JPH06327979A - Catalyst body for catalyst oxidation - Google Patents

Abstract

PURPOSE:To prevent the particle growth and to suppress the vaporization and transpiration of a catalytically active material and to effectively prevent the deterioration of catalyst body by carrying on a heat resistant base body the catalytically active material microcapsuled prepared by using a porous heat resistant material at its wall material. CONSTITUTION:A W/O type emulsion is prepared by adding and dispersing the catalycally active material into an aq. solution of inorganic compound for forming the microcapsule wall to make suspension and adding a nonionic surfactant and an organic solvent thereinto. Next, the microcapsule including the catalytically active material is made by mixing the emulsion with an inorganic compound aq. solution to be precipitated by reacting with the suspending inorganic compound to induce interfacial reaction. After that, a slurry is made by stirring and mixing the carrier component powder and water therewith and is applied on the surface of the heat resistant base body by dipping the base body, which is finally fired at 600-900 deg.C. Thus, the excellent catalyst stable over a long even in a severe condition for use is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to combustion of combustible gas contained in exhaust gas from catalytic combustion by a gas turbine, combustion equipment such as an engine and various combustion treatment equipment in order to suppress NO _x generation. , A catalytic body for catalytic oxidation used in catalytic combustion for heat recovery.

[0002]

2. Description of the Related Art As a catalyst for catalytically oxidizing a combustible gas in a low temperature range of about 400.degree. C. to a medium temperature range of about 1000.degree. C., noble metals such as platinum and palladium, and nickel oxide and cobalt are used. In many cases, a catalytically active substance such as copper, chromium, or manganese is supported on a heat-resistant substrate such as a ceramic honeycomb via a porous carrier. When preparing such a catalyst body,
Generally, a method of coating a heat-resistant substrate with a mixed slurry of a powder of a catalytically active substance, a carrier powder and water and firing the mixture is used.

However, in the thus obtained catalyst body, particles of the catalytically active substance are associated with each other during use at a high temperature, particles are easily grown (sintering), and the active surface area of the catalyst body is lowered. Alternatively, when the catalytically active substance is a noble metal, there is a problem that the catalytic activity is likely to decrease due to evaporation of the noble metal.

Japanese Patent Publication No. 3-4251 discloses a means for coating the surface of a catalyst layer made of a catalytically active substance with a porous heat-resistant material in order to prevent the catalytically active component made of a noble metal from being evaporated. There is. However, in the catalyst body thus formed, the thermal expansion coefficient of the catalyst layer and that of the coating layer are not necessarily the same, and thus the thermal shock accompanying ON / OFF of combustion easily causes cracks in the coating layer. It has the drawback of In particular, when forming such a heat-resistant coating layer on a honeycomb-shaped catalyst body that is often used for combustion catalysts, it is necessary to coat the entire surface of the inner wall of the honeycomb with a heat-resistant material, so thermal stress easily occurs. , Cracks easily occur in the heat resistant material. And once cracks occur in the heat resistant material,
The reaction is promoted on the exposed surface of the catalyst layer, the temperature of the catalyst surface rises, and the catalytically active metal evaporates through the cracked portion to accelerate the deterioration of the catalyst body.

[0005]

SUMMARY OF THE INVENTION Therefore, according to the present invention, in a catalytic body for catalytic oxidation, particle growth of a catalytically active substance is prevented and vaporization thereof is suppressed to effectively prevent deterioration of the catalytic body. The main purpose is that.

[0006]

The inventors of the present invention have made intensive studies while paying attention to the problems of the prior art relating to the catalytic body for catalytic oxidation as described above, and as a result, have made a heat-resistant porous material a wall material. As a result, it has been found that in the case of encapsulating the catalytically active substance in microcapsules, the problems of the prior art are greatly reduced or substantially eliminated.

That is, the present invention provides the following catalytic oxidation catalyst body: 1. A catalytically active substance is microencapsulated using a porous heat-resistant substance as a wall material, and is supported on a heat-resistant substrate. A catalytic body for catalytic oxidation, which is characterized in that

The microcapsules containing the catalytically active substance used in the present invention can be prepared according to the methods disclosed in JP-B-54-6251 and JP-B-57-55454.

That is, for example, a W / O emulsion is prepared from a suspension prepared by dispersing fine particles of a catalytically active substance together in an aqueous solution of an inorganic compound for forming a microcapsule wall, a nonionic surfactant and an organic solvent. After that, this emulsion and an aqueous solution of an inorganic compound that reacts with the above-mentioned inorganic compound to form a water-insoluble precipitate are mixed, and an interfacial reaction is performed to produce a microcapsule containing a catalytically active substance. it can.

Alumina, silica, silica-alumina, zirconia, etc. are suitable as the wall material of the microcapsules, but other heat resistant materials may be used. Further, in order to improve the heat resistance of the wall material of the microcapsule, one or more kinds of zirconium oxide, lanthanum oxide, calcium oxide, barium oxide, yttrium oxide and the like may be contained. The wall material of the microcapsule thus formed has a large number of through pores with uniform pore diameters and is excellent in heat resistance.

The size of the microcapsules is not particularly limited, but is preferably about 0.2 to 11 μm. The pore size of the wall material of the microcapsule can be adjusted by appropriately selecting the reaction conditions (type and concentration of suspension and reaction solution, hydrogen ion concentration during reaction, etc.). The pore size is not particularly limited, but is preferably about 0.002 to 0.06 μm in order to keep the diffusion rate of the reaction gas (fuel and oxygen) within a preferable range.

As the catalytically active substance, a platinum group metal such as platinum, palladium, iridium or ruthenium, which is used in a usual catalytic body for catalytic oxidation and has a high oxidation activity and easily deteriorates, can be used. Nickel oxide, cobalt, chromium, manganese or the like may be used in combination with this catalytically active substance as a co-catalyst.

The microcapsules encapsulating the catalytically active substance may be replaced by the above-mentioned method. First, hollow porous microcapsules containing no catalytically active substance are prepared. It can also be produced by injecting a substance in the form of an aqueous salt solution and decomposing the salt according to a conventional method. As the salt of such a catalytically active substance, there may be used a hydrochloride, a nitrate, an ammine complex salt and the like which are commonly used in the production of catalytic bodies for catalytic oxidation.

The amount of the catalytically active substance contained in the microcapsules may be appropriately selected depending on the conditions of use of the catalyst body and is not particularly limited, but is usually about 5 to 50% by weight.

The combustion catalyst body according to the present invention is manufactured as follows, in the same manner as a normal catalyst. First, microcapsules encapsulating the catalytically active substance obtained as described above, lanthanum, barium, by stirring and mixing with carrier component powder such as alumina stabilized by silica and the like and water, to prepare a slurry, A heat-resistant substrate such as cordierite, alumina, or zirconia is immersed in this, and the slurry is applied to the surface of the substrate.
Bake at about ℃. Since the catalyst particles have been microencapsulated in advance, the amount of the carrier component used may be smaller than in the usual catalyst production. The amount ratio of the microcapsules to the carrier component may be appropriately determined in consideration of the activity of the catalyst, heat resistance, the strength of the catalyst layer composed of the microcapsules and the carrier, and the like. The thickness of the catalyst layer formed of the microcapsules and the carrier formed on the heat resistant substrate is usually 3
It is about 0 to 300 μm, and more preferably 50 to 10 μm.
It is about 0 μm.

[0016]

INDUSTRIAL APPLICABILITY In the catalytic body for catalytic oxidation according to the present invention, the catalytically active substance has a large number of microcapsules which have relatively uniform fine pores and are provided with wall materials having high strength and excellent heat resistance It exists in the state of being included in. Therefore, in the catalytic body for catalytic oxidation according to the present invention, the sintering phenomenon due to the association of the catalytically active substance between independent microcapsules is substantially prevented, and the evaporation of the catalytically active substance is also significantly suppressed. Therefore, even under severe usage conditions (combustion in the temperature range of 400 to 1000 ° C.), the catalyst body stably exhibits excellent catalytic activity for a long period of time.

As a result, the amount of catalytically active substance required to obtain the same performance is reduced, and the economy is improved.

Further, in the form of the catalyst body having the honeycomb-shaped heat-resistant substrate supported thereon, even if a crack is generated in the catalyst layer portion composed of the carrier and the catalytically active substance, the catalytically active substance itself is contained in the microcapsules. Because it is included,
Combustion ON-OFF with almost no adverse effects
Even in operation, a long catalyst life can be achieved.

The present invention, when using platinum as a catalytically active substance whose oxidation activity rapidly increases at 800 ° C. or higher,
Particularly effective. The reason is (1) the surface diffusion rate of platinum, which rapidly rises as the temperature rises, can be controlled by the pore diffusion rate of the microcapsule wall material, so the surface temperature of platinum is controlled to be 1000 ° C. or less at all times. Then, the vapor pressure of platinum can be reduced, and (2) the migration speed of platinum can be controlled by the pore diffusion resistance of the wall material of the microcapsules.

[0020]

EXAMPLES Reference examples, examples and experimental examples are shown below,
The features of the present invention will be further clarified.

Reference Example 1 JIS No. 3 sodium silicate solution (as SiO ₂ 4 m
ol / l) 83 ml platinum fine particles having a particle size of 0.2 μm 8.
After dispersing 5 g, 166 ml of a 3% toluene solution of a sorbitan monostearate / polyoxyethylene sorbitan monooleate (1: 2) mixture and the resulting dispersion were stirred at 7000 rpm for 30 seconds to emulsify, and W / O
A type emulsion was prepared. Then, this is 2 mol /
After adding 1000 l of ammonium sulfate solution (1000 ml) to react, the mixture was left for 3 hours.

Next, the reaction solution is filtered, the solid product is washed, and dried to obtain a porous microcapsule (particle size: 0.5 to 8 μm) having a platinum inclusion rate of 30% and a wall material of silica.
m) About 28 g was obtained.

25 g of the microencapsulated platinum catalyst obtained above was added to 11.2 g of tetraethoxysilane and 10 parts of tetraethoxyzirconium in a 100 ml Erlenmeyer flask.
g and 30 g of ethanol, and dispersed by an ultrasonic disperser.

Next, 1 ml of 1N-ammonia water was further added to the above dispersion liquid, and the mixture was heated for 30 minutes while being ultrasonically dispersed in a constant temperature bath at 60 ° C., so that the surface of the porous silica as the wall material of the microcapsules was heated. Silica fine particles and zirconium oxide fine particles as a carrier were deposited.

Reference Example 2 JIS No. 3 sodium silicate solution (as SiO ₂ 4 m
ol / l) platinum fine particles 20 with a particle size of 0.2 μm in 83 ml
After dispersing g, 166 ml of a 3% solution of polyoxyethylene sorbitan monooleate in toluene and the resulting dispersion are stirred at 7000 rpm for 30 seconds to emulsify and
A / O type emulsion was prepared. Then add this to 1.5
The mixture was added to 1000 ml of a mol / l ammonium sulfate solution, reacted, and left for 3 hours.

Next, the reaction solution is filtered, the solid product is washed and dried to have a platinum inclusion rate of 50% and a wall material made of porous microcapsules (particle size 0.5 to 8 μm).
m) About 38 g was obtained.

25 g of the microencapsulated platinum catalyst obtained above was added to 12 g of triisopropyl oxide aluminum, 10 g of tetraethoxyzirconium and 30 g of isopropanol in a 100 ml Erlenmeyer flask,
It was dispersed by an ultrasonic disperser.

Next, 1 ml of 1N-hydrochloric acid was further added to the above dispersion liquid, and the mixture was heated for 30 minutes while being ultrasonically dispersed in a thermostat at 60 ° C., and the carrier was applied to the surface of the porous silica, which is the wall material of the microcapsules. As a result, alumina fine particles and zirconium oxide fine particles were deposited.

Reference Example 3 JIS No. 3 sodium silicate solution (as SiO ₂ 4 m
ol / l) 83 ml platinum fine particles having a particle size of 0.2 μm 8.
After dispersing 5 g, 166 ml of a 3% hexane solution of polyoxyethylene sorbitan monooleate and the resulting dispersion were stirred at 7000 rpm for 30 seconds to emulsify,
A W / O type emulsion was prepared. Then, this is 1m
The mixture was added to 1000 ml of an ol / l sodium aluminate solution to cause a reaction, and then left for 3 hours.

Then, the reaction solution is filtered, the solid product is washed, and dried to obtain a porous microcapsule (particle size: 0.5 to 8 μm) having a platinum inclusion rate of 25% and a wall material of silica.
m) About 35 g was obtained.

25 g of the microencapsulated platinum catalyst obtained above was added to 12 g of triisopropyl oxide aluminum, 10 g of tetraethoxyzirconium and 30 g of isopropanol in a 100 ml Erlenmeyer flask,
It was dispersed by an ultrasonic disperser.

Then, 1 ml of 1N-hydrochloric acid was further added to the above dispersion liquid and heated for 30 minutes while ultrasonically dispersing in a constant temperature bath at 60 ° C., and the carrier was applied to the surface of the porous zeolite which is the wall material of the microcapsules. As a result, alumina fine particles and zirconium oxide fine particles were deposited.

Examples 1 to 3 Each of the three types of platinum-encapsulated microcapsules obtained in Reference Examples 1 to 3 was added and mixed to a mixed sol prepared from alumina containing 8.3% by weight of lanthanum oxide and water in advance. Three kinds of sol solutions for catalyst coating were prepared.

Next, 20 cells per square inch
A cordierite honeycomb substrate having an aperture ratio of 0, an aperture ratio of 69%, a diameter of 50 mm, and a layer height of 15 mm was immersed in the above-mentioned three sol solutions, dried, and heat-treated at 900 ° C. for 3 hours.

Each of the three types of honeycomb-shaped catalytic oxidation catalysts obtained supported 10 g / l (per honeycomb volume) of platinum. The amount of the carrier carried in each catalyst was about 80 g / l (per honeycomb volume).

Comparative Example 1 20 platinum particles were prepared in the same manner as in Examples 1 to 3 except that platinum particles having a particle size of 0.2 μm which were not encapsulated were used.
A honeycomb-like catalytic oxidation catalyst supporting g / l (per honeycomb volume) was prepared. The amount of carrier is 100 g / l
(Per honeycomb volume).

Comparative Example 2 Platinum particles of 20 g / l and a carrier of 80 g / l were carried per volume of honeycomb by the same method as in Examples 1 to 3 except that platinum particles having a particle size of 0.2 μm which were not encapsulated were used. The product was prepared. Next, this was immersed in a mixed sol prepared from alumina containing 8.3% by weight of lanthanum oxide and water in advance, dried, and heat-treated at 900 ° C. for 3 hours to coat the surface of the platinum catalyst layer with a porous alumina layer. A honeycomb-shaped catalytic oxidation catalyst was prepared. The supported amount of the surface coating layer is 2
It was 0 g / l (per honeycomb volume).

Experimental Example 1 Catalyst Durability Test For the honeycomb-shaped catalytic bodies of Examples 1 to 3 and Comparative Examples 1 to 2, the maximum steady temperature was set to 1000 ° C. in an air atmosphere using an electric furnace, as shown in FIG. A durability test in which heating and cooling were repeated in the indicated cycle was performed 100 cycles.

A sample having a diameter of 10 mm was cut out from each of the catalyst bodies before and after the above durability test, set in a reaction test apparatus whose outline is shown as a sectional view in FIG. 2, and subjected to methane under the condition of a space velocity of 400000 / hr. The catalytic activity in the oxidation reaction was investigated. In FIG. 2, the catalyst body sample 1 is arranged in the center of the reactor 3. The reactor 3 is heated by electric heaters 5, 7, 9 and the periphery of these electric heaters is insulated by a heat insulating material 11. 0.5 supplied from supply path 13
After reacting in the reactor 3, the% methane-air mixed gas is discharged from the system through the exhaust passage 15. The temperature of the catalyst body sample 1 is measured by the thermocouples 17 and 19.

The measurement results of the catalytic activity are shown in FIGS.

The catalysts of Examples 1 to 3 all showed almost the same excellent initial (before durability test) activity, and even after the durability test, all the catalysts exhibited almost the same excellent methane oxidation activity. I was keeping. Therefore, only the results of Example 1 are shown in FIG.

On the other hand, the catalyst according to Comparative Example 1 is shown in FIG.
As shown in, the initial activity was higher than that in this example, but the methane oxidation activity was significantly reduced after the durability test.

As shown in FIG. 5, the catalyst according to Comparative Example 2 had almost the same initial activity as that of this Example, but after the durability test, the methane oxidation activity also decreased significantly. Was.

In order to investigate the cause of the activity decrease of the catalyst body according to the tested comparative example, the honeycomb wall surface was sliced and observed with a scanning electron microscope equipped with a fluorescent X-ray probe. The amount of platinum particles decreased, and it was confirmed that the remaining platinum particles had grown considerably large.

Further, it was found that in the catalyst body of Comparative Example 2, many cracks were generated in the alumina coating layer, and the protective effect of the coating layer was largely lost. Also in the catalyst body according to the present invention, cracking was observed in a part of the carrier layer, but there was almost no decrease in the amount of platinum particles, and
No growth of platinum particles was observed between the capsules, and the effect of microencapsulation of the catalytically active component was clearly seen.

[Brief description of drawings]

FIG. 1 is a graph showing an outline of a cycle (heating-cooling) of a durability test performed on each honeycomb-shaped catalyst body obtained in Examples 1 to 3 and Comparative Examples 1 and 2.

FIG. 2 is a drawing showing an outline of a methane-air reaction test device used in an experimental example of the present invention.

FIG. 3 is a graph showing the catalytic activity of the catalyst body obtained in Example 1 of the present invention before and after the durability test.

FIG. 4 is a graph showing the catalyst activity before and after a durability test of the catalyst body obtained in Comparative Example 1 of the present invention.

FIG. 5 is a graph showing the catalyst activity before and after a durability test of the catalyst body obtained in Comparative Example 2 of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshio Nishida 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi, Osaka Within Osaka Gas Co., Ltd. (72) Shinichi Adachi 4-chome, Hirano-cho, Chuo-ku, Osaka-shi, Osaka 1-2 No. 2 in Osaka Gas Co., Ltd. (72) Inventor Takayuki Inoue 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi, Osaka Prefecture Osaka Gas Co., Ltd. (72) Inventor Masaaki Mizuguchi 1 Shimoshinjo, Higashiyodogawa-ku, Osaka-shi, Osaka 8-22 No. Inside Suzuki Yushi Kogyo Co., Ltd.

Claims (1)

[Claims] 1. A catalytic body for catalytic oxidation, characterized in that a catalytically active substance is microencapsulated by using a porous heat-resistant substance as a wall material and is supported on a heat-resistant substrate.