JPH06191810A - Phosphoric acid composition, method for producing the same, and NOx reduction decomposition catalyst using the same - Google Patents

Abstract

(57) [Summary] [Constitution] After the water-soluble phosphorus-containing compound solution is mixed with the water-soluble Cu-containing compound and Zr-containing compound mixed solution, the pH of the solution is adjusted to 6.0 ± 0.5. , Filtered, and the residue is heat-treated at 650 to 1050 ° C. for 10 hours or more to contain at least Cu, Zr, phosphorus (P) and oxygen (O), and have a molar ratio represented by Zr / Cu of 3.9.
To 4.1 and a composition having a P / Cu molar ratio of 5.9 to 6.1, and powder X-ray diffraction measurement has peaks at specific lattice plane intervals as shown in FIG. It is a composition consisting of a crystalline phase and is used as a catalyst for NOx reduction decomposition. [Effect] It has a NOx reduction decomposition action even in an atmosphere of high oxygen concentration, and is useful for purification of exhaust gas from future diesel engines and the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel phosphoric acid composition, and more particularly to a composition suitable for a catalyst for NOx reduction decomposition and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, environmental pollution has become an important issue, and among them, there is an urgent need to develop a method for decomposing and removing harmful substances such as NOx and COx in exhaust gas of automobiles. Thus, as a conventional exhaust gas purifying catalyst for automobiles, a three-way catalyst that simultaneously oxidizes carbon monoxide (COx) and hydrocarbons (CxHy) and reduces nitrogen oxides (NOx) is widely used. Has been done. As such a catalyst, γ-Al ₂ O of a noble metal such as Pd, Pt, Rh is used.
A mixture with ₃ is used, and this catalyst is supported on a refractory carrier such as cordierite.

[0003]

However, such a catalyst can efficiently purify the exhaust gas only at an oxygen concentration of about 1%, and the oxygen concentration of the exhaust gas is higher than the above optimum value. There is a problem that it cannot work effectively when it gets higher. Therefore, it is usually practiced to measure the oxygen concentration in the exhaust gas and control it so that the air-fuel ratio will always be the optimum value. is there.

On the other hand, in a gasoline engine, research and development of a lean burn system has been carried out in order to reduce fuel consumption. In this case, the oxygen concentration in the exhaust gas becomes several%,
There is a drawback that exhaust gas cannot be purified due to poisoning of precious metals. Also in the diesel engine, the oxygen concentration in the exhaust gas is high in the current combustion system,
The current situation is that exhaust gas is not purified at all.

Further, in a fixed type combustion apparatus such as a factory, NOx in the exhaust gas having a high oxygen concentration is reduced by mixing a reducing agent such as ammonia into the exhaust gas. There was a problem in terms of safety when it was attached to a mobile combustion device such as an automobile.

Therefore, the present invention provides a composition which is capable of effectively purifying exhaust gas in the above-described exhaust gas having a high oxygen concentration and which is useful as a catalyst which does not require a toxic reducing agent such as ammonia. It is provided.

[0007]

[Means for Solving the Problems] The inventors of the present invention have conducted research on the above problems, and as a result, at least Cu, Z
It contains r, phosphorus (P) and oxygen (O) and has a molar ratio represented by Zr / Cu of 3.9 to 4.1 and a molar ratio represented by P / Cu of 5.9 to 6.1. In the powder X-ray diffraction measurement, the following lattice plane spacing was 4.45 ± 0.1 Å 3.98 ± 0.08 Å 3.78 ± 0.08 Å 3.35 ± 0.07 Å 3.14 ± 0. In the exhaust gas having a high oxygen concentration, the composition having a content of 07Å 3.05 ± 0.05Å 2.88 ± 0.05Å 2.80 ± 0.05Å 2.75 ± 0.05Å 2.56 ± 0.05Å It was also found that they also have an excellent catalytic action for reducing NOx.

In particular, such a composition was prepared by mixing the water-soluble Cu-containing compound and the Zr-containing compound with the water-soluble phosphorus-containing compound solution and then adjusting the pH of the solution to 6.0 ± 0.5. After that, it is filtered and the residue is 650 to 1050 ° C.
It can be easily obtained by heat treatment for 10 hours or more.

The present invention will be described in detail below. The phosphoric acid-based composition in the present invention is a phosphoric acid compound containing Cu, Zr, phosphorus (P) and oxygen (O) as constituent elements, and the composition of each element has a Zr / Cu ratio of 3. 9 to 4.
1 and a P / Cu ratio of 5.9 to 6.1.

Further, the composition of the present invention is mainly composed of a crystal having the following lattice spacing (d value) in X-ray diffraction measurement, and the relative intensity of the peak at each lattice spacing is as follows. On the street.

Lattice plane spacing Relative strength 4.45 ± 0.1 Å VS 3.98 ± 0.08 Å W 3.78 ± 0.08 Å M 3.35 ± 0.07 Å W 3.14 ± 0.07 Å M 3 .05 ± 0.05 Å W 2.88 ± 0.05 Å W 2.80 ± 0.05 Å W 2.75 ± 0.05 Å W 2.56 ± 0.05 Å M In the composition of the present invention, the composition of each element Is limited to the above range because, if the composition deviates from the above range, a large amount of crystal phase other than the above crystal phase is precipitated and the catalytic action is lowered. However, even if a small amount of zirconium phosphate or zirconium phosphate or an amorphous phase is contained, the catalyst characteristics are not affected.

Next, in the present invention, the phosphoric acid-based composition is produced by a sol-gel method. That is, first, as a raw material, a water-soluble compound containing Cu and a water-soluble compound containing Zr were prepared,
These are in a predetermined ratio, that is, the molar ratio of Cu and Zr is 3.
An aqueous solution is prepared by mixing in an amount of 9 to 4.1. On the other hand, a water-soluble phosphorus-containing compound solution is prepared, and this is added dropwise to the above aqueous solution containing Cu and Zr. At this time, the amount of P is mixed so that the P / Cu molar ratio is in the range of 5.9 to 6.1.

Next, the pH of the mixed solution obtained as described above is adjusted to a range of 6.0 ± 0.5. Ammonia water or urea is used for adjustment. By adjusting the pH in this way, the mixed solution becomes a sol. After filtering this, the residue is 650 to 1050 ° C,
In particular, it can be obtained by heat treatment at a temperature of 700 to 1000 ° C. for 10 hours or more.

This is because, in the above production method, if the pH value deviates from the above range, it becomes difficult to accurately control the Zr / Cu molar ratio and the P / Cu molar ratio. Further, if the heat treatment temperature is lower than 650 ° C, crystallization is not sufficiently carried out, so that the crystal phase having the X-ray diffraction peak does not precipitate, and if it exceeds 1050 ° C, another crystal phase precipitates and the catalyst characteristics are deteriorated. This is because it will decrease.

NO using the composition obtained according to the invention
x When a catalyst for reductive decomposition is produced, the synthetic powder obtained as described above is appropriately crushed and then used as a catalyst, but the powder that is calcinated again at 1200 to 1600 ° C. and crushed is used. May be. The specific surface area of the powder as a catalyst is preferably controlled so that the BET value is 10 m ² / g or more.

[0016]

According to the present invention, in a phosphoric acid compound consisting of Cu, Zr, P (phosphorus) and O (oxygen), the action of reductively decomposing NOx is exhibited by precipitating the specific crystal phase. To be done. The mechanism of this reductive decomposition is not clear, but probably because the valence of the contained metal element is changed, the electronic state of the metal element and its surroundings is changed, which promotes the adsorption, reduction, and decomposition of NOx. Conceivable.

[0017]

【Example】

Example As starting materials, Cu (NO ₃ ) ₂ and ZrO (NO ₃ ) were used.
₂ · 8H ₂ O, using NH ₄ H ₂ PO _4, such that the molar ratio shown in Table 1 were weighed, firstly, Cu
(NO _{3) 2} and ZrO (NO ₃₎ the ₂ · 8H ₂ O were dissolved in pure water and stirred thoroughly. No. ₅ , while stirring, NH ₄ H ₂ PO ₄ aqueous solution is gradually added dropwise to this solution, and then the pH is slowly adjusted to a predetermined value with aqueous ammonia. Then, after suction filtration, washing with water and drying, heat treatment was performed at the temperature and time shown in Table 1, and the crystal phase was examined by X-ray diffraction. Table 1
In the above, what is described as A as a crystal phase is composed of the X-ray diffraction chart specified by the present invention in FIG.
What is described as B consists of an X-ray diffraction chart of a crystal phase other than the present invention as shown in FIG.

The obtained sample was press-molded and then sized into powder of 40 mesh pass and 80 mesh on. Then, using this sample, NO = 1000 ppm, O ₂ =
2%, C ₂ H ₄ = 1000 ppm, He = balance, SV
From 50 ° C to 50 under the condition of (space velocity) = 4800 / h
The reductive decomposition activity of NO was measured using a gas chromatograph in the range of 0 ° C. The results are shown in Table 1.

[0019]

[Table 1]

In Table 1, the results of Sample Nos. 1 to 5 are as follows:
When the pH during synthesis exceeds 6.0 ± 0.5, the Zr / Cu molar ratio before heat treatment and / or the P / Cu molar ratio becomes 4.0 ± 0.1 and 6.0 ± 0.1, respectively. It turns out that it deviates. Further, the Zr / Cu molar ratio and / or the P / Cu molar ratio are 4.0 ± 0.1 and 6.0 ±, respectively.
When it exceeds 0.1, the amount of zirconium phosphate increases after heat treatment, resulting in a N ₂ conversion rate of 30% or less, which is lower than the results of Sample Nos. 2 to 4.

Next, from the results of Sample Nos. 6 to 9, it was found that crystallization does not occur when the heat treatment temperature is lower than 650 ° C.
It can be seen that when the temperature exceeds 50 ° C., a heterogeneous crystal phase different from the X-ray powder characteristics appears. As a result, the N ₂ conversion rate is 3
It was found to be 0% or less, which is lower than Sample Nos. 7 and 8.

Finally, from the results of sample No. 9, Zr / C
u molar ratio and P / Cu molar ratio are 4.0 ± 0.1,
In the case where the crystal phase does not show the above-mentioned specific peak in the X-ray diffraction measurement even in the range of 6.0 ± 0.1, the N ₂ conversion rate becomes 30% or less, and the sample No. 3 is obtained. You can see that it is lower than that. Further, according to the results of Sample Nos. 10 and 11, even if the crystal phase is the same, if the Zr / Cu molar ratio and the P / Cu molar ratio are different, the N ₂ conversion rate becomes 30% or less, which is lower than that of Sample No. 3. I understand.

[0023]

As described above in detail, the phosphoric acid-based composition of the present invention has a NOx reducing decomposition action even in an atmosphere of high oxygen concentration, and is useful for purification of exhaust gas in future diesel engines and the like. It is a thing.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction measurement chart of a phosphoric acid-based composition of the present invention.

FIG. 2 is an X-ray diffraction measurement chart of a phosphoric acid-based composition as a comparative product.

Claims (4)

[Claims] 1. At least Cu, Zr, phosphorus (P) and oxygen (O) are contained, and the molar ratio represented by Zr / Cu is 3.
9 to 4.1, the composition represented by P / Cu has a molar ratio of 5.9 to 6.1, and in the powder X-ray diffraction measurement, the following lattice plane spacing: lattice plane spacing 4.45 ± 0.1 Å 3.98 ± 0.08Å 3.78 ± 0.08Å 3.35 ± 0.07Å 3.14 ± 0.07Å 3.05 ± 0.05 Å 2.88 ± 0.05 Å 2.80 ± 0.05 Å 2 0.75 ± 0.05 Å 2.56 0.05 Å The phosphoric acid composition. 2. A mixed solution of a water-soluble Cu-containing compound and a Zr-containing compound is mixed with a water-soluble phosphorus-containing compound solution,
A process for producing a phosphoric acid-based composition, which comprises adjusting the pH of a solution to 6.0 ± 0.5, filtering the residue, and heat-treating the residue at 650 to 1050 ° C. for 10 hours or more. 3. At least Cu, Zr, phosphorus (P) and oxygen (O), and the molar ratio represented by Zr / Cu is 3.
9 to 4.1, the composition represented by P / Cu has a molar ratio of 5.9 to 6.1, and in the powder X-ray diffraction measurement, the following lattice plane spacing: lattice plane spacing 4.45 ± 0.1 Å 3.98 ± 0.08Å 3.78 ± 0.08Å 3.35 ± 0.07Å 3.14 ± 0.07Å 3.05 ± 0.05 Å 2.88 ± 0.05 Å 2.80 ± 0.05 Å 2 A catalyst for reducing and decomposing NOx, wherein the catalyst has 0.75 ± 0.05 Å 2.56 ± 0.05 Å. 4. The catalyst for NOx reduction decomposition according to claim 3, which has a BET specific surface area of 10 m ² / g or more.