JPH0626669B2 - Coating composition for combustion catalyst - Google Patents

Description

TECHNICAL FIELD The present invention relates to a coating composition for a combustion catalyst, and more particularly to a coating composition for a combustion catalyst suitable for producing a long-life honeycomb catalyst.

(Prior Art) A catalytic combustion apparatus carries out combustion by supporting a catalyst on a honeycomb having a characteristic that the pressure loss of a fluid is small despite its large surface area. NOx because it can be lowered to around ℃
2) It has the characteristics that it can burn lean fuel (blast furnace gas: CO content 0.5 Vol%) that cannot be burned by a burner, and it can be used for household gas stoves, exhaust heat recovery boilers, etc. Application is in progress.

The honeycomb, which is the heart of this apparatus, is made of ceramics having excellent heat resistance, and in particular, cordierite, mullite, titanate aluminate, etc. having a small coefficient of thermal expansion are used to prevent damage due to thermal stress. However, since the specific surface area of these materials themselves is small, even if a catalyst is directly supported on these honeycombs, the activity is low and they are not suitable for use. Therefore, β ・ Al ₂ O ₃ and γ-A are formed on the surface of these honeycombs.
A treatment for improving the activity of the honeycomb catalyst is performed by coating a ceramic having a high specific surface area such as l ₂ O ₃ as a catalyst supporting layer (Japanese Patent Laid-Open No. 49-36596). However, since the bonding force between the honeycomb carrier surface and the coating layer and between the coated particles is weak,
The difference in thermal expansion between the two during use and the coating layer and the coating particles peel off during the catalyst impregnation operation in the honeycomb catalyst manufacturing process, so that unevenness in the catalyst loading in the honeycomb is likely to occur. Therefore, not only the peeling of the coating causes a decrease in activity and a problem in maintenance of the apparatus, but also thermal stress due to non-uniform combustion is likely to cause a large reduction in life.

(Problems to be Solved by the Invention) In the above conventional technique, the bonding force between the surface of the honeycomb carrier and the layer having a high specific surface area coated on the surface of the honeycomb carrier and between the particles to be coated is weak, and the coating layer and the coated particles are separated. However, there is a problem of shortening the life of the honeycomb catalyst.

An object of the present invention is to provide a coating composition for a combustion catalyst, which can strengthen the bonding force between the surface of the catalyst carrier and the coating layer.

(Problems to be Solved by the Invention) The above-mentioned object is to provide a high specific surface area ceramic composition for coating on the surface of a catalyst carrier by heat treatment at 300 ° C. or lower, such as aluminum phosphate, alumina sol, silica sol. This is accomplished by adding a binder that creates a bond between the and the ceramic coating layer and between the coating particles.

That is, the present invention is a coating composition for forming a catalyst supporting layer having a high specific surface area on the surface of a catalyst carrier having a low coefficient of thermal expansion and a low specific surface area, the composition comprising 20 to 40 wt% of a transition alumina compound and phosphorus. 0.5 to 15 wt% of at least one binder of aluminum oxide, silica sol and alumina sol, 0 to 5 wt% of curing accelerator and 0.5 to 10 wt% of organic binder are contained in water or an organic solvent. Characterize.

The catalyst carrier used in the present invention is made of, for example, mullite, cordierite, aluminate titanate or the like having a low coefficient of thermal expansion and a low specific surface area, and its shape is such that the catalyst device is often provided in the gas passage. The honeycomb shape is most preferable.

The coating composition of the present invention is La-β · Al ₂ O ₃
And transition alumina compound 2 such as Ba-β · Al ₂ O ₃
0 to 40 wt%, a binder comprising at least one of aluminum phosphate, silica sol and aminasol 0.5 to
15 wt%, 0 to 5 wt% of at least one oxidation promoter selected from oxides of Al or Mg, hydroxides or silicates, magnesium carbonate and titanium oxide, and an organic binder such as polyvinyl alcohol (PVA). 5 to 10 wt% is dispersed in water or an organic solvent.

The transition alumina compound which is the main component (aggregate) of the coating composition of the present invention is La-β · Al ₂ O ₃ or Ba.
A -β · Al ₂ O _3, these compounds have a high specific surface area, be heated above 1000 ° C. does not lose its high specific surface area.

The larger the particle size of the transition alumina compound, the greater the surface roughness of the honeycomb after construction, which is advantageous in terms of the activity of the catalyst, but since the honeycomb structurally increases the surface area,
Since the cell shape is made small, the cross-sectional area is reduced by the amount of the large particle size adhering to the cell wall, the pressure loss is increased, and the cell is easily clogged during coating. Therefore, in order to obtain a practical coating slurry, the maximum particle size is preferably 150 μm or less. In addition, when coating the honeycomb, considering the workability such as infiltration of slurry into cells, discharge of excess slurry, and amount of adhered slurry, in order to perform stable coating, the slurry has high viscosity and high viscosity at low shear rate. Low viscosities are preferred at shear rates. That is, when the coating slurry adheres to the honeycomb cell wall, it is in a low shear rate state,
At this time, the higher the viscosity, the greater the amount of adhesion. Conversely, when the excess slurry is blown off with compressed air, a high shear rate state is reached, and the lower the viscosity at this time, the easier the discharge of the excess slurry. For this purpose, it is preferable that 10 wt% or more of fine powder of 1 μm or less is present in the slurry.

In the present invention, a binder that forms an inorganic condensate having a three-dimensional structure by heat treatment and develops an adhesive force is added to the slurry. The above-mentioned binder has a chain structure by, for example, a condensation reaction or a hydrogen bond as shown below, and such a structure is formed by heating at 300 ° C. or lower to form an inorganic polymer, and further 300 ° C. or lower. When the heating is continued, a condensation dehydration reaction and a hydrogen bond proceed to form a three-dimensional structure by a crosslinking reaction.

Since these inorganic polymers contain a large amount of hydroxyl groups, silanol bonds and hydrogen bonds are generated with the particles of the honeycomb carrier and the coating layer, so that a strong adhesive force is generated. Therefore, a strong bonding force is generated between the surface of the honeycomb carrier and the coating layer and the coating particles by these reactions, so that peeling does not occur due to thermal stress during use or expansion of the honeycomb during impregnation of the catalyst.

The binder is, for example, Na, K, or Ca that forms a low melting point reaction product with a transition alumina compound and causes a decrease in activity during combustion.
It is important not to contain chlorides that cause activity inhibition to alkali metals and catalysts such as. Several kinds of such binders can be used in combination depending on the specific surface area and particle size distribution of the transition alumina compound, the usage conditions of the honeycomb catalyst, and the like.

The larger the amount of the binder added, the more the bonding force between the coating layer and the honeycomb carrier increases, but the activity of the honeycomb catalyst decreases because the inorganic condensate itself formed by the additive has a low specific surface area. Therefore, although the addition amount varies depending on the use conditions of the honeycomb catalyst and the kind of the binder, it is about 0.5 to 15
A range of wt% is suitable.

In the present invention, the use conditions of the honeycomb and the β
It is preferred in some and properties of Al ₂ O ₃ adding a curing accelerator of the binder. The selection conditions are the same as for the binder, but as such, Al or Mg oxide,
There are hydroxides, silicates, magnesium carbonate, titanium oxide and the like, and any of them can be used alone or in combination. The effect is exhibited when the added amount is 5 wt% or less, but the bonding force tends to decrease conversely when the added amount is increased (Fig. 7).

FIG. 5 is a diagram showing the relationship between the amount of transition alumina compound and the amount of adhesion in the coating slurry of the present invention. If the amount of adhesion is too large, cell clogging will occur, and if it is too small, the coating effect will not be sufficient and the amount of binder in the slurry will be 2
It has been found that a range of 0-40 wt% is suitable.

Water or an organic solvent is used as the dispersion medium in the present invention.

(Example) Hereinafter, the Example of this invention is described according to drawing.

Example 1 FIG. 1 shows the shape of a cordierite honeycomb catalyst for catalytic combustion used for coating. The outer shape is 140 x 150 x 20 (unit: mm), and each cell is 1.4 mm
It is a horn. This carrier was washed, degreased and dried, and immersed in a slurry of Ba-β.Al ₂ O ₃ (specific surface area 15 m ³ / g, heat resistant temperature 1400 ° C.) having the composition shown in Table 1 for 1 minute. It should be noted that Ba-β · Al ₂ O ₃ used in the examples.
Fig. 3 shows the particle size distribution of the above, and Fig. 4 shows the flow characteristics of the coating slurry.

The coated honeycomb was sufficiently dried to remove water, and then fired at 300 ° C. for 2 hours to burn the coating layer. The manufacturing process of the honeycomb catalyst is shown in FIG.

FIG. 8 shows that the honeycomb catalyst coated with the coating slurry of the present example and the conventional slurry without the addition of the binder were repeatedly heated at 1000 ° C. and room temperature, and the weight change at that time resulted in the durability of the coating. It shows the data of comparative examination of sex. When the coating of this example is applied, the amount of change in weight is 1/3 or less as compared with the conventional example, and the improvement of the coating layer binding force by the binder is recognized.

FIG. 9 shows a catalyst combustion test apparatus for a long time of a catalyst in which 5 g of platinum is loaded on a coated honeycomb carrier according to this embodiment and a similar honeycomb catalyst in which a conventional binder-free coating is applied. The change in the reaction rate when burned for a time is for comparison. At the initial stage of combustion, the honeycomb of this example is slightly inferior in activity to the conventional example, but since the reaction rate is stable, the reaction rate is reversed from that of the conventional honeycomb that deteriorates in a short time.

Since the coating composition according to the present invention has a small influence of the affinity between the honeycomb carrier material and the aggregate of the coating slurry, it is possible to coat materials other than cordierite and mullite. In this example, the Si ₃ N ₄ honeycomb carrier was coated. The coating slurry and coating method and method used are the same as the above-mentioned example conditions, but in order to improve the wettability of the slurry, a surfactant (trade name of Mama Lemon, Lion Co., Ltd.) was added to 0.4 wt% slurry. Was added. In the case where the conventional binder is not added, the relaxation property between β · Al ₂ O ₃ or γ-Al ₂ O ₃ of the coating material and SiC of the carrier is poor, and the coating layer hardly adheres. Due to the effect of the binder, a coating amount of 31 wt% of the weight of the honeycomb carrier was obtained by the two coatings, and by impregnating the catalyst, the same combustion characteristics as the cordierite honeycomb carrier were exhibited (see FIG. 10).

Example 2 A honeycomb carrier having the same specifications as in Example 1 was immersed in a slurry having the composition shown in Table 2 for 1 minute and fired at 300 ° C to coat the catalyst supporting layer on the surface of the carrier. La-β · Al ₂ O ₃ has a specific surface area of 12 m ³ / g and a heat resistant temperature of 1350 ° C., and the washcoat conditions are the same as in Example 1.

FIG. 11 shows the amount of Ba-β · Al ₂ O ₃ coating layer peeling in the repeated heating test and the Ba value.
-Pd on the carrier coated with β-Al ₂ O ₃ 5g
/ It shows the relationship between the burning rate of the supported catalyst and the amount of silica sol in the coating slurry.

If the silica sol in the slurry is 0.5 wt% or less, the effect of the addition is not recognized, but if the addition amount is increased to 0.5 wt% or more, the binding force of the coating layer to the honeycomb increases,
The rate of the coating layer remaining after the repeated heating test is high. However, even if added in an amount of 15 wt% or more, the binding force does not improve, and the specific surface area of the coating layer decreases with the addition of silica sol and the activity decreases, so the combustion rate decreases. Further, the viscosity of the coating slurry also increases, resulting in poor workability. Therefore, the amount of silica sol added to the slurry is 0.5 wt.
% To 15 wt% is suitable.

Example 3 A honeycomb carrier having the same specifications as in Example 1 was immersed in a slurry having the composition shown in Table 3 for 1 minute and fired at 300 ° C to coat the catalyst supporting layer on the surface of the carrier. γ-Al ₂ O ₃ has a specific surface area of 300 m ³ / g and a heat resistant temperature of 800 ° C., and the washcoat conditions are the same as in Example 1.

FIG. 12 shows the amount of peeling of the coating layer in the repeated heating test of the γ-Al ₂ O ₃ coating layer and this γ-Al ₂
2 shows the relationship between the burning rate of a catalyst in which 5 g of Pd is loaded on a carrier coated with O ₃ and the amount of alumina sol in the coating slurry.

Similar to the case of silica sol, if the silica sol in the slurry is 0.5 wt% or less, the effect of addition is not recognized. 0.
If it is increased to 5 wt% or more, the rate of the coating layer remaining after the repeated heating test becomes high. Further, if it is added in an amount of 15 wt% or more, the burning rate is lowered and the workability of the wash coating is deteriorated. Therefore, the amount of alumina sol added to the slurry is preferably in the range of 0.5 wt% to 15 wt%.

Example 4 A honeycomb carrier having the same specifications as in Example 1 was immersed in a slurry having the composition shown in Table 4 for 1 minute and fired at 300 ° C. to coat the catalyst supporting layer on the surface of the carrier. The characteristics and specifications of Ba-β · Al ₂ O ₃ are the same as in Example 1.

FIG. 13 shows the relationship between the amount of coating layer peeling and the organic binder (PVA) in the coating slurry in the repeated heating test of the Ba-β.Al ₂ O ₃ coating layer.

If the amount of the organic binder in the slurry is 0.5 wt% or less, the effect of addition is not recognized, but if the amount of addition is increased to 0.5 wt% or more, an appropriate viscosity and stability of the slurry can be obtained.
The coating layer can be evenly attached, and the peeling resistance is improved. However, if it is added in an amount of 15 wt% or more, the viscosity becomes too high, so that the coating layer becomes nonuniform and peeling easily occurs. In addition, the workability of wash coating is also reduced. Therefore, the amount of organic binder (PVA) added to the slurry is 0. wt% to 10 wt%
The range is appropriate.

Examples 5,6,7,8,9 and 10 Ba-β · _Al 2 O having compositions shown from Table 5 to Table 10
_Three slurries were prepared, and each of the slurries was dipped in a honeycomb carrier having the same specifications as in Example 1 for 1 minute and fired at 300 ° C. to coat the catalyst supporting layer on the surface of the carrier.

FIG. 14 shows Ba− of Examples 5, 6, 7, 8, 9 and 10.
It shows the amount of peeling of the coating layer in the repeated heating test of the β-Al ₂ O ₃ coating layer.

When a curing agent for an inorganic binder such as magnesium oxide, magnesium hydroxide, magnesium carbonate, aluminum silicate, and titanium oxide is added to the slurry, the curing of the inorganic binder aluminum phosphate is promoted, so that no additive is added. As compared with 5, the bonding strength of the coating layer is improved, and the peeling amount of the coating layer in the repeated heating test is reduced.

(Effects of the Invention) According to the present invention, since the bonding force between the honeycomb carrier and the catalyst holding layer coated and between the coating particles is improved, the following effects can be obtained.

1) It is possible to prevent the catalyst activity from deteriorating due to peeling of the catalyst holding layer, and to extend the life of the honeycomb catalyst for catalytic combustion by, for example, about 3 times.

2) It is possible to prevent the occurrence of an accident due to the separated catalyst holding layer accumulating in the combustion device. Especially when applied to a household stove, it is possible to prevent indoor pollution due to the peeled catalyst holding layer.

3) Since materials other than cordierite and mullite that could not be coated by conventional methods can be catalyzed, the performance of the catalytic combustion device can be improved and application to gas turbines and the like becomes possible.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a honeycomb carrier to which the coating composition according to the present invention is applied, FIG. 2 is a block diagram showing a coating process in an embodiment of the present invention, and FIG. Ba-β · A used in the examples of the invention
Fig. 4 is a diagram showing the particle size distribution of l ₂ O ₃ , Fig. 4 is a diagram showing the flow characteristics of the coating slurry in the example of the present invention, and Fig. 5 is β ・ Al ₂ O in the coating slurry that affects the coating layer on the honeycomb. Fig. 6 shows the effect of the amount of ₃ and Fig. 6 shows the effect of the amount of aluminum phosphate in the coating slurry on the amount of peeling and the specific surface area of the coating layer. Fig. 7 shows that AlPO ₄ was used as the binder. FIG. 8 is a diagram showing the effect of the addition amount of a curing agent (MgO) on the peeling amount of the coating layer at this time, and FIG. 8 is a peeling property between the conventional coated honeycomb and the coated honeycomb according to the present invention. FIG. 9 and FIG. 9 are graphs for comparison with each other, showing the burning rate curves of a conventional coated honeycomb and a coated honeycomb according to the present invention in a combustion test. FIG. 10 shows the changes, FIG. 10 shows the combustion characteristics of the cordierite honeycomb catalyst coated with the coating material according to the present invention and the reaction-sintered SiC honeycomb catalyst, FIG. 11, FIG. 12, FIG. 13 and FIG. FIG. 14 is a diagram showing the effect of another embodiment of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location // B01J 23/42 M 8017-4G 23/56 301 M 8017-4G 23/58 M 8017-4G 27/185 M 9342-4G 37/02 301 B 7821-4G F23D 14/18 E

Claims (3)

[Claims] 1. A coating composition for forming a catalyst supporting layer having a high specific surface area on the surface of a catalyst carrier having a low coefficient of thermal expansion and a low specific surface area, the composition comprising 20 to 40 wt% of a transition alumina compound and phosphoric acid. At least one binder of aluminum, silica sol and alumina sol 0.5 to
A coating composition for a combustion catalyst, comprising 15 wt%, a curing accelerator 0 to 5 wt% and an organic binder 0.5 to 10 wt% in water or an organic solvent. 2. A claims the first term range, transition alumina _{compound-La β · Al 2 O 3} , Ba-β · Al 2
At least one compound selected from O ₃ and γ-alumina, the maximum particle size of which is 150 μm or less and 1
A coating composition for a combustion catalyst, which comprises 10 wt% or more of particles having a particle diameter of μm or less. 3. The curing accelerator according to claim 1 or 2, wherein the curing accelerator is at least one selected from oxides or hydroxides of Al or Mg, or silicates, magnesium carbonate and titanium oxide. A coating composition for a combustion catalyst, comprising: