JP3524478B2 - High heat transfer catalyst and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention can catalyze a metal surface, which is a heat transfer surface, to directly supply heat necessary for a reaction by heat conduction or to efficiently remove heat generated by a reaction by heat conduction. The present invention relates to a highly heat-transferable catalyst and a method for producing the same.

[0002]

2. Description of the Related Art As a technique for forming a silica coating on the surface of a metal plate, for example, as disclosed in JP-A-10-73227, a silica layer is formed on an alumina layer on a substrate whose aluminum surface is anodized. There is a technology to form. When the catalyst thus obtained is used by supporting a catalyst on it, alumina is solid and acidic, and the following problems occur in reactions such as methanol decomposition reaction where alumina is unsuitable as a carrier. (1) When two or more kinds of metal oxides are combined, strong solid acidity may be exhibited. In particular, the solid acidity of silica-alumina is strong. (2) The alumina layer cannot be completely covered with silica, and the alumina layer remains on the surface, which causes the generation of by-products due to methanol decomposition or the like. Further, when the anodized alumina is immersed in an aqueous solution of 40 to 100 ° C. at the time of silica coating or catalyst loading, the alumina is hydrated, and when this is baked, it becomes γ-alumina and solid acidity increases. (3) Silica is coated on the alumina layer, and the alumina portion that does not function as a catalyst remains, so that the thermal conductivity decreases.

[0003]

As a conventional technique as described above, there is a method of coating the catalyst layer or the carrier layer by immersing anodized alumina in a sol solution. Therefore, the catalyst layer or the carrier layer is thin, and the properties of alumina having the above-mentioned problems cannot be completely suppressed. Further, the invention described in JP-A-10-73227 is a method of forming a silica layer on an alumina layer, and the silica layer is thin and the properties of alumina cannot be completely suppressed.

The present invention has been made in view of the above points, and an object of the present invention is to immerse porous anodized alumina in a solution containing a weak acid or alkali and a catalyst or a carrier substance to form an alumina layer. It is possible to form a porous catalyst layer or support layer thickly by dissolving the pores of the catalyst to expand the pore size, immersing the catalyst or support to the inside of the alumina layer, further dissolving the alumina layer and removing alumina. It is an object of the present invention to provide a high heat transfer catalyst and a method for producing the same.

[0005]

To achieve the above object, according to the Invention The high thermally conductive catalyst of the present invention, a substrate having an alumina layer surface was formed by the positive electrode oxidation, it contains a weak acid or alkali and carrier substances By immersing it in a solution for 10 to 96 hours , the pore size of the alumina layer is expanded and
And it meets the carrier material of the pore size of smaller particle size fine, to dissolve the Rutotomoni alumina layer to form a carrier layer
It is characterized in that a catalyst metal is supported on a catalyst carrier obtained by forming large pores .

The method for producing a highly heat-conductive catalyst of the present invention comprises the steps of immersing a substrate having an alumina layer surface formed by anodic oxidation in a solution containing a weak acid or alkali and a catalyst to obtain a fine pore diameter of the alumina layer. And to fill the catalyst in the pores, dissolve and remove the alumina layer,
It is characterized in that a catalyst layer is formed. Further, the method of the present invention, by immersing the substrate having an alumina layer surface formed by anodic oxidation in a solution containing a weak acid or alkali and a catalyst, to fill the catalyst in the pores,
Next, the catalyst layer is characterized by being immersed in an acid or alkali solution to dissolve the alumina layer.
By repeating any of the above methods, the alumina in the coating may be dissolved to form the catalyst layer.
In addition, a substrate having an alumina layer surface formed by anodic oxidation is immersed in an acid or alkali solution to expand the pore size of the alumina layer, and then any of the above methods is performed at least once (once By performing the above), a catalyst layer may be formed in some cases.

Further, the method of the present invention comprises immersing a substrate having an alumina layer surface formed by anodization in a solution containing a weak acid or alkali and a carrier substance for 10 to 96 hours. to expand the pore size of the alumina layer, and meet the carrier material of the pore size of smaller particle size fine in the pores,
This dissolving Rutotomoni alumina layer to form a carrier layer
And are used to form large pores to form a catalyst carrier, and a catalyst metal is supported on the obtained catalyst carrier. In addition, the method of the present invention comprises immersing a substrate having an alumina layer surface formed by anodic oxidation in a solution containing a weak acid or alkali and a carrier substance for 10 to 96 hours to form the carrier substance in the pores. filled, then, is immersed in the liquid of the acid or alkali to dissolve the alumina layer, it size to dissolve the Rutotomoni alumina layer to form a carrier layer
The catalyst carrier is characterized by forming holes to form a catalyst carrier, and supporting the catalyst metal on the obtained catalyst carrier. By repeating any of the above methods, the alumina in the coating may be dissolved to form the carrier layer. In addition, a substrate having an alumina layer surface formed by anodic oxidation is immersed in an acid or alkali solution to expand the pore size of the alumina layer, and then any of the above methods is performed at least once (once By performing the above), a carrier layer may be formed in some cases.

In these methods of the present invention, the specific surface area of the catalyst can be adjusted by adjusting the particle size of the carrier substance. Further, in the present invention, as the carrier substance, for example, silica, zirconia, titania,
Ceria, zinc oxide, vanadium oxide, molybdenum oxide,
Any one of tin oxide, chromium oxide, iron oxide, cordierite, zeolite, perovskite and magnesium oxide or a mixture thereof can be used. Further, in the present invention, as the catalyst metal, as an example, one of palladium, platinum, ruthenium, rhodium, iridium, nickel, cobalt, iron, copper, zinc, gold, silver, rhenium, manganese and tin, or an alloy thereof. Alternatively, a mixture can be used. In addition, the catalyst carrier obtained by any of the above methods, impregnation method, ion exchange method,
The catalytic metal can be supported by a precipitation method or the like.
Further, in these methods of the present invention, it is preferable to use oxalic acid as the weak acid.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments, and can be appropriately modified and implemented. . By immersing a substrate whose aluminum surface is made porous by anodic oxidation in a solution (sol solution) containing only a weak acid (or alkali) and a catalyst or carrier substance, the pore diameter of the alumina layer is expanded and A catalyst body is obtained in which the pores are filled with the catalyst or support material. In this case, the porous anodized alumina is dipped in a solution containing a weak acid (or alkali) and a catalyst or a carrier substance to fill the catalyst or the carrier substance in the pores and dissolve the alumina layer. Alternatively, a single layer of carrier material can be formed. Then, in the case of a carrier layer, a catalyst is obtained by supporting a catalyst metal on the carrier layer by an impregnation method, an ion exchange method, a precipitation method or the like.

The substrate used in the present invention includes not only aluminum itself but also a substrate having an aluminum layer on its surface. For example, it is also possible to use a substrate made of iron, copper, a stainless alloy or the like whose surface is coated with an aluminum layer. Further, the shape is not limited to a plate shape, and various shapes such as a tube and a corrugated plate can be used. The anodizing conditions are preferably set appropriately so that the BET specific surface area of the formed alumina layer is large, and in the present invention, the anodizing treatment liquid temperature is preferably 10 to 40 ° C. The treatment time of anodic oxidation varies depending on the treatment conditions. For example, when the treatment liquid is an oxalic acid aqueous solution, the treatment liquid temperature is 20 ° C., and the current density is 50 A · m ⁻² , 2 hours or more, particularly 4 It is preferable that the time is longer than that. A weak acid or alkali is added to the sol solution in which the anodized alumina is dipped, and oxalic acid is preferably used as the weak acid to be added. Further, sodium carbonate or the like can be used as the alkali.

Further, by immersing the porous anodized alumina in a solution (sol solution) containing a weak acid (or alkali) and a catalyst or a carrier substance, the pores are filled with the catalyst or the carrier substance, and then, It is preferable to dissolve the alumina layer by immersing it in an acid or alkali solution to form a layer containing only the catalyst or the carrier. In this case, by repeating any of the above methods, the alumina in the coating film can be dissolved to form a layer containing only the catalyst or the carrier. Further, the porous anodized alumina is immersed in a liquid of a weak acid (or alkali) to expand the pore diameter of the alumina layer, and then any of the above methods is performed at least once to form a catalyst layer or It is preferable to form a carrier layer. Further, the specific surface area of the catalyst can be adjusted by adjusting the particle size of the carrier substance. As the above-mentioned carrier substance, as an example, silica, zirconia, titania, ceria, zinc oxide, vanadium oxide, molybdenum oxide, tin oxide, chromium oxide,
Any one of iron oxide, cordierite, zeolite, perovskite and magnesium oxide, or a mixture thereof is used. Examples of the catalyst metal include palladium, platinum, ruthenium, rhodium, iridium, nickel, cobalt, iron, copper, zinc, gold, silver, rhenium, manganese and tin, or an alloy or mixture thereof. Used.

[0012]

EXAMPLES Next, examples of the present invention and comparative examples will be described. 1) Preparation of catalyst body An Al plate (JIS standard A1050) with a thickness of 0.3 mm was washed with an aqueous solution of sodium hydroxide and nitric acid and then at 20 ° C.
Current density of 15-50A ・ m ^-2 in 4wt% oxalic acid solution
The anodic oxidation was performed for 16 hours with the DC current. Next, 50wt
% Commercial colloidal silica sol 300 ml, oxalic anhydride 12.5 g added sol solution (oxalic acid 4 wt%
Addition) was prepared. In addition, for comparison, those without oxalic acid, nitric acid, hydrochloric acid, sulfuric acid, and acetic acid were added respectively.
The one adjusted to pH 1 was also prepared. Liquid temperature of these solutions 1
The anodized substrate adjusted to 0 to 25 ° C. was dipped for 10 to 96 hours, taken out, and then baked at 400 ° C. for 1 hour.
Table 1 shows the immersion time, the oxide layer thickness, and the Si analysis value per apparent area. When oxalic acid was not added, the film thickness was almost constant regardless of the immersion time, but when oxalic acid was added, the film thickness decreased as the immersion time increased. On the other hand, when comparing the Si analytical values, the immersion for 10 hours with or without the addition of oxalic acid, is substantially the same as about 14g · m ^-2, SiO ₂ the longer the immersion time when the addition of oxalic acid The weight increased and the oxide layer decreased, while it was almost constant without addition.

[0013]

[Table 1]

2) Comparison of Acids (Comparative Example) For comparison, the types of acids added to the colloidal silica sol were compared and examined. When sulfuric acid, nitric acid, hydrochloric acid, and acetic acid were added, all gelled in 50 to 100 hours. On the other hand, when oxalic acid was added, it did not gel even after about 100 hours. Oxalic acid has been found to be suitable when acid is added. 3) Effect of silica sol temperature The effect of temperature of the silica sol solution containing oxalic acid (oxalic acid 4 wt% added) was examined. The anodizing condition was a current density of 50 A · m ⁻² . Table 2 shows immersion time, film thickness, Si
The relationship between analytical values is shown. As the temperature increased, the weight of SiO ₂ increased and the weight of the oxide layer decreased. However, the thickness of the oxide layer decreases as the temperature of the sol increases and the soaking time increases.
When immersed at 40 ° C. for 40 hours, the thickness of the oxide layer was less than half that before the immersion.

[0015]

[Table 2]

4) Comparison of Alumina Layer Thickness The current density during anodic oxidation was changed and substrates having different film thicknesses were compared. The immersion temperature was fixed at 15 ° C. Table 3 shows the immersion time, the film thickness, and the Si analysis value. It is considered that the rate of decrease of the coating is almost constant regardless of the current density of anodic oxidation, and the elution rate of alumina is constant. S
The analysis value of i increases as the immersion time increases at 50 A · m ⁻² , but does not increase at 15 and 25 A · m ⁻² . If the initial film thickness is thin, it is considered that the alumina layer becomes too thin when immersed in silica sol containing oxalic acid. To increase the amount of silica, a certain amount of alumina layer thickness is required. I understood it.

[0017]

[Table 3]

5) Measurement of pore distribution 15 substrates with anodic oxidation conditions of 50 A · m ^-2 (immersion for 16 hours) were used.
The pore distribution was measured on the substrate immersed in the sol solution at 0 ° C. FIG. 1 shows the pore distribution per unit apparent area.
Immediately after the anodization, there was a peak of the pore diameter near 40 nm in diameter, whereas after coating with silica, the pores around 40 nm disappeared and the peak of the pore diameter shifted to 10 to 20 nm. It is known as a power widening method that the pore size is enlarged by immersing the anodized film in an aqueous solution of oxalic acid, but it is smaller on the contrary. Also, 40 ℃
When the anodic oxide coating was immersed in warm water for about several hours, the pores of the alumina layer were hydrated and sealed, and when fired, the pore diameter decreased to about 4 to 20 nm depending on the conditions. As a precaution, when the specific surface area and pore distribution of the substrate immersed in distilled water at 15 ° C. for 40 hours were measured, it was almost the same as immediately after anodization. It was confirmed that hydration and sealing did not occur at 15 ° C. On the other hand, the particle size of the silica sol used is 2
Since it is 7 nm, it can sufficiently penetrate into the pores formed by anodic oxidation. From this, it is considered that the change in the pore diameter is not due to the change in the alumina layer itself, but because the silica particles penetrated into the pores generated by the anodic oxidation and filled the inside.

6) Cross-section analysis by EPMA 15 substrates with anodic oxidation conditions of 50 A · m ⁻² (16 hours immersion) were used.
For the substrate immersed in the sol solution at ℃, the element distribution of the substrate cross section was measured by EPMA (electron probe probe).
It was measured by the micro analysis. The results are shown in Figure 2. When the immersion time was 10 hours, the thickness of the alumina layer was about 120 μm, while Si was 20 μm from the surface.
It was distributed only up to the vicinity. After soaking for 40 hours,
Since the alumina dissolves, the thickness of the oxide layer becomes thinner, but as the pore walls dissolve, silica particles tend to penetrate, and the Si layer becomes thicker. After 96 hours of immersion, the bottom of the alumina layer is completely removed. Si has been reached. Further, due to the dissolution of the alumina layer, the strength of Al becomes weaker as the immersion time becomes longer.

7) Observation by SEM (electron microscope) The anodic oxidation conditions were 50 A.m ^-2 (16 hours immersion), silica sol containing oxalic acid was immersed for 96 hours at 15 ° C, and the substrate before silica sol immersion Were compared. 3 and 4
Photographs of the surface before immersion in silica sol and after immersion in silica sol are shown in FIG. As shown in FIG. 3, pores with a diameter of about 50 nm were observed immediately after anodic oxidation. After immersion in silica sol, as shown in FIG. 4, the particles were covered with silica particles having a diameter of about 30 nm, and the pores were about 10 to 30 nm. It was confirmed that both of them agreed with the measurement results of the pore distribution. FIG. 5 and FIG. 6 show photographs of a cross section before immersion in silica sol and after immersion in silica sol, respectively. As shown in FIG. 5, the entire oxide layer was almost uniform immediately after the anodization. On the other hand, after soaking in silica sol for 96 hours, as shown in FIG. 6, a dense layer is formed from the surface to around 20 μm, but a large hole of about 2 to 5 μm is formed inside the layer due to dissolution of alumina. It was From the adsorption / desorption curve of N _2, the diameter is several hundred nm
Since the above pores cannot be measured, they do not appear in the pore distribution of FIG. Further, in Table 1, it was found that the decrease amount of alumina was considerably larger than the increase amount of silica, because such large pores were generated. Considering the function as a catalyst carrier, only pores with a diameter of about 10 nm
When the oxide layer is thick, the diffusion of the gas is rate-determining for the reaction, but the presence of such large pores facilitates the diffusion of the gas, and excellent properties as a catalyst carrier can be expected.

8) Catalytic activity A 5 × 10 cm substrate (anodic oxidation conditions of 50 A · m ⁻² , 16 hours of immersion, silica sol immersion time of 0, 10 hours, 40 hours) obtained by the above method was treated with palladium acetate. 0.0
After soaking in 02 mol / L acetone solution for 24 hours,
The mixture was calcined at 0 ° C. for 3 hours to be catalyzed. It is known that in the decomposition reaction of methanol, the amount of dimethyl ether by-product increases depending on the strength of the solid acid amount. These plate-shaped catalysts were cut into 5 mm squares, and a methanol decomposition activity evaluation test was conducted in a packed bed reactor under the following conditions. Catalyst loading: 24 cm ² Methanol concentration: 40% (N ₂ dilution) Gas flow rate: 250 ml / min Reaction temperature: 250 ° C. Pressure: 1.7 atm Table 4 shows the results. It was found that the silica-coated catalyst has an effect of suppressing the amount of dimethyl ether by-produced.

[0022]

[Table 4]

9) Increasing the amount of silica supported by the acid immersion treatment The anodized aluminum substrate was immersed in acid sol to expand the pores and then immersed in silica sol. Anodizing (current density 5
0A · m ^-2, was immersed in the immersion conditions shown in Table 5 at 20 ° C. The immersion time 16 h) the substrate to 4 wt% oxalic acid solution, dried by air blowing at 15 ℃ colloidal silica sol solution 20 It was immersed for an hour and baked at 400 ° C. for 1 hour. If the acid immersion is not performed in the above-mentioned embodiment, the same value is 1
Since the amount of Si supported at 5 ° C. for 20 hours was 16.9 g / m ² , the amount of Si supported was larger when the acid immersion was performed as the pretreatment. In addition, since the film thickness decreases as the immersion time in acid increases, the amount of Si supported decreases.

[0024]

[Table 5]

10) Control of Specific Surface Area by Silica Particle Size 4 wt% of oxalic acid was added to silica sols having different particle sizes to prepare a silica sol solution. Here, the current density is 50A
An aluminum substrate anodized under the condition of m ⁻² and immersion time of 16 hours was immersed in the above silica sol solution at 20 ° C. for 10 hours to compare the specific surface areas. As shown in Table 6, the smaller the particle size of the silica sol, the larger the BET specific surface area per apparent area of the substrate.

[0026]

[Table 6]

11) Expansion of pore size by addition of alkali In the case of oxalic acid, weak alkaline sodium carbonate was added to silica sol instead of oxalic acid, and anodized alumina was immersed in the same manner as in the above-mentioned embodiment. Almost the same result was obtained.

[0028]

Since the present invention is configured as described above, it has the following effects. (1) Melting the pores of the alumina layer to expand the pore size,
By immersing the catalyst or the carrier in the alumina layer and further dissolving the alumina layer to remove the alumina, a porous catalyst layer or carrier layer can be formed thickly. (2) In the present invention, since the carrier layer is formed and the alumina layer is dissolved and removed, the alumina and the carrier substance do not form a complex compound, and solid acidity does not develop. (3) Since the alumina layer is dissolved and removed, the influence of alumina, which is a solid acid, can be removed, and alumina can be used as a catalyst even in a reaction unsuitable as a carrier. (4) Since there is no alumina layer between the catalyst (support) layer and the metal, the thermal conductivity does not decrease. Furthermore, since the catalyst or carrier layer is large, the specific surface area can be increased. Further, after the alumina layer is dissolved, large macropores are formed, so that the reaction gas easily permeates.

[Brief description of drawings]

FIG. 1 is a graph showing a pore size distribution per unit apparent area of a substrate in an example of the present invention.

FIG. 2 is a graph showing a cross-sectional analysis result of a substrate by EPMA according to an example of the present invention.

FIG. 3 is an electron micrograph showing a result of observing a structure of a substrate surface before immersion in silica sol in an example of the present invention (magnification: 50,000).

FIG. 4 is an electron micrograph showing a result of observing a structure of a substrate surface after immersion in silica sol in an example of the present invention (magnification: 50,000).

FIG. 5 is an electron micrograph showing a result of observing a structure of a substrate cross section before immersion in silica sol in an example of the present invention (magnification: 500 times).

FIG. 6 is an electron micrograph showing a result of observing a structure of a substrate cross section after immersion in silica sol in an example of the present invention (magnification: 500 times).

Front Page Continuation (72) Inventor Hideo Kameyama 2-13-28 Inokashira, Mitaka City, Tokyo (56) References JP-A-10-73227 (JP, A) JP-A-3-80940 (JP, A) JP 54-78391 (JP, A) JP-A-10-73226 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B01J 21/00 -38/74 B01D 53 / 86,53 / 94

Claims (12)

(57) [Claims] 1. A substrate having an alumina layer surface formed by anodic oxidation is dipped in a solution containing a weak acid or alkali and a carrier substance for 10 to 96 hours to expand the pore size of the alumina layer to reduce the fineness. Smaller than the above pore size in the hole
And meets the carrier material again diameter, the Ru to form a carrier layer
Large pores are formed by melting the alumina layer together.
A high heat transfer catalyst, characterized in that a catalyst metal is supported on the catalyst carrier thus obtained. 2. The carrier material is one of silica, zirconia, titania, ceria, zinc oxide, vanadium oxide, molybdenum oxide, tin oxide, chromium oxide, iron oxide, cordierite, zeolite, perovskite and magnesium oxide, or a mixture thereof. high thermally conductive catalyst according to claim 1, wherein a mixture. 3. The catalyst metal is palladium, platinum, ruthenium, rhodium, iridium, nickel, cobalt,
Any one of iron, copper, zinc, gold, silver, rhenium, manganese and tin, or an alloy or mixture thereof.
The high heat transfer catalyst according to 1 or 2 . 4. A substrate having an alumina layer surface formed by anodic oxidation is dipped in a solution containing a weak acid or alkali and a carrier substance for 10 to 96 hours to expand the pore diameter of the alumina layer and reduce the fineness. Smaller than the above pore size in the hole
And meets the carrier material again diameter, the Ru to form a carrier layer
Large pores are formed by melting the alumina layer together.
A method for producing a highly heat-conductive catalyst, characterized in that a catalyst metal is supported on the obtained catalyst carrier. 5. A substrate having an alumina layer surface formed by anodization is immersed in a solution containing a weak acid or an alkali and a carrier substance for 10 to 96 hours to fill the pores with the carrier substance, and then, Immerse in an acid or alkali solution to dissolve the alumina layer and form a carrier layer.
In addition, the large pores are formed by melting the alumina layer.
A method for producing a highly heat-conductive catalyst, which comprises forming a catalyst carrier and supporting a catalyst metal on the obtained catalyst carrier. 6. A method for producing a highly heat-conductive catalyst, which comprises dissolving the alumina in the coating to form a carrier layer by repeating the method according to claim 4 or 5 . 7. The method according to claim 4 or 5 , after the substrate having an alumina layer surface formed by anodic oxidation is immersed in an acid or alkali solution to expand the pore size of the alumina layer. A method for producing a highly heat-conductive catalyst, which comprises forming the carrier layer by carrying out once. By 8. By adjusting the particle size of the carrier material, the method of producing a high thermally conductive catalyst according to any one of claims 4-7 for adjusting the specific surface area of the catalyst. 9. A carrier material such as silica, zirconia,
Titania, ceria, zinc oxide, vanadium oxide, molybdenum oxide, tin oxide, chromium oxide, iron oxide, cordierite, zeolites, claim 4-8 using one or a mixture of these perovskites and magnesium oxide
The method for producing a highly heat-conductive catalyst according to any one of 1. 10. A catalyst metal, such as palladium, platinum,
Use of any one of ruthenium, rhodium, iridium, nickel, cobalt, iron, copper, zinc, gold, silver, rhenium, manganese and tin, or alloys or mixtures thereof, high heat conductivity according to any one of claims 4 to 10. Method for producing catalyst. 11. A catalyst support impregnation method, according to claim 4 to 10 for carrying the catalyst metal by an ion exchange method or deposition-precipitation method
The method for producing a highly heat-conductive catalyst according to any one of 1. 12. The method of claim 4 using the oxalic acid as a weak acid
A method for producing the highly heat-conductive catalyst according to any one of claims 1 to 11 .