JP2002126525A - Oxidation catalyst coat structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxidation catalyst coat structure having the function of making the amount of reaction uniform along the direction of the gas stream in the oxidation combustion of hydrogen in an integrated catalyst/heat exchanger so as to heighten the efficiency of the heat exchanger. SOLUTION: By coating the heating surface with an oxidation catalyst comprising a catalyst component and a catalyst support component, wherein the amount of the catalyst component has a distribution in the direction of the flow of a feedstock gas to establish the uniformity of the amount of reaction along the flow of the gas and uniform heat supply, the thermal efficiency of the heat exchanger can be increased, and the apparatus is freed from troubles such as damage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating structure of an oxidation-combustion catalyst suitable for applying to a surface such as a heat transfer surface of a heat exchanger used in a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art A solid fuel cell device (hereinafter also referred to as PEFC) obtains an electromotive force by a cell reaction of obtaining water from hydrogen and oxygen. In this device, the catalyst-integrated heat exchanger burns and removes hydrogen gas remaining after the battery reaction, and also uses the combustion heat to vaporize methanol and water as raw materials for the battery reaction.

[0003] A conventional catalyst-integrated heat exchanger will be described below with reference to the drawings. FIG. 9 shows a conventional catalyst-integrated heat exchanger 5. In the conventional catalyst-integrated heat exchanger 5, the oxidation catalyst 6 is uniformly applied to the heat transfer surface 7 of the heat exchanger 8. Hydrogen contained in the source gas 9 flowing from the source gas inlet 10 is oxidized and combusted on the surface of the oxidation catalyst 6 to become water. This reaction is an exothermic reaction, and the generated reaction heat is absorbed from the heat transfer surface 7 and is used in the heat exchanger 8 for vaporizing methanol and water.

As described above, conventionally, in a system in which the heat of reaction generated by oxidizing and burning H ₂ is taken out by the heat exchanger 8, the oxidation catalyst 6 is applied to the heat transfer surface 7 of the heat exchanger 8, and the reaction is carried out. A method of performing heat exchange simultaneously has been used.

[0005] However, the above-mentioned oxidative combustion reaction of hydrogen has a very high reaction rate. Therefore, in the above-described catalyst-integrated heat exchanger 5, since the catalyst 6 is usually uniformly applied to the heat transfer surface 7, the oxidation combustion reaction of hydrogen as a reactant is terminated near the raw material gas inlet 10. . That is, source gas inlet 1
0, for example, about 1 in front of the heat transfer surface 7 which is the catalyst application surface.
Most reactions occur at 0%. Therefore, the generated combustion heat is absorbed from about 10% of the upstream of the heat transfer surface 7. As described above, the reactant hydrogen is supplied to the source gas outlet 11.
Since it is consumed in the reaction at the upstream of the heat transfer surface 7 without remaining to the vicinity, almost no reaction occurs near the raw material gas outlet 11 and the amount of heat supplied to the heat exchanger 8 is small.

FIG. 10 is a graph schematically showing the heat of combustion of hydrogen generated in the conventional catalyst coat structure by the temperature of the heat transfer surface. In this graph, source gas inlet 1
It can be seen that a large temperature difference occurs near 0 and near the source gas outlet 11.

As described above, since the amount of generated heat is not uniform, the heat is not uniformly supplied from the heat transfer surface 7 to the integrated heat exchanger 8, and the efficiency of the heat exchanger is lowered or the temperature difference is caused. Breakage due to stress has been a problem.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems. In the above-mentioned evaporator integrated with a heat exchanger, a catalyst having a uniform reaction amount along a gas flow direction is provided. Provide a coat structure.

The present inventors have found that the reaction rate of the hydrogen oxidation reaction is extremely high, so that only the catalyst located near the raw material gas inlet participates in the oxidation reaction and locally generates a large amount of heat. We paid attention to that. Therefore, by distributing the substantially effective coating amount of the catalyst component on the heat transfer surface with respect to the flow direction of the gas, the catalyst active site is controlled so that only the catalyst near the raw material gas inlet does not participate in the reaction. To solve the above problem.

The present invention is configured as follows. The present invention provides a coating structure for an oxidation catalyst, characterized in that the catalyst component amount is distributed with respect to the flow direction of the raw material gas, and the oxidation catalyst comprising the catalyst component and the catalyst carrier component is applied to the heat transfer surface. provide. In the coating structure of the oxidation catalyst, it is preferable that a catalyst-coated portion and a non-catalyst-coated portion are alternately provided between a raw material gas inlet and an outlet. Alternatively, in the coating structure of the oxidation catalyst, it is preferable that the application amount of the catalyst is reduced in the upstream part with respect to the flow direction of the raw material gas, and the application amount of the catalyst is increased in the downstream part. Further, the catalyst component of the oxidation catalyst is preferably an oxide of an element of Group VIII or an element containing Mn, Co, and La, and the catalyst support component of the oxidation catalyst is Al ₂ O ₃ , ZrO ₂ , ₂ or SiO ₂ , or a mixture thereof. Pt or Pd is preferably used as the Group 8 element. The present invention
Further, the present invention provides a catalyst-integrated heat exchanger, which has a coating structure of the oxidation catalyst on the surface. By using the catalyst coat structure according to the present invention, uniformity of the reaction on the heat transfer surface and high efficiency of the heat exchanger can be achieved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The coating structure of a catalyst according to the present invention will be described below in detail with reference to the drawings. The following description is intended to illustrate the present invention, but not to limit it. The same members will be described with the same reference numerals.

FIG. 1 is a cross-sectional view and FIG. 2 is a plan view of a preferred embodiment of the catalyst coating structure according to the present invention. The coat structure shown in FIG.
2 and the catalyst non-coated portion 13 are provided alternately. Hydrogen contained in the source gas 9 flowing from the source gas inlet 10 reacts according to the following equation. H ₂ + 1 / 2O ₂ → H ₂ O (1) Here, if the above reaction is a reaction using a conventional uniformly coated catalyst, the oxidative combustion reaction of hydrogen is carried out at the raw material gas inlet 1
It is completed by the action of the catalyst near zero, and the raw material gas outlet 11
The reactant hydrogen did not reach the vicinity. The structure shown in FIG. 1 and FIG.
Since the catalyst non-coating portion 13 is provided in the vicinity, hydrogen that has not been completely reacted in the first catalyst coating portion 12 reaches the next catalyst coating portion and the reaction proceeds.

FIG. 3 shows the amount of heat transmitted to the heat exchanger provided with the catalyst coat structure shown in FIG. 1 and FIG.
4 shows a graph schematically representing the temperature of the heat transfer surface. By alternately providing the catalyst coating portions 12 and the non-catalyst coating portions 13 in this manner, sites where an oxidation reaction occurs can be dispersed, and local heat generation can be suppressed.

In a preferred embodiment of the present invention, the catalyst component of the oxidation catalyst includes Group VIII elements such as Pd and Pt;
Alternatively, an oxide of an element of Group VIII, an oxide of an element containing Mn, Co, or La, such as a metal or oxide of Pd, Pt, Ru, Ir, or Rh, or MnO ₂ , CoO, or La ₂ O ₃ It is preferred to use
In addition to the above, an oxidation combustion catalyst such as CrO ₂ or CeO ₂ can be used as appropriate. Further, as the carrier component, Al ₂ O ₃ , ZrO ₂ , T
iO ₂ or SiO ₂ , or a mixture or composite oxide thereof can be used, but WO ₃ or the like can also be used.

These oxidation catalysts are in the form of a slurry,
Mullite, cordierite, aluminum titanate,
It is applied by wash-coating a heat-resistant ceramic such as zirconia or a heat-resistant metal substrate.
In the coat structure shown in FIG. 1, a catalyst non-coat portion 13 where no catalyst is applied is provided. At this time, the uncoated portion of the catalyst is masked. As a method of application, besides wash coating, a method such as immersion of the catalyst coat portion in a slurry solution, thermal spraying of a catalyst component, or plating may be used, but is not limited thereto.

It is preferable that the catalyst-coated portion and the non-catalyst-coated portion are alternately provided at a length of about 0.1 to 10% of the entire length of the catalyst-coated surface. However, since it differs depending on the amount of the applied catalyst, the total length of the coated surface of the catalyst, and the flow rate of the raw material gas, the present invention is not limited to this, and a structure in which the catalyst coated portion and the catalyst non-coated portion are provided at an appropriate pitch is designed. be able to. For example, the coating may be performed so that the pitch is small near the source gas inlet and the pitch is increased as approaching the outlet.

In another embodiment of the present invention, the coating is performed with a gradient from the raw gas inlet 10 to the raw gas outlet 11 such that the effective catalyst component amount increases substantially. The substantially effective amount of the catalyst component depends on the point at which the reaction substantially occurs, that is, the number of catalytically active sites. Therefore, when a metal having a different activity such as an oxide of Pt and Mn is used among the catalyst components, the effective amount of the catalyst component changes substantially. For example, the substantially effective amount of the catalyst component near the outlet is usually about 5 to 100 with respect to the amount of the catalyst component near the inlet.
It is preferable to apply the coating with a gradient so as to make the application time, preferably about 10 to 80 times, for example, about 50 times, but is not limited to this.

FIG. 4 shows another embodiment of the present invention. In this embodiment, a catalyst section 15 using an oxide such as Mn, Ni, Co or the like having relatively low catalytic activity in the upstream of the flow of the raw material gas.
However, it has a coat structure in which a Pd and Pt catalyst portion 14 having relatively high catalytic activity is applied to a downstream portion. By applying in this manner, the reaction is not completed in the vicinity of the raw material gas inlet 10, and the hydrogen as a reactant reaches the vicinity of the raw material gas outlet 11 where more active points exist, and the reaction occurs.

FIG. 5 shows a coating structure of an oxidation catalyst according to still another embodiment of the present invention. In the catalyst coat structure shown in FIG. 5, the raw material gas inlet 1 extends along the gas flow direction.
0 to a catalyst portion 15 using an oxide of Mn, Ni, Co, etc .;
d, the Pt catalyst section 14 is provided alternately. In this case, for the same reason as described for the coat structure shown in FIG. 1, the distribution of heat as shown in FIG. 3 is observed by alternately arranging the high-activity catalyst and the low-activity catalyst. The type of the catalyst is not limited to these, and the same effect can be achieved by alternately providing a relatively high activity catalyst and a low activity catalyst. As a relatively active catalyst, for example, a metal or oxide such as Pt or Pd can be used, and for a relatively low active catalyst, MnO ₂ , CoO, La ₂ O ₃ or the like can be used.

Next, an embodiment of a PEFC device using a catalyst-integrated heat exchanger having a catalyst coat structure according to the present invention will be described. FIG. 6 is a block diagram illustrating an outline of an embodiment of a PEFC device to which a catalyst-integrated heat exchanger having a catalyst coat structure according to the present invention is suitably applied. This PEFC device 1
Includes an evaporator 2, a methanol reformer 3, and a fuel cell 4. The function will be described together with the outline of each device.

The evaporator 2 includes a catalyst-integrated heat exchanger 5 having a catalyst coating structure according to the present invention. The supplied water and methanol are supplied to the catalyst-integrated heat exchanger 5.
And is sent to the methanol reformer 3.

The methanol reformer 3 is a device for performing methanol reforming with a methanol reforming catalyst, and receives supply of methanol and water to obtain hydrogen from methanol.

The obtained hydrogen is sent to the fuel cell 4.
In the fuel cell 4, H ⁺ generated by the reaction of the anode electrode catalyst at the anode electrode diffuses. On the other hand, H ₂ O is generated at the cathode electrode by the reaction of the cathode electrode catalyst. A battery reaction is configured by combining these reactions, and an electromotive force can be obtained.

The off-gas containing hydrogen from the fuel cell 4 is sent to the evaporator 2 and functions to gasify water and methanol by combusting about 20% of hydrogen contained in the off-gas with a combustion catalyst.

FIG. 7 is a perspective view of the evaporator 2 including the catalyst-integrated heat exchanger 5 used in the PEFC apparatus. The evaporator 2 has a structure in which many fins are arranged in parallel,
As shown in FIG. 8, each fin 17 constitutes a catalyst-integrated heat exchanger 5. The source gas 9 containing hydrogen is supplied between the fins 17, and the oxidative combustion reaction of the hydrogen occurs. Further, the evaporator 2 is supplied with an evaporating liquid stream 16 containing water and methanol, and evaporates them by reaction heat generated in the combustion reaction.

When the catalyst-integrated heat exchanger provided with the oxidation catalyst coat structure according to the present invention is used in a PEFC device,
Since the oxidative combustion reaction of hydrogen occurs uniformly on the heat transfer surface of the heat exchanger, the thermal efficiency can be increased as compared with the conventional one. Further, since heat is uniformly supplied to the heat transfer surface, there is no problem such as breakage of the device due to stress. Hereinafter, the present invention will be described in more detail with reference to Examples of the present invention, but this is not intended to limit the present invention.

[0027]

EXAMPLES Example 1 Preparation of Catalyst (1) ZrO_Two-Al_TwoO_ThreePreparation of carrier 106 g of zirconium oxychloride octahydrate in ion-exchanged water
Dissolve and add ion-exchanged water to pH = 2. next
After adding 365 g of γ-alumina and stirring for 3 hours,
It was added dropwise until pH = 9. After stirring for 1 hour, precipitate
The material was filtered and washed. After drying with a dryer all day and night,
Bake at 500 ° C for 5 hours in an air furnace and ZrO_Two-Al_TwoO _ThreeCarrier (ZrO_Two: A
l_TwoO_Three= 10: 90 weight ratio).

(2) Preparation of PdO—Pt—La ₂ O ₃ / ZrO ₂ —Al ₂ O ₃ Catalyst 100 g of the carrier prepared in the above (1) was charged with palladium nitrate (Pd (N
O ₃ ) ₂ Mw 230.4), dinitrodiamine platinum (Pt (NO ₂ ) ₂ (NH
₃ ) ₂ Mw 321.0) nitric acid solution and lanthanum nitrate (La (NO ₃ ) ₃
・ 6H ₂ O Mw 432.9) Immersion in an aqueous solution, drying at 120 ° C., calcination at 500 ° C. for 3 hours, 11.5 wt% of PdO, 5 wt% of Pt, and La ₂ O ₃
Was prepared at 5 wt%.

Example 2 Catalyst Coating Structure Example 1
500g of water to 100g of catalyst powder prepared by
Mix 15g, mix with ball mill for 5h, average catalyst diameter about 10μm
Was prepared. In addition, the catalyst application part was immersed in the slurry solution to a heat exchanger, or the catalyst containing slurry was made into the mist form, and it carried out by the wash coat which sprays on a catalyst coating part. In the case of partial coating, the uncoated portion was masked.

[0030]

As described above, the amount of the catalyst component is distributed with respect to the flow direction of the raw material gas, and the oxidation catalyst comprising the catalyst component and the catalyst carrier component is applied to the heat transfer surface by using a catalyst coating structure. By reacting, it is possible to make the reaction amount uniform along the gas flow direction. Further, by providing the catalyst coat structure of the present invention on the heat transfer surface of the heat exchanger with integrated catalyst, heat can be uniformly supplied, and the efficiency of the heat exchanger can be increased.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a catalyst-integrated heat exchanger in which a catalyst coat portion and a catalyst non-coat portion are provided alternately.

FIG. 2 is a plan view of a catalyst-integrated heat exchanger in which a catalyst coat portion and a catalyst non-coat portion are provided alternately.

FIG. 3 is a graph schematically showing the amount of heat generated in the catalyst-integrated heat exchanger shown in FIGS. 1 and 2 using the temperature of a heat transfer surface.

FIG. 4 is a cross-sectional view of a catalyst-integrated heat exchanger in which a catalyst having a substantially less effective amount of a catalyst component is applied to a upstream portion and a catalyst having a large amount is applied to a downstream portion.

FIG. 5 is a cross-sectional view of a catalyst-integrated heat exchanger in which catalysts having substantially different effective catalyst component amounts are alternately applied.

FIG. 6 is a block diagram illustrating an outline of an embodiment of a PEFC device having an evaporator including a catalyst-integrated heat exchanger of the present invention as a component.

FIG. 7 is a perspective view of an evaporator used in a PEFC device.

FIG. 8 is an enlarged view of a fin portion of the evaporator shown in FIG. 7;

FIG. 9 is a cross-sectional view of a conventional catalyst-integrated heat exchanger.

FIG. 10 is a graph schematically showing the amount of heat generated by a conventional catalyst-integrated heat exchanger by the temperature of a heat transfer surface.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 PEFC apparatus 2 Evaporator 3 Methanol reformer 4 Fuel cell 5 Catalyst integrated heat exchanger 6 Oxidation catalyst 7 Heat transfer surface 8 Heat exchanger 9 Raw material gas 10 Raw material gas inlet 11 Raw material gas outlet 12 Catalyst coat part 13 Catalyst non-catalyst Coating part 14 Pd, Pt catalyst part 15 Catalyst part using oxides of Mn, Ni, Co, etc. 16 Evaporation liquid flow 17 Fin

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 8/04 H01M 8/06 A 5H027 8/06 8/10 8/10 B01J 23/56 301M (72) Inventor Masanao Yonemura 4-2-2 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd. Hiroshima Research Laboratory F-term (reference) 4G040 EA02 EA06 EB03 EB44 4G069 AA01 AA03 AA08 BA01A BA01B BA02A BA04A BA05A BA05B BB06A BB06A BC42 BC BC65A BC67A BC69A BC72B BC75B CC32 DA06 FA02 FB16 FB17 FB18 4G075 AA03 AA62 BA06 BD14 CA45 CA54 DA02 EA05 EE03 FB02 FB04 4G140 EA02 EA06 EB03 EB44 5H026 AA06 5H027 AA06 BA09

Claims (6)

[Claims] 1. A coating structure for an oxidation catalyst, wherein an oxidation catalyst comprising the catalyst component and a catalyst carrier component is applied to a heat transfer surface with a distribution in the amount of the catalyst component in the flow direction of the raw material gas. . 2. The oxidation catalyst coating structure according to claim 1, wherein catalyst coating portions and catalyst non-coating portions are provided alternately between a raw material gas inlet and an outlet. 3. The oxidation catalyst according to claim 1, wherein the amount of the applied catalyst is reduced in the upstream portion with respect to the flow direction of the raw material gas, and the applied amount of the catalyst is increased in the downstream portion. Coat structure. 4. The oxidation according to claim 1, wherein a catalyst component of the oxidation catalyst is an oxide of an element belonging to Group 8 or an element containing Mn, Co, and La. Catalyst coating structure. 5. The catalyst carrier component of the oxidation catalyst is Al ₂ O ₃ , Z
and rO _2, TiO _2, or wherein the SiO _2, or mixtures thereof, coated structure of the oxidation catalyst according to claim 1. 6. A catalyst-integrated heat exchanger having a coating structure of the oxidation catalyst according to claim 1 on a surface thereof.