JPH022878A - Steam reforming catalyst for fuel cell - Google Patents

Abstract

PURPOSE:To obtain a steam reforming catalyst having high activity, inhibiting the deposition of carbon and prolonging the service life by supporting Rh, Ru, Pd, Pt or an alloy thereof on a tetragonal or cubic zirconia carrier contg. yttria. CONSTITUTION:Rh, Ru, Pd, Pt or an alloy thereof is supported on a tetragonal or cubic zirconia carrier contg. a small amt. of yttria to obtain a steam reforming catalyst. This catalyst is incorporated into a fuel cell and performs efficient steam reforming of hydrocarbons to produce fuel for the cell. Since the catalyst inhibits the deposition of carbon, the service life is prolonged.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a steam reforming catalyst for fuel cells, and in particular to a steam reforming catalyst for hydrocarbons that has high activity and suppresses carbon deposition to extend its life. Regarding quality catalysts.

[Conventional technology]

A typical conventional catalyst for steam reforming is one in which nickel is supported on an alumina-based carrier containing an alkali metal oxide, an alkaline earth metal oxide, or silica. It is known that in addition to nickel, iron, cobalt, platinum, rhodium, ruthenium, palladium, and the like can also be used as catalysts (for example, JP-A-50-126005 and JP-A-61-260554).

Additionally, it has been reported that catalysts made of nickel, cobalt, or ruthenium supported on a zirconia carrier have excellent performance in steam reforming reactions of hydrocarbons (
Special Publication No. 43-12410; Tetsu Igarashi et al.'Rh
/ “Steam reforming reaction of n-butane over ZrO2” No. 5
8th Catalyst Symposium (A), 4th series B12, pp. 176-177: etc.).

On the other hand, steam reforming catalysts have traditionally been widely used industrially for reforming petroleum, petroleum fractions, etc., but recently such steam reforming catalysts have been installed inside fuel cells to convert hydrogen or A fuel cell has been proposed that uses hydrocarbons as raw materials instead of so-called fuel gases mainly composed of hydrogen and carbon oxide (Japanese Patent Application Laid-Open No. 61-280554).

[Problem to be solved by the invention]

Conventional catalysts made of alumina supporting nickel and other materials are used when the water vapor/carbon (carbon in the raw material gas) molar ratio (S/C) is small, or when the raw material gas is relatively molecular weight such as olefins or heavy hydrocarbons. When using a raw material with a large carbon content, there is a drawback that carbon adhesion (coking) is significant, the raw material gas supply pressure increases, and eventually clogging occurs. A high steam/carbon ratio requires extra steam for the reaction, which is economically disadvantageous. Also,
An increase in the raw material gas supply pressure increases the load on the system, and if the catalyst is clogged, the catalyst must be replaced or regenerated, and for this purpose, the reaction must be stopped temporarily or the catalyst must be replaced without stopping the reaction. There is a disadvantage that a complicated device is required for reproduction. In particular, in internal reforming fuel cells, it is more difficult to replace and regenerate the catalyst, so it is desirable to suppress carbon adhesion to the catalyst as much as possible.

Furthermore, it is natural that it is desirable for the reaction efficiency in steam reforming to be high, and especially in fuel cells, the efficiency of the cell itself is an important key to the practical application of the fuel cell.
It is more important that the reforming efficiency of the catalyst installed in the fuel cell is high.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a steam reforming catalyst for fuel cells that has high steam reforming efficiency and exhibits less carbon deposition.

[Means to solve problems]

In order to achieve the above object, the present invention provides rhodium in a tetragonal or cubic zirconia carrier containing ittria, which is installed inside a fuel cell and used to reform hydrocarbons to produce cell fuel. The present invention provides a steam reforming catalyst for fuel cells, which supports ruthenium, palladium, platinum, or an alloy thereof.

According to the research conducted by the present inventors, a catalyst using a tetragonal or cubic zirconia support doped with yttria (Y2O2) has superior steam reforming catalytic performance compared to conventional catalysts, and It was found that it is excellent as a steam reforming catalyst. Tetragonal or cubic zirconia containing a small amount of ittria is known as partially stabilized zirconia and is known to have high oxygen ion conductivity. ) It is speculated that this may be related to the effect of inhibition.

The content of ittria is preferably in the range of 0.5 to 20 mol%, more preferably 1.5 to 10 mol%. If the content of ittria becomes too large, the crystal system will not be stabilized. On the other hand, if the yttria content is low, the effect of yttria content is lost.

The production of tetragonal or cubic zirconia containing ittria is carried out by firing a powder mixture of ittria and zirconia in a predetermined ratio, or by a coprecipitation method using a zirconia compound, a hydrolysis method, or an alkoxide method. be able to. Preferred is the coprecipitation method. Particularly suitable is a coprecipitation method using yttrium chloride (YCum) and zirconium oxychloride (ZrOCl2).

In the present invention, the catalyst metal for steam reforming supported on the tetragonal or cubic zirconia support containing ittria is rhodium, ruthenium, palladium, platinum, or The amount of the catalyst metal supported on the yttria-containing zirconia support using these alloys, preferably rhodium or ruthenium, is not particularly limited, but is 0.01 to 10% by weight based on the total weight of the support and metal. It is preferably within the range of 0.1 to 3% by weight, more preferably 0.1 to 3% by weight. If the amount of metal is too large, it will be uneconomical, while if the amount of metal is too small, the activity will be low and the reforming of hydrocarbons will be insufficient.

The catalyst metal can be supported on the yttria-containing zirconia support by any conventional method, but an impregnation method is usually employed. The catalyst carrier used in the present invention is generally cylindrical, ring-shaped, or particulate, but is not necessarily limited thereto. It may be a fibrous or three-dimensional structure, and it can also be used as a composite structure with other carriers. As the internal reforming catalyst, a granular catalyst carrier with a small particle size is preferable.

In the present invention, the steam reforming reaction is represented by the following reaction formula.

CH, + [20= Co + 3H2Co + II
□0=CO□+11□ The reaction temperature is 300 to 1000°C, but 700°C
Since it is difficult to cause coking even at temperatures below .degree. C., it is suitable as a reforming catalyst for internal reforming fuel cells.

Reaction pressure is approximately 0.01kg/cm2c+-50kg
/ cm2G, particularly preferably about 0.1 kg/cm2
G~30kg/cm2G.

Although it is desirable that S/C be smaller, it is preferably 1.2 or more to avoid the problem of coking.

The steam reforming reaction for which the catalyst of the present invention is effective includes all conventionally known steam reforming reactions, especially all those conducted using a catalyst in which the same metal as the present invention, such as rhodium or ruthenium, is supported on a ceramic carrier. Although it is a steam reforming reaction, for example, gases containing light hydrocarbons such as LNG and LPG, petroleum fractions such as naphtha and kerosene, and mainly hydrocarbons such as coal liquefied oil, especially hydrocarbons with a not very large molecular weight (01 to This is a reaction that produces hydrogen, carbon oxide, carbon dioxide, or low molecular weight hydrocarbons (methane, ethane, etc.) by steam catalytic cracking of a raw material gas consisting of carbon (about 2°C). The raw material gas preferably consists of only hydrocarbons, but may contain trace amounts of other components. The content of sulfur compounds as a foreign component is desirably 0.5 ppm or less when the raw material is naphtha, and desirably 50 ppm or less when the raw material is kerosene. Purification methods such as hydrodesulfurization are employed to remove foreign components from raw materials.

Further, in an internal reforming fuel cell, if oxygen or air is mixed in with water vapor, it is not preferable because problems such as deterioration of the electrodes, reduction in catalyst activity, and further reduction in the conversion rate to hydrogen will occur.

Note that the specific gravity of the raw material is 0.80 or less, preferably 0.7
5 or less, and the C78 weight ratio is 6.5 or less, preferably 6.5 or less.
Zero or less hydrocarbons are used.

The catalyst of the present invention is particularly suitable for application in internal reforming fuel cells. This is because the reforming (conversion) efficiency is high and it has the effect of suppressing carbon deposition (coking).1 Although the application of the present invention is not limited, in the molten carbonate fuel cell, the molten carbonate of the electrolyte is scattered. It has been pointed out that the catalyst adheres to the catalyst surface and the activity decreases due to the elution of catalyst components, but the catalyst of the present invention has been confirmed to be stable against carbonates, and its application to this type of fuel cell. It is also useful. A catalyst is usually installed in a fuel cell by attaching the catalyst to the wall of a fuel gas flow path.

〔Example〕

(Example 1) Tetragonal zirconia powder containing 3 mol % or 8 mol % ittria obtained by a coprecipitation method was press-molded to form pellets (10 mmφ×3 mm).

After calcining this at 100°C for 3 hours, it was crushed and classified to form a catalyst carrier with a size of 6 to 16 meshes (pore volume 0).
．． Next, this was immersed in an aqueous rhodium chloride solution for 24 hours, taken out, dried, and heated at 500°C.
, and calcined for 1 hour to obtain a catalyst containing 0.5 u+t% rhodium.

Catalysts having tetragonal zirconia as carriers containing 3 mol % and 8 mol % ittria are referred to as catalyst A and catalyst B, respectively.

Reaction jLfL Desulfurized light naphtha (specific gravity 0.702, C/H weight ratio 5.52, sulfur content 500r) was used as a hydrocarbon raw material.
Jb or less), the reaction was carried out at 650° C. and 0.2 kg/cm 2 G while changing the steam/carbon (S/C) molar ratio and the raw material supply space velocity (G) ISv) as follows.

S/C molar ratio 3-1.5 GHSV 8,000-12,000 Tables 1 and 2 show the results of quantitative analysis of these reaction products by gas chromatography.

Here, the unconverted ratio refers to the ratio of unconverted (remained) hydrocarbons of C2 or higher to the hydrocarbons of the raw material, and indicates a measure of coking.

(Comparative Example 1) For comparison, the above reaction tests were repeated using commercially available steam reforming catalysts x, y, and z for naphtha. The results are also shown in Tables 1 and 2.

Note that the catalysts x, y, and z had the following composition.

Catalyst P was prepared by supporting rhodium on a zirconia support not containing itria in the same manner as in the case of supporting rhodium.
The reaction test described above was repeated. The results are also shown in Tables 1 and 2.

Below are the margin components: XY Ni 11.1 16.2 ^1203 88.9 . 24.7 Mg0 − ・ 10.7 Ca0 19.3 to 20 6.7 SiOz 19.0 15.6 25.7 11.9 16.1 6.2 13.6 In addition, Rhodium Table 1 was applied to the ittria-containing zirconia carrier. , Table 2 shows that according to catalysts A and B, which are examples of the present invention, compared to the Ni/8j to ZO-based catalyst (catalyst X) and the Ni composite oxide-based catalyst (Y, Z), , an improvement in the conversion rate was observed especially when the raw material supply space velocity was increased, and S/
Even if C is lowered, there is an effect that the required pressure for steam supply does not increase and the catalyst does not become clogged. Also,
Compared to Rh/ZrO□-based catalyst (catalyst P), H2/
The effect of improving c (the production efficiency of H2, which is the fuel of the fuel cell) was observed.

(Example 2) Catalyst A (rhodium supported on zirconia containing 3 mol% ittria) prepared in Example 1 was crushed into 8 to 16 meshes, 4.6 g of the mesh was weighed, and molten carbonate (L
i/K = 62/38) immersed in 70 g.

Then, the elution amount of the catalyst component was measured after 2 days, 4 days, and 7 days.

The results are shown in Figure 1. The figure shows that zirconia hardly elutes, and yttrium elutes on the surface, but about 2
It is seen that the amount is on the order of 5 ppm.

Therefore, Rh/Y20. The ZrO2-containing catalyst is found to be stable towards molten carbonate.

(Comparative Example 2) Catalyst Y (nickel supported on composite oxide) prepared in Comparative Example 1 was crushed in the same manner as in Example 2, and 5.0 g of it was weighed.
The sample was immersed in molten carbonate in the same manner as in Example 2, and the amount of the catalyst component eluted was measured.

The results are shown in Figure 2, which shows that alkaline earth metals were eluted significantly, with 26% of the total eluted M and 59% of the eluted Ca.

(Example 3) A tetragonal zirconia catalyst carrier (powder) containing 3 mol % of ittria was prepared in the same manner as in Example 1, and 12.0 g of it was immersed in an aqueous ruthenium chloride solution and impregnated by boiling. The impregnation process was repeated twice to support 0.5 wt % (based on the catalyst) of ruthenium on the ittria-containing zirconia support. After drying this at 120℃, it was heated to 500℃ for 2 hours.
Baked for an hour.

A reaction test similar to that described in Example 1 was conducted using this catalyst. However, the GHSV was set to 8000, and the S/C was varied from 3 to 1.5.

The results are shown in Table 3.

From Table 3 below, it is shown that the catalyst of the present invention has excellent reaction efficiency, suppresses carbon deposition, and high hydrogen production efficiency even when ruthenium is used as the catalyst metal, and is useful.

〔Effect of the invention〕

According to the present invention, a steam reforming catalyst with high hydrogen production efficiency, which has excellent reaction efficiency and significantly suppresses carbon deposition even at a low steam/carbon ratio, is provided, and is suitable as a catalyst for internal reforming fuel cells. It is.

[Brief explanation of the drawing]

FIG. 1 is a graph showing changes in the amount of components eluted from the catalyst of the example in the molten carbonate, and FIG. 2 is a graph similar to FIG. 1 in the comparative example.

Claims (1)

[Claims] 1. Rhodium, ruthenium, palladium, platinum, or an alloy thereof on a tetragonal or cubic zirconia carrier containing yttria, which is installed in a fuel cell and used to reform hydrocarbons to produce cell fuel. A steam reforming catalyst for fuel cells that supports