JP2004089812A - Hydrogen producing catalyst and preparation method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen producing catalyst capable of avoiding the deterioration of a catalyst or the blocking of a reaction place caused by the accumulation of carbon even if hydrogen is produced by steam reforming reaction under a low S/C condition. <P>SOLUTION: The hydrogen producing catalyst is used in the steam reforming reaction of hydrocarbon. In this hydrogen producing catalyst, Ni or Ru is supported on a carrier as an active metal component and at least one component selected from the group consisting of Fe, Co, Cr and Ce is supported as a metal component other than the active metal component. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a catalyst for producing hydrogen by steam reforming of hydrocarbons and a method for preparing the same, and more particularly to a catalyst suitably used in a hydrogen producing apparatus in a preceding stage of a polymer electrolyte fuel cell system.
[0002]
[Prior art]
In recent years, with the increasing global environmental issues, polymer electrolyte fuel cells (PEFCs) are a low-pollution method that can produce electric energy efficiently and cleanly. The application of is expected. In a fuel cell system including this PEFC, for example, in a reformer, hydrogen is produced from a raw material gas hydrocarbon and water by a steam reforming reaction using a reforming catalyst at a high temperature, and the hydrogen is supplied. Is performed. The hydrogen-containing gas produced in the reformer is supplied as fuel to a PEFC provided at a later stage of the system.
[0003]
For example, when methane is used as a hydrogen source to be sent to the reformer, a steam reforming reaction is performed according to the following reaction formula.
CH ₄ + H ₂₀ → 3H ₂ + CO (endothermic reaction) (1)
Usually, this reaction is carried out at about 650 to 800 ° C., and the S / C (steam / carbon ratio), which is a molar ratio of water and carbon C of methane, is carried out at S / C = 3 or more. The reaction (1) is an endothermic reaction, and the reaction is more easily promoted at a higher temperature.
However, raising the temperature of the reaction requires heat energy for heating not only methane but also water to a high temperature, and when operating as a system, energy loss increases. Therefore, as an operating condition in which the amount of water to be heated is small, it is desirable to be able to operate at a low S / C of S / C of less than 3, since energy loss as a system is reduced.
However, when the steam reforming reaction is performed under the low S / C conditions, a phenomenon occurs in which carbon is deposited on the catalyst, and the catalytic activity is significantly reduced. If the operation is continued under these conditions, carbon may accumulate in the catalyst and block the gas flow.
[0004]
[Problems to be solved by the invention]
In view of the above problems, the inventors of the present invention have proposed a hydrogen generation method capable of avoiding catalyst deterioration due to carbon accumulation and clogging of a reaction field even when performing hydrogen production by a steam reforming reaction under low S / C conditions with a small amount of water. We worked diligently to develop a production catalyst.
As a result, the present inventors have found that the above problems can be solved by supporting Fe on the catalyst component in addition to the active metal and preventing the precipitation of carbon even at low S / C by the action of Fe. I found it. The present invention has been completed from such a viewpoint.
[0005]
[Means for Solving the Problems]
That is, the present invention relates to a hydrogen production catalyst used for a steam reforming reaction of hydrocarbons, wherein Ni or Ru is supported on a carrier as an active metal component, and Fe, Co, An object of the present invention is to provide a hydrogen production catalyst characterized in that at least one selected from the group consisting of Cr and Ce is supported.
Here, as the carrier, a carrier in which a supported metal component other than an active metal such as Fe is not dissolved or a carrier in a saturated state after being dissolved is suitable. Specific examples include an inorganic component having a spinel structure or a perovskite structure, or an inorganic carrier containing these inorganic components and MgO and having a structure in which the supported metal component does not dissolve. As the carrier of the present invention, for example, a spinel structure of a component represented as FeAl ₂ O ₄ , NiAl ₂ O ₄ or MgAl ₂ O ₄ , a perovskite structure of a component represented as MgTiO ₃ or CaTiO ₃ , or Carriers containing MgO are preferred.
[0006]
When Ni is used as the active metal component and Fe is used as a supporting metal other than the active metal, Ni is contained in an amount of 5.0 to 20% by weight, and Fe is contained as a supporting metal component other than the active metal in an amount of 1 mol of the Ni. An embodiment supporting 0.5 to 2 mol is preferred. For example, when Ni as an active metal component and Fe as a component other than the active metal are supported on a Fe spinel structure carrier (FeAl ₂ O ₄ ), the weight of supported Ni / (weight of supported Ni + weight of supported Fe + support) The value of (FeAl ₂ O ₄ weight) × 100 is 5.0 to 20% by weight. The amount of Fe supported on the carrier is 0.5 to 2 mol per 1 mol of Ni. Instead of Fe, at least one or more of Co, Cr and Ce may be used, or at least two or more of Fe, Co, Cr and Ce may be used.
When Ru is used as the active metal component, the content of Ru is 0.3 to 5.0% by weight, and for example, Fe is 0.5 to 10 wt. An embodiment containing moles is preferred.
[0007]
In addition, the present invention provides a step of dropping aqueous solutions of aluminum salt, magnesium salt, nickel salt and Fe salt in a pH range of 9 to 11 to a basic solution, and aging and drying the solution to obtain hydrotalcite. A method for preparing a hydrogen production catalyst, comprising: a step of preparing a precursor having a specific structure composed of a basic double salt such as a mold; and a step of calcining the precursor to obtain a catalyst powder. Is provided.
Further, as a similar preparation method, in the present invention, a step of dropping an aqueous solution of an aluminum salt or a magnesium salt and an aqueous solution of one of a nickel salt and an Fe salt in a basic solution in a pH range of 9 to 11, After aging the solution, drying, to produce a precursor having a specific structure consisting of a basic double salt such as hydrotalcite type, calcining the precursor to obtain a catalyst powder, A method for preparing a hydrogen production catalyst including a step of impregnating with an aqueous solution containing at least one of a Ni salt and an Fe salt, and drying and calcining such that both Ni and Fe are supported on the catalyst powder. You can also.
Here, instead of the Fe salt, at least one member selected from the group consisting of Co salt, Cr salt and Ce salt, or at least two member selected from the group consisting of Fe salt, Co salt, Cr salt and Ce salt is used. It can also be used. Further, instead of the Ni salt, a Ru salt or a combination of a Ni salt and a Ru salt can be used.
[0008]
Further, the present invention provides a step of adding alumina powder to an aqueous solution containing a Ni salt and an Fe salt to disperse Ni and Fe, and a step of heating the alumina powder to obtain a NiFe salt impregnated alumina powder. Calcining the impregnated alumina powder at 500 ° C. to 1200 ° C. for 1 to 10 hours to obtain a catalyst powder carrying nickel oxide and iron oxide. It is. Further, a step of impregnating a catalyst in which Ni is supported on alumina powder with an aqueous solution containing an Fe salt, and a step of firing the catalyst to form a catalyst powder in which nickel oxide and iron oxide are supported are included. And a method for preparing a hydrogen production catalyst.
Here, the catalyst support may further include a step of reducing nickel oxide and iron oxide to Ni and Fe with a reducing gas.
[0009]
ADVANTAGE OF THE INVENTION According to the hydrogen production catalyst of this invention, even if it produces | generates hydrogen by performing a steam reforming reaction under low S / C conditions with a small amount of water, catalyst deterioration and blockage of a reaction field due to accumulation of carbon can be avoided. . When used in a reformer of a fuel cell system, it can be used under low S / C conditions, so that less heat energy for heating water is sufficient than usual, and the load due to operation is reduced. .
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the hydrogen production catalyst of the present invention will be described in detail.
The hydrogen production catalyst of the present invention is one in which a hydrogen-containing gas is obtained by causing a steam reforming reaction using a hydrocarbon such as city gas, methane, propane, kerosene, or dimethyl ether as a raw material. In a fuel cell system, this reaction is usually performed in a reformer installed in a stage preceding the fuel cell body.
In the hydrogen production catalyst of the present invention, Ni or Ru is supported as an active metal component on a carrier. Usually, one of Ni and Ru is used, but both active metals may be supported on a carrier.
In the hydrogen production catalyst of the present invention, at least one selected from the group consisting of Fe, Co, Cr and Ce is supported as a metal component other than the active metal component. Again, two or more of these metal components may be supported. It is particularly preferable that Fe is contained as the metal component.
[0011]
As the carrier of the present invention, a carrier in which a supported metal component other than an active metal such as Fe is not dissolved or a carrier in a saturated state after being dissolved is suitable. Specific examples include an inorganic component having a spinel structure or a perovskite structure, or an inorganic carrier containing these inorganic components and MgO and having a structure in which the supported metal component does not dissolve. For example, a spinel structure of a component represented as FeAl ₂ O ₄ , NiAl ₂ O _4, or MgAl ₂ O ₄ , a perovskite structure of a component represented as MgTiO ₃ or CaTiO ₃ , or a carrier containing MgO therein is preferable. It is listed. As described above, a carrier having a spinel structure or a perovskite structure is preferable because, when an alumina component or the like remains alone on the carrier, the metal component such as Fe is further dissolved and taken into that portion. This is to prevent that.
[0012]
The spinel-type structure is a crystal structure generally represented as an AB ₂ O ₄ type compound (A and B are metal elements) in a double oxide, such as FeAl ₂ O ₄ , NiAl ₂ O ₄ or MgAl ₂ O ₄ Is represented as This structure belongs to a cubic lattice, and oxygen atoms are almost packed in the cubic close-packing, so that metal components that do not constitute a crystal structure cannot fit inside the spinel structure, but exist on the outer surface etc. .
The perovskite type structure does not strictly take a cubic lattice, but refers to a simple cubic lattice structure as an ideal lattice. A metal element enters a gap formed by a three-dimensional frame structure. As a result, when oxygen atoms and metal elements are combined, the structure is such that other metal elements enter the gaps by cubic close packing. Therefore, like the spinel structure, the metal component that does not constitute the crystal structure cannot fit inside the perovskite structure, but exists on the outer surface or the like.
[0013]
When Ni is used as the active metal component and Fe is used as a supporting metal other than the active metal, Ni is contained in an amount of 5.0 to 20% by weight, and Fe is contained as a supporting metal component other than the active metal in an amount of 1 mol of the Ni. An embodiment supporting 0.5 to 2 mol is preferred. For example, when Ni as an active metal component and Fe as a component other than the active metal are supported on a Fe spinel structure carrier (FeAl ₂ O ₄ ), the weight of supported Ni / (weight of supported Ni + weight of supported Fe + support) The value of (FeAl ₂ O ₄ weight) × 100 is 5.0 to 20% by weight. The amount of Fe supported on the carrier is 0.5 to 2 mol per 1 mol of Ni. Instead of Fe, at least one or more of Co, Cr and Ce may be used, or at least two or more of Fe, Co, Cr and Ce may be used.
When Ru is used as the active metal component, the content of Ru is 0.3 to 5.0% by weight, and for example, Fe is 0.5 to 10 wt. An embodiment containing moles is preferred.
When the active metal component is contained within the above range, the steam reforming reaction is efficiently performed. In addition, the metal component such as Fe is supported at the above molar ratio with respect to the active metal component, thereby effectively preventing catalyst deterioration due to carbon adhesion (caulking) and maintaining the catalyst activity for a long period of time. Can be.
[0014]
Next, a method for producing the hydrogen production catalyst of the present invention will be described. The catalyst of the present invention can be produced by either the impregnation method or the coprecipitation method.
In the case of the impregnation method, in addition to the method of impregnating alumina pellets with an aqueous solution of Ni and Fe salts and firing, the method of impregnating alumina powder with an aqueous solution of Ni and Fe salts, firing and then pelletizing is used.
In the case of the production method by such an impregnation method, after sintering, even if all of the Fe element is taken into alumina, a predetermined amount of Fe is impregnated with a Fe salt solution containing an excessive amount of Fe so as to remain on the carrier. The salt solution concentration at that time is not limited.
[0015]
In the production of a hydrogen production catalyst by the coprecipitation method, first, an aqueous solution of an aluminum salt, a magnesium salt, a nickel salt, and an Fe salt in a pH range of 9 to 11 is dropped into a basic solution. Next, after aging the solution, it is dried to prepare a precursor of a basic double salt. Finally, the obtained precursor is calcined to obtain a catalyst powder.
Examples of the basic solution include an aqueous solution of sodium carbonate.
[0016]
In the production of a hydrogen production catalyst by another coprecipitation method, first, an aqueous solution of an aluminum salt or a magnesium salt and an aqueous solution of one of a nickel salt and an Fe salt are added to a basic solution in a pH range of 9 to 11. Is dropped. Next, the solution is aged and dried to prepare a precursor, and the precursor is calcined to obtain a catalyst powder A.
Finally, the obtained catalyst powder A is impregnated with an aqueous solution containing at least one of a nickel salt and an Fe salt, and dried and calcined. In this last step, for example, (a) a method in which the catalyst powder A is impregnated with an aqueous solution of a Ni salt or an Fe salt, or both salts, dried, calcined, and pelletized; A method of pelletizing, impregnating with an aqueous solution of Ni salt or Fe salt, or both salts, drying and calcining; (c) coating the catalyst powder A on a substrate such as a honeycomb, and then coating the Ni salt (or Fe salt or these salts) A method of impregnating, drying and calcining an aqueous solution of both salts) (d) impregnating the catalyst powder A with an aqueous solution of Ni salt or Fe salt, or both of these salts, drying and calcining the obtained powder as a base material Any of coating methods may be adopted. Here, instead of the Fe salt, at least one or more selected from the group consisting of Co salt, Cr salt and Ce salt, or at least two or more selected from the group consisting of Fe salt, Co salt, Cr salt and Ce salt Can also be used. Further, instead of the Ni salt, a Ru salt or a combination of a Ni salt and a Ru salt can be used.
Here, pelletization refers to granulation by tablet molding, pressure molding or granulation.
[0017]
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
[0018]
【Example】
Example 1 and Comparative Example 1
[Catalyst preparation method (preparation of catalyst by impregnation method)]
85 g of alumina powder was weighed into an evaporating dish, and an aqueous solution in which 138.7 g of Ni (II) nitrate hexahydrate and 722.0 g of Fe (III) nitrate 9 hydrate were dissolved in 1 liter of ion-exchanged water was added thereto. , Ni and Fe ions are dispersed in alumina. This is heated on a hot plate to evaporate water so that nickel and iron salts are not spotted, thereby obtaining alumina powder impregnated with NiFe salts. This is fired in air at 800 ° C. to 1000 ° C. for 5 hours to obtain a catalyst powder carrying nickel oxide and iron oxide, and pelletized. In order to obtain the activity as a steam reforming catalyst, nickel oxide and iron oxide are reduced to metal with a reducing gas before use.
[0019]
[Performance evaluation of obtained catalyst]
The performance of the Ni-supported alumina catalyst not supporting Fe (Comparative Example 1) and the performance of the Fe and Ni-supported alumina of Example 1 were compared. After hydrogen reduction at 500 ° C. under the conditions of S / C = 1.2, temperature 700 ° C., and space gas velocity 10000 h ⁻¹ , a steam reforming reaction was performed using desulfurized city gas.
As a result of the continuous operation for 230 hours, in the catalyst of Comparative Example 1, coking occurred and the catalyst deteriorated, whereas in the catalyst of Example 1, the occurrence of coking was not recognized and the catalyst did not deteriorate. .
FIG. 1 shows the change over time of the methane conversion of the catalysts of Example 1 and Comparative Example 1.
[0020]
Example 2
[Catalyst preparation method (preparation of catalyst by coprecipitation method)]
715.2 g of sodium carbonate decahydrate is dissolved in 5 liters of ion-exchanged water, and the temperature is kept at 60 ° C. to make this alkali solution A. Next, 625.20 g of aluminum nitrate nonahydrate, 1068.3 g of magnesium nitrate hexahydrate, 242.3 g of nickel (II) nitrate hexahydrate and 673.3 g of iron (III) nitrate nonahydrate were ion-exchanged. An acidic solution dissolved in 10 liters of water and kept at 60 ° C. is referred to as solution B. First, the solution B is slowly and uniformly dropped into the solution A while maintaining the pH of the solution B with an aqueous solution of sodium hydroxide with stirring to obtain a precipitation product liquid C.
[0021]
The sedimentation solution C is aged for 2 hours, and sufficiently filtered and washed so that Na ion and nitrate ion are not detected in the filtrate of the sedimentation solution C. Then, after drying at 100 ° C. for 24 hours, it is pulverized in a mortar and calcined at 850 ° C. for 5 to 10 hours to obtain nickel oxide and iron oxide supported on MgAl 2 O 4 and MgO. This catalyst powder is pressed and formed into steam reforming catalyst pellets. Before performing the steam reforming reaction, nickel oxide and iron oxide are reduced with hydrogen at 500 ° C. before use.
[0022]
Example 3
[Catalyst preparation method (preparation of catalyst by coprecipitation method)]
715.2 g of sodium carbonate decahydrate is dissolved in 5 liters of ion-exchanged water, and the temperature is kept at 60 ° C. to make this alkali solution A. Next, 625.20 g of aluminum nitrate nonahydrate, 1068.3 g of magnesium nitrate hexahydrate, and 242.3 g of nickel (II) nitrate hexahydrate were dissolved in 15 liters of ion-exchanged water, and the acid was kept at 60 ° C. The solution is referred to as solution D. First, the solution D is slowly and uniformly dropped into the solution A while maintaining the pH of the solution D with an aqueous solution of sodium hydroxide with stirring to obtain a precipitation liquid E.
[0023]
The sedimentation solution E is aged for 2 hours, and is sufficiently filtered and washed so that Na ion and nitrate ion are not detected in the filtrate of the sedimentation solution E. Then, after drying at 100 ° C. for 24 hours, the mixture is pulverized in a mortar and calcined at 850 ° C. for 5 to 10 hours to obtain a powder F in which nickel oxide is supported on MgAl ₂ O ₄ and MgO. The powder F is placed in an evaporating dish, and an aqueous solution obtained by dissolving 673.3 g of iron (III) nitrate nonahydrate in 1 liter of water is added to impregnate the powder F, and the water is evaporated on a hot plate. Thereafter, the powder is fired in air at 500 ° C. for 5 hours to obtain a powder G. The powder G is pressed and formed into steam reforming catalyst pellets. Before performing the steam reforming reaction, nickel oxide and iron oxide are reduced with hydrogen at 500 ° C. before use.
[0024]
[Performance evaluation of obtained catalyst]
After reducing the catalyst of Example 2 with hydrogen at 500 ° C. to reduce nickel oxide and iron oxide, the steam reforming reaction was performed at a temperature of 700 ° C. under low S / C conditions (S / C = 1.2). At a space gas velocity of 10,000 h ^-1 .
As a result of the operation for 200 hours, no occurrence of coking was observed in the catalyst of this example, and no deterioration of the catalyst occurred.
[0025]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the hydrogen production catalyst of this invention, even if it produces | generates hydrogen by performing a steam reforming reaction under low S / C conditions with a small amount of water, catalyst deterioration and blockage of a reaction field due to accumulation of carbon can be avoided. . Then, when used in a reformer of a fuel cell system, it can be used under low S / C conditions, so that less heat energy for heating water is sufficient than usual, and the efficiency is improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing the change over time in the methane conversion of the catalysts of Example 1 and Comparative Example 1.

Claims (14)

A hydrogen production catalyst for use in a steam reforming reaction of hydrocarbons, wherein Ni or Ru is supported on a carrier as an active metal component, and a metal component other than the active metal is Fe, Co, Cr and Ce. A hydrogen production catalyst, wherein at least one member selected from the group consisting of at least two is supported. The hydrogen production catalyst according to claim 1, wherein the support is an inorganic support having a spinel structure or a perovskite structure. The carrier includes a spinel structure of a component represented as FeAl ₂ O ₄ , NiAl ₂ O ₄ or MgAl ₂ O ₄ , or a perovskite structure of a component represented as MgTiO ₃ , CaTiO ₃ , BaTiO ₃ or SrTiO _3. The hydrogen production catalyst according to claim 1, wherein: Wherein said _{carrier, FeAl 2 O 4, NiAl 2} O 4 or claim 1, wherein the hydrogen production catalyst comprising a spinel structure and MgO components, expressed as MgAl ₂ O _4. The nickel is contained as 5.0 to 20% by weight as the supported active metal component, and 0.5 to 2 mol of Fe is supported as 1 mol of supported Ni as the supported metal component. 4. The catalyst for producing hydrogen according to any one of 3. The hydrogen production catalyst according to any one of claims 1 to 3, wherein Ru is contained as 0.3 to 5.0% by weight as the supported active metal component. A step of dropping an aqueous solution of an aluminum salt, a magnesium salt, a Ni salt and an Fe salt in a pH range of 9 to 11, respectively,
After aging the solution, drying to produce a precursor,
Calcining the precursor to obtain a hydrogen production catalyst;
A method for preparing a hydrogen production catalyst, comprising: A step of dropping an aqueous solution of an aluminum salt, an aqueous solution of a magnesium salt, and an aqueous solution of either a Ni salt or an Fe salt in a pH range of 9 to 11 to the basic solution;
After aging the solution, drying to produce a precursor,
A step of calcining the precursor to obtain a catalyst powder;
A step of impregnating with an aqueous solution containing at least one of a Ni salt and an Fe salt, and drying and calcining, so that the catalyst powder supports both Ni and Fe;
A method for preparing a hydrogen production catalyst, comprising: The method for preparing a hydrogen production catalyst according to claim 7, wherein at least one selected from the group consisting of a Co salt, a Cr salt, and a Ce salt is used instead of the Fe salt. 9. The method for preparing a hydrogen production catalyst according to claim 7, wherein at least two or more types selected from the group consisting of Fe salts, Co salts, Cr salts, and Ce salts are used instead of the Fe salts. The method for preparing a hydrogen production catalyst according to claim 7 or 8, wherein a Ru salt or a combination of a Ni salt and a Ru salt is used instead of the Ni salt. Adding alumina powder to an aqueous solution containing Ni salt and Fe salt to disperse Ni and Fe;
Heating the alumina powder to obtain a NiFe salt impregnated alumina powder;
Calcining the impregnated alumina powder to form a catalyst powder carrying nickel oxide and iron oxide. Impregnating a catalyst in which Ni is supported on alumina powder with an aqueous solution containing an Fe salt;
Calcining the catalyst to form a catalyst powder carrying nickel oxide and iron oxide. 14. The method for preparing a hydrogen production catalyst according to claim 12, further comprising a step of reducing nickel oxide and iron oxide to Ni and Fe with a reducing gas for the catalyst carrier.

Images