JPH0810622A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To provide a catalyst efficiently purifying exhaust gas discharged from an internal combustion engine or various combustors. CONSTITUTION:In a catalyst based on crystalline alumnosilicate and containing a copper (Cu) component and a phosphorus (p) component, an SiO2/Al2O3 mol ratio is 20-60 and the contents of Cu and P are respectively 4-15% and 0.01-1.7% by wt. of crystalline aluminosilicate from which adsorbed water is removed. An atomic ratio of P/Cu is above 0-0.5 and the ratio [s(Cu/Si)/b(Cu/Si)@{9147/28 }of an atomic ratio of Cu/Si of the whole of the catalyst that is [s(Cu/Si)] and an atomic ratio of Cu/Si in the part up to a depth of 5nm from the surface of the catalyst calculated by an X-ray photoelectronic spectrum analysis method (XPS method) that is [s(Cu/Si)] is above 0-10.0.

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 to efficiently purifying exhaust gas discharged from an internal combustion engine such as an automobile engine and various combustors, as well as low temperature activity, heat resistance and durability. And an exhaust gas purifying catalyst excellent in

[0002]

2. Description of the Related Art Conventionally, catalysts obtained by supporting various metals on crystalline aluminosilicate (hereinafter referred to as zeolite) have been widely used in various fields. Furthermore, in recent years, this catalyst system, in particular content is high in the exhaust gas of oxygen, if hydrocarbons are present, being noted that there are remarkable ability of being able to purify the NO _X There is.

[0003] Especially, a metal as copper (Cu) carrying a Cu- zeolite catalyst has high activity, high flow rate gas conditions, NO _X even better in a relatively wide temperature range
Has purification performance. For this reason, great expectations are placed on purification of exhaust gas emitted from mobile sources such as automobiles and on-site type engines for private power generation.

However, when the Cu-zeolite catalyst is exposed to a high temperature of 600 ° C. or higher, the exhaust gas contains a large amount of water, or the oxidation-reduction atmosphere of the exhaust gas fluctuates, the exhaust gas purification performance is deteriorated with time. However, it has not been put to practical use because it has a drawback that it cannot withstand long-term use.

The main cause of deterioration when the above catalyst is exposed to high temperature is thought to be that Cu ions retained at the ion exchange site in zeolite move out of the supporting site due to heat and migrate to cause sintering. Has been. When the water content in the exhaust gas and the atmospheric conditions fluctuate greatly, this sintering is further promoted. Therefore, in order to improve the heat resistance and durability of the catalyst, it is necessary to stabilize Cu as an active ingredient and suppress sintering.

Therefore, vigorous research and proposals have been made on methods of stabilizing Cu ions by various additives.
For example, JP-A-3-131345 proposes a catalyst in which zeolite is loaded with Cu and at least one selected from the group consisting of Ca, Sr and Ba. Further, JP-A-3-202157 proposes a catalyst supporting Cu and at least one kind of alkaline earth metal and at least one kind of rare earth metal. Further, in JP-A-3-135437, Cu, Fe (iron), Co
A catalyst supporting at least one variable valence metal selected from the group consisting of (cobalt), Ni (nickel), V (vanadium) and the like has been proposed. In addition, Japanese Patent Laid-Open No. 4-4045 proposes a catalyst in which crystalline silicate having a specific X-ray diffraction pattern and a chemical formula carries at least one component selected from Cu and 27 kinds of elements. There is.

[0007]

However, it is not clear whether the catalysts according to the above publications are expected to have a significant effect in improving the heat resistance or durability of the catalysts, and they are still sufficient for practical use. The actual situation is that a Cu-zeolite catalyst having performance has not been obtained. In particular, it has been desired to develop a catalyst having excellent heat resistance and durability that can be used even under severe conditions such as automobile exhaust gas. Therefore, the present invention is
It is an object of the present invention to provide a catalyst which has excellent low-temperature activity, little deterioration even when used at high temperatures for a long time, and has excellent heat resistance and durability.

[0008]

Means and Action for Solving the Problems The present inventors have
As a result of earnest research to solve the above-mentioned problems, in a catalyst body comprising a Cu component and a P component in an inorganic material containing zeolite as a main component, limited SiO ₂ / Al ₂ O
_A specific amount of Cu and P is contained in a zeolite having a molar ratio of ₃ and the P / Cu atomic ratio is controlled within a specific range, and the Cu / Si atomic ratio of the catalyst surface to the Cu / Si atomic ratio of the entire catalyst is The inventors have found that the above objects can be achieved when the ratio and the ratio of the P / Si atomic ratio on the catalyst surface to the P / Si atomic ratio of the entire catalyst are controlled within a specific range, and have reached the present invention.

An object of the present invention is to provide a catalyst body comprising a Cu component and a P component in an inorganic substance containing zeolite as a main component, wherein the zeolite has a SiO ₂ / Al ₂ O ₃ molar ratio of 20 to 60. The content of Cu and P is in the range of 4 to 15% by weight and 0.01 to 1.7% by weight, respectively, with respect to the zeolite in a state where adsorbed water is excluded, and P / Cu Has an atomic ratio of more than 0 and 0.5 or less, and the atomic ratio of Cu / Si [b (C
u / Si)] and the atomic ratio of Cu / Si [s (Cu / Si)] in the portion from the catalyst surface to a depth of 5 nm, which is determined by X-ray photoelectron spectroscopy (XPS method) [s (Cu / Si) / b (Cu / Si)] is more than 0 and 10.0 or less, and the P / Si atomic ratio [b (P / Si)] of the entire catalyst and the catalyst surface obtained by the XPS method Ratio [s (P / Si) / b] with atomic ratio of P / Si [s (P / Si)] up to a depth of 5 nm
(P / Si)] is more than 0 and 14.0 or less. Here, the Cu / Si atomic ratio [s (Cu / Si)] on the catalyst surface
And P / Si atomic ratio [s (P / Si)] can be determined by X-ray photoelectron spectroscopy (XPS method), and the analysis depth is approximately 5 nm from the surface. Hereinafter, the present invention will be described in more detail.

In order to suppress the activity deterioration of the Cu-zeolite type catalyst upon exposure to high temperature, a technique of stabilizing Cu and suppressing sintering is indispensable. Therefore, various methods have been vigorously studied and proposed for stabilizing Cu ions. As a result of extensive and detailed research on the effect of adding various components, the present inventors have come to pay attention to the P component.

The P component has a relatively strong interaction with Cu to stabilize it, but if the interaction is too strong, the catalytic activity will decrease. Therefore, it is essential to control this interaction force to an appropriate strength, and thereby, the thermal stability of the Cu component and the catalytic activity are effectively balanced to obtain an extremely high performance catalyst.

The important parameters that determine this are
They are (1) the amount of Cu and P in the catalyst, and (2) the ratio of Cu and P on the surface of the catalyst to the entire catalyst. Since the P component is difficult to penetrate into the zeolite pores, it tends to segregate in the surface layer portion thereof, and due to the strong interaction with the Cu component, C
It lowers the dispersibility of u and causes a decrease in catalytic activity. It is considered that such an inconvenience can be avoided by setting the above parameters within the range of the present invention. The feature of the present invention is to find out this parameter and its appropriate range.

Here, the zeolite SiO ₂ / Al ₂ O
The molar ratio of ₃ is limited to the range of 20 to 60 because it is necessary for the supported amounts of Cu and P on the catalyst to fall within the range of the present invention. Zeolite SiO ₂ / Al ₂ O
_When the molar ratio of ₃ is less than 20, in addition to the amount of Cu and P supported exceeding the range of the present invention, the heat stability and durability of the catalyst decrease due to insufficient thermal stability of the zeolite itself. . On the other hand, if this molar ratio exceeds 60, the required amount of supported Cu component cannot be obtained, and the catalytic activity becomes insufficient.

The zeolite used in the present invention can be appropriately selected and used from known zeolites, and the pentasil type is particularly effective. Examples of such zeolite include mordenite, ferrierite, ZSM-5, ZSM-11 and the like. Further, when zeolite is used to improve crystallinity or stabilize it by hydrothermal treatment or resynthesis, a catalyst having higher heat resistance and durability can be obtained.

As the raw material of the P component used in obtaining the exhaust gas purifying catalyst of the present invention, various compounds such as inorganic acid salts, oxides, organic acid salts, chlorides, carbonates, sodium salts and ammonium salts are used. However, in order to support this component on zeolite, it is preferable to use a raw material having a high solubility in water, because it is simple and effective to carry it as an aqueous solution by an ion exchange method or an impregnation method. Even a raw material having a low solubility in water can be similarly supported by using various alcohols and organic solvents. Furthermore, a vapor phase supporting method using chloride is also possible.

Similarly, as the raw material of the Cu component, various compounds such as inorganic acid salts, oxides, organic acid salts, chlorides, carbonates, sodium salts, ammonium salts and ammine complex compounds can be used. The same loading method as for the P component can be used. It is preferable to adjust the pH by adding a suitable acid or base to the aqueous solution of the P or Cu component.

In the present invention, the contents of Cu and P are in the ranges of 4 to 15% by weight and 0.01 to 1.7% by weight, respectively, with respect to the zeolite excluding the adsorbed water. When the content of Cu is less than 4% by weight, the amount of the active component is not sufficient, and when it exceeds 15% by weight, the excess copper oxide (CuO) on the surface of the catalyst is excessive and the pores of the zeolite are blocked. It causes an adverse effect on the catalytic activity such as causing. On the other hand, the P component is effective even if it is a very small amount, but when it is less than 0.01% by weight, almost no effect is observed, and conversely, when it exceeds 1.7% by weight, the stabilization of Cu by P progresses. Too much, rather, causes a decrease in catalytic activity. A more desirable content of Cu and P is 5 to 5, respectively.
It is in the range of 12% by weight and 0.1 to 1.2% by weight.

In order to maximize the effect of the P component while suppressing the excessive stabilization of Cu by the P component, P / C
It is important to control u (atomic ratio), and in the present invention, when it exceeds 0.5, inactivation of Cu becomes remarkable and the catalytic activity is lowered.

Cu / Si atomic ratio [b
(Cu / Si)] and Cu / in the catalyst particle surface layer portion
Si atomic ratio [s (Cu / Si)] and ratio [s (Cu /
Si) / b (Cu / Si)] is effectively in the range of more than 0 and 10.0 or less, and particularly preferably 7.0 or less.

On the other hand, the P / Si atomic ratio [b (P
/ Si)] and the P / Si atomic ratio [s of the catalyst particle surface layer portion [s
(P / Si)] ratio [s (P / Si) / b (P / S)
i)] is effectively more than 0 and 14.0 or less, and particularly preferably 11.0 or less.

The shape of the catalyst of the present invention 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 for use.
As the honeycomb material, a cordierite material is generally used, but the material is not limited to this, and a honeycomb carrier made of a metal material can be used. Further, the catalyst powder itself is formed into a honeycomb shape. You may. By making the shape of the catalyst a honeycomb,
Since the contact area between the catalyst and the exhaust gas is large and the pressure loss is suppressed, it is extremely advantageous when used as an automobile catalyst which requires processing of a large amount of exhaust gas in a limited space with vibration.

[0022]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

Example 1 Sodium pyrophosphate (Na_FourP₂O₇) And copper acetate
Dissolve in ion-exchanged water to obtain a mixed aqueous solution containing P and Cu.
Was. Ammonia water and nitric acid are appropriately added to this mixed aqueous solution.
The pH of the solution was adjusted to 8.0 and then added to this solution.
SiO₂/ Al ₂O₃Na-type ZSM with a molar ratio of about 30-
The powder of No. 5 was added and stirred well. When stirring,
Add nitric acid and ammonia appropriately to adjust the pH of the solution to 8.5.
I kept it at 9.0.

The amount of P in the mixed solution is an amount corresponding to 0.5% by weight (as P) with respect to the zeolite powder in a state where the adsorbed water is removed, and the amount of Cu also corresponds to the ion exchange capacity of the zeolite. The amount was 300% when converted.
After carrying out the stirring operation for 8 hours, the zeolite cake obtained by filtering the mixed solution was placed in an oven at 120 ° C. for 24 hours.
By drying for at least hours, and then calcining at 500 ° C. for 4 hours in an air atmosphere, Cu-P-ZSM-5 catalyst powder was obtained. Quantitative analysis result of the obtained catalyst powder (by ICP method)
Is shown in Table 1.

[0025]

[Table 1]

All the values in Table 1 are based on the zeolite powder with adsorbed water removed. 2250 g of the catalyst powder obtained as described above, 1250 g of silica sol (solid content 20% by weight) and 1500 g of water were put into a ball mill pot and pulverized and mixed for 4 hours to obtain a slurry. About 400 of this slurry per square inch cross section
The catalyst (1) of Example 1 was obtained by coating on a cordierite honeycomb carrier having individual channels, drying with hot air at 120 ° C., and then firing at 400 ° C. for 1 hour. The coating amount of the catalyst powder on the honeycomb of this catalyst was 230 g / L.

Example 2 The same Na-type ZSM-5 powder as in Example 1 was subjected to ion exchange using an aqueous ammonium chloride solution, and then 80-1 in an oven.
It was dried at 00 ° C. for 24 hours or more to obtain NH ₄ type ZSM-5. The obtained zeolite powder was allowed to stand still in a glass reaction tube, and phosphorus trichloride (PCl ₃ ) vapor was gradually blown in while maintaining the temperature at about 150 ° C. in a dry nitrogen stream,
A powder of ZSM-5 carrying P was obtained. The amount of P supported on ZSM-5 was 0.56% by weight, based on the zeolite powder in the state where adsorbed water was removed.

On the other hand, copper acetate was dissolved in ion-exchanged water to form C.
A u aqueous solution was obtained. The P-ZSM-5 powder obtained as described above was added to this aqueous solution, the mixture was stirred for 8 hours in the same manner as in Example 1, and then the mixed solution was filtered, dried, and calcined, and then Cu- P-ZSM-5 catalyst powder was obtained. The results of quantitative analysis of this catalyst powder are shown in Table 2.

[0029]

[Table 2]

The catalyst powder obtained as described above was treated exactly as in Example 1 to obtain a honeycomb catalyst (2) of Example 2.

Examples 3 to 10 Catalysts having different loadings of Cu and P were obtained in the same manner as in Example 1 except that the amounts of Cu and P in the P-Cu mixed solution were changed. Honeycomb catalysts (3) to (10) were obtained.
Table 3 shows the quantitative analysis results of each catalyst.

[0032]

[Table 3]

Examples 11 to 13 Na-type ZSM-5 having different SiO ₂ / Al ₂ O ₃ molar ratios
A honeycomb catalyst was prepared in the same manner as in Example 1 except that
(11) to (13) were obtained. SiO ₂ / Al ₂ O in each catalyst
_{The 3} molar ratios were about 23, 45 and 58, respectively. Table 4 shows the results of quantitative analysis of each catalyst.

[0034]

[Table 4]

Example 14 Na-type ZSM-having a SiO ₂ / Al ₂ O ₃ molar ratio of about 30
Instead of 5, N ₂ with a SiO ₂ / Al ₂ O ₃ molar ratio of about 28
A honeycomb catalyst (14) was obtained in exactly the same manner as in Example 1 except that a-type mordenite was used. Table 5 shows the quantitative analysis results of this catalyst.

[0036]

[Table 5]

Comparative Example 1 The same Na-type ZSM-5 as in Example 1 was used in an aqueous solution of copper nitrate.
After stirring for an hour, Cu was supported by the ion exchange method. Then, the honeycomb catalyst (15) was obtained in the same manner as in Example 1 through the steps of drying and firing. The quantitative analysis results of this catalyst are as follows. Cu; 3.3% by weight, P; 0% by weight, P / Cu atomic ratio;
0

Comparative Examples 2 to 3 Catalysts having different loadings of Cu and P were obtained in the same manner as in Examples 3 to 7, and catalysts (16) to (17) of Comparative Examples 2 to 3 were obtained in the same manner.
I got Table 6 shows the quantitative analysis results of each catalyst.

[0039]

[Table 6]

Comparative Examples 4 to 5 Na-type ZSM-5 having different SiO ₂ / Al ₂ O ₃ molar ratios
Comparative Examples 4-5 in the same manner as in Example 1 except that
The following honeycomb catalysts (18) to (19) were obtained. Si in each catalyst
The O ₂ / Al ₂ O ₃ molar ratio was about 18,70, respectively. Table 7 shows the quantitative analysis results of each catalyst.

[0041]

[Table 7]

Comparative Example 6 A catalyst having different loadings of Cu and P was obtained in the same manner as in Example 3, and a honeycomb catalyst (20) of Comparative Example 6 was obtained in exactly the same manner. Table 8 shows the quantitative analysis results of the obtained catalyst.

[0043]

[Table 8]

Comparative Example 7 An aqueous solution of orthophosphoric acid (H ₃ PO ₄ ) was brought into contact with the same Na-type ZSM-5 powder as in Example 1, impregnated with the P component, and then dried at 150 ° C. for 24 hours or more, Further, the P component was fixed to the ZSM-5 zeolite by calcining at 450 ° C. The obtained P-supporting ZSM-5 was added to an aqueous solution of copper acetate and stirred, and a honeycomb catalyst (21) of Comparative Example 7 was obtained in exactly the same manner as Comparative Example 1. Table 9 shows the results of quantitative analysis of the obtained catalyst.

[0045]

[Table 9]

Comparative Example 8 In Comparative Example 1, the copper nitrate was replaced with copper acetate, the ZSM-5 powder was stirred in an aqueous solution of copper acetate for 8 hours, and nitric acid and aqueous ammonia were added appropriately to adjust the pH of the solution. To 8.0
The temperature was controlled to 8.2, and stirring was continued for another 4 hours. This mixed solution was filtered and dried and calcined in the same manner as in Comparative Example 1 to obtain Cu-ZSM-5 powder. On the other hand, the above-mentioned C was added to an aqueous solution of ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ).
u-ZSM-5 powder was added, and the liquid slurry was stirred for about 2 hours to impregnate and carry the P component on the Cu-ZSM-5 powder. Then, after drying in an oven at 120 ° C., a catalyst powder was obtained through a calcination process at 500 ° C. for 2 hours in an air atmosphere. Thereafter, a honeycomb catalyst (22) was obtained in the same manner as in Comparative Example 1. Table 10 shows the quantitative analysis results of the obtained catalyst.

[0047]

[Table 10]

(1) X-ray photoelectron spectroscopy (XPS) analyzer for catalyst; ESCA 5600 type X manufactured by Parkin Elmer
X-ray photoelectron spectroscopy analyzer Analysis conditions: Mg-Kα ray (1253.6e as X-ray source
V) and operated at 15 KV × 26.7 mA. Charge correction; binding energy of SiO ₂ is 103.2 eV
As a result, the charge was corrected. Measurement sample: A pressure molding machine was used to mold a disk at a pressure of 230 Kg / cm ² . By the above method, for each catalyst of Examples and Comparative Examples,
Si, C in the part from the catalyst surface to a depth of 5 nm
From the results of quantitative analysis of u and P, the atomic ratio of Cu / Si [s (Cu / Si)] and the atomic ratio of P / Si [s (P /
Si)] was calculated. On the other hand, Cu, P, Si of the entire catalyst
Content of Cu / Si atomic ratio [b (Cu / Si)] and P / Si atomic ratio [b (P /
Si)] was calculated. From the above, the [s (Cu / Si) / b (Cu / Si)] ratio and [s
(P / Si) / b (P / Si)] was calculated and shown in Tables 11 and 12 together with the performance evaluation results.

(2) Example of catalyst performance test Table 1 shows the durability performance of the catalysts of the above Examples and Comparative Examples by the rapid durability test using the actual exhaust gas of the engine and the activity evaluation.
1 and Table 12.

[0050]

[Table 11]

[0051]

[Table 12]

Activity evaluation condition evaluation device: Fixed bed flow type device using actual exhaust gas from engine Catalyst capacity: 50 cc Gas space velocity: Approximately 54000 h ^-1 engine; Air-fuel ratio (A / F); about 18 Fuel; unleaded regular gasoline

Rapid endurance treatment conditions Exhaust gas temperature at catalyst inlet: 630 ° C engine; V6 6L 3L engine manufactured by Nissan Motor Co., Ltd. Average air-fuel ratio (A / F); Approx. 15 fuel; Unleaded regular gasoline Treatment time: 20 time

Tables 11 and 12 show the NO _x purification performance of the catalysts of Examples and Comparative Examples before and after the rapid durability treatment. The NO _x purification rate at a catalyst inlet temperature of 300 ° C. before the rapid durability treatment and at the catalyst inlet temperature of 370 ° C. after the rapid durability treatment are shown. Catalysts exceeding the specified range of the parameters defined in the present invention are all inferior in initial activity, heat resistance and durability, whereas the catalyst of the present invention is excellent in initial low temperature activity,
And high N even after rapid durability treatment at temperatures over 600 ° C
It maintains the O _x purification performance and is excellent in heat resistance and durability.

[0055]

As described above, the catalyst for purifying exhaust gas of the present invention can efficiently purify NO _x in exhaust gas containing a large amount of oxygen and is excellent in heat resistance and durability. It can be used for a long time even under a temperature condition of ℃ or more. Therefore, according to the exhaust gas purifying catalyst of the present invention, it is possible to purify NO _x from the exhaust gas of an automobile equipped with a lean burn engine, so that environmental pollution is reduced,
An automobile excellent in economy (fuel efficiency) can be provided.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location B01D 53/36 102 H 104 A (72) Inventor Yoshimi Kawashima 1280, Kamizumi, Sodegaura, Chiba Idemitsu Kosan Stock company (72) Inventor Hiroshi Akama 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Inventor Goji Masuda 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa (72) Invention Hiroyuki Kanasaka, 2 Takara-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. (72) Inventor Maki Kamikubo 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd.

Claims (1)

[Claims] 1. A catalyst body comprising a copper (Cu) component and a phosphorus (P) component in an inorganic substance containing crystalline aluminosilicate as a main component, wherein SiO ₂ / Al ₂ of the crystalline aluminosilicate is used. The molar ratio of O ₃ is in the range of 20 to 60, and the crystalline aluminosilicate in the state in which the water adsorbed by the contents of Cu and P is removed is 4 to 15 respectively.
% By weight and in the range of 0.01 to 1.7% by weight, the atomic ratio of P / Cu is more than 0 and 0.5 or less, and the atomic ratio of Cu / Si of the entire catalyst [b (Cu / Si)] and X / ray photoelectron spectroscopy (XPS method), and Cu / Si in the portion from the catalyst surface to a depth of 5 nm
And atomic ratio [s (Cu / Si)] of [s (Cu / S
i)] ratio [s (Cu / Si) / b (Cu / S
i)] is more than 0 and not more than 10.0, and the P / Si atomic ratio [b (P / Si)] of the entire catalyst and P in the portion from the catalyst surface to a depth of 5 nm determined by the XPS method. / Si atomic ratio [s (P / Si)] and ratio [s
(P / Si) / b (P / Si)] exceeds 0 to 14.0
An exhaust gas-purifying catalyst characterized by being: