JPH0763634B2 - Method for producing inorganic oxide structure having transition metal-containing layer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides a transition metal-containing layer at a specific position, for example, a method of forming a spherical shell-shaped nickel-containing layer having a specific radius on a spherical alumina carrier. The present invention relates to a method for producing an inorganic oxide structure having:

The inorganic oxide structure obtained by the present invention is expected to be used as a catalyst for various reactions and other functional materials.

[Conventional technology and its problems]

Since catalysts that are put into practical use in a wide range of fields such as the chemical industry and environmental science are often used under severe conditions, various performances are required.

For example, the catalyst used to remove NO _x , SO _x , hydrocarbons and carbon monoxide in the exhaust gas discharged from fixed combustion devices such as boilers and mobile combustion devices such as automobiles is a reaction at high temperature. Therefore, in addition to having heat resistance, it must have mechanical strength or toxicity resistance for reducing poisoning by heavy metals contained in exhaust gas. In order to satisfy these performances, not only the search for the optimum catalytically active component or support, but also the investigation on the geometrical structure of the catalyst is being continued.

As one of them, by supporting a catalytically active component inside the catalyst carrier particles, heavy metals are adsorbed on the outer surface of the catalyst,
A lot of researches have been conducted to reduce the poisoning of active ingredients with heavy metals. For example, in order to concentrate the metal particles in a spherical shell shape inside the carrier, a sulfur-containing carboxylic acid such as thiomalic acid or a dibasic acid such as citric acid (USP3259589, USP3259453), ammonium citrate is added to the impregnating solution containing the metal salt. Organic acid salts such as (JP-A-54-136589, JP-A-54-149391)
It is known that the acid points on the surface of the carrier are controlled by adding a.

However, in such a conventional method, although a spherical shell-shaped metal band appears inside the carrier, it is extremely difficult to control the radius vector of the metal band with good reproducibility, and the pH value of the impregnating solution is strictly controlled. There must be. In addition, the particle diameter of the metal particles in the metal strip that appear by these methods is not always uniform, and it is hard to say that the metal dispersity is high.

The present invention aims to solve these problems.

[Means for solving problems]

The present inventors, as a result of diligent studies, mixed one or more ester compounds selected from silicic acid esters, aluminate esters or titanic acid esters in a polyhydric alcohol solution of a transition metal salt, and using this mixed solution as an impregnating solution, The inventors have found that the above-mentioned problems can be solved by immersing the inorganic oxide carrier here for a predetermined time and then pulling it up and gelling it in water vapor, resulting in the present invention.

That is, the present invention, a carrier composed of an inorganic oxide, a mixed solution (impregnation solution) of a polyhydric alcohol solution of a transition metal salt and one or more ester compounds selected from silicate esters, aluminate esters or titanate esters. A method for producing an inorganic oxide structure having a transition metal-containing layer, which comprises immersing and then gelling in water vapor.

Hereinafter, the present invention will be described more specifically.

Examples of the inorganic oxide used in the present invention include silica, alumina, titanium oxide, silica-alumina and the like.
The shape of the carrier made of these is preferably granular for a catalyst carrier, but is not particularly limited to a cylindrical shape, a plate shape, or the like.

Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, butanediol, hexanediol and their alkyl-substituted products, or their structural isomers.

The transition metal salt is a salt of a transition metal such as Fe, Co, Ni, V, Cr, Mn, Cu and Zn, and a mineral acid salt such as nitrate and an organic acid salt such as acetate can be used.

The ester compound of the present invention is an alkoxide compound such as silicic acid ester, aluminate ester, and titanic acid ester, and specifically, ethyl silicate, methyl silicate, aluminum isopropoxide, ethyl titanate, butyl titanate, and the like. Examples thereof include, but are not limited to, compounds having two or more alkoxy groups.

The mixed solution of the present invention, that is, the impregnated solution is prepared by dissolving a predetermined amount of a transition metal salt in, for example, ethylene glycol, and then heating and mixing with an ester compound at 40 to 90 ° C. Further, the concentration of each component of the impregnating liquid or the immersion time is appropriately selected depending on the target structure.

The temperature of the water vapor atmosphere in the case of gelation is not particularly limited, and the gelation can be performed in a water vapor atmosphere of 60 to 100 ° C., for example.

[Work]

Taking the case where spherical alumina is used as the carrier, nickel nitrate is used as the transition metal salt, ethylene glycol is used as the polyhydric alcohol, and ethyl silicate is used as the ester compound as an example, the mechanism of action for producing the desired structure will be discussed.

First, when nickel nitrate and ethylene glycol are mixed, nickel ethylene glycolate is produced by the reaction represented by the following formula.

When ethyl silicate is mixed therein and heated and stirred, a molecular species having a "Si-O-Ni-O-Si" structure is produced according to the following formula.

That is, nickel in the impregnating liquid is "Si-O-Ni-O-Si".
This structure is incorporated in the SiO ₂ network, and a compound having a structure of “Si—O—Ni ion” is locally produced.

When the inorganic oxide carrier is immersed in this impregnating solution, the "Si-O-metal ion" structure adsorbed on the outer surface of the carrier is broken, the metal ion diffuses inside the carrier, and the carrier surface becomes "Si-O-Si".
-O "network. Therefore, the amount of metal ions diffused inside the carrier is determined by the amount of the initially adsorbed "Si-O-metal ion" structure, that is, the concentration of metal ions in the impregnating solution. The diffusion distance of metal ions is determined by the impregnation time. That is, the radial position of the metal content concentrated inside the carrier is controlled by the immersion time. Also, the "Si-O-Si-O" network covering the outer surface of the catalyst becomes a thin film of, for example, about 50 µm after the firing process, resulting in coating the outer surface of the catalyst carrier. The SiO ₂ thin film thus produced has uniform pores of about 20Å.

Therefore, the spherical alumina structure obtained after drying, calcination, and reduction is coated with a silica thin film having an outer surface of the carrier with uniform pores of about 20Å, and Ni ions diffused inside the carrier have a uniform particle size. It becomes the fine metal particles and has a spherical shell shape. This concentrated portion is the transition metal-containing layer in the present invention.

Further, as described above, the amount of metal diffused can be controlled by the metal concentration of the impregnating liquid, and the position of the metal content can be controlled by the immersion time, but the particle size of the metal is also controlled by the metal concentration in the impregnating liquid.

Note that the above is the same in the case of combining with a metal other than nickel or with another ester compound, and also when using a carrier having a shape other than spherical.

〔The invention's effect〕

According to the present invention, by a simple method, a thin film of silica or the like having a uniform pore size is formed on the outer surface of a carrier made of an inorganic oxide, and at the same time, a predetermined amount having a uniform particle size at an arbitrary predetermined position inside the carrier. It is possible to form a layer containing the above transition metal particles.

The structure obtained by the present invention has heat resistance and is excellent in mechanical strength and can be used as various transition metal catalysts. In this case, it has excellent toxicity resistance against poisoning of the catalyst by heavy metals, phosphorus, sulfur and the like. Further, since a thin film having a uniform pore size is formed on the surface of the carrier, it also has an effect of reducing side reactions by preventing diffusion of molecules larger than the reaction substrate into the carrier.

The structure obtained by the present invention is expected to be used as a conductive material or a magnetic material in addition to the above-mentioned use as a catalyst.

〔Example〕

 The present invention will be described in more detail with reference to the following examples.

Example 1 8.92 g of nickel nitrate was dissolved in 150 ml of ethylene glycol, mixed with 30 ml of ethyl silicate, heated and stirred at 80 ° C., and further added with 3 ml of nitric acid to prepare an impregnating solution. A spherical alumina carrier having a diameter of 3 mm was immersed for 2 hours and then left in a steam atmosphere for 10 minutes to cause gelation on the surface of the alumina sphere. This alumina sphere in air at 110 ℃
After drying in air for 24 hours, bake in air at 300 ° C for 4 hours,
Reduction was carried out at 700 ° C. for 4 hours in a hydrogen stream. The nickel in the catalyst after reduction is completely reduced, and the reduction rate is 100%.
It was confirmed by measuring the magnetic susceptibility.

<Measurement of Cross-Sectional Structure> The reduced catalyst spheres were embedded in a polyester resin and the resin was polished to expose the diametric cross section of the catalyst spheres. FIG. 1 shows a micrograph of a diameter cross-sectional view. In the cross-sectional view, it was confirmed that the black band-shaped portion was a layer containing concentrated nickel fine particles and was distributed in a spherical shell shape. The result of the X-ray microanalyzer (XMA) measured using this sample is shown in FIG. It was confirmed from FIG. 4 that the spherical shell-like distribution of nickel fine particles was confirmed, and that Si was coated on the outer surface of the spherical alumina carrier as a SiO ₂ thin film (about 50 μm).

<Measurement of Nickel Particle Diameter by Microscope> The particle diameter of nickel particles in the catalyst after reduction was measured by a transmission electron microscope. The obtained photograph is shown in FIG. 2, and the particle size of the nickel particles was almost uniform and was about 80Å.

Thus, it was confirmed that nickel fine particles were in a highly dispersed state in the catalyst prepared according to the production method of the present invention.

<Measurement of Nickel Particle Size by Hydrogen Adsorption Method> When the particle size and dispersity of the nickel fine particles in the catalyst after reduction were measured by the hydrogen absorption method, the dispersity was 14% and the average particle size was about 70Å.

<Measurement of Properties of Silica Thin Film> With respect to the catalyst after reduction, the film thickness of the silica thin film and the pore distribution were measured by a gas injection type device. At the same time, the pore distribution was similarly measured for unimpregnated alumina carrier spheres.

The thickness of the silica thin film was about 50μ. FIG. 3 shows the results of measuring the pore size distribution of the silica thin film and the alumina carrier sphere.

The unimpregnated alumina spheres have a pore distribution that has a peak at about 50Å, but the catalyst after impregnation has a pore distribution peak at about 20Å. The distribution is also very sharp, and in the catalyst prepared by the method of the present invention, the pores of the silica thin film covering the outer surface of the catalyst are controlled to about 20Å. It is considered that this is convenient for excluding poisonous substances such as dust particles from the outside during the catalytic reaction and introducing only the reaction gas into the inside of the catalyst. In addition, as a result of acid measurement using n-butylamine, no acidity was observed in this silica thin film.

Example 2 (Control of distribution position) A catalyst was prepared in the same manner as in Example 1 except that the impregnation time was changed. XM cross-sectional structure of each catalyst with different impregnation time
As a result of measurement using A, as the impregnation time increased, the distribution position of the spherical shell-shaped nickel metal fine particles moved to the center of the alumina sphere, but the SiO ₂ thin film still existed on the outer surface of the alumina sphere. It could be confirmed.

FIG. 4 shows the measurement results by XMA of the catalyst prepared by adjusting the impregnation time of 1 minute, 2 hours, and 15 hours. Further, FIG. 5 shows the relationship between the impregnation time and the distribution position of the spherical shell-shaped nickel fine particles.

As described above, according to the production method of the present invention, the distribution position of the spherical shell-shaped nickel fine particles can be arbitrarily controlled only by adjusting the impregnation time.

Example 3 (Control of Carrying Rate) The concentration of nickel nitrate in the impregnating liquid was set to 24.4, 48.4 and 97.6 g /
The nickel loading rate in the catalyst prepared in the same manner as in Example 1 except that the impregnation time was changed was measured by fluorescent X-ray analysis. The result is shown in FIG.

From FIG. 6, if the nickel concentration in the impregnating liquid is the same, the nickel supporting rate in the catalyst is almost constant regardless of the impregnation time, and the supporting rate is controlled only by adjusting the nickel concentration in the impregnating solution.

That is, according to the production method of the present invention, the nickel loading rate in the catalyst can be controlled by the nickel concentration in the impregnation liquid.

Example 4 In the same manner as in Example 1, 150 ml of 13.0 g of iron (III) nitrate.
After dissolving in 30 ml of ethyl silicate and mixing with 30 ml of ethyl silicate, 3 ml of nitric acid was further added dropwise to prepare an impregnating solution. A spherical alumina carrier having a diameter of 3 mm was immersed therein for 1 minute and then left in water vapor for 10 minutes to cause gelation on the surface of the alumina sphere. FIG. 7 shows the result of measuring the XMA distribution in the diameter cross-section of the catalyst produced through the steps of drying, calcination and reduction in the same manner as in Example 1.

As is apparent from FIG. 7, as in the case of nickel, the iron fine particles are spherical shell-shaped and distributed inside the alumina carrier, and the outer surface portion thereof is coated with a silica thin film.

[Brief description of drawings]

FIG. 1 is a photomicrograph of the diameter cross section showing the particle structure of the catalyst spheres obtained in Example 1, and FIG. 2 is a transmission electron micrograph showing the particle structure of the nickel fine particles in the catalyst obtained in Example 1. 3 is a graph showing the results of measuring the pore distribution of the silica thin film and the alumina carrier sphere, and FIG. 4 is the impregnation time of 1 minute, 2 hours, 15
FIG. 5 is a graph showing the measurement results of an X-ray microanalyzer of a catalyst calcined for a time, FIG. 5 is a graph showing the relationship between the impregnation time and the distribution position of spherical shell-shaped nickel fine particles, and FIG. 6 is the concentration of nickel nitrate in the impregnation liquid and the impregnation. FIG. 7 is a graph showing the relationship between time and nickel loading, and FIG. 7 shows X of the catalyst obtained in Example 4.
It is a figure which shows the measurement result by a line microanalyzer.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/74 ZAB 23/745 23/755 B01D 53/36 ZAB C

Claims (1)

[Claims] 1. A carrier comprising an inorganic oxide is dipped in a mixed solution of a polyhydric alcohol solution of a transition metal salt and one or more ester compounds selected from silicic acid ester, aluminate ester or titanate ester, and then steamed. A method for producing an inorganic oxide structure having a transition metal-containing layer, which comprises gelling in a medium.