JP2001199707A - Method for reducing carbon monoxide in hydrogen- containing gas and catalyst therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a catalyst that can efficiently reduce the concentration of carbon monoxide in the hydrogen-containing gas resultant from methanol reforming process at a low temperature. SOLUTION: The carbon monoxide in the hydrogen-containing gas is brought into contact with oxygen in the presence of a copper-platinum binary catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for reducing carbon monoxide in a hydrogen-containing gas, and more particularly to hydrogen produced by a reforming reaction of hydrocarbons and methanol for use as a hydrogen source for fuel cells. The present invention relates to a method and a catalyst for reducing carbon monoxide in a contained gas.

[0002]

2. Description of the Related Art Hydrogen-containing gas is produced by reforming hydrocarbons, methanol and the like with steam, and is used as a raw material for organic chemicals. ing. These hydrogen-containing gases contain carbon monoxide, and when used as a hydrogen source for a fuel cell, the carbon monoxide is adsorbed on the platinum catalyst of the electrode of the fuel cell and deteriorates its function as a catalyst. It is necessary to lower the hydrogen concentration as much as possible. The allowable concentration of carbon monoxide is, for example, several percent or less in the case of a phosphoric acid fuel cell, and 10 ppm or less in the case of a polymer electrolyte battery. Methanol can perform a reforming reaction with steam at a relatively low temperature, and has a low content of carbon monoxide, so that it can be advantageously used as a hydrogen source for a fuel cell. For this reason, development of a fuel cell using methanol as a raw material, particularly development of a fuel cell for a vehicle that can be mounted on a vehicle, is being promoted.

As a method for reducing carbon monoxide in a hydrogen-containing gas, Japanese Patent Application Laid-Open No. 5-245376 discloses copper oxide, aluminum oxide, and the like.
A method of performing conversion of carbon monoxide by steam using a magnesium oxide catalyst is described.Japanese Patent Application Laid-Open No. 8-295502 describes a method of converting carbon monoxide using a catalyst in which ultrafine gold particles are dispersed and supported on a metal oxide. A method for selectively reducing oxidation is described. Japanese Patent Application Laid-Open No. 9-30802 discloses an apparatus for reducing the concentration of carbon monoxide in a hydrogen-containing gas obtained by a reforming reaction of methanol using a platinum-ruthenium catalyst.

[0004]

SUMMARY OF THE INVENTION A method using a prior art copper oxide / aluminum oxide / magnesium oxide catalyst.
(Japanese Unexamined Patent Publication No. 5-245376) has a high reaction temperature of 300 to 400 ° C. and a low conversion of carbon monoxide. A method using a catalyst in which ultrafine gold particles are dispersed and supported on a metal oxide (Japanese Patent Application Laid-Open No.
No. 02) reacts at low temperature, but the catalyst is very expensive. Also, a method using a platinum / ruthenium catalyst (Japanese Patent Laid-Open
9-30802) is also expensive, and some of the carbon monoxide reacts with hydrogen to cause methanation. Methanation consumes a large amount of hydrogen, generates a large amount of heat during the reaction, easily causes a temperature runaway, and has difficulties in controlling the reaction temperature. An object of the present invention is to provide a method and a catalyst for efficiently reducing the concentration of carbon monoxide in a hydrogen-containing gas at a low temperature, mainly for the development of a fuel cell using methanol as a raw material.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies on a method for reducing the concentration of carbon monoxide in a methanol reformed gas having the above-mentioned problems, and as a result, have found that a method using a copper-platinum coexisting catalyst has been proposed. The present inventors have found that carbon monoxide in a hydrogen-containing gas can be efficiently reduced at a low temperature by bringing carbon oxide and oxygen into contact with each other, and arrived at the present invention. That is, the present invention provides a method for reducing carbon monoxide in a hydrogen-containing gas, which comprises contacting carbon monoxide and oxygen in the presence of a copper-platinum coexisting catalyst, and supporting a copper and platinum-containing component on a carrier. Is a catalyst for reducing carbon monoxide.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The hydrogen-containing gas as a raw material in the present invention is not particularly limited, but is usually produced by steam reforming or partial oxidation of hydrocarbon or methanol.
As the hydrocarbon, gaseous natural gas containing methane as a main component, liquid LPG, naphtha, light oil and the like are used. Nickel-based catalysts are used in hydrocarbon steam reforming furnaces and are reacted at 800 to 1000 ° C to produce synthesis gas containing hydrogen, carbon monoxide and carbon dioxide as main components. As the hydrogen-containing gas as the raw material in the present invention, a gas obtained by converting carbon monoxide in the synthesis gas into carbon dioxide using an iron-based catalyst or a copper-based catalyst is used. The hydrogen-containing gas usually contains 1%
Although carbon monoxide is contained by the method of the present invention, the oxygen-containing gas is added thereto, and the reaction is carried out using a copper-platinum coexisting catalyst. It becomes a gas and carbon monoxide is reduced.

In the present invention, the steam reforming of methanol is performed using a copper-zinc catalyst or a noble metal catalyst such as Pd or Pt.
The reaction is performed at about 200 to 350 ° C. to produce a synthesis gas containing hydrogen and carbon dioxide as main components. The synthesis gas is used as a raw material hydrogen-containing gas in the present invention. Generally, when a noble metal-based catalyst is used, the hydrogen-containing gas contains 1 to 5
% Of carbon monoxide, and when a copper-zinc catalyst is used, the hydrogen-containing gas contains 1% or less of carbon monoxide. Is added and reacted using a copper / platinum coexisting catalyst, carbon monoxide is selectively oxidized to carbon dioxide gas, and carbon monoxide is reduced.

In the present invention, as the composition containing copper and platinum as catalytically active components, forms such as a supported catalyst and a coprecipitation catalyst can be selected. For use in a vehicle-mounted fuel cell, it is preferable to use a catalyst having a carrier carrying copper and platinum-containing components. As the catalyst carrier, alumina, silica or the like having a high surface area is suitable, but the order and method for carrying the active ingredient are not particularly limited, and known methods such as impregnation method and precipitation method can be used in combination. As the coprecipitation catalyst, a method of precipitating from an aqueous solution containing copper and platinum with, for example, an alkali carbonate precipitant can be used. In addition, a platinum component can be supported on a copper catalyst obtained by a known method such as a method of adding a carrier component slurry to a copper precipitation slurry and carbonating with a carbon dioxide gas. As the content of the catalyst composition, copper is 0.1 to 70% by weight,
Preferably 0.5 to 50% by weight, Pt 0.1 to 10% by weight, preferably 0.2 to 5% by weight.

The reaction conditions for selectively oxidizing carbon monoxide are as follows. The reaction temperature is usually from 100 to 200 ° C, preferably from 120 to 160 ° C. The amount of oxygen added to the reforming raw material gas is 0.5 to 4 times, preferably 0.5 to 2 times the carbon monoxide content. The reaction pressure is from normal pressure to about 20 atm. The amount of the catalyst used is 500 to 50000 [1 / h], preferably 1000 to 30000 [1 / h] as a gas hourly space velocity (GHSV).

The copper / platinum coexisting catalyst used in the method of the present invention is characterized by a high oxygen reaction rate and a remarkably high CO oxidation selectivity at low temperatures. That is, at temperatures up to 260 ° C., the methanation reaction due to the reaction between carbon monoxide and hydrogen hardly occurs. At a temperature below 160 ° C, the reverse shift reaction between carbon dioxide and hydrogen does not occur, and the carbon dioxide generation reaction by oxidation of carbon monoxide is performed with a selectivity of 40% or more with respect to the consumption of oxygen. In the method of the present invention, when treating a hydrogen-containing gas by steam reforming of methanol containing about 1 mol% of CO, the CO concentration is reduced at a low temperature of about 120 to 160 ° C.
0.1 mol% or less, and the amount of hydrogen combustion is extremely small. Therefore, the hydrogen-containing gas treated in the temperature range of about 120 to 160 ° C. by the method of the present invention can be directly used for a phosphoric acid type fuel cell or a solid polymer type cell. Therefore, the hydrogen-containing gas treated by the method of the present invention can be used very suitably for a fuel cell of a vehicle type or the like.

[0011]

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited by the following examples. In addition, the raw material gas in the evaluation of the catalyst performance in each of Examples and Comparative Examples includes CO 0.5 to 1.0 mol%, O ₂ 0.5 to 1.0 mol%, CO ₂ 25 mol%, H ₂ 73 to
An oxygen-containing reformed gas having a composition of 74 mol% was used. Under normal pressure, the space temperature (SV) should be 5000 ~ 11500 hr ^-1
The gas composition after the reaction when the temperature was changed to 40 to 260 ° C. was analyzed by gas chromatography. In the graph showing the results of the evaluation of the catalyst performance, the oxygen reaction rate indicates the reaction rate (conversion rate) of oxygen in the raw material gas, and the CO oxidation selectivity indicates the ratio of reaction oxygen that contributed to the CO oxidation reaction. . Most of the reactive oxygen that has not contributed to the CO oxidation reaction is consumed for hydrogen combustion.

Example 1 Commercially available alumina spheres (average diameter 1.5 mm, BET specific surface area: 200)
240240 m ³ / g) into an aqueous solution in which copper nitrate trihydrate is dissolved and stirred. Thereafter, an excess sodium carbonate solution was added to precipitate 0.25 wt% of basic copper carbonate as Cu on the alumina carrier. The carrier was filtered and dried, then 0.75
Using an acetone solution of acetylacetonato platinum equivalent to wt% Pt, 0.5% by weight of platinum is further supported by drying under reduced pressure with an evaporator, and after drying, calcination is performed at 400 ° C. to obtain 0.25% by weight of Cu-0.75.
A wt% Pt / alumina catalyst was obtained. CO 1.0 mol%, O ₂ 1.0
Used mol%, CO ₂ 25 mol%, H ₂ 73 mol% of the gas,
FIG. 1 shows the results of the catalyst performance evaluation at a space velocity of about 5200 [1 / h]. When this catalyst was used, methane was not generated in the temperature range of 100 to 220 ° C, and the CO concentration was reduced to 0.1 mol% or less when the reaction temperature was in the range of 115 to 155 ° C. The oxygen reaction rate in this temperature range was 95% or more, and the CO oxidation selectivity was in the range of 45 to 55%.

Example 2 A 0.5 wt% Cu-0.5 wt% Pt / alumina catalyst was obtained in the same manner as in Example 1. CO 0.5 mol%, O ₂ 0.5 mol%, CO
₂ Using a gas of 25 mol% and 74 mol% of H ₂ ,
FIG. 2 shows the results of the catalyst performance evaluation of 6200 [1 / h]. When this catalyst is used, methane is not generated in the temperature range of 100 to 220 ° C, and the CO concentration becomes lower in the reaction temperature range of 120 to 160 ° C.
It has decreased to 0.1 mol% or less. The oxygen reaction rate in this temperature range was 95% or more, and the CO oxidation selectivity was in the range of 45 to 55%.

Example 3 A 0.75 wt% Cu-0.25 wt% Pt / alumina catalyst was obtained in the same manner as in Example 1. CO1.0 mol%, O ₂ 1.0 mol%, C
FIG. 3 shows the results of a catalyst performance evaluation using a gas of 25 mol% of O _{2 and} 73 mol% of H ₂ and a space velocity of about 6200 [1 / h]. When this catalyst is used, methane is not generated in the temperature range of 100 to 220 ° C, and the CO concentration falls to 0.1 mol% or less when the reaction temperature is in the range of 130 to 175 ° C. The oxygen reaction rate in this temperature range was 95% or more, and the CO oxidation selectivity was in the range of 45 to 55%.

Example 4 177 g of sodium carbonate (anhydrous) was put into a 5 liter round bottom flask together with 1000 ml of ion-exchanged water and dissolved at 40 ° C. A solution in which 315 g of copper sulfate (pentahydrate), 19.7 g of boric acid and 800 ml of ion-exchanged water were adjusted to 40 ° C. was poured, and then a slurry in which 77.0 g of zinc oxide was dispersed in 300 ml of ion-exchanged water was added. In addition, carbon dioxide gas was immediately blown at a rate of 6 L / h. After 1 hour, the temperature was raised to 80 ° C. and maintained for 30 minutes. Carbon dioxide was stopped in 2 hours. Then cooled to 60 ° C. Here, a solution obtained by dissolving 51.4 g of aluminum sulfate in 150 ml of ion-exchanged water and 21.9 g of sodium hydroxide were added to 1 solution.
A slurry prepared from a solution dissolved in 60 ml of ion-exchanged water was added and stirred for 20 minutes. The mixed slurry thus prepared was filtered and washed with 12 liters of a 0.05% aqueous sodium hydroxide solution and 3 liters of ion-exchanged water. Subsequently, drying was performed at 80 ° C. to obtain a Cu—Zn—Al catalyst. Cu-Z
20 g of n-Al catalyst powder was immersed in 50 ml of acetone solution of 0.158 g of acetylacetonato platinum,
The acetone was evaporated off at ℃. Then at 360 ° C 2
After calcination for 0.5 hour, a 0.5 wt% Pt-Cu-Zn-Al catalyst was obtained. The catalyst is
The mixture was molded to a bulk density of 2.5 g / milliliter with a tableting machine, pulverized, and sized with a sieve in a range of 0.5 to 1.0 mm for reaction. CO 0.5 mol%, O ₂ 0.5
Used mol%, CO ₂ 25 mol%, H ₂ 74 mol% of the gas,
FIG. 4 shows the results of the catalyst performance evaluation at a space velocity of about 11500 [1 / h]. When this catalyst is used, methane is not generated in the temperature range of 100 to 220 ° C, and the CO concentration falls to 0.1 mol% or less when the reaction temperature is in the range of 130 to 170 ° C. The CO conversion to oxygen in this temperature range was such that the oxygen conversion was 95% or more and the CO oxidation selectivity was in the range of 45 to 55%.

Comparative Example 1 In Example 1, 1 wt% Cu / alumina was obtained without carrying platinum. The reaction was carried out under the same conditions as in Example 2. FIG. 5 shows the results. With this catalyst, methane is not generated in the temperature range of 100 to 220 ° C, but the oxygen reaction rate cannot be increased to 80% or more unless the temperature is increased to about 210 ° C or higher. Could not be reduced to 0.4 mol% or less.

Comparative Example 2 In Example 1, 1 wt% Pt / alumina was obtained without carrying copper. The reaction was carried out under the same conditions as in Example 2. FIG. 6 shows the results. With this catalyst, methane is not generated in the temperature range of 100 to 220 ° C, but the oxygen reaction rate cannot be increased to 95% or more unless the temperature is increased to about 150 ° C or higher. The temperature range in which the concentration was 0.1 mol% or less was about 140 to 190 ° C.

Comparative Example 3 Using 1 wt% Pt / alumina obtained in Comparative Example 2, Example 1
The reaction was carried out under the same conditions as described above. FIG. 7 shows the results. With this catalyst, methane is not generated in the temperature range of 100 to 220 ° C, but the oxygen reaction rate cannot be increased to 95% or more unless the temperature is increased to about 170 ° C or higher, and the CO selectivity is about 50%. CO
The temperature range where the concentration is 0.1 mol% or less is about 170-200 ° C
Met.

Comparative Example 4 In Example 1, acetylacetonatoruthenium was used instead of acetylacetonatoplatinum without supporting copper, and
wt% Ru / alumina was obtained. The reaction was carried out under the same conditions as in Example 2. FIG. 8 shows the results. With this catalyst, methane is generated at 150 ° C or higher, and methane generation increases sharply as the temperature rises. If the temperature does not exceed 135 ° C, the oxygen reaction rate
Although it cannot be set to 95% or more and the CO selectivity is about 50%, the temperature range where the CO concentration is 0.1 mol% or less is about
140 ° C or higher.

Comparative Example 5 In Example 4, calcination was carried out without carrying platinum to obtain a Cu-Zn-Al catalyst. The particles were sized in the same manner as in Example 4 and reacted under the same conditions. FIG. 9 shows the results. This catalyst does not generate methane in the temperature range of 100 to 220 ° C, and has an oxygen reaction rate of 95% or more at about 115 ° C or higher, but has a CO selectivity of 31% or less and a CO concentration of 0.2 mol% or less. Couldn't be.

[0021]

As is clear from the above examples, according to the method of the present invention, the hydrogen-containing gas obtained by steam reforming of methanol containing about 1% of CO can be used at a low temperature of about 120-160 ° C. The concentration can be 0.1 mol% or less,
Very low hydrogen loss. Therefore, the hydrogen-containing gas treated by the method of the present invention can be very suitably used for a fuel cell of a vehicle type or the like, and the present invention has great industrial significance.

[Brief description of the drawings]

FIG. 1 is a drawing showing the results of performance evaluation of a catalyst of Example 1.

FIG. 2 is a drawing showing the results of performance evaluation of a catalyst of Example 2.

FIG. 3 is a drawing showing the results of performance evaluation of the catalyst of Example 3.

FIG. 4 is a drawing showing results of performance evaluation of a catalyst of Example 4.

FIG. 5 is a drawing showing the results of performance evaluation of the catalyst of Comparative Example 1.

6 is a drawing showing the results of performance evaluation of the catalyst of Comparative Example 2. FIG.

FIG. 7 is a drawing showing the results of performance evaluation of the catalyst of Comparative Example 3.

FIG. 8 is a drawing showing the results of performance evaluation of the catalyst of Comparative Example 4.

FIG. 9 is a drawing showing the results of performance evaluation of the catalyst of Comparative Example 5.

Claims (3)

[Claims] 1. A method for reducing carbon monoxide in a hydrogen-containing gas, comprising contacting carbon monoxide with oxygen in the presence of a copper / platinum coexisting catalyst. 2. The reduction of carbon monoxide in a hydrogen-containing gas according to claim 1, wherein 0.5 to 4 times of oxygen is brought into contact with carbon monoxide contained in the hydrogen-containing gas and the reaction is carried out at 100 to 200 ° C. Method. 3. A catalyst for reducing carbon monoxide, comprising a carrier carrying copper and platinum-containing components.