JP2014030808A - Catalyst component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide, for the purpose of solving, in light of the desirability of an oxide film having a nano-sized three-dimensional structure as the supporter of a catalyst carrier supporting a metal catalyst, the problem that, although a three-dimensionally structured oxide film of aluminum can be realized either by a porous film provided by anodic oxidation or by a feathery film provided by boiling, composite effects cannot be realized in a case where both are composited due to the clogging, by the feathery hydroxide formed as a result of boiling, of the porous oxide film obtained as a result of anodic oxidation, a catalyst component capable of increasing the number of pores by adjusting pore intervals to the extent that the feathery structure does not clog pores and of improving the catalyst reaction efficiency based on an enlarged surface area of the porous oxide film.SOLUTION: As a catalyst component having a catalyst function on a metal surface, a catalyst component wherein the metal is aluminum having a porous oxide film and a feathery structure on the surface wherein pore intervals of the porous oxide film range from 300 nm to 1200 nm is used.

Description

The present invention relates to a catalyst member, and more particularly to a catalyst member having a catalytic function on a metal surface.

  Conventionally, since the catalytic activity depends on the size of the surface area of the catalyst, the catalyst is made into ultrafine particles or the surface area of the catalyst member is increased. Therefore, the shape of the catalyst or the catalyst member is a powdery body or a pellet shape obtained by solidifying this.

  However, since the powdery body has poor thermal conductivity, in order to effectively conduct heat conduction in the catalytic reaction, Patent Document 1 includes anodizing the aluminum flat plate surface and providing a porous oxide film, It has been proposed to obtain a dehydrogenation catalyst member for taking out hydrogen using a medium in which a metal catalyst is supported on the porous oxide film to form a support, which chemically repeats hydrogen storage and supply.

  FIG. 1 is an example of a schematic diagram of a hydrogen reaction vessel and a hydrogen reaction unit, and shows a hydrogen engine. The hydrogen medium 1 to which hydrogen is added is sent from the hydrogen medium tank 2 to the hydrogen reaction vessel 3 through a pipe. In this hydrogen reaction vessel 3, a catalyst carrier having a metal catalyst such as platinum supported on a porous oxide film is disposed to cause a dehydrogenation reaction. By the way, this dehydrogenation reaction is an endothermic reaction and requires heat, but this heat is obtained by heat exchange with the combustion exhaust gas from the engine 4. The hydrogen medium 1 added with hydrogen sent into the hydrogen reaction vessel 3 releases hydrogen 5 by this dehydrogenation reaction. Next, hydrogen 5 exiting the hydrogen reaction vessel 3 and other substances are separated in the gas-liquid separation vessel 6, and the hydrogen medium from which hydrogen has been released and the unreacted hydrogen medium 7 are stored in the waste liquid tank 8. . On the other hand, the hydrogen 5 is sent to the engine 4 and becomes fuel.

Here, platinum and other metal catalysts are expensive, and in order to reduce costs, it is necessary to increase the reaction surface area / volume and limit the amount used. In order to increase the surface area / volume, it is necessary to reduce the particle size of the metal catalyst, and a nano-sized colloidal solution is used. However, if the carrier carrying this is smooth, the colloid will condense / unify and become enlarged, so the carrier needs to have a nano-sized three-dimensional structure. Further, since the catalyst reacts by exchanging electrons, the support needs to be an insulator. On the other hand, since the reaction is an exothermic reaction by hydrogen addition and an endothermic reaction by dehydrogenation, heat conduction is required, and it is desirable that the insulator of the support is formed of metal as a metal.
A porous film formed by anodic oxidation of aluminum is raised as one of the supports that meet these requirements. Although the shape of the film depends on the chemical composition, etc., for example, oxalic acid forms a hole-shaped porous film called a pore at the center in a hexagonal cell structure.
Another method is the formation of feather-like structures by boiling a pure water of aluminum or anodized aluminum.
As a result, a carrier having a nano-sized three-dimensional structure is formed.

JP 2007-326000 A

In the case of a pore (pore) structure formed by a porous film formed by anodization, deep pores can be obtained depending on the chemical conversion conditions, and the surface area of the support can be increased. However, it cannot prevent the intrusion metal catalyst nanocolloid from condensing into the pores.
On the other hand, a feather-like structure has a complicated three-dimensional structure, and the coalescence of metal catalyst nanocolloids is easily prevented.
From the above, it is desirable that the carrier structure has a structure having both, that is, a deep pore and a feather-like structure on the surface including the pore. In particular,
(1) A porous oxide film having a three-dimensional pore structure is formed by anodization.
(2) It is immersed in an acid (alkali) and the pore diameter is expanded by dissolution.
(3) A feather-like aluminum hydroxide film is formed on the surface of the porous oxide film by boiling with pure water.
(4) Aluminum hydroxide is converted to aluminum oxide by heat treatment.
What should I do?

  The film obtained by boiling is composed of feather-like hydroxide on the surface layer and dense hydroxide on the bare metal side. The thickness of the feather-like structure (hereinafter referred to as the feather-like structure) is approximately proportional to the square root of the boiling time, but if it is too thick, the pores are blocked. In order to store a thick feather-like structure, it is necessary to widen the pore diameter, but when the pore interval is narrow, the pores merge when the pores are widened. Therefore, the pore interval is increased according to the required pore diameter. Since the pore interval is generally proportional to the formation voltage of anodic oxidation, the formation voltage is adjusted according to the conditions. Here, when the pore interval is narrow and the pore diameter is small, the surface area of the porous oxide film can be increased because the number of pores is large, but since the feather-like structure cannot be thickened, the surface area of the feather-like structure is small. Conversely, when the pore interval is wide, the pore diameter can be increased, the feather-like structure can be thickened, and the surface area of the feather-like structure is large, but the number of pores is small, and the surface area of the porous oxide film is small.

  As a result of intensive studies, the present invention has found an optimal pore interval for catalytic reaction, and provides an excellent catalyst member having a porous oxide film on the surface of aluminum and a feather-like structure on the surface. is there.

  In order to solve the above problems, the present invention provides a catalyst member having a catalytic function on a metal surface, wherein the metal is a porous oxide film and aluminum having a feather-like structure on the surface, and the porous oxide film The catalyst member has a pore interval of 300 nm to 1500 nm.

  The pore spacing is optimal for the pore diameter that accommodates the feather-like structure, and the catalytic reaction efficiency can be improved by optimizing the catalytic reaction surface area.

An example of the schematic diagram of a hydrogen reaction vessel and a hydrogen reaction unit is shown. The model figure of the porous membrane by anodization is shown. The pore closing state of the feather-like structure is schematically shown by the pore interval of the porous oxide film. The image of the scanning electron microscope after the anodic oxidation process of this invention is shown. The image of the scanning electron microscope after the anodization of this invention and the alkaline aqueous solution immersion process is shown. The image of the scanning electron microscope after the anodic oxidation of this invention, alkaline aqueous solution immersion, a pure water boiling, and a heat processing process is shown. The relationship between KOH immersion time and a pore diameter is shown. The relationship between boiling time of pure water and the thickness of a feather-like structure is shown.

  The aluminum described in the present invention includes aluminum alone or aluminum added with palladium, niobium, tantalum, zirconium, vanadium, or the like. As the shape, foil, fiber, powder or the like can be used.

  The porous oxide film described in the present invention is a porous oxide film among oxide films formed by anodizing aluminum. The film obtained by anodic oxidation of aluminum is not necessarily porous, but a porous oxide film can be obtained by adjusting chemical conversion conditions such as a chemical conversion liquid composition. The chemical conversion solution is an aqueous solution, and as the main solute, for example, oxalic acid, sulfuric acid, phosphoric acid, chromic acid, citric acid aqueous solution and the like can be used.

The pore interval of the porous oxide film described in the present invention is the distance between the centers of other pores close to the center of the pore of the porous oxide film formed by anodizing aluminum, and the pore interval is preferably 300 nm to 1500 nm. 400 nm to 900 nm is more preferable. If it is less than this, the pore diameter cannot be increased, and the feather-like structure cannot be prevented from blocking the pore. If it is more than this, the pore diameter can be increased and the pores can be prevented from being clogged with pores, but the number of pores is small and the surface area of the porous oxide film itself is reduced.
In addition, the pore interval depends on the formation voltage, and the formation voltage when it is 1200 nm or more is, for example, about 800 V, and the formation solution that achieves this has a porous film structure whose main solute concentration is thinner than the spark voltage. hard.
The distance between the pores depends on the formation voltage and can be increased by using a high voltage. However, it is necessary to adjust the chemical conversion liquid to increase the voltage. If the chemical conversion voltage is simply increased, sparks are generated and the chemical conversion power becomes large, making it difficult to control the chemical conversion liquid temperature.
By adjusting the main solvent concentration and adding a water-soluble polymer such as polyvinyl alcohol, the spark voltage is increased to a value higher than the chemical voltage, and the chemical power is suppressed by controlling the reactivity, making it easy to control the chemical liquid temperature.
If the temperature of the chemical conversion liquid is high, a shape abnormality called burning is generated in the film. On the other hand, lowering is less economical than cooling costs. It is preferable that the temperature is 0 ° C to 50 ° C, particularly 20 ° C to 30 ° C.
Further, the treatment time of this anodization varies depending on the treatment conditions and the film thickness to be formed. An anodized layer of about 6 μm can be formed.

The pore diameter can also be adjusted according to the chemical conversion conditions, but the chemical formation conditions affect not only the pore diameter, but also the pore spacing, film thickness, etc., so the optimal shape may not be obtained. The pore diameter is preferably adjusted by a subsequent acid or alkaline aqueous solution immersion step.
The acid and aqueous alkali solution used are not particularly limited, but phosphoric acid, caustic soda, potassium hydroxide and the like can be used. Concentration, temperature, and time are selected so as to achieve a predetermined pore size. The optimum pore diameter is a diameter at which the pore is not blocked by a feather-like film grown in the subsequent boiling treatment step, and the optimum value varies depending on the boiling conditions. The boiling is preferably 90 ° C. to 98 ° C. with pure water. However, when the pressure of the treatment is increased, the treatment time can be shortened by further increasing the temperature.

  The feather-like structure described in the present invention is a feather-like aluminum hydroxide film in which a porous oxide film obtained by anodizing aluminum is formed on the oxide film surface by boiling with pure water, or a feather-like structure. The aluminum hydroxide film is converted into aluminum oxide by heat treatment.

The catalyst member described in the present invention has a porous oxide film provided on the surface of aluminum and a feather-like structure provided on the surface, but the aluminum is roughened by etching before forming the porous oxide film. Also good.
Further, although aluminum oxide itself has a catalytic function, in some cases, it may be better to carry a metal catalyst on the surface.
As the metal catalyst, metals such as nickel, palladium, platinum, rhodium, iridium, rhenium, ruthenium, molybdenum, tungsten, vanadium, osmium, chromium, cobalt, iron, and alloys thereof can be used. The method for supporting the metal catalyst on the porous oxide film is by immersing the catalyst metal in a colloidally dispersed liquid.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 2 shows a model diagram of a porous film formed by anodization. FIG. 2A shows a perspective sectional view of an aluminum foil provided with a porous oxide film. FIG. 2B shows an enlarged perspective sectional view of the porous oxide film. A porous oxide film 10 provided on the aluminum base metal 9 is an aggregate of hexagonal cells 12 having a hexagonal column shape and a pore (pore) 11 at the center. Here, the pore diameter (φp) mainly depends on the chemical composition and temperature, the film thickness (t) mainly depends on the amount of chemical conversion, and the wall thickness (d) mainly depends on the chemical voltage. Therefore, the pore interval (P) generally depends on the formation voltage.

FIG. 3 schematically shows how the pores of the feather-like structure are blocked by the pore interval of the porous oxide film.
FIG. 3A shows a state in which the pores 11 are narrow and the feather-like structures 13 provided on the surfaces thereof block the pores 11.
FIG. 3B shows a state where the pore interval is just right, and the feather-like structure 13 provided on the surface thereof does not block the pore 11.
FIG. 3C shows a state where the pore interval is wide and the feather-like structure 13 does not block the pore 11, but the surface area of the entire porous oxide film 10 is thereby reduced.

EXAMPLES The present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

Example 1
First, as a step of forming a porous oxide film by anodic oxidation, an aluminum foil having a thickness of 100 μm and a purity of 99.99% is suspended in an aqueous solution of 30 ° C. with 0.35 wt% citric acid and 70 wt% ethylene glycol, and 500 VDC Was applied for 15 minutes. (The scanning electron microscope SEM image after this process is shown in FIG. 4.)
Next, the step of immersing in an aqueous acid or alkali solution was 2 g / l, 30 ° C. aqueous KOH solution, 26 minutes. (The SEM image after this process is shown in FIG. 5.)
Next, as a step of forming feather-like aluminum hydroxide by boiling, it was boiled with pure water at 98 ° C. for 2 minutes. Next, the aluminum hydroxide was converted into aluminum oxide by heat treatment. (FIG. 6 shows an SEM image after this step. The pore interval is about 800 nm.)
Next, after being immersed in a platinum colloid aqueous solution (particle diameter 2 nm, 4 wt%, protective agent) for 3 minutes, it was pulled up at 0.5 mms ⁻¹ and heated at 200 ° C. for 10 minutes. This was cut into a width of 50 × 100 mm, rolled up and stored in a stainless steel tube having an inner diameter of φ10 mm to obtain a hydrogen generation reaction vessel.
While the reaction vessel was heated to 400 ° C., methylcyclohexane was inserted from one side of the tube at a constant rate, and the gas exiting from the other side was gas-liquid separated and the amount of hydrogen was measured. This test was performed for 30 minutes and the hydrogen generation rate was calculated.

Table 1 shows a case where the chemical conversion voltage, the KOH immersion time, and the pure water boiling time were changed. The KOH immersion time was selected considering that the pores do not coalesce.
FIG. 7 shows the relationship between the KOH immersion time and the pore diameter. The KOH immersion time was adjusted so that pore diameter = 0.75 × pore interval. The pure water boiling time was selected considering that the feather-like structure does not block the pores.
FIG. 8 shows the relationship between the boiling time of pure water and the thickness of the feather-like structure. The boiling time of pure water was selected so that the thickness of the feather-like structure = 0.4 × pore diameter with 30 seconds as the lower limit.
However, at a conversion voltage of 1000 V or more, citric acid was 0.2 wt% and ethylene glycol was 85 wt% for convenience of spark voltage.
These were examined for hydrogen generation in the same manner as in Example 1, and are shown in Table 1.

  As a result of the test, hydrogen generation increases from a pore interval of 300 nm and becomes maximum at about 1000 nm. Even if the pore spacing is 1200 nm or more, the hydrogen generation amount is not small, but if it is 1000 nm or more, it tends to decrease, and if the formation voltage is high, the formation power cost is expensive, and the formation liquid temperature control is more difficult than the formation power. Become. As described above, the pore interval of 300 to 1200 nm is good, and a good catalyst member is obtained at 400 to 900 nm.

  DESCRIPTION OF SYMBOLS 1 ... Hydrogen medium which added hydrogen, 2 ... Hydrogen medium tank, 3 ... Hydrogen reaction container, 4 ... Engine, 5 ... Hydrogen, 6 ... Gas-liquid separation container, 7 ... Hydrogen medium which discharge | released hydrogen, and unreacted hydrogen medium , 8 ... Waste liquid tank, 9 ... Aluminum ingot, 10 ... Porous oxide film, 11 ... Pore, 12 ... Hex cell, 13 ... Feather-like structure

Claims (1)

  A catalyst member having a catalytic function on a metal surface, wherein the metal is aluminum having a porous oxide film and a feather-like structure on the surface, and a pore interval of the porous oxide film is 300 nm to 1200 nm.

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