reason for Adjusting the pH of the solution to 7.0 or less, in the catalyst carrier is not ion-exchanged To incorporate copper component or phosphor component, which in the solution is included before the pH adjustment.

It There is no special restriction for the Acid to Adjusting the pH of the solution, and nitric acid, hydrochloric acid or sulfuric acid can used according to the invention become. Of these, nitric acid to the effect that a catalyst having excellent durability can be easily obtained.

The Add the acid is preferred at a pH decrease rate of about 0.2 to 2 / minute performed. If the rate is two or more, a copper component becomes light in the surface the catalyst incorporated in the form of aggregates, resulting in a Failure in the preparation of a catalyst with sufficient Performance in the purification of exhaust gas results while, when the rate is 0.2 or less, the effect of preventing the Aggregation in the same degree as the time spent is not received.

The Acid is preferably with stirring added to the occurrence of sudden local pH changes in the solution to prevent.

According to the invention solution continue to stand or while 0.5 to 4 hours, preferably 0.5 to 2 hours with heating or Cool to a temperature range of 10 to 50 ° C, more preferably 15 to 40 ° C, after addition the acid touched. The copper component or the phosphorus component contained in the solution is incorporated by this step in the desired amount in the catalyst support.

According to the invention Incorporation of the copper component and the phosphorus component of the solution to Insulation of a solid filtered, which washed and through a common one Method is dried. For example, filtration becomes more typical by using a Buchner funnel, a pressure filtration apparatus, a filter press, etc., performed, and the solid is dried in air at 100 to 200 ° C for 6 to 24 hours. According to the invention, a desired Amount of the copper component and the phosphorus component typically in the catalyst support by a step of training or by repeated steps of Incorporation be incorporated to a further homogeneous incorporation to realize the copper component and the phosphor component.

Of the shaped catalyst supports, the one desired Having the amount of the copper component and a desired amount of the phosphorus component supported, is by a usual Burned method, thereby obtaining a catalyst. For example Burning is done by using a usually for burning a Catalyst used apparatus such as a muffle furnace or a rotary kiln, in air at 500 to 700 ° C for 0.5 to 8 hours.

According to the invention of calcined catalyst further with a substance such as an acid, an alkali, Steam, ammonia, a halogen or other non-metallic compounds or with heat be treated to provide a catalyst used in the invention.

Of the The catalyst obtained is usually in the form of powder and can be used as is. The catalyst is preferred after molding into any shape, such as a spherical, columnar, stellate or honeycomb-shaped Form by using a binder such as silica, alumina, Silica-alumina, magnesia or zirconia in dependence used by the user. Alternatively, the catalyst of the invention also by applying powder therefrom to separately prepared carrier substrates be used with a variety of shapes. There is no special restriction in terms of the material used as a carrier substrates, and a variety of heat-resistant materials like ceramics and metals can selected and used. For example, as a catalyst for exhaust gases from automobiles preferably uses a catalyst, the ceramics with excellent strength, especially at high temperatures and long-term heat resistance, including a honeycomb-shaped carrier substrate made of cordierite consists, and with a powder of the catalyst of the invention is coated.

Examples

The The present invention is next described in detail with the help of examples.

example 1

Three solutions were made; a solution comprising aluminum sulfate dodecylhydrate (337.5 g), 97% sulfuric acid (362.5 g) and water (8250 g) (designated solution I); a solution comprising water glass (SiO ₂ ; 28.5%, Na ₂ O 9.5%, water 62%) (5275 g) and water (5000 g) (referred to as Solution II); and a solution comprising sodium chloride (987.5 g) and water (2300 g) (referred to as Solution III).

Then Solution I and Solution II were mixed while simultaneously dropwise added to Solution III. The pH of the raw material mixture was adjusted to 9.5 and mordenite (SiO ₂ / Al ₂ O ₃ ) (molar ratio = 2.0) (12.5 g) was added as seed crystals.

The Raw material mixture was then placed in a 25 liter autoclave and at 170 ° C and 3000 rpm and in the sealed state during 20 Hours stirred. After cooling the reaction mixture was filtered off, giving a precipitate was obtained thoroughly washed with pure water and dried at 120 ° C for 20 minutes was, whereby crystalline aluminosilicate of the pentasil type with a ZSM-5 structure (MFI structure) was prepared. The measurement results from the powder X-ray diffraction of this aluminosilicate are shown in the following Table 1.

Table 1

The ratio SiO ₂ / Al ₂ O ₃ (molar ratio) of this aluminosilicate was 32. This aluminosilicate was then fired at 550 ° C in a stream of air for 6 hours.

A solution for incorporation containing a copper component and a phosphorus component was then prepared as follows; Copper nitrate trihydrate (132.5 g), ammonium dihydrogen phosphate (11.17 g), and ammonium nitrate (178 g) were added sequentially to water (2080 g) and 5% aqueous ammonia was added to the solution while the solution temperature was at 30 ° C was controlled to adjust the pH to 8.5. To the resulting solution, the above-described aluminosilicate (500 g) was added, and the ion exchange in the mixture was allowed to proceed for 4 hours while controlling the solution temperature at 30 ° C. Subsequently, 30% nitric acid was added to the solution to adjust the pH to 6.0, and the ion exchange in the mixture was allowed for an additional hour. The resulting slurry solution was filtered to isolate a solid, then washed with water, dried at 120 ° C for 24 hours, and fired at 500 ° C for 4 hours to thereby obtain the intended catalyst. The copper content of the catalyst reduced to CuO was 7.5% by weight, and the phosphorus content thereof reduced to P ₂ O ₅ was 1.3% by weight.

Next, the reduction-reduction performance of NO _{x of} the above-described catalyst was evaluated based on the initial activity and the steam-treatment (hydrothermal treatment) activity described below.

(1) Evaluation of the initial activity

A sample of the obtained catalyst (2 cc) was placed in a stainless steel reaction tube, and the tube was maintained at the temperatures described below. A model gas was passed through the above-described reaction tube as a gas to be treated at GHSV = 80,000 h ^-1 . The model gas included NO _x (500 ppm), O ₂ (6.0%), C ₃ H ₆ / C ₃ H ₈ (C ₃ H ₆ / C ₃ H ₈ = 2 (about 2500 ppm as THC concentration)) , and the rest of nitrogen. The THC (Total Hydrocarbon Concentration) means the concentration of hydrocarbons reduced to methane. Next, the gas discharged from the outlet of the reaction tube was introduced into a chemiluminescence analyzer for measuring the NO _x content of the gas. The removal factor of NO _x after the catalytic reaction was calculated by comparing the NO _x content thus obtained with the concentration of NO _x in the model gas before introduction into the reaction tube. The removal factor of NO _x was evaluated at the reaction tube temperatures of 300 ° C, 350 ° C and 400 ° C, respectively. The results are shown in Table 2.

(2) Assessment of the activity after the Steam treatment (hydrothermal treatment)

A sample of the catalyst prepared in Examples of the invention was introduced into a quartz reaction tube and the tube was maintained at 750 ° C. A nitrogen gas containing C ₃ H ₆ / C ₃ H ₈ (C ₃ H ₆ / C ₃ H ₈ = 2 (about 2500 ppm as THC concentration)), O ₂ (0.5%) and water (10 vol. %) was introduced into the tube at a GHSV = 80,000 h ^-1 for 16 hours to carry out the steaming.

After cooling the reaction tube, the catalyst isolated from the tube was introduced into a stainless steel reaction tube, and the NO _x removal ratio of the model gas was evaluated under the conditions identical to those in the above-described initial activity evaluation. The results are shown in Table 2.

Example 2

The procedure of Example 1 was carried out by using 5 aqueous ammonia in place of ammonium nitrate to adjust the pH of the solution to 11.5 to prepare a catalyst of Example 2. The copper content of the catalyst reduced to CuO was 6.7 wt% and the phosphorus content reduced to P ₂ O ₅ was 1.1 wt%.

Example 3

The procedure of Example 1 was carried out by using ammonium carbonate instead of ammonium nitrate to prepare the catalyst of Example 3. The copper content of the catalyst reduced to CuO was 6.0 wt%, and the phosphorus content reduced to P ₂ O ₅ was 1.2 wt%.

Example 4

The procedure of Example 1 was carried out by using ammonium pyrophosphate in place of ammonium dihydrogen phosphate to prepare a catalyst of Example 4. The copper content of the catalyst reduced to CuO was 7.3 wt%, and the phosphorus content thereof reduced to P ₂ O ₅ was 0.8 wt%.

Comparative Example 1

The procedure of Example 2 was conducted except that the pH of the solution was adjusted by using 5% aqueous ammonia (pH of the solution 2.5) and the use of nitric acid was omitted to prepare the catalyst of Comparative Example 1 has been. The copper content of the catalyst reduced to CuO was 2.6 wt%, and the phosphorus content thereof reduced to P ₂ O ₅ was 0.2 wt%.

Comparative Example 2

The procedure of Example 2 was carried out using 5% aqueous ammonia to adjust the pH of the solution to 6.0 to thereby prepare a catalyst of Comparative Example 2. The copper content of the catalyst reduced to CuO was 6.0 wt%, and the phosphorus content thereof reduced to P ₂ O ₅ was 1.0 wt%.

Comparative Example 3

The procedure of Example 2 was followed except that the pH adjustment of the solution was omitted by using nitric acid to thereby prepare a catalyst of Comparative Example 3. The copper content of the catalyst reduced to CuO was 3.2 parts by weight. %, and the phosphorus content thereof reduced to P ₂ O ₅ was 0.01% by weight.

The initial activity and the activity after the steam treatment (hydrothermal treatment) were used for the catalysts Examples 2 to 4 and Comparative Examples 1 to 3 among the identical conditions as in Example 1 assessed. The results are shown in Table 2.

Table 2

As shown in Table 2, the catalysts of the present invention achieve high NO _x removal factors even after steaming and, accordingly, show excellent durability. Table 2 also shows extremely low NO _X removal factors after the steaming for Comparative Example 1, in which the pH of the solution was not adjusted, resulting in almost no formation of copper-amine complex and no substantial ion exchange by copper aqualons. Similar to the case of Comparative Example 1, for Comparative Example 2, extremely low NO _X removal factors are obtained after the steaming as compared with those of the present invention, in Example 2, the pH of the solution is adjusted to as low as 6.0, which resulting in poor formation of a copper-amine complex. Moreover, extremely low NO _x removal factors are obtained after the steaming treatment for Comparative Example 3, in which the pH of the solution is not adjusted by using an acid, resulting in almost no incorporation of a phosphorus component.

As described above, provides the method for producing a catalyst for purifying exhaust gas according to the present invention Invention a catalyst for the purification of exhaust gas with high durability and Efficiency ready.

Claims (7)

A method of producing a catalyst for purifying exhaust gas, the catalyst comprising a crystalline aluminosilicate catalyst carrier of the pentasil type or a zeolite catalyst carrier selected from ferrierite and mordenite, supported thereon at least one copper component and a phos phor component, which process is characterized in that the catalyst support is placed in a solution containing at least one copper component, a phosphorus component, ammonia and a buffer and having a pH of 8.0 or more, and then adding an acid to the solution to adjust the pH of the solution to 7.0 or less to thereby incorporate at least the copper component and the phosphorus component into the catalyst carrier. Process for the preparation of a catalyst for Purification of exhaust gas according to claim 1, wherein the pH of the solution is before Add the catalyst support 8.0 to 12.0. Process for the preparation of a catalyst for Purification of exhaust gas, wherein the catalyst is a crystalline aluminosilicate catalyst support from Pentasil type or a zeolite catalyst support selected from ferrierite and mordenite, includes, who carried on it has at least one copper component and one phosphorus component, the process being characterized in that the catalyst support is placed in a solution which is at least one copper component, a phosphorus component and ammonia and having a pH of 9.0 or more, and then a Acid too the resulting solution is given to the pH of the solution to set to 7.0 or less, thereby at least the copper component and the Incorporate phosphorus component into the catalyst support. Process for the preparation of a catalyst for Purification of exhaust gas according to claim 1, wherein the pH of the solution is before Add the catalyst support 9.0 to 12.0. Process for the preparation of a catalyst for Purification of exhaust gas according to one of claims 1 to 4, wherein the crystalline Aluminosilicate of the pentasil type has an MFI structure. Process for the preparation of a catalyst for Purification of exhaust gas according to claim 1 or claim 2, wherein the buffer is at least one species selected from ammonium nitrate, Ammonium chloride, ammonium acetate and sodium acetate. Process for the preparation of a catalyst for Purification of exhaust gas according to any one of claims 1 to 6, wherein the acid is at least a species is chosen is made from nitric acid, hydrochloric acid and sulfuric acid.